Patent Publication Number: US-2011077495-A1

Title: Detection indicator

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation-in-Part of application Ser. No. 12/799,123, filed Apr. 19, 2010, which is a Continuation of application Ser. No. 11/769,597, filed Jun. 27, 2007, which is a Continuation-in-Part of application Ser. No. 11/548,086, filed 10 Oct. 2006, which is a Continuation-in-Part of application Ser. No. 11/347,481, filed 3 Feb. 2006, which claims the benefit under 35 U.S.C. Sec. 119(e) of application No. 60/650,806, filed 8 Feb. 2005, the disclosures of which are incorporated by reference. 
    
    
     BACKGROUND 
     In medical practice, it is common to obtain a sample of a fluid for evaluation of various characteristics to aid in evaluation of a patient&#39;s health. Examples of such fluids include blood, urine, and stomach contents, which may be taken for analysis. Characteristics of the fluids that may be measured include pH and the presence or levels of various chemicals or medication. Fluids may be taken as a diagnostic aid and also to aid in placement of medical devices such as medical tubing for feeding, breathing, medication, and other uses. 
     There are many different clinical situations in which it is beneficial to know the gastric pH of a patient, or other chemical properties associated with the patient. Currently to determine the pH, a practitioner aspirates the stomach contents from a lumen (e.g., nasogastric tube, feeding tube, gastric tube) that is in communication with the stomach into a syringe. The contents are then expelled from the syringe and placed in a test tube and sent to a lab for a gastric pH analysis. It is also possible to place a pH probe down the lumen to attain a reading of the stomach contents. However these methods take a considerable amount of time and both can be costly. Another method is to aspirate the stomach contents into the syringe and then expel the contents of the syringe onto litmus paper or other pH indicating paper. This method is also timely and forces the practitioner to handle bodily fluids in the open. This can be both messy and inaccurate. 
     The pH is measured for multiple reasons. The most common reason being to monitor an intubated or critically ill patient&#39;s gastric pH. This is often measured because these critically ill patients develop gastric ulcers due to a lower gastric pH. These ulcers can bleed rapidly and are a cause for significant morbidity and mortality. These often require emergent endoscopy and cauterization to stop the bleeding. 
     Patients that are critically ill are often on medications that raise the gastric pH. However, dosages needed to adequately raise the pH of the stomach in critically ill patients may vary for each patient and are difficult to determine without measuring the gastric pH. This is often not done because it can be timely and costly to do so. 
     Detection of the desired characteristic is typically shown using a visual indicator, such as a colorimetric medium that changes from a first color to a second color upon sufficient contact with the fluid. For example, determining the pH for a sample of stomach contents can be performed with a litmus paper which turns red or blue upon contact with acids or bases, respectively. 
     Determination of the characteristics is often performed by a practitioner (e.g., nurse or doctor) who views the colorimetric medium for the change to occur. However, with many indicator mediums, the color change may be gradual and include a range of colors. For example, a pH paper may be designed to change colors between a range of blue, green, and brown or between red, orange, and yellow to indicate specific levels of pH. The practitioner must then compare the colors of the pH paper with a known reference color to estimate the pH value. Reference colors are often provided on a separate chart for comparison with the visual indicator. 
     SUMMARY 
     The invention in one implementation encompasses an apparatus. The apparatus comprises a detection indicator and a housing. The detection indicator is configured to change from a first visual indication to a second visual indication upon contact with a fluid based on a characteristic of the fluid. The housing comprises an interior chamber configured to receive the fluid and to provide contact between the fluid and the detection indicator. The housing is configured to removably engage a lumen inserted into a patient to receive the fluid from the patient through the lumen. 
     Another implementation of the invention encompasses a method. A first opening of a removable housing is engaged to a proximal end of a lumen inserted into a patient. A transfer of a fluid sample from a distal end of the lumen, through the lumen, and into the removable housing through the first opening is caused such that the fluid sample contacts a detection indicator coupled with the removable housing. A visual comparison of the detection indicator with a reference indicator, coupled to the removable housing, is performed to determine a characteristic of the fluid sample. The first opening of the removable housing is removed from the proximal end of the lumen. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features of example implementations of the invention will become apparent from the description, the claims, and the accompanying drawings in which: 
         FIG. 1  is an overall side view of an exemplary embodiment of a nasogastric tube insertion system  100  constructed according to an aspect of the present invention; 
         FIG. 2  is a side view of a guide element  120  of the nasogastric tube insertion system  100  of  FIG. 1 , showing the guide element in another configuration; 
         FIG. 3  is an enlarged side view of the leading section  154  of the guide element  120  of  FIGS. 1-2 ; 
         FIG. 4  is a partial cross-section view of the leading section  154  of the guide element  120  of  FIGS. 1-3  taken along section line  4 - 4  of  FIG. 3 ; 
         FIG. 5  is a cross-section view of the trailing section  152  of the guide element  120  of  FIG. 1  taken along section line  5 - 5  thereof; 
         FIG. 6  is a cross-section view of an alternate embodiment of the trailing section  152  of the guide element  120  of  FIG. 1  taken along section line  5 - 5  thereof; 
         FIG. 7  is a cross-section view of another alternate embodiment of the trailing section  152  of the guide element  120  of  FIG. 1  taken along section line  5 - 5  thereof; 
         FIG. 8  is a cross-section view of the leading section  154  of the guide element  120  of  FIG. 1  taken along section line  8 - 8  thereof; 
         FIG. 9  is a cross-section view of an alternate embodiment of the leading section  154  of the guide element  120  of  FIG. 1  taken along section line  8 - 8  thereof; 
         FIG. 10  is a cross-section view of a nasogastric tube  110  of the nasogastric tube insertion system  100  of  FIG. 1 , taken along section line  10 - 10  thereof; 
         FIG. 11  is a side view of an inserter element  130  of the nasogastric tube insertion system  100  of  FIG. 1 ; 
         FIG. 12  is an enlarged side view of the insertion section  174  of inserter element  130  of  FIGS. 1 and 11  and the leading section  154  of guide element  120  of  FIGS. 1-4  showing the insertion section  174  about to be attached to the guide element  120 ; 
         FIG. 13  is an enlarged perspective view of the tip  186  of insertion section  174  of inserter element  130  of  FIGS. 1 ,  11 , and  12  and a portion of the leading section  154  of guide element  120  of  FIGS. 1-4 ; 
         FIG. 14  is a side view showing the guide element  120  of  FIGS. 1-4  attached to the inserter element  130  of  FIGS. 1 ,  11 , and  12 , and depicting a stage in an exemplary method of inserting the nasogastric tube insertion system  100  in which the swallowable weight  158  is held on the tip  186  of inserter element  130  by tension on the guide element  120  provided by the user; 
         FIG. 15  is a side view showing the guide element  120  of  FIGS. 1-4  attached to the inserter element  130  of  FIGS. 1 ,  11 , and  12 , and depicting another stage in the method of inserting the nasogastric tube insertion system  100  in which the swallowable weight  158  is held on the tip  186  of inserter element  130  by tension on the guide element  120  provided by the user; 
         FIG. 16  is a side view and stylized partial cross-section view showing the inserter element  130  and guide element  120 , depicting another stage in the method of inserting the nasogastric tube insertion system  100 , in which the inserter element  130  and guide element  120  are being inserted through the patient&#39;s nasal passages to the nasopharynx or oropharynx; 
         FIG. 17  is a side perspective view and stylized partial cross-section view showing the inserter element  130  and guide element  120 , depicting another stage in the method of inserting the nasogastric tube insertion system  100 , in which the inserter element  130  is removed and the swallowable weight  158  of the guide element  120  is being swallowed past the epiglottis; 
         FIG. 18  is a side view showing the nasogastric tube  110  and the guide element  120 , depicting another stage in the method of inserting the nasogastric tube insertion system  100 , in which the guide element  120  is threaded through an opening of the guide element retaining structure  136  of the nasogastric tube  110 ; 
         FIG. 19  is a side view and stylized partial cross-section view showing the nasogastric tube  110  and the guide element  120 , depicting another stage in the method of inserting the nasogastric tube insertion system  100 , in which the nasogastric tube  110  is pushed along the guide element  120  as the tube is inserted into the patient&#39;s nasal passage; 
         FIG. 20  is a flow diagram depicting steps of exemplary methods  310 ,  310   a  of inserting the nasogastric tube insertion system  100  into the patient; 
         FIG. 21  is an enlarged side view of an alternative embodiment  270  of the insertion section of inserter element  130  of  FIGS. 1 and 11  and an alternative leading section  250  of guide element  120  of  FIGS. 1-2 , showing the alternative insertion section  270  about to be attached to the guide element  120 ; 
         FIG. 22  is an enlarged cross-section view of an alternative embodiment  250  of the leading section of the guide element  120  of  FIG. 21 , taken along the section line  22 - 22  thereof; 
         FIG. 23  is an enlarged perspective view of the tip  272  of alternative insertion section  270  of inserter element  130  of  FIGS. 1 and 21  and a portion of the alternative leading section  250  of guide element  120  of  FIG. 22 ; 
         FIG. 24  is a side perspective view of a first embodiment of a proximal end section of an alternate nasogastric tube, in the form of a nasogastric feeding tube, for use in conjunction with the guide element  120  and inserter element  130  of the present invention; 
         FIG. 25  is a side perspective view of a second embodiment of a proximal end section of an alternate nasogastric tube, in the form of a nasogastric feeding tube, for use in conjunction with the guide element  120  and inserter element  130  of the present invention; 
         FIG. 26  is a side perspective view of a first embodiment of a distal end section of an alternate nasogastric tube, in the form of a nasogastric feeding tube, for use in conjunction with the guide element  120  and inserter element  130  of the present invention; 
         FIG. 27  is a cross section view of the distal end section of  FIG. 26 , taken along the section lines  27 - 27  thereof; 
         FIG. 28  is a side perspective view of a second embodiment of a distal end section of an alternate nasogastric tube, in the form of a nasogastric feeding tube, for use in conjunction with the guide element  120  and inserter element  130  of the present invention; 
         FIG. 29  is a flow diagram depicting steps of exemplary methods  510 ,  510   a  of inserting the nasogastric tube insertion system  100  into the patient using a nasogastric feeding tube of the type shown in  FIGS. 24-28 ; and  FIG. 30  is a side view showing the leading section of an alternate embodiment of a guide element, and the distal end of an alternate embodiment of a nasogastric tube, constructed according to an aspect of the present invention; 
         FIG. 31  is a cross section view of the alternate embodiments of the guide element and nasogastric tube of  FIG. 30 , taken along the section lines  31 - 31  of  FIG. 30 ; 
         FIG. 32  is a side view showing the alternate embodiments of the guide element and nasogastric tube of  FIGS. 30 and 31 , showing a weight element thereof in a deflated condition; 
         FIG. 33  is a side view showing the leading section of an alternate embodiment of a guide element with a weight element thereof having a first example configuration; 
         FIG. 34  is a side view showing the leading section of an alternate embodiment of a guide element with a weight element thereof having a second example configuration; 
         FIG. 35  is a side view showing the leading section of an alternate embodiment of a guide element with a weight element thereof having a third example configuration; 
         FIG. 36  is a side view showing the leading section of an alternate embodiment of a guide element with a weight element thereof having a fourth example configuration; 
         FIG. 37  is a side view showing the leading section of an alternate embodiment of a guide element before the weight element thereof is installed, depicting a first example configuration of members for retaining the weight element; 
         FIG. 38  is a side view showing the leading section of an alternate embodiment of a guide element before the weight element thereof is installed, depicting a second example configuration of members for retaining the weight element; 
         FIG. 39  is a side view showing the leading section of an alternate embodiment of a guide element before the weight element thereof is installed, depicting a third example configuration of members for retaining the weight element; 
         FIG. 40  is a side view showing the leading section of an alternate embodiment of a guide element before the weight element thereof is installed, depicting a fourth example configuration of members for retaining the weight element; 
         FIG. 41  is a flow diagram showing an example method according to an aspect of the invention for reconfiguring the shape of a guide element, such as that shown in  FIGS. 30-32 , and removing the guide element while the nasogastric tube remains in place; 
         FIG. 42  is a flow diagram showing an example method according to an aspect of the invention for reconfiguring the shape of a guide element, such as that shown in  FIGS. 33-40 , and removing the guide element while the nasogastric tube remains in place; 
         FIG. 43  is a side view of the proximal end section of an alternate embodiment of a nasogastric tube showing a chemical-property indicating element thereof; 
         FIG. 44  is a cross section view of the alternate embodiment of the nasogastric tube of  FIG. 43 , taken along the section lines  44 - 44  of  FIG. 43 ; 
         FIG. 45  is a side view of the proximal end section of a further alternate embodiment of a nasogastric tube showing a chemical-property indicating medium thereof in a first example configuration; 
         FIG. 46  is a side view of the proximal end section of a further alternate embodiment of a nasogastric tube showing a chemical-property indicating medium thereof in a second example configuration; 
         FIG. 47  is a cross section view of the alternate embodiment of the nasogastric tube of  FIG. 45 , taken along the section lines  47 - 47  of  FIG. 45 ; 
         FIG. 48  is a cross section view of the alternate embodiment of the nasogastric tube of  FIG. 46 , taken along the section lines  47 - 47  of  FIG. 45 ; 
         FIG. 49  is a side view of the further alternate embodiment of a nasogastric tube, showing a chemical-property indicating medium thereof in a third example configuration; 
         FIG. 50  is a side view of the further alternate embodiment of a nasogastric tube, showing a chemical-property indicating medium thereof in a fourth example configuration; 
         FIG. 51  is a side view of the leading section of a further alternate embodiment of a guide element, showing a chemical-property indicating medium thereof in a first example configuration; 
         FIG. 52  is a side view of the leading section of a further alternate embodiment of a guide element, showing a chemical-property indicating medium thereof in a second example configuration; 
         FIG. 53  is a flow diagram showing an example method according to an aspect of the invention for determining correct insertion of a nasogastric tube by exposing a chemical property indicator such as those shown in  FIGS. 43-50 ; and 
         FIG. 54  is a flow diagram showing an example method according to an aspect of the invention for determining correct insertion of a nasogastric tube by exposing a chemical property indicator such as those shown in  FIGS. 51-52 . 
         FIG. 55  is a top view of one implementation of a housing for a detection indicator. 
         FIGS. 56A and 56B  are top and side views of the housing of  FIG. 55  with the detection indicator in place. 
         FIG. 57  is a perspective view of one implementation of an adapter configured for use with the housing of  FIG. 55 . 
         FIGS. 58 and 59  are top and side views of the housing of  FIG. 55  engaged with a lumen at a first opening with the adapter of  FIG. 57  and also engaged with a fluid retrieval component at a second opening. 
         FIG. 60  is a side view of another implementation of the housing and the fluid retrieval component formed as a bulb-syringe. 
         FIG. 61  is a side view of another implementation of the housing and the fluid retrieval component formed as a syringe. 
         FIG. 62  is a side view of an implementation of the housing formed as a test tube. 
         FIG. 63  is a side view of another implementation of the housing formed as a vacutainer. 
         FIG. 64  is a partial side view of one implementation of the housing illustrating the detection indicator molded into a wall of the housing. 
         FIG. 65  is a cross section of another implementation of the housing illustrating a separate channel for the detection indicator. 
         FIGS. 66-69  are partial side views of the housing with various implementations of the detection indicator. 
         FIG. 70  is a logic flow for use of one implementation of the housing. 
         FIG. 71  is another logic flow for an alternate use of the housing. 
     
    
    
     DETAILED DESCRIPTION 
     One embodiment of a nasogastric tube insertion system  100  constructed according to the present invention is shown generally in  FIGS. 1-20 . The nasogastric tube insertion system  100  is intended for use with a patient who is conscious, alert, and able to swallow. 
     As best seen in  FIG. 1 , the nasogastric tube insertion system  100  comprises a nasogastric tube  110 , a guide element  120 , and an inserter element  130 . The function of the inserter element  130  is to aid in the initial placement of a portion of the guide element  120  in the patient&#39;s oropharynx. 
     The function of the guide element  120  is to establish a desired path for passage of nasogastric tube  110  through the patient&#39;s nasal passages, the oropharynx, the esophagus, and the stomach, and to guide the nasogastric tube  110  along that path during the tube&#39;s insertion. 
       FIGS. 24-28 , discussed further in greater detail, depict alternate embodiments of a nasogastric tube which may be used in conjunction with the guide element  120  and inserter elements of the present invention. One of skill in the art will appreciate that although several embodiments of nasogastric tubes are described herein as examples by which aspects of the present invention may be implemented, the inserter element, guide element, and associated methods could be used for other types of nasogastric tubes and for other similarly configured objects which are desired to be inserted through the patients nostrils. 
       FIG. 1  depicts a configuration in which the nasogastric tube  110 , guide element  120 , and inserter element  130  are simultaneously connected to or engaged with one another, and a commercial embodiment of the nasogastric tube insertion system  100  could be so constructed. However, it will be appreciated that is not necessary that these components ever actually be arranged in that configuration. It is sufficient that the guide element  120  be attached to the inserter element  130  during the insertion of a portion of the guide element into the patient&#39;s oropharynx. In a subsequent step, it is sufficient that the guide element  120  be partially enveloped by or threaded through a portion of the nasogastric tube  110  during the insertion of the tube  110  in order that the tube  110  follow the path established by the guide element  120 . 
     As best seen in  FIGS. 1 and 11 , the inserter element  130  is constructed as a generally thin, longitudinal member having predominantly straight, slender, and elongate main body section  172  and a curved insertion section  174  which is adapted to engage an end of guide element  120  to enable insertion of the guide element into the patient&#39;s nasal passage or oropharynx. The insertion section  174  shown and described in connection with these figures is a first exemplary embodiment constructed according to an aspect of the present invention. An alternative embodiment  270  of the insertion section, adapted for use with an alternative embodiment  250  of the leading section of guide element  120 , is shown in  FIGS. 21-22  and described further in greater detail. 
     The inserter element  130  preferably comprises a handle  176  to allow the inserter element  130  to be readily grasped and controlled by a user. An exemplary configuration for handle  176  is shown in  FIGS. 1 and 11 , in which the handle is formed as two loops of structural material attached to and extending downward from the main body  172 . The loops form handle openings  178 , which may, for example, receive the user&#39;s index and middle fingers and allow the inserter element  130  to be grasped. A stabilizing extension  180  extending from the main body section rearward of the handle  176  improves stability during handling of the inserter element  130 . Other handle configurations could also be used. 
     The main body  172  of the inserter element  130  may be constructed of any suitable material having sufficient thickness and strength to be handled and to support the modest weight of the insertion section  174  and a portion of the guide element  120  which is attached thereto during the insertion process. For example, the insertion section  174  may be constructed of semi-flexible, biologically inert material, such as clear poly-vinyl chloride. Other materials could also be used. The cross section and exact dimensions of the main body  172  are non-critical but may be selected to optimize cost, user comfort, and compatibility with the insertion section  174 . 
     The insertion section  174  preferably has one or more curved portions such that it generally conforms to the anatomy of a typical patient&#39;s nasal passages and oropharynx. The curved portions may cumulatively provide curvature in the range of approximately 70 to 100 degrees of arc in the direction of the handle  176 . 
     The insertion section  174  is preferably constructed of a flexible, biocompatible material, providing sufficient stiffness to support the swallowable weight  158  of guide element  120 , but also providing enough flexibility to deform as needed, during insertion of the insertion section  174  into the patient&#39;s nasal passages, to pass any obstacles encountered without injury or abrasion. For example, the insertion section  174  may be constructed of semi-flexible, biologically inert material, such as clear poly-vinyl chloride. Other materials could also be used. The insertion section  174  may have any suitable cross section, including without limitation a generally circular, semi-circular, oval, oblong, or rectangular cross section. The cross-section of insertion section  174  may permit more flexibility in the direction of curvature than in directions perpendicular thereto. As discussed further in greater detail, the insertion section  174  preferably has a groove or channel  194  ( FIG. 13 ) along at least a portion of its dorsal surface to receive a portion of the guide element  120 . The insertion section  174  is preferably free of sharp exterior edges or other structures that may cause injury or abrasion of tissues in the nasal passages. 
     The exact dimensions of the insertion section  174  are non-critical, but preferably are selected as appropriate for the material used, to provide a desired amount of stiffness and flexibility, and to allow the inserter to easily enter and pass through the nasal passages of a patient. The insertion section  174  should be long enough that, when inserted, the tip  186  can reach into the patient&#39;s oropharynx without requiring the handle  176  to impinge on the patient&#39;s face. It is believed that an insertion section  174  having a width less than or equal to about 0.75 cm, a thickness less than or equal to about 0.5 cm, and a length of approximately 25 cm or more, would be appropriate for use with an adult patient of typical size. Smaller dimensions may be needed for use with smaller patients, including children and infants. In addition, the dimensions could be varied to achieve desired variations in stiffness or other mechanical parameters. For example, if increased flexibility is desired toward the end of the insertion section  174 , the thickness or width may be gradually reduced in that section. The main body  172  and insertion section  174  may be separately constructed and later assembled to form a unit. Alternately, the main body  172  and insertion section  174  may be constructed as a single unit, and there may be no visible structural characteristics that signal when one ends and the other begins. 
     The inserter element  130  preferably has measurement lines  182  or other suitable indicia to allow the user to readily ascertain when the inserter has been inserted to a predetermined insertion depth, corresponding to the placement of the end of the insertion section  174 , and the swallowable weight  158  attached thereto, in a desirable location in the patient&#39;s oropharynx. 
     For most patients, an optimal predetermined insertion depth may be found by measuring the distance between the patient&#39;s earlobe and the tip of the patient&#39;s nose. The inserter element  130  may also have measurement legend indicia  184  specifying units of measurement or other related information associated with measurement lines  182 . However, the user may perform the distance measurement using the inserter element  130  itself, e.g., by marking the distance on the measurement lines  182 . 
     Although it is normally expected that the desired inserter-assisted placement of the swallowable weight  158  be into the patient&#39;s oropharynx, it may be preferable in some situations to use the inserter element  130  to place the swallowable weight  158  only part way into the nasal passages. In those situations, the swallowable weight  158  would then be released from the inserter element  130 , and the user would advance the guide element  120  into the oropharynx by applying longitudinal pressure, relying on the stiffness of the guide element to assist placement. A shorter inserter element  130  could be used for such situations, and the desired insertion distance could be measured using different benchmarks on the patient&#39;s face or body. 
     As best seen in  FIG. 13 , the insertion section  174  preferably has walls  196  forming a groove or channel  194  along at least a portion of its dorsal surface  244  to receive the guide element  120 . An alternative embodiment  270  of the insertion section is shown in  FIGS. 21-23  and described further in greater detail. Once the swallowable weight  158  of the guide element  120  is placed on the end of the inserter element  130 , in order to retain the swallowable weight  158  in position, the user must apply light tension on the guide element  120 . The channel  194  is adapted to retain the guide element  120  along the top surface of the inserter element  130  while tension is applied. This avoids undesirably deforming the insertion section  174  and prevents the guide element  120  from taking on a “bow string” configuration, which would interfere with the insertion process. 
     Although channel  194  is depicted in  FIG. 13  as a generally U-shaped channel of considerable depth, other configurations could also be used provided they retain the guide element  120  along the dorsal surface  244  of the inserter element  130  while light tension is applied to the guide element  120 . For example, the depth of the channel could be significantly less than depicted. For another example, the channel-forming walls  196  could be formed as two or more longitudinal ridges on the dorsal surface of the guide element  120 , which might otherwise be flat. The ridges could be of any height that satisfactorily retains the guide element  120  while light tension is applied. The term “dorsal” is used here to refer to the upper surface  244  of the inserter element  130 , as shown in  FIGS. 1 and 11 , without respect to the orientation in which the inserter element  130  is held. 
     As best seen in  FIGS. 11-13 , the tip  186  of the insertion section  174  has a stepped engagement section  188  of reduced thickness for loosely engaging the swallowable weight  158  of the guide element  120 . As mentioned above, once the swallowable weight  158  is placed onto the tip  186  of the insertion section  174 , the tip is preferably held in place by light tension on guide element  120 . The loose engagement preferably allows the swallowable weight  158  to be released from the tip  186  by releasing tension on the guide element  120 , allowing the swallowable weight  158  to fall away.  FIGS. 12 and 13  depict the tip  186  and stepped engagement section  188  in alternate configurations.  FIGS. 21 and 23  depict an alternative embodiment  270  of the insertion section and will be discussed further in greater detail. 
     In  FIG. 12 , there is shown a first embodiment in which the tip  186  has an angular chamfered section  190  adapted to engage a mating receptacle  168  of the swallowable weight  158  of the guide element  120 . Substantially vertical step walls mark the boundary between the full-thickness portion of the insertion section  174  and the stepped engagement section  188 . The stepped engagement section  188  extends a short distance from the step walls  198  to the tip  186 . The leading section  154  of guide element  120  is retained in channel  194  ( FIG. 13 ) when the swallowable weight  158  is placed on tip  186  and light tension is applied to guide element  120 . 
     In  FIG. 13 , there is shown a second embodiment in which the tip  186  has a substantially vertical wall section  192  instead of the angular chamfered section  190  of  FIG. 12 . Angular step walls  242  mark the boundary between the full-thickness portion of the insertion section  174  and the stepped engagement section  188 . The stepped engagement section  188  extends a short distance from the step walls  242  to the tip  186 . The leading section  154  ( FIG. 12 ) of guide element  120  is retained in channel  194  when light tension is applied to guide element  120 . 
     As best seen in  FIGS. 1-2 , the guide element  120  is constructed as a thin, elongate or generally longitudinal element, which may be a cord or line, having a leading section  154  having sufficient flexibility to be easily inserted into and swallowed by the patient, and trailing section  152  having sufficient rigidity to guide the nasogastric tube  110  as the tube is inserted. The trailing section also functions as a tether. A swallowable weight  158  is attached to the leading section  154 . A transition  156  joins the trailing section  152  and leading section  154 . A stopper  160  may be provided near the end  150  of guide element  120  opposite the swallowable weight  158  to prevent the end from being swallowed by the patient. Alternatively, the trailing section  152  could be extremely long, such that it cannot be swallowed. An alternative embodiment  250  of the leading section of guide element  120  is shown in  FIGS. 21-22  and described further in greater detail. 
     The trailing section  152  of the guide element  120  may be constructed of any suitable material having sufficient thickness, flexibility and strength to be handled and to reliably avoid breakage. The trailing section  152  is preferably be rigid enough to navigate over the trachea and into the esophagus, but flexible enough to be readily swallowed. For example, the trailing section  152  may be constructed of a silicone elastomer or of a polymer in the nylon family. Other highly-flexible, biologically inert materials could also be used. 
     The leading section  154  is preferably constructed of any suitable biocompatible material, having sufficient thickness, flexibility and strength to be handled and to reliably avoid breakage. The leading section  154  is preferably flexible enough to be very easily swallowed. Because the leading section  154  will be swallowed and will be subject to digestive acids and enzymes for some period, the material from which the leading section  154  is constructed is preferably highly resistant to attack from such agents. For example, the leading section  154  may be constructed of a silicone elastomer or of a polymer in the nylon family. Other highly-flexible, biologically inert materials could also be used. Preferably, the trailing section  152  is free of sharp edges and has suitable outer surface features and finish to avoid injury or abrasion of tissues when the leading section  154  is swallowed and removed. In some situations, it may be desirable to use the inserter element  130  to assist the insertion of the leading section  154  of guide element  120  only part way into the patient&#39;s nasal passages, and then to use longitudinal pressure on the guide element  120  to further advance the leading section  154  into the patient&#39;s oropharynx without the continued assistance of the inserter element  130 . 
     In such situations, it is desirable that leading section  154  possess sufficient stiffness accommodate advancement of the leading section into the oropharynx, while retaining sufficient flexibility to avoid damaging tissues during insertion and removal. 
     As best seen in  FIGS. 5-7  and  8 - 9 , the longitudinal elements  152 ,  154  of the guide element  120  may be constructed as a unitary or monofilament line or piece, or as a string or cord, or similar form of stranded or woven multifilament line.  FIGS. 5 and 8  depict in cross section a first exemplary embodiment of the guide element  120  in which the trailing section  152   a  is formed as an element of generally oval or oblong cross section, and the leading section  154   a  is also formed as an element of generally oval or oblong cross section of somewhat reduced size. 
       FIGS. 6 and 9  depict in cross section a second exemplary embodiment of the guide element  120  in which the trailing section  152   b  is formed as an element of generally circular cross section, and the leading section  154   b  is also formed as an element of generally circular cross section of somewhat reduced size.  FIG. 7  depicts in cross section a third exemplary embodiment of the guide element  120  in which both the trailing and leading section  152   c  are formed as a twisted bifilar cord. 
     The elements may be formed by molding, extrusion, drawing, or any other suitable method of manufacture. These particular configurations are provided by way of example, not limitation, and it will be appreciated that other cross sections, number of filaments, stranding configurations, and the like could also be used, and that the configuration used for the leading section  154  may differ from that used for the trailing section  152 . 
     The exact dimensions of the leading section  154  and the trailing section  152  of guide element  120  are non-critical but may be selected to optimize cost, compatibility with one another, and with a guide element retaining structure  136  of nasogastric tube  110  ( FIGS. 1 ,  10 ), discussed further in greater detail. A leading section  154  having a width in the range of approximately 0.1-2.5 mm and a thickness in the range of approximately 0.1-2.5 mm, would be appropriate, but the necessary dimensions may vary depending on material choices, the flexibility or stiffness desired, and other factors. A trailing section  152  having a width in the range of approximately 0.1-3.5 mm, and a thickness in the range of approximately 0.1-3.5 mm would be appropriate, but the necessary dimensions may vary depending on material choices, the flexibility or stiffness desired, and other factors. The trailing section  152  and leading section  154  may be separately constructed and later assembled to form a unit. Alternately, the trailing section  152  and leading section  154  may be constructed as a single unit. 
     A transition area  156  designates the area at which trailing section  152  is joined to leading section  154 . If these components are formed as an integrated unit of the same size and cross-section throughout, the transition area may not be apparent. If the trailing section  152  and leading section  154  are dissimilar, the leading section  154  is preferably long enough to allow the patient to swallow the swallowable weight  158  into the stomach without ingesting part of the trailing section  152 . Also, the change from leading section  154  to the trailing section  152  may be gradual rather than abrupt. 
     As best seen in  FIGS. 3 ,  4 , and  12 , the swallowable weight  158  is attached to the leading section  154  of guide element  120 . The swallowable weight  158  preferably comprises a resilient body  246  and an interior attachment structure  164  for affixing the shell to the leading section  154  of the guide element  120 . An alternative embodiment  252  of the swallowable weight is shown in  FIGS. 21 and 22 , and described further in greater detail. 
     The body  246  is preferably soft and resilient so that it may be easily swallowed with minimal discomfort to the patient and so that it avoids abrading or irritating tissues when it is inserted through the patient&#39;s nasal passages into the oropharynx. The body  246  is preferably constructed from a flexible, absorbent, biocompatible material, which may, for example, be a spongiform material such as open-cell foam. Other materials could also be used. Because the body  246  will be swallowed and will be subject to digestive acids and enzymes for some period, the material from which the body  246  is constructed is preferably highly resistant to attack from such agents. Although the swallowable weight  158  is referred to as a weight, it need not be heavy or constructed of dense materials. It is sufficient that the weight be easily swallowed. The dimensions of the swallowable weight  158  are not critical, but the weight is preferably of a size that can be easily swallowed and can easily pass through the patient&#39;s nasal passages. A diameter in the range of approximately 0.4-1.25 cm, and a length in the range of approximately 0.7-1.7 cm are believed to be suitable for most adult patients. Other sizes could also be used; a smaller weight may be required for smaller patients, such as children and infants. 
     The interior attachment structure  164  may be any suitable structure that can be securely affixed to the body  246 . For example, the attachment structure  164  may be formed as a cup-like element having a cylindrical attachment wall  166 . However, other structures could also be used. The attachment structure  164  may be secured to the body  246  using any suitable fastening technology, including but not limited to glue, ultrasonic or chemical bonding or welding, structural features such as barbs or hooks, or a tight friction fit. 
     The leading section  154  of guide element  120  extends outward from the attachment structure  164  through an opening  162  in the body  246 . The leading section  154  may be secured to the attachment structure  164  using any suitable fastening technology, including but not limited to glue, ultrasonic or chemical bonding or welding, or interlocking structural features. 
     Alternatively, the attachment structure  164  may be formed as an integrated part of the leading section  154 . As best seen in  FIG. 3 , the bottom  168  of the attachment structure  164 , the attachment wall  166 , and the leading section  154  form an evacuated-toroid-shaped space to receive the tip  186  of the insertion section  174  of the inserter element  130 . This configuration enables the tip  186  to be held against the attachment structure  164  without piercing the resilient material of the body  246 , which would undesirably produce a frictional engagement of these components. A loose engagement between swallowable weight  158  and tip  186  of leading section  154  of inserter element  130  is desirable to allow the swallowable weight  158  to be released from the tip  186  by releasing tension on the guide element  120 , causing the swallowable weight  158  to fall away. 
     As best seen in  FIGS. 1 and 8 , the nasogastric tube  110  is preferably constructed as an elongate, generally tubular, body structure comprising a main tubular section  112 , a proximal end section  114 , and a distal end section  116 . The distal end section  116  is intended to be inserted into the patient. The proximal end section  114  is intended to remain outside of the patient. The nasogastric tube  110  includes one or more interior bores or lumina extending approximately the length of the tube  110 . As best seen in  FIG. 10 , an exemplary embodiment of nasogastric tube  110  has three interior bores or lumina  144 ,  146 , and  148 , but more or fewer lumina could be used depending on the application and the permissible thickness of the nasogastric tube  110 . For example, nasogastric tube  110  may have a single lumen for use as a feeding tube to allow the direct introduction of food or nutritional supplements into the patient&#39;s stomach. Nasogastric tube  110  may also comprise a radiopaque tracer strip  142  to allow the position of the nasogastric tube  110  to be verified using radiographic or fluoroscopic examination. 
     The proximal end section  114  may separate into two or more breakout segments, each including one or more of the lumina  144 ,  146 ,  148 . As best seen in  FIG. 1 , in an exemplary embodiment, proximal end section  114  separates into a first breakout tube  118 , carrying lumen  144 , and a second breakout tube  124  carrying lumina  146  and  148 . Second breakout tube  124  provides openings  126  and  128  into lumina  146  and  148  to allow connection of the lumina to a source of fluid to be introduced into the stomach, or a vacuum “supply to remove fluid from the stomach, or to allow the lumen to be vented to the atmosphere. First breakout tube  118  has an opening (not shown) into first lumen  144 . As best seen in  FIG. 1 , a one-way valve  122  may be connected to one of the lumina to control ventilation of the stomach. 
     The distal end section  116  has a leading end  132 . Adjacent the leading end  132 , there is provided a plurality of openings  134  leading to the interior bores or lumina  144 ,  146 , and  148  and allowing fluid and gas communication between the lumina  144 ,  146 , and  148  and the exterior space surrounding the leading end  132 . The opening or openings leading to a particular one of the lumina may be spaced from the openings leading to other lumina as required by the application. For example, if one lumen is assigned to introduce fluids into the stomach, and another lumen is assigned to remove fluids from the stomach, it may be desirable to separate the corresponding openings so that the fluids newly introduced are not immediately removed. 
     The distal end section  116  of nasogastric tube  110  further comprises a guide element retaining structure  136  adapted to move slidably along guide element  120 . As best seen in  FIGS. 1 and 10 , the guide element retaining structure preferably comprises a generally tubular protrusion or intrusion attached and parallel to proximal end section  114  having a tubular opening  140  to receive the guide element  120 . Once the guide element has been inserted, the guide element retaining structure  136  allows the nasogastric tube  110  to move slidably and telescopically along the guide element  120 . Thus, the guide element  120  may serve to establish a path for the nasogastric tube  110  to follow as it is inserted through the patient&#39;s nasal passages, oropharynx, esophagus, and into the patient&#39;s stomach. The leading end  138  and a trailing end  248  of the guide element retaining structure  136  are preferably chamfered to avoid abrading or irritating tissues which are encountered as the nasogastric tube  110  is inserted and removed. 
     Although the guide element retaining structure  136  is shown in  FIGS. 1 and 10 , and described herein as a tubular element attached to the distal end section  116 , other structures could also be used to form the guide element retaining structure  136  adapted for slidable and/or telescopic movement along the guide element  120 . For example, the guide element retaining structure  136  could be formed as one or more loops or retaining tabs attached to the distal end section  116 . For another example, the guide element retaining structure  136  could be formed as a tunnel-style bore through an unused portion of the cross section of the nasogastric tube  110 . This configuration has the advantage that no enlargement of the cross-sectional size of the nasogastric tube  110  is needed, but it may not be possible to implement if the tube is crowded. As a further alternative to a separate structure  136  dedicated to retaining the guide element  120 , features of the distal end  116  of the nasogastric tube  110  may be used to form a guide element retaining structure. For example, guide element  120  could be threaded or telescoped through an aperture placed at or adjacent the tip  132  of the distal end section  116  of the nasogastric tube  110 , extend through one of lumina  144 ,  146 , or  148 , and could exit through one of the openings or apertures  134  in communication with such lumen and spaced from the tip  132 . 
     The dimensions of the nasogastric tube  110  are non-critical, but must be selected to allow the tube to be inserted through the nasal passages and into the stomach, and to remain there without interfering with the patient&#39;s respiration. A smaller diameter, if permitted by the requirements for the lumina inside the tube, is generally preferable in that it minimizes patient discomfort. A nasogastric tube  110  having a diameter of approximately 0.25 inches is believed to be suitable for most adult patients. The length of the nasogastric tube  110  should be long enough to extend into the patient&#39;s stomach, with some additional length outside the patient to allow for convenient external connections and to prevent the patient from inadvertently swallowing the proximal end section  114  of the nasogastric tube  110 . 
     The nasogastric tube  110  is preferably constructed of any suitable biocompatible material, having sufficient thickness, flexibility and strength. Because the nasogastric tube  110  will be swallowed and will be subject to digestive acids and enzymes for some period, the material from which the nasogastric tube  110  is constructed is preferably non-porous and highly resistant to attack from such agents. For example, the nasogastric tube  110  may be constructed of a silicone elastomer. Other flexible, biologically inert materials could also be used. The nasogastric tube  110  is preferably transparent or translucent to allow visual inspection of the lumina for proper operation. 
       FIGS. 14-19  depict several steps in exemplary methods  310 ,  310   a  ( FIG. 20 ) according to an aspect of the present invention for use in conjunction with the nasogastric tube insertion system  100  of  FIGS. 1-13 . 
       FIG. 20  is a flow diagram depicting steps of exemplary methods  310 ,  310   a.  In method  310 , the inserter element  130 , with the swallowable weight  158  engaged to the insertion end thereof, is used to insert the swallowable weight through the patient&#39;s nasal passages and into the oropharynx. 
     In method  310   a,  the inserter element  130  is used to insert the swallowable weight through the patient&#39;s nasal passages. Then the swallowable weight  158  is released from the end of inserter element  130  and is advanced into the patent&#39;s oropharynx, by, for example, gentle longitudinal pressure on the guide element  120  in the direction of the patient&#39;s oropharynx. 
     In other respects, the methods  310  and  310   a  are similar. The term “step” is used herein to refer to both the general steps associated with one of methods  310 ,  310   a,  and to more detailed substeps which may be comprised as part of a more general step. Some steps are optional. 
     A first group of steps  312 ,  314 ,  316  is generally depicted in  FIG. 14 . The user grasps the handle  176  ( FIGS. 1 and 11 ) of inserter element  130  using a first hand  212 . The user places the swallowable weight  158  on the tip  186  of insertion section  174  of inserter element  130  (step  314 ). The user then uses a second hand  210  to apply light tension on guide element  120 , thereby maintaining the swallowable weight  158  in position on the end of inserter element  130  (step  316 ) A second group of steps is generally depicted in  FIG. 15 . The user uses the second hand  210  to gently pull the guide element  120  rearward, in order to position the guide element  120  in channel  194  ( FIG. 13 ) on the dorsal surface of inserter element  130 . The user must allow controlled slippage of the guide element  120  to allow the second hand to move rearward while maintaining light tension on guide element  120 . The user then uses the thumb  214  of the first hand to trap the guide element  120  under light tension against the dorsal surface of the inserter element  130 . This prevents the swallowable weight  158  from falling off of the inserter element  130 . 
     In an optional step, the user may transfer the inserter element  130  and guide element  120  from the first hand to the second hand. Subsequent steps assume this has been done. 
     In another optional step, the user may apply one or more of an anesthetic (such as lidocaine), and a vasoconstrictor (such as epinephrine), to the absorbent material of the swallowable weight  158 . The anesthetic numbs the passage to the stomach. The vasoconstrictor causes vasoconstriction of the nasal mucosa allowing for easier passage and decreased bleeding. This step may be performed, for example, by dipping the swallowable weight  158  into a container of these substances. The anesthetic and vasoconstrictor agents may be packaged with the nasogastric tube insertion system  100 , to promote their use. Also, the swallowable weight  158  may be pre-moistened with the anesthetic and vasoconstrictor agents by a manufacturer or distributor, to relieve the user of the burden of applying the agents, and to minimize the risk of contamination which might occur in bulk containers of the agents in a clinical environment. 
     A third group of steps  318  is generally depicted in  FIG. 16 . The user inserts the inserter element  130  and guide element  120  through the nostril  222  of patient  220 , through the nasal passages, and into the oropharynx  224  (step  318 ). The user maintains pressure on guide element  120  using the thumb  218  during this process to keep the swallowable weight  158  in position. The user is preferably guided by measurement indicia  182  to insert the inserter element  130  to a predetermined insertion depth measured earlier. For most patients, an optimal predetermined insertion depth may be found by measuring the distance between the patient&#39;s earlobe and the tip of the patient&#39;s nose. 
     A fourth group of steps  320 ,  322 ,  326  is generally depicted in  FIG. 17 . The user releases thumb  218 , thereby relieving pressure on the guide element  120 , and freeing the swallowable weight  158 , allowing it to fall (steps  320 ,  322 ). At approximately the same time, the patient  220  is instructed to swallow the swallowable weight  158  (step  326 ). The patient may be given some water to sip to assist in swallowing. As a consequence of swallowing, the patient&#39;s epiglottis  230  covers the trachea  228 , ensuring that the swallowable weight  158  is carried into the esophagus  226 , and then into the stomach. The trailing section  152  and proximal end  150  of guide element  120  remains outside the patient. The user then removes the inserter element  130 , which is no longer required for this procedure. 
     Although the steps heretofore described in connection with  FIGS. 16-17  contemplate that the inserter  130  be used to place the swallowable weight  158  all the way into the patient&#39;s oropharynx  224 , it may be preferable in some situations to use the inserter element  130  to place the swallowable weight  158  only part way into the nasal passages-that is, between the nostril  222  and the oropharynx  224 . In an alternative submethod  310   a  according to an aspect of the present invention for use in conjunction with the nasogastric tube insertion system  100  of  FIGS. 1-13 , the steps of  FIGS. 16-17  may be modified as follows: The user inserts the inserter element  130  and guide element  120  through the patient&#39;s nostril  222 , and into a predetermined location in the nasal passages, but not as far as the oropharynx  224  (step  312   a - 318   a ). The user maintains pressure on guide element  120  using the thumb  218  during this process to keep the swallowable weight  158  in position (step  316 ). 
     The user is preferably guided by measurement indicia  182  to insert the inserter element  130  to a predetermined insertion depth measured earlier. For most patients, an optimal predetermined insertion depth may be found by measuring the distance between selected benchmarks on the patient&#39;s face or body. A shorter inserter element  130  may be used. The user releases thumb  218 , thereby relieving pressure on the guide element  120 , and freeing the swallowable weight  158  (steps  320 ,  322 ). The inserter element  130  may optionally be retracted, or it may be temporarily left in place to support the guide element  120  during advancement of the swallowable weight into the oropharynx. 
     The user applies gentle longitudinal pressure to guide element  120  to further advance the swallowable weight  158  into the oropharynx  224 , noting by feel or by patient reaction when the weight has arrived in the desired position (step  324   a ). The patient is then instructed to swallow the swallowable weight  158  (step  326 ). The patient may be given some water to sip to assist in swallowing. As a consequence of swallowing, the patient&#39;s epiglottis  230  covers the trachea  228 , ensuring that the swallowable weight  158  is carried into the esophagus  226 , and then into the stomach. The trailing section  152  and proximal end  150  of guide element  120  remains outside the patient. The user then removes the inserter element  130 , if present. The remaining steps of methods  310  and  310   a  are similar. 
     A fifth group of steps  328 ,  330  is generally depicted in  FIG. 18 . The user threads the proximal end  150  of the guide element  120  through the retaining section opening  140  of the guide element retaining structure  136  of nasogastric tube  110  (step  330 ). This step is optional; the nasogastric tube  110  may be supplied by the manufacturer, or otherwise distributed to the user, in the condition in which the guide element  120  is already telescoped through the guide element retaining structure  136 . 
     A sixth group of steps  328 ,  332  is generally depicted in  FIG. 20 . Holding the guide element  120  firmly in a first hand  212 , and the nasogastric tube  110  in a second hand  210 , the user pushes the nasogastric tube  110  telescopically along the guide element  120 . The user inserts the nasogastric tube  110  through the nostril  222  and the tube safely follows the path established by the guide element  120  into the patient&#39;s stomach (step  332 ). The guide element  120  and nasogastric tube  110  remain together until the nasogastric tube  110  is to be removed. Then, the nasogastric tube  110  and the guide element  120  are removed together. As described further in greater detail, in other embodiments, the guide element  120  may be removed prior to removing the nasogastric tube  110 . 
     Although the shape of the swallowable weight  158  has been shown in  FIGS. 1  and as generally cylindrical, there may be situations in which a different shape is advantageous. Especially upon removal of the nasogastric tube  110  and guide element  120 , a gentler transition from the thin leading section  154  of the guide element to the full diameter of the swallowable weight  158  may ease passage of the swallowable weight through the patient&#39;s esophagus, nasal passages, and the like, and may minimize damage to tissues and deterioration of the weight.  FIG. 21  is an enlarged side view of an alternative embodiment  250  of the leading section of guide element  120 .  FIG. 21  also depicts an alternative embodiment  270  the insertion section of inserter element  130  which may advantageously be used in conjunction with the alternative leading section  250  of guide element  120 .  FIG. 22  is an enlarged cross-section view of the alternative leading section  250 . 
       FIG. 23  is an enlarged perspective view of the tip  272  of the alternative insertion section  270  of inserter element  130  portion of the alternative leading section  250  of guide element  120 . The features of these  FIGS. 21-23  will generally be described together. Except for the points of departure mentioned in connection with  FIGS. 21-23 , guide element  120  and inserter element  130  may be constructed in the same manner, and may have the same properties, as generally described earlier. 
     As best seen in  FIGS. 21-22 , alternative leading section  250  preferably has a slender longitudinal portion similar to that of leading section  154  ( FIG. 1 ). Alternative leading section  250  preferably also has a body  252  which may include a first section  254  of generally cylindrical shape adjacent to a second section  258  of generally conical shape at a transition  262 . The front or leading edge  256  of body  252  may have a rounded or partially-spherical contour to aid insertion. It is not essential that the shape of the first section  254  be cylindrical, but it is preferable that it have sufficient diameter that the body  252  serve as a weight and be acted upon by the patient&#39;s swallowing mechanism, and it may be preferable that the contour be relatively free from large topological features that may interfere with anatomical structures during insertion. It is not essential that the shape of the second section  258  be conical, but is it preferable that its diameter gradually increase from that of the slender longitudinal portion of alternative leading section  250  to the full diameter of the body  252 . The transition  262  from the first section  254  to the second section  258  may be so gradual as to be invisible, and these sections may be integrally constructed. 
     The body  252  is preferably securely attached to the slender longitudinal portion of alternative leading section  250  using an attachment structure  260 . For example, the longitudinal portion of the alternative leading section  250  may extend into the body, and an attachment structure  260  may be formed as an anchor or other structure for securely mechanically engaging the body  252 . However, the attachment structure  260  may also be formed as any part of leading section  250  in contact with body  252  and fastened thereto using any suitable fastening technology, including but not limited to glue, ultrasonic or chemical bonding or welding, structural features such as barbs or hooks, or a tight friction fit. The body  252  and the alternative leading section  250  may be constructed of materials and attached as described in connection with the swallowable weight  158  of the earlier-described embodiment. 
     As best seen in  FIGS. 21 and 23 , alternative insertion section  270  of inserter element  130  may include a relatively slender longitudinal portion  270  and a flared end portion  272  for engaging the body  252  of the swallowable weight of the alternative leading section  250  of guide element  130 . The terminal end  276  of the flared end portion  272  may have a conical-concave shape to receive and engage the conical second section  258  of the alternative leading section  250  of the guide element  120 . A slot extending along the dorsal surface of the alternative insertion section  270 , formed by walls  280 , and leading to a central lumen  282  forms a channel for receiving the longitudinal portion of alternative leading section  250 , similar in structure and operation to channel  194  of insertion section  174  ( FIG. 13 ). 
     Although slot  270  and central lumen  282  are shown as separate structures, they could also be formed as an integral U-shaped channel or any other appropriate structure for receiving the longitudinal portion of alternative leading section  270 . 
     It is not essential that the shape of the terminal end  276  exactly mate with the second section  258  of alternative leading section  250 , but it is important that the shape be compatible so that when light tension is provided on guide element  120 , the body  252  of the alternative leading section  250  is retained on the end of the alternative insertion section  270 , and when such tension is released, the body  252  of the alternative leading section falls away. The alternative leading section  250  may be constructed of materials as described in connection with leading section  174  the earlier-described embodiment. 
     One of skill in the art will appreciate that nasogastric tubes of various designs and functions may be inserted using the inserter element  130 , the guide element  120 , and the associated methods described earlier. In accord with a further aspect of the present invention, a nasogastric tube adapted for use as a feeding tube may be advantageously used with the aforementioned elements. Feeding tubes are used by medical practitioners in a number of situations, including those where the patient is unable to feed himself or herself, and those where the patient lacks desire to feed. 
     A nasogastric feeding tube is generally similar to the earlier-described nasogastric tube  110 , but has several differences to accommodate its use as a feeding tube. A nasogastric feeding tube generally has a distal end intended for placement into the patient&#39;s stomach, a proximal end intended to remain outside the patient, and a main tubular section joining the distal and proximal ends. Because feeding tubes are often left in position in the patient for an extended period, and the tubes are typically used to deliver fluid under slight positive pressure but are not subject to suction, the main tubular section is usually constructed of very flexible material having thin walls to minimize damage and discomfort to the patient. The feeding tube diameter is often smaller than that of other types of nasogastric tube. Typical feeding tubes have a single lumen, but some feeding tubes have more lumina and some feeding tubes are adapted to permit suction to be used to remove material from the stomach. 
       FIGS. 24 and 25  are side perspective views of first and second embodiments  414  and  414   a,  respectively, of proximal end sections of a nasogastric feeding tube which may be used as the nasogastric tube portion of a nasogastric tube insertion system, similar to the nasogastric tube insertion system  100  earlier described.  FIGS. 26 and 28  are side perspective views of first and second embodiments  450  and  450   a,  respectively, of distal end sections of a nasogastric feeding tube which may be used as the nasogastric tube portion of a nasogastric tube insertion system. That is, a feeding tube having any of the proximal ends  414  or  414   a,  and any of the distal ends  450  or  450   a,  may be substituted for the feeding tube  110  of nasogastric tube insertion system  100 , and used in conjunction with the guide element  120  and inserter element  130  the present invention.  FIG. 27  is a cross section view of the distal end section of  FIG. 26 , viewed toward the proximal end. 
     Although not shown in the drawings as an integrated unit, the proximal end of the feeding tube is connected to its distal end by the main tubular section  412 , and that section is sufficiently long that the distal end may rest in the patient&#39;s stomach while the proximal end extends a distance from the patient&#39;s nostril to accommodate a connection to a source of nutritional material or other fluid. The main tubular section  412  may be formed as a single integrated component or may be constructed as an assembly of longitudinally mated subsections. Similarly, the main tubular section  412 , proximal end  414  or  414   a,  and distal end  450  or  450   a  may be formed as an integrated unit, or may be constructed as separate components and mated together prior to use. The assembly of separate sections may be performed during manufacturing or by the user. 
     As best seen in  FIG. 24 , a first embodiment  414  of a feeding tube proximal end includes at least one terminal port housing  420  coupled to the main tubular section  412 . The port housing  420  has an opening  426  that forms a port adapted for connection to a source of fluid material (e.g., any appropriate nutritional, hydration, irrigation, or drug product material in fluid form), via appropriate tubing or a connector thereon (not shown). The opening  426  communicates with a lumen  424  of the main tubular section  412 , which lumen extends to the distal end of the feeding tube. The opening  426  may have a concave or funnel shape or other appropriate shape for mating with the tubing or connector from the fluid source. A flexible cap  422  is preferably tethered to the housing  420  to allow the opening  424  to be closed to avoid entry of foreign matter. 
     In feeding tubes which are not designed for use with suction, the walls of the main tubular section  412  may be quite thin and extremely flexible. As a result, it is difficult or impossible to insert the feeding tube though the nasal passages, oropharynx, esophagus, and the like, because any forward pressure on the tube causes it to bend. As best seen in  FIG. 24 , an optional stylet  428  may be provided to temporarily stiffen the feeding tube to facilitate insertion. The stylet  428  has a handle  432  and a thin wire  430  attached thereto. The stylet wire  430  extends through the lumen  424  of main tubular section  412  to the distal end of the feeding tube. The wire  430  adds stiffness, so that forward pressure may be applied to the tube to advance it into the patient. Where a stylet is used, it may be installed into the feeding tube by a medical professional performing the insertion procedure, or may preferably be installed by the device manufacturer. 
     If the main tubular structure  412  is constructed of a soft, flexible material, the terminal port housing  420  and related elements are preferably constructed of a suitable stiffer material. Also, if the feeding tube is intended for additional uses, including suction, the walls of the main tubular section  412  may be thicker and constructed of a stiffer, less flexible material. Further, the terminal port housing  420  could be formed integrally with the main tubular section  412  by incorporating one more ports at or near the proximal end thereof. 
     As best seen in  FIG. 25 , a second embodiment  414   a  of a proximal end of a feeding tube is generally constructed in a manner similar to that of the first embodiment, and therefore, only the differences between the two will be described. 
     The second embodiment  414   a  has a second port extension  436  that forms a port adapted for connection to an additional source of fluid material via appropriate tubing or a connector thereon (not shown). The second port extension  436  has an opening  438  in communication with the lumen  424  of main tubular section  412 . A cap  440  is preferably tethered to the housing  420  to allow the opening  438  to be closed. An adaptor  442  may also be tethered to the housing  420  or to the cap  440 . The adaptor  442  may be optionally inserted into the opening  438  to accommodate a second size or configuration of tubing or connector from the additional fluid source. The second port allows additional fluid to be introduced without disconnecting the first source from the first port. For example, an irrigating fluid may be introduced to clear blockage in the main tubular section. 
     As best seen in  FIGS. 26-27 , a first embodiment  450  of a distal end section of a feeding tube has an exit port housing  452  coupled to the main tubular section  412 . The housing  452  may have a generally hollow cylindrical shape including a blunt convex tip  458  and cylindrical walls  454  forming a chamber in communication with lumen  424  of the main tubular section  412 . Other shapes for housing  452  could also be used. At least one exit “window” or opening  456  is provided in the housing  452  to allow fluid carried by main tubular section  412  to escape the chamber. As best seen in  FIG. 27 , two opposed window openings may be provided, but any other appropriate configuration could also be used. 
     Stylet wire  430  extends into the housing and terminates in an end structure  434 . The end structure  434  is preferably shaped to removably engage a portion of the housing during feeding tube insertion and to avoid puncturing the feeding tube when the stylet is withdrawn after the feeding tube has been successfully inserted into a desired position. For example, the end structure  434  may be constructed as a tight helical winding of the end of wire  430  into a conical shape. Other shapes and structures could also be used. The stylet may be radiopaque to allow it to be seen using an appropriate imaging procedure. 
     The distal end section  450  of the feeding further comprises a guide element retaining structure  470  adapted to move slidably along guide element  120 , similar to that the guide element retaining structure  136  of  FIGS. 1 and 10 . The guide element retaining structure  470  preferably comprises a generally tubular protrusion or intrusion attached and parallel to the exit port housing  452  and a portion of the main tubular section  412 . The guide element retaining structure  470  has a tubular opening  472  to receive the guide element  120 . Once the guide element has been inserted, the guide element retaining structure  470  allows the feeding tube to move slidably and telescopically along the guide element  120 . Thus, the guide element  120  may serve to establish a path for the feeding tube to follow as it is inserted through the patient&#39;s nasal passages, oropharynx, esophagus, and into the patient&#39;s stomach. The leading end  474  and the trailing end of the guide element retaining structure  470  are preferably chamfered to avoid abrading or irritating tissues which are encountered as the feeding tube is inserted and removed. 
     Although the guide element retaining structure  470  is shown in  FIG. 26  and described herein as a tubular element attached to the exit port housing  452  and a portion of the main tubular section  412 , the guide element retaining structure could extend only along the exit port housing  452 . In addition, structures could also be used to form the guide element retaining structure  470  adapted for slidable and/or telescopic movement along the guide element  120 . For example, the guide element retaining structure  470  could be formed as one or more loops or retaining tabs attached to the exit port housing  452 . For another example, the guide element retaining structure  470  could be formed as a tunnel-style bore through an unused portion of the cross section of the exit port housing. This configuration has the advantage that no enlargement of the exit port housing  452  is needed, but it may not be possible to implement if the housing is crowded. As a further alternative to a separate structure  470  dedicated to retaining the guide element  120 , features of the exit port housing  452  or the main tubular section  412  may be used to form a guide element retaining structure. For example, guide element  120  could be threaded or telescoped through an aperture placed at or adjacent the tip  458  of the exit port housing  452  of the feeding tube, extend through the chamber, and could exit through one of exit “window” openings  456 . 
     If the main tubular section  412  is constructed of a soft, flexible material, the exit port housing  450  and related elements are preferably constructed of a stiffer material. 
     Also, if the feeding tube is intended for additional uses, including suction, the walls of the main tubular section  412  may be thicker, and a channel or lumen may be formed therein. Further, the exit port housing  452  could be formed integrally with the main tubular section  412  by incorporating one more exit ports at or near the end thereof. 
     As best seen in  FIG. 28 , a second embodiment  450   a  of a distal end of a feeding tube is generally constructed in a manner similar to that of the first embodiment, and therefore, only the differences between the two will be described. 
     The second embodiment  450   a  of a distal end section comprises an exit port housing  452   a  coupled to the main tubular section  412  and a weight section  460  attached to the exit port housing  452   a.  The housing  452   a  may have a generally hollow cylindrical shape with cylindrical walls  454   a  forming a chamber in communication with lumen  424  of the main tubular section  412 . Because the weight section  460  is attached to the end of the housing  452   a,  any suitable end configuration of the housing may be used. A plurality of exit “windows” or openings  456   a,    456   b,  etc., may be provided in the housing  452   a  to allow fluid carried by main tubular section  412  to escape the chamber. The stylet wire is not shown. The weight section  460  is a generally tubular structure having a cylindrical wall  462  and a blunt tip  464 . Other appropriate structural configurations could also be used. One or more weights may be provided interior of walls  462  to facilitate insertion and to maintain the position of the distal end section thereafter. The weights are preferably radiopaque to allow them to be seen under an appropriate imaging procedure. Any other appropriate configuration of exit openings and weights could also be used. For example, a single section could incorporate the weights in the chamber, using a plurality of smaller exit opening to allow escape of fluid while retaining the weights. 
     A guide element retaining structure  470   a  is preferably formed on the outside of the weight section  460 . The guide element retaining structure  470   a  preferably comprises a generally tubular protrusion or intrusion attached and parallel to the weight section  460 . The guide element retaining structure  470   a  has a tubular opening  472   a  to receive the guide element  120 . The guide element retaining structure  470   a  may also be located on the exit port housing  452   a,  or any of the aforementioned alternatives for the configuration of the guide element retaining structure  470  could also be used. 
     Although the feeding tube has been described herein as having a single lumen, multiple lumina could be used by providing appropriate terminal and exit ports at proximal and distal ends, respectively. For example, some feeding tubes are used simultaneously to introduce nutritional, hydrating, or irrigational materials, while withdrawing other fluids. If suction is used, it is necessary to select suitable materials and thickness for the walls of the corresponding lumen to avoid collapse. The main tubular section  412  may be provided with a radiopaque tracer strip, wire, or other markings, to allow the position of the feeding tube to be verified even if no stylet or weights are used. 
     The nasogastric feeding tube may be inserted using a method similar to that described earlier in connection with nasogastric tube  110 , but preferably incorporates additional steps of verifying correct positioning of the distal end of the tube. The patient must be cooperative and must be able to swallow. Determining this is a clinical decision that must be made by a medical professional at the time the feeding tube is needed. 
     According to a further aspect of the invention,  FIG. 20  is a flow diagram showing the steps of an example method  510  for inserting a nasogastric feeding tube in conjunction with the a nasogastric tube insertion system described herein. Step  534  encompasses all the steps of either method  310  or  310   a  of  FIG. 20 , with corresponding elements of a nasogastric feeding tube substituted for the elements of nasogastric tube  110 . At the end of step  534 , the feeding tube is believed to have been initially placed into position in the patient&#39;s stomach. 
     In practice, feeding tubes are often incorrectly placed in the patient&#39;s duodenum, esophagus, or lungs. Improper placement of a feeding tube in the lungs is extremely dangerous, because the nutritional material can fill the lungs, preventing the patient from breathing, causing permanent lung damage, and in a significant fraction of cases, causing death. Accordingly, it is usually appropriate to verify correct placement using a conventional X-Ray or fluoroscopy. In step  536 , a medical professional verifies the position of the distal end section  450  or  450   a  by observing the position of the stylet end, weights, or the radiopaque tracer using an appropriate imaging modality, such as conventional X-Ray or fluoroscopy. In step  538 , the medical professional determines whether the position is acceptable, and if so, the method continues in step  538 . If the position is wrong, the method continues in step  546 . 
     Step  540  is a further optional position check. In step  540 , a radiopaque substance, such as gastrografin may be delivered through the tube, while the patient is examined under fluoroscopy or another appropriate imaging modality. The pattern of diffusion of the radiopaque substance may be observed to determine whether the distal end section  450  or  450   a  has been properly inserted into the stomach, or improperly, e.g., into the duodenum or the esophagus. In step  542 , the medical professional determines whether the position is acceptable, and if so, the method continues in step  544 . In step  544 , the stylet is removed, and the feeding tube is ready for use. If the position is determined to be wrong, the method continues in step  546 . 
     If, in steps  538  or  542 , the position is determined to be wrong, the method continues in step  546 . The tube is repositioned, and the method returns to step  536 , where the position is again verified. 
     In some instances, it may be desirable to remove the guide element, while the nasogastric tube remains in position in the patient. 
     According to a further aspect of the invention, a guide element may be provided having a swallowable weight which may be retracted while the nasogastric tube remains in position. The weight may, for example, be constructed in a way that allows it to change shape or form to enable its retraction through a guide element retaining structure or through the nasogastric tube itself. A nasogastric tube that is adapted to facilitate the withdrawal of the guide element may also be provided. 
     According to an aspect of the invention, there is shown in  FIG. 30  a side view of the leading section of an alternate embodiment of a guide element, and the distal end of an alternate embodiment of a nasogastric tube, in which the weight is formed as an inflatable sac or balloon, showing the weight in an inflated condition.  FIG. 31  is a cross section view of the alternate embodiments of the guide element and nasogastric tube of  FIG. 30 . taken along the section lines  31 - 31  of  FIG. 30 ;  FIG. 32  is a side view showing the alternate embodiments of the guide element and nasogastric tube of  FIGS. 30 and 31 , showing the weight a deflated condition. 
     As best seen in  FIGS. 30-32 , the distal end section  116  of an alternate embodiment of a nasogastric tube may be formed having at least one lumen  146 . The alternate embodiment of the nasogastric tube may generally be constructed as heretofore described in connection with nasogastric tube  110 , with modifications as described in this section. Lumen  146  has an inner wall  616 , an end opening  618 , and a number of side openings or apertures  134 . The end and side openings  618  and  134  allow communication of fluids between the lumen and the exterior of the tube. The surfaces of the leading end  132  of the nasogastric tube in the area of the end opening  618  are preferably rounded or smoothed to avoid abrasion or other injury to the patient during insertion of the tube. The particular configuration, including size and arrangement, of the openings shown is an example and may vary in different embodiments. Although only a single lumen is shown, the nasogastric tube could have any appropriate number and size of lumina. 
     An alternate embodiment  610  of a guide element preferably comprises an inflatable guide element swallowable weight body envelope  612  coupled to a substantially hollow guide element tube  620 . The body envelope  612  encloses an interior space  614  for containing fluid, which may be any appropriate gas, such as air, or liquid, such as water. The guide element tube  620  preferably has an exterior wall  622  and inner wall  624  forming a guide element tube lumen  626 , which is preferably arranged for fluid communication between the lumen  626  and the interior  614 . Swallowable weight body envelope  612  may be inflated by introducing fluid into lumen  626  at the proximal end (not shown) of the guide element  610 , as depicted in  FIG. 30 . The swallowable weight body envelope  612  may be deflated by withdrawing fluid (or allowing the fluid to withdraw) from lumen  626 , as depicted in  FIG. 32 . 
     The distal end of alternate guide element  610  preferably extends through lumen  146 . Lumen  146 , or at least one of the lumina if there are several, is preferably large enough to allow passage, for example via slidable movement therethrough, of the alternate embodiment of guide element  610 , including the guide element tube  620  and the swallowable weight in its deflated form. Thus, the alternate embodiment of guide element  610  may be withdrawn from the patient while the nasogastric tube remains in a desired position therein. 
     The body envelope  612  may be constructed of any suitable flexible material which is bio-compatible for insertion in a patient (human) or subject (animal) and compatible with stomach fluids, including but not limited to latex. The body envelope  612  may be formed from an expandable resilient material, similar to that of a conventional balloon, or from a material that does not resiliently expand, such as a bag or pouch. The materials considered appropriate may vary depending on locality-specific practice and regulation. Guide element tube  620  may be constructed from any suitable flexible material which is bio-compatible for insertion in a patient and compatible with stomach fluids, and which has sufficient strength and rigidity to allow its safe insertion into and withdrawal from the patient. For example, guide element tube  620  may be constructed of a silicone elastomer, but other materials could also be used. The materials considered appropriate may vary depending on locality-specific practice and regulation. 
     The alternate embodiment of the nasogastric tube system, including the alternate embodiment of the guide element, of  FIGS. 30-32  may be inserted in the same manner as earlier-described embodiments. Although the alternate embodiment  610  of the guide element is depicted in  FIG. 30-32  as extending through the main lumen of the nasogastric tube, which thus serves as a guide element retaining structure, any lumen, or a guide element retaining structure similar to the retaining structure  136  of  FIG. 1 , could also be used. 
     According to a further aspect of the invention, the swallowable weight of the guide element may be constructed from a material which ablates, e.g., via dissolution, disintegration, melting, etc., in the presence fluids present in the patient&#39;s stomach to allow the remainder of the guide element to be withdrawn without disturbing the position of the nasogastric tube. 
     According to an aspect of the invention, there is shown in  FIG. 33  the leading section of an alternate embodiment  630  of a guide element with a swallowable weight thereof having a first example configuration. The alternate embodiment  630  of the guide element of  FIG. 33  may generally be constructed as heretofore described in connection with guide element  120 , with modifications as described in this section. The guide element  630  preferably comprises a guide element leading section  154  generally constructed as earlier described. A swallowable weight in a first example configuration  640  is attached to the guide element leading section  154  near the end  648  thereof. In the first example configuration, swallowable weight  640  preferably has a generally cylindrical body section  642 , an end section  644  having rounded or smoothed corners, and a conical tail section  646 . However, other configurations could also be used. The rounded or smoothed corners help avoid abrasion or other injury to the patient during insertion, removal, or swallowing of the guide element  630 . The conical tail section  646  may mate or engage a corresponding structure on the insertion section  174  of inserter element  130 . This prevents the swallowable weight  640  from falling off the end of inserter element  130  if some slack occurs in the guide element  120 . 
     Swallowable weight  640  is preferably constructed from a material that ablates in the presence of stomach fluids or the temperature present in the body. The term “ablate” and terms derived therefrom are used herein to refer to any process where the material of the swallowable weight  640 , initially in a solid or cohesive form, dissolves, disintegrates, melts, sublimates, decomposes, falls away, erodes, softens to allow reshaping with minimal force, or the like, when exposed to stomach fluids or to the temperature present in the body, such that thereafter, the weight either no longer exists as a relatively solid mass attached to the guide element  120  or no longer provides a barrier or resistance to withdrawal of the guide element without disturbing the nasogastric tube. The ablation preferably occurs within a short time after arrival of the swallowable weight  640  in the stomach, and does not require digestion of the weight. The time acceptable for the ablation to occur may depend on the application but may, for example, be less than about five minutes. The material is preferably bio-compatible for insertion in the patient. Prior to exposure to stomach fluids, the material is preferably substantially solid; however, the material may exhibit a rigidity within a range extending from completely rigid to a rubbery or gelatinous flexibility. The swallowable weight  640  may be formed using any appropriate method and technology, including but not limited to molding, casting, depositing, precipitating, compressing, or sintering the material about the end  648  of guide element leading section  154 . The swallowable weight  640  may be formed, for example, from a liquid or fluid material which sets due to chemical action or temperature, including a gelatin. An example of such a material which is known for use for pharmaceutical formulations and approved in the U.S. is a gelatin compound, which may include glycerin. The swallowable weight  640  may also be formed from a powder which is compressed or sintered to form a generally solid mass. An example of such a material which is known for use for pharmaceutical formulations and approved in the U.S. is compressed glucose. Other materials could also be used, and any appropriate manner of coupling or attaching the swallowable weight  640  to the guide element leading section  154  could be used. The leading section  154  could also be constructed of a material that is soluble in stomach fluids, or disintegrates or becomes extremely soft when exposed to stomach fluids, or changes from a solid to liquid state when exposed to stomach fluids. 
     According to an aspect of the invention, there is shown in  FIG. 34  the leading section of an alternate embodiment  632  of a guide element with a swallowable weight thereof having a second example configuration. The guide element  632  of  FIG. 34  may generally be constructed as heretofore described in connection with guide element  630 , with modifications as described in this section. The guide element  632  preferably comprises a guide element leading section  154  generally constructed as earlier described. A swallowable weight in the second example configuration  650  is attached to the guide element leading section  154  near the end  648  thereof. In the second example configuration, swallowable weight  650  preferably has a generally cylindrical body section  652 , an end section  644  having rounded corners, and a tail section  654  also having rounded corners. However, other configurations could also be used. Swallowable weight  650  may be constructed and may use materials as earlier described for swallowable weight  640 . 
     According to an aspect of the invention, there is shown in  FIG. 35  the leading section of an alternate embodiment  634  of a guide element with a swallowable weight thereof having a third example configuration. The guide element  634  of  FIG. 35  may generally be constructed as heretofore described in connection with guide element  630 , with modifications as described in this section. The guide element  634  preferably comprises a guide element leading section  154  generally constructed as earlier described. A swallowable weight in the third example configuration  656  is attached to the guide element leading section  154  near the end  648  thereof. In the third example configuration, swallowable weight  656  preferably has a generally cylindrical body section  658 , an end section  644  having rounded corners, and a tail section having a concave conical wall  660  forming a generally conical opening  662 . The opening  662  facilitates a loose engagement of the swallowable weight  656  with the insertion section  174  of inserter element  130  in a manner similar to that shown in  FIG. 12  and described in connection therewith. This prevents the swallowable weight  656  from falling off the end of the inserter element  130  if some slack occurs in the guide element  120 . Other configurations of swallowable weight  656  could also be used. Swallowable weight  656  may be constructed and may use materials as earlier described for swallowable weight  640 . 
     According to an aspect of the invention, there is shown in  FIG. 36  the leading section of an alternate embodiment  636  of a guide element with a swallowable weight thereof having a second example configuration. The guide element  636  of  FIG. 34  may generally be constructed as heretofore described in connection with guide element  630 , with modifications as described in this section. The guide element  636  preferably comprises a guide element leading section  154  generally constructed as earlier described. A swallowable weight in the fourth example configuration  664  is attached to the guide element leading section  154  near the end  648  thereof. In the fourth example configuration, swallowable weight  664  preferably has a generally cylindrical body section  666 , an end section  644  having rounded corners, and a tail section having an end wall  668 , a cylindrical inner wall  670 , and a base wall  672 , forming a generally cylindrical depressed opening  674 . The opening  674  facilitates a loose engagement of the swallowable weight  664  with the insertion section  174  of inserter element  130  in a manner similar to that shown in  FIG. 12  and described in connection therewith. This prevents the swallowable weight  664  from falling off the inserter element  130  if some slack occurs in the guide element  120 . The corner between body section  666  and tail section end wall  668  is preferably rounded or smoothed to avoid abrasion or other injury to the patient during insertion, removal, or swallowing of the guide element  636 . However, other configurations of swallowable weight  664  could also be used. Swallowable weight  650  may be constructed and may use materials as earlier described for swallowable weight  640 . 
     According to a further aspect of the invention, retaining structures may be provided on the guide element leading section  154  near the end  648  thereof to improve engagement between the leading section  154  and the swallowable weight, e.g.,  640 ,  650 ,  656 ,  654 . The retaining structures may be needed or helpful if the material from which the swallowable weight is constructed is not completely rigid, or if the material does not adhesively attach to the surface of guide element leading section  154 . 
     According to an aspect of the invention, there is shown in  FIG. 37  a side view of an example embodiment  676  of the leading section  154  of the guide element  120  having retaining structures  678  constructed thereon. In this example embodiment  676 , the retaining structures  678  are formed as disk-shaped elements extending transversely from the leading section  154  near the end  648  thereof. Any appropriate swallowable weight (not shown) may be used with the retaining structures  678 , and the weight preferably surrounds the retaining structures, at least until the weight arrives in the patient&#39;s stomach. 
     According to an aspect of the invention, there is shown in  FIG. 38  a side view of an example embodiment  680  of the leading section  154  of the guide element  120  having retaining structures  682  constructed thereon. In this example embodiment  680 , the retaining structures  682  are formed as generally conical cup-shaped elements extending from the leading section  154  near the end  648  thereof. Any appropriate swallowable weight (not shown) may be used with the retaining structures  682 , and the weight preferably surrounds the retaining structures, at least until the weight arrives in the patient&#39;s stomach. 
     According to an aspect of the invention, there is shown in  FIG. 39  a side view of an example embodiment  684  of the leading section  154  of the guide element  120  having retaining structures  686  constructed thereon. In this example embodiment  684 , the retaining structures  686  are formed as spike-shaped elements extending from alternate radial positions of the leading section  154  near the end  648  thereof. Any appropriate swallowable weight (not shown) may be used with the retaining structures  686 , and the weight preferably surrounds the retaining structures, at least until the weight arrives in the patient&#39;s stomach. 
     According to an aspect of the invention, there is shown in  FIG. 40  a side view of an example embodiment  688  of the leading section  154  of the guide element  120  having retaining structures  690  constructed thereon. In this example embodiment  688 , the retaining structures  690  are formed as a plurality of small spaced indentations in the leading section  154  near the end  648  thereof. The retaining structures  690  may be ring-like indentations extending around the entire circumference of the leading section  154 , but could also extend less than the entire circumference or could take the form of dimples. The retaining structures  690  may be regularly or irregularly spaced. Any appropriate swallowable weight (not shown) may be used with the retaining structures  690 , and the weight preferably surrounds the retaining structures, at least until the weight arrives in the patient&#39;s stomach The retaining structures  678 ,  682 ,  686 ,  690  may also be formed in other appropriate shapes. The retaining structures  678 ,  682 ,  686 ,  690  may be formed integrally with the guide element leading section  154 , for example by molding, or may be applied to leading section  154  after its formation. The retaining structures  678 ,  682 ,  686 ,  690  may be constructed of any appropriate material, and are preferably flexible and adapted to minimize any abrasion or injury to the patient during insertion, removal, or swallowing of the guide element. The retaining structures are preferably sized to permit removal of the guide element through either the nasogastric tube (if the guide element is threaded through a lumen thereof as depicted in  FIGS. 30-32 ), or the guide element retaining structure  136  (if the guide element is threaded through such a structure as depicted in  FIG. 1 ). 
     According to a further aspect of the invention, there is shown in  FIG. 41  a flow diagram of a method  710  for use in removing a guide element of the type shown in  FIGS. 30-32  when used in conjunction with a nasogastric tube of the type shown in  FIGS. 30-32 . Step  734  incorporates steps  310  or  310   a  through step  332  of  FIG. 20 , at the end of which, the guide element, including the swallowable weight thereof, in its inflated condition, has been positioned in the patient&#39;s stomach, and the nasogastric tube has been inserted into the patient&#39;s stomach using the guide element. The swallowable weight may be inflated as part of the manufacturing process or may be inflated by the user in preparation for its introduction into the patient. 
     In step  736 , the user causes reconfiguration of the swallowable weight to enable its withdrawal from the patient while the nasogastric tube remains in position. The implementation of step  736  may be further defined by optional substep  738 , in which the user allows the guide element to deflate. The user may accomplish this by allowing fluid to exit the lumen  626  of the guide element, or by actively withdrawing fluid through the lumen. 
     In step  740 , the user withdraws the guide element from the patient while maintaining the nasogastric tube in position. In step  742 , removal of the guide element is complete. According to a further aspect of the invention, there is shown in  FIG. 42  a flow diagram of a method  760  for use in removing a guide element of the type shown in  FIGS. 33-36 , when used in conjunction with a nasogastric tube of the type shown in  FIG. 1  or  FIGS. 30-32 . Step  784  incorporates steps  310  or  310   a  through step  332  of  FIG. 20 , at the end of which, the guide element, including the swallowable weight thereof, has been positioned in the patient&#39;s stomach, and the nasogastric tube has been inserted into the patient&#39;s stomach using the guide element. 
     In step  786 , the guide element weight is exposed to stomach fluid. In step  788 , the guide element weight is allowed to dissolve, disintegrate, soften, melt, or the like, enabling the guide element leading section  154  to be withdrawn without disturbing the position of the nasogastric tube. In step  790 , the user withdraws guide element from the patient while the nasogastric tube is retained in position. In step  792 , removal of the guide element is complete. 
     According to a further aspect of the invention, the nasogastric tube or the guide element may incorporate a chemical-property indicating medium to facilitate verification that the nasogastric tube has been inserted properly into the patient&#39;s stomach, and has not been inserted into the lung or other undesirable location. The fluids present in a patient&#39;s stomach have an acidic pH below 5.0, while fluids present in locations into which it is possible to erroneously insert the nasogastric tube generally have pH above 5.0. By exposing the indicating medium to the fluids surrounding the distal end of the nasogastric tube, the indicating medium enables the user to verify that the pH of those fluids is below 5.0, thus confirming correct insertion of the nasogastric tube. If the indicating medium is incorporated in the nasogastric tube, the fluids surrounding the distal end of the tube may be aspirated through the tube and into contact with the medium, the condition of which may then be observed by the user. If the indicating medium is incorporated in the guide element, the fluids surrounding the distal end of the tube will come in contact with the medium without additional overt action by the user, although the guide element must subsequently be withdrawn from the patient so that the condition of the medium may be observed. The indicator may generally be used to obtain a measurement of the gastric pH. This measurement may be employed for purposes in addition to establishing correct insertion of the nasogastric tube, including determination that the stomach is prepared to receive a therapeutic agent, or that an appropriate quantity of a therapeutic agent affecting pH, has been introduced. As an alternative to a pH-sensitive medium, media indicating chemical properties other than pH, which may verify correct insertion of the nasogastric tube, signal incorrect insertion of the nasogastric tube, or verify correct or sufficient introduction of a therapeutic, buffering, or irrigation agent, could also be used. 
     According to an aspect of the invention, there is shown in  FIG. 43  a side view of an example embodiment  810  of a nasogastric tube in which a chemical-property indicating medium is incorporated near the proximal end section  114  thereof.  FIG. 44  is a cross section view of the example embodiment  810  taken along section lines  44 - 44  of  FIG. 43 . The example embodiment  810  may be generally constructed in a manner similar to the nasogastric tube  110  of  FIG. 1 , with modifications described in this section. 
     As best seen in  FIGS. 43-44 , nasogastric tube  810  preferably comprises a generally tubular proximal end section  114  having an interior wall  814  forming at least one lumen  146 . If plural lumina are provided in tube  810 , the lumen  146  is preferably the one adapted for use in aspirating fluid near the distal end of the tube. The nasogastric tube  810  preferably includes a section  812  for housing a chemical property indicating medium  820 . Section  812  may be enlarged, compared to the diameter of other sections of the nasogastric tube. A channel  822  is preferably provided in which the chemical property indicating medium  820  is captured. Several openings  816  are preferably provided between the main bore of lumen  146  and the channel  822  to allow communication of fluid between the lumen  146  and the channel  822 . The openings  816 , channel  822 , and medium  820  are preferably adapted such that when fluid is present in lumen  146 , it inundates channel  822  and exposes medium  820 . 
     Medium  820  preferably furnishes a visual indication of a chemical property, such as pH, which may, for example, be manifested as a change in color, reflectivity, or the like. Section  812  is preferably clear or translucent to allow the medium  820  to be viewed externally. The shape of section  812  may act as a magnifying lens to allow a small medium to be easily viewed. Any appropriate chemical-property indicating medium, including but not limited to litmus, pH indicating strips, paper, cloth, or any other substrate impregnated with or bearing a pH indicator, or the like, may be used to implement medium  820 . The position and size of section  812  is preferably selected such that the condition of the indicator strip is visually apparent when fluids are initially aspirated through lumen  146  so that the user need not take any additional steps in order to confirm correct insertion of the nasogastric tube in the patient&#39;s stomach. 
     According to a further aspect of the invention, there is shown in  FIG. 45  a side view of an additional example embodiment  830  of a nasogastric tube in which a chemical-property indicating medium is incorporated near the proximal end section  114  thereof. There is shown in  FIG. 46  a side view of an additional example embodiment  840  of a nasogastric tube in which a chemical-property indicating medium is incorporated near the proximal end section  114  thereof.  FIG. 47  is a cross section view of the embodiment  830  taken along the section lines  47 - 47  thereof.  FIG. 48  is a cross section view of the embodiment  840  taken along the section lines  48 - 48  thereof. The example embodiments  830  and  840  may be generally constructed in a manner similar to the nasogastric tube  110  of  FIG. 1 , with modifications described in this section. 
     As best seen in  FIGS. 45-48 , each of nasogastric tubes  830  and  840  preferably comprises a generally tubular proximal end section  114  having an interior wall  814  forming at least one lumen  146 . If plural lumina are provided in tube  830  or  840 , the lumen  146  is preferably the one adapted for use in aspirating fluid near the distal end of the tube. Nasogastric tube  830  comprises a chemical-property indicating medium applied to the interior wall  814  in the form of a plurality of indicating elements  832  spaced circumferentially along the interior wall  814 . Nasogastric tube  840  comprises a chemical-property indicating medium applied to the interior wall  814  in the form of an indicating element  842  that covers the circumference of the interior wall  814 . These particular configurations of the indicating elements  832  and  842  are examples. Other configurations could also be used. 
     The indicating elements  832  and  842  may be formed using any suitable chemical-property indicating medium or substance, including but not limited to a coating, litmus, pH-indicating strips, paper, cloth, or the like. For example, the medium may be formed as a coating or gelatin bearing phenolphthalein. The term medium is also intended to refer to any indicating substance, regardless of whether or not the indicating chemical or component is carried in or on a substrate, matrix, or similar carrier. Other indicating media could also be used. If the medium is integrated with a substrate such as a paper strip, such substrate is preferably applied to the interior wall  814  using an appropriate adhesive or fastening technology, which may include infrared or ultrasonic bonding. The positions and sizes of the indicating elements  832  and  842  are preferably selected such that the condition of the indicating elements is visually apparent when fluids are initially aspirated through lumen  146 , so that the user need not take any additional steps in order to confirm correct insertion of the nasogastric tube in the patient&#39;s stomach. In some applications, aspirated fluid that contacts the indicating medium may be reintroduced into the patient or may otherwise come in contact with the patient. 
     Also, the indicating medium must be firmly attached or adherent to the interior wall  814 , or particles or fragments of the indicating medium itself may be inadvertently introduced into the patient through the nasogastric tube or may otherwise contact the patient. In such applications, an indicating medium is preferably selected for bio-compatibility to avoid any potentially toxic effects. 
     According to a further aspect of the invention, there is shown in  FIG. 49  a side view of an additional example embodiment  850  of a nasogastric tube in which a chemical-property indicating medium is incorporated near the proximal end section  114  thereof. 
     As best seen in  FIG. 49 , a plurality of distinct indicating elements, such as  852 ,  854 , and  856  are provided, each having a medium for visually and distinctly indicating a different chemical property or a different value of a chemical property. The indicating elements  852 ,  854 , and  856  may, for example, change appearance to indicate different pH thresholds have been sensed, or may change appearance to indicate the presence or absence of specific chemicals, proteins, or other detectable components in the fluid aspirated from the vicinity of the distal end of the nasogastric tube. This would give a measurement of gastric pH, as well as verify proper placement of the nasogastric tube. The activated appearance of each of the indicating elements  852 ,  854 ,  856  may be visually distinctive. For example, they may appear as distinguishably different colors, thereby minimizing ambiguity as to which indicators are activated. Although the indicating elements are shown in the shape of dots, any suitable shape could also be used, and the elements may be provided in any practical size and number. Any suitable indicating media could be used to implement the indicating elements  852 ,  854 , and  856 , such as those described in connection with the embodiments  830  and  840  of  FIGS. 45-46 . 
     According to a further aspect of the invention, there is shown in  FIG. 50  a side view of an additional example embodiment  860  of a nasogastric tube in which a chemical-property indicating medium is incorporated near the proximal end section  114  thereof. As best seen in  FIG. 50 , a plurality of distinct indicating elements, such as  862 ,  864 , and  866  are provided, each having a medium for visually and distinctly indicating a different chemical property or a different value of a chemical property, and each having a different shape, size, or other characteristic so that there is no ambiguity as to which indicators are activated. The indicating elements  862 ,  864 , and  866  may, for example, change appearance to indicate different pH thresholds have been sensed, or may change appearance to indicate the presence or absence of specific chemicals, proteins, or other detectable components in the fluid aspirated from the vicinity of the distal end of the nasogastric tube. The shape, size, or other characteristics of the indicating elements may be selected to correspond to the property indicated. By way of example but not limitation, the indicating elements  862 ,  864 , and  866  may be designed to change appearance when fluid pH crosses specific pH thresholds of 4.0, 5.0, and 3.0, respectively, and the indicating elements may be formed as recognizable characters, symbols, or glyphs corresponding to these thresholds. Other distinctive shapes and forms and other schemes defining correspondence between the visual distinctiveness of the indicating element and the property being sensed could also be used. The activated appearance of each of the indicating elements  862 ,  864 ,  866  may be visually distinctive in ways in addition to their shape, for example, they may appear as distinguishably different colors, to further minimize ambiguity as to which indicators are activated. Any suitable indicating media could be used to implement the indicating elements  862 ,  864 , and  866 , such as those described in connection with the embodiments  830  and  840  of  FIGS. 45-46 . 
     According to a further aspect of the invention, there is shown in  FIG. 51  a side view of an additional example embodiment  870  of a guide element with which a chemical-property indicating medium is incorporated on or near the leading section  154  thereof. Guide element  870  may generally be constructed as heretofore shown and described in connection with guide element  120  ( FIG. 1 ),  610  ( FIG. 30 ) or  630  ( FIG. 33 ), with modifications as described in this section. As best seen in  FIG. 51 , one or more indicating elements  872  are provided on the outer surface of the leading section  154  of the guide element, each having a medium for visually indicating a chemical property. The indicating elements  872  are exposed to fluids in the vicinity of the end of the leading section  154 . When the guide element is withdrawn from the patient, the indicating elements are visually apparent and can be used to confirm that the guide element and nasogastric tube were properly inserted in the patient&#39;s stomach. Different, visually distinctive indicating elements may be used to indicate different chemical properties or values thereof, as described more fully in connection with embodiment  850  of  FIG. 49 . Any suitable indicating media could be used to implement the indicating elements  872 , such as those described in connection with the embodiments  830  and  840  of  FIGS. 45-46 . 
     According to a further aspect of the invention, there is shown in  FIG. 52  a side view of an additional example embodiment  880  of a guide element with which a chemical-property indicating medium is incorporated on or near the leading section  154  thereof. Guide element  880  may generally be constructed as heretofore shown and described in connection with guide element  120  ( FIG. 1 ),  610  ( FIG. 30 ) or  630  ( FIG. 33 ), with modifications as described in this section. As best seen in  FIG. 52 , one or more indicating elements  884  are provided on the outer surface of the leading section  154  of the guide element near the end thereof, each having a medium for visually indicating a chemical property. A swallowable weight  882  surrounds the indicating elements  884 . Swallowable weight  882  is preferably constructed from a material that is soluble in stomach fluids, or disintegrates or becomes extremely soft when exposed to stomach fluids, or changes from a solid to liquid state when exposed to stomach fluids or to the temperature present in the body, as more fully explained in connection with the embodiment  630  of  FIG. 33 . After exposure to stomach fluids (or other fluids in the vicinity of the weight  882 , the weight  882  dissolves, melts, ablates, or disintegrates, thereby exposing the indicating elements  884 . When the guide element is withdrawn from the patient, the indicating elements are visually apparent and can be used to confirm that the guide element and nasogastric tube were properly inserted in the patient&#39;s stomach. Different, visually distinctive indicating elements may be used to indicate different chemical properties or values thereof, as described more fully in connection with embodiment  850  of  FIG. 49 . Any suitable indicating media could be used to implement the indicating elements  872 , such as those described in connection with the embodiments  830  and  840  of  FIGS. 45-46 . 
     According to a further aspect of the invention, there is shown in  FIG. 53  a flow diagram of a method  910  for use in positioning a nasogastric tube of the types shown and described in connection with  FIGS. 43-50 . Step  926  incorporates steps  310  or  310   a  through step  322  or  234   a  of  FIG. 20 , at the end of which, the guide element has been inserted through the nostrils and is ready to be swallowed by the patient. 
     In step  928 , the guide element is swallowed by the patient. In step  930 , the nasogastric tube is inserted along the guide element to an apparent terminal location. The apparent terminal location may be in the patient&#39;s stomach, as desired, or may be in some other undesired location, such as the lung. The implementation of step  930  may be further defined by optional substeps  932  and  934 . In substep  932 , inserting the nasogastric tube along the guide element is partially implemented by threading an opposite end of the guide element through a retaining structure of the nasogastric tube. In substep  934 , inserting the nasogastric tube along the guide element is partially implemented by slidably moving the nasogastric tube along a path established by the guide element to an apparent terminal location. 
     In step  936 , fluid from the vicinity of the terminal location is aspirated to expose a chemical-property indicating component to the fluid. In step  938 , the user observes the indicator. In step  940 , the user determines whether the indicator shows correct placement of the nasogastric tube. If the placement is determined to be correct, the method ends at step  942 . If the placement is determined to be incorrect, the method continues in step  944 , in which the user repositions the tube. The method then returns to step  936  and steps following. 
     According to a further aspect of the invention, there is shown in  FIG. 54  a flow diagram of a method  960  for use in positioning a nasogastric tube in conjunction with a guide element of the types shown and described in connection with  FIGS. 51-52 . Step  926  incorporates steps  310  or  310   a  through step  322  or  234   a  of  FIG. 20 , at the end of which, the guide element has been inserted through the nostrils and is ready to be swallowed by the patient. 
     In step  978 , the guide element is swallowed by the patient. In step  980 , the nasogastric tube is inserted along the guide element to an apparent terminal location. The apparent terminal location may be in the patient&#39;s stomach, as desired, or may be in some other undesired location, such as the lung. The implementation of step  980  may be further defined by optional substeps  982  and  984 . In substep  982 , inserting the nasogastric tube along the guide element is partially implemented by threading an opposite end of the guide element through a retaining structure of the nasogastric tube. In substep  984 , inserting the nasogastric tube along the guide element is partially implemented by slidably moving the nasogastric tube along a path established by the guide element to an apparent terminal location. 
     In step  986 , a chemical-property indicating component of the guide element is exposed to fluid present near the terminal location. In step  988 , the guide element is withdrawn, while the nasogastric tube remains in place. Removal of the guide element allows the indicating component to be viewed by a user. 
     In step  990 , the user observes the indicator. In step  992 , the user determines whether the indicator shows correct placement of the nasogastric tube. If the placement is determined to be correct, the method ends at step  994 . If the placement is determined to be incorrect, the method continues in step  996 , in which the nasogastric tube is removed. Then in step  998 , the nasogastric tube is inserted again, using a guide element. Because the chemical-property indicating component will already have been exposed to fluids, it may be necessary to use a new guide element, or to renew the indicator on the previously-used guide element. Step  998  may incorporate steps  978  through  984 , and the method may continue in step  986 . 
     Turning to  FIGS. 55-56 , an apparatus  5500  in one example comprises a housing  5502  and a detection indicator  5504 . The detection indicator  5504  in one example is analogous to the chemical-property indicating medium or indicating elements described above. For example, the detection indicator is configured to change from a first visual indication to a second visual indication upon contact with a fluid or fluid sample based on a characteristic of the fluid. However, in the embodiment shown in  FIGS. 55-56 , the detection indicator  5504  is engaged or coupled with the housing  5502 , which is separate from the nasogastric tube, the guide element, and the inserter element. The housing  5502  is configured to removably engage the proximal end of a lumen or tube inserted into the patient&#39;s body, such as the nasogastric tube. Accordingly, the apparatus  5500  provides a removable housing  5502  with the detection indicator  5504 . 
     The housing  5502  comprises an interior chamber  5506  such as a channel, lumen, or reservoir that is configured to receive the fluid. The interior chamber  5506  provides sufficient contact between the fluid and the detection indicator  5504  to cause the visual change of the detection indicator  5504 . In a first implementation, the detection indicator  5504  is located inside the interior chamber  5506 . The detection indicator  5504  may be secured in place by adhering it to a surface in the interior chamber  5506 , by a friction fit, or by placing the detection indicator  5504  in a matrix that is adherent to the surface in the interior chamber  5506 . The surface may be an interior surface of the interior chamber  5506  or a face of a protrusion specifically designed to support the detection indicator  5504  within the interior chamber  5506 . In another example, the interior chamber  5506  comprises a slot or engagement component configured to receive and/or secure the detection indicator  5504 . The housing  5502  in one example is configured to removably secure the detection indicator  5504  to allow replacement of the detection indicator  5504 , as will be appreciated by those skilled in the art. 
     In a second implementation, the detection indicator  5504  is located adjacent to and/or in fluid communication with the interior chamber  5506 . For example, the housing  5502  may comprise at least one detection opening to the interior chamber  5506 . The housing  5502  may comprise a fenestrated wall to provide the detection openings. Referring to  FIG. 55 , the housing  5502  comprises detection openings  5508  and  5510 . In this implementation, the detection openings  5508  and  5510  are adjacent and partially separated by a support post  5512 , which may provide structural integrity to the housing  5502 . The support post  5512  in one example is configured with a raised rib  5513  to form at least one channel  5514  adjacent to the raised rib  5513 . The channel  5514  provides a path for fluid communication between the detection openings  5508  and  5510 . The channel  5514  promotes a flow of the fluid between the detection openings to provide a more thorough saturation of the detection indicator  5504  by the fluid and accordingly, a more complete or easily recognizable visual change in the detection indicator  5504 , as will be appreciated by those skilled in the art. 
     The detection indicator  5504  is configured to abut the detection opening to provide the contact between the fluid and the detection indicator  5504 . In one example, the detection indicator  5504  is configured to provide a seal against the detection opening to prevent leakage of the fluid to an exterior of the housing  5502 . In another example, the housing  5502  comprises a sealing member  5516  configured to secure the detection indicator  5504  to the detection opening to provide the seal. The sealing member may be formed integrally with the housing  5502  or as a separate component that is secured and/or bonded to the housing  5502 , such as by plastic welding, heat sealing, and/or with an adhesive. Examples of the adhesive include silicone based RTV adhesives such as Nusil MED3-4013 (Nusil Technology LLC; Carpinteria, Calif.). The housing  5502  may comprise one or more channels  5518  and  5520 , adjacent to the detection openings, configured to receive the adhesive, epoxy, or other sealing components  5524  to secure the sealing member to the housing  5502 . The channels  5518  and  5520  may extend partially or completely around the detection openings  5508  and  5510 . The channels  5518  and  5520  in one example are formed by raised ribs  5519  and  5521 , respectively. In alternate implementations, the sealing member  5516  and the housing  5502  may be configured with interlocking slots and tabs to provide the seal. 
     In one implementation, the sealing member  5516  comprises a flap configured to cover the detection indicator  5504  by wrapping over the detection indicator  5504  and around the housing  5502 . In a further implementation, the detection indicator  5504  is coupled with the sealing member  5516 . 
     The housing  5502  in one example comprises one or more raised ribs  5522  that surround the detection openings  5508  and  5510 . The raised ribs  5522  and  5513  provide a raised point of contact which increases engagement pressure between the detection indicator  5504  and the sealing member  5516  for sealing the interior chamber  5506  from leaks, as will be appreciated by those skilled in the art. In alternative implementations, one or more of the raised ribs  5513  and  5522  may be formed on the sealing member  5516 . 
     Referring to  FIGS. 56A and 56B , in one implementation the detection indicator  5504  is placed over the detection openings  5508  and  5510 . The detection indicator  5504  abuts the raised ribs  5513  and  5522 . In one example, the detection indicator  5504  is sized to fit between the raised ribs  5519  and  5521  to aid positioning of the detection indicator  5504  on the housing  5502 . 
     In one implementation, the housing  5502  comprises a tubular structure with a first opening  5540  configured to removably engage with the proximal end of the lumen. An adapter  5700  ( FIG. 57 ) may be used between the housing  5502  and the lumen to ensure a sealed connection, as described herein. Advantageously, this implementation reduces a risk of contamination of the fluid sample and also exposure of the practitioner to bodily fluids. Additionally, results of the determination are readily available, typically within minutes and conveniently at the patient&#39;s bedside, which significantly reduces the typical time required to send a fluid sample to a lab for analysis. Examples of a housing  5502  for this implementation include a test tube  6200  ( FIG. 62 ), vial, “vacutainer”  6300  ( FIG. 63 ) or other evacuated chamber, or a needle/syringe  6100  ( FIG. 61 ). The size of the first opening  5540  may be selected according to the lumen, tube, or adapter that the housing  5502  is intended to engage. Accordingly, various sizes of the housing  5502  are contemplated for nasogastric tubes, feeding tubes, catheters, and other variations such as those appropriate for adult or infant-sized tubes. The housing  5502  and/or adapter  5700  in one example includes a Y-fitting, T-fitting, or other juncture. 
     In a further implementation, the housing  5502  comprises a second opening  5550  configured to removably engage with a fluid retrieval component  5802  (e.g., a syringe, suction pump, wall suction or vacuum system) for retrieving the fluid from a distal end of the lumen into the interior chamber  5506 . Another adapter, tube, and/or coupling element may be used between the housing  5502  and the fluid retrieval component. As with the first opening  5540 , the size of the second opening  5550  may be selected according to the lumen, fluid retrieval component, or adapter size. The housing  5502  and/or adapters may be formed or molded from plastic, glass, or other medical-grade materials. The housing  5502  and/or adapters in one example are configured to be disposable and are formed from relatively inexpensive materials, as will be appreciated by those skilled in the art. 
     The detection indicator  5504  is configured to provide a visual indication of a characteristic of a fluid, upon contact with the fluid. In one example, the detection indicator  5504  is configured to change from a first visual indication to a second visual indication upon contact with the fluid based on a characteristic of the fluid (such as the pH). The first and second visual indications may be different colors, patterns, or other indicators. In another example, the first and second visual indications are within a range of possible colors. For example, a detection indicator  5504  may gradually change from red, to orange, to yellow or from yellow to brown to blue as an indication of different levels of pH, as will be appreciated by those skilled in the art. 
     The visual indication in another example comprises one or more dots or symbols that change color based on different pH readings. In another example, individual letters, numbers or symbols may change color or appearance (e.g., from low visibility to high visibility) to allow the practitioner to read or approximate the pH. As described above, the detection indicator  5504  may be any appropriate chemical-property indicating medium, including but not limited to litmus, pH indicating strips, paper, cloth, or any other substrate impregnated with or bearing a pH indicator, or the like. Other examples include nitrazine paper, pHydrion, Hydrion, and pHizatest paper (Micro Essential Laboratory, Inc.; Brooklyn, N.Y.). 
     The apparatus  5500  in a further example comprises one or more reference indicators  5530  configured to provide a reference visual indication for visual comparison with the detection indicator  5504 . In one example, the reference indicator  5530  is coupled with the housing  5502 . The reference indicator  5530  and/or the detection indicator  5504  in one example are configured and/or located such that the reference indicator  5530  and the detection indicator  5504  are simultaneously viewable from at least one viewpoint by the practitioner. For example, both the reference indicator  5530  and detection indicator  5504  are viewable by the practitioner without undue effort by the practitioner. In a first example, the detection indicator  5504  and reference indicator  5530  are located adjacent to each other. In another example, the detection indicator  5504  is located inside the housing  5502  and the reference indicator  5530  is located outside of the housing  5502 . In this example, the detection indicator is visible through at least a portion of the housing  5502  (e.g., through a window, viewport, or with a clear/transparent housing) such that the detection indicator and reference indicator  5530  can be viewed simultaneously. An optically clear adhesive may be used to facilitate viewing of the detection indicator through the housing  5502 . 
     In one example, the detection indicator, the reference indicator  5530 , and the housing  5502  are configured such that the detection indicator and the reference indicator  5530  are viewable from multiple angles or positions. Accordingly, the detection indicator and reference indicator  5530  are viewable by the practitioner without a need to rotate the housing  5502  to a required viewing angle. The detection indicator and the reference indicator  5530  may be configured in a “wraparound” arrangement or wrapped around a portion of the perimeter of the housing  5502 , such as half of the perimeter. In another example, the detection indicator and the reference indicator  5530  are wrapped or positioned around the entire perimeter of the housing  5502  to facilitate viewing from any angle or rotation of the housing  5502 . For example, the reference indicator  5530  may be coupled with the sealing member or flap prior to wrapping the sealing member around the housing  5502 . In alternative implementations, multiple detection indicators and reference indicators may be used with the housing  5502 . 
     The adapters  5700  in one example comprise any of a barb fittings, cone-shaped fittings, fluid connectors, couplers, or the like. The adapter may be configured with multiple ribs or engagement surfaces of different diameters to facilitate engagement with a variety of tube or device sizes and shapes. Turning to  FIG. 57 , the adapter  5700  in one example may have barb fittings  5702  and  5704  on opposing ends. The adapter may be a separate component or integral with the housing  5502  and/or fluid retrieval component. Where two adapters are used for the first and second openings, the adapters may be identical or different. The adapters are configured to securely engage via a compression fit, interference fit, friction fit, or screw-type engagement. 
     In one implementation, one or more of the housing  5502 , fluid retrieval device, adapters, and reference indicator  5530  are provided together in a kit. For example, a pre-packaged container may include the fluid retrieval device, two adapters, and a plurality of housings  5502  so that multiple readings can be taken with the contents of one kit. Advantageously, the contents of the kit can be sterilized prior to shipping to a hospital or clinic and provide a practitioner with necessary components for analysis of patient fluids. Other combinations of elements within the kit are possible and additional contents of the kit may be provided to facilitate use of the apparatus, such as extra tubing and/or adapters for coupling to a wall suction or vacuum system. 
     Turning to  FIGS. 58 and 59 , the apparatus  5500  is shown in one implementation engaged with the fluid retrieval component  5802  and engaged with a lumen  5804  via the adapter  5700 . The detection indicator  5806  in this example comprises a strip of litmus paper that is placed over the detection openings  5508  and  5510  and secured in place by the flap  5810 . The reference indicator  5530  is shown coupled with the flap  5810  such that when the flap  5810  is wrapped, closed, and/or sealed around the housing  5502 , the reference indicator  5530  is near or adjacent to the detection indicator  5806 . In other examples, the adapter  5700  or the housing  5502  may be coupled with a suction lumen of a nasogastric tube. 
     In alternative implementations, the fluid retrieval component  5802  and the housing  5502  may be integrally formed as a single piece. Turning to  FIG. 60 , in one example the housing  5502  and fluid retrieval component  5802  may be formed as a bulb-syringe  6000 . The bulb-syringe comprises a bulb  6002  of a transparent, elastically deformable plastic, a nozzle  6004 , and a one-way valve  6006 . The detection indicator  6008  is shown embedded or attached to the bulb  6002 , however in alternate implementations the detection indicator could be within the nozzle  6004 . The practitioner may squeeze the bulb  6002  to expel air through the one-way valve  6006  (analogous to the second opening  5550 ) and then release the bulb to cause a suction force through a first opening  6010  of the housing  5502 , as will be appreciated by those skilled in the art. 
     In yet another implementation, the housing  5502  is configured to engage a fluid retrieval component through the first opening  5540  (optionally, with an adapter). In this implementation, the fluid retrieval component is configured to expel the fluid sample into the interior chamber  5506  (through the first opening  5540 ) and the second opening  5550  is configured as a vent to relieve excess pressure as the fluid sample and/or any associated gases enter the housing  5502  while preventing the fluid sample from escaping the housing  5502 . For example, the second opening  5550  comprises a “tortuous path” (e.g., with one or more corners or bends) that is sufficient to prevent the fluid sample from leaking or escaping the housing  5502  while allowing the escape of the associated gases or gases that are displaced from the housing  5502  by the fluid sample. Accordingly, the fluid sample is captured without an increase in pressure within the interior chamber  5506  and the fluid sample is prevented from escaping the housing  5502 , as will be appreciated by those skilled in the art. 
     Turning to  FIG. 61 , the housing  5502  and fluid retrieval component are formed as a syringe  6100  that comprises a needle  6102 , interior chamber  6104 , and a plunger  6106 . In a further example, a combination of fluid pressure (e.g., blood pressure) and pressure provided by the plunger are used to draw fluid into the interior chamber  6104  of the syringe  6100 . The detection indicator  6108  in one example is adhered to the inside of the reservoir body  6104 . 
     Turning to  FIG. 62 , the housing in one example comprises a test tube  6200  or vial with a first opening  6204 . The detection indicator  6202  in this implementation comprises a color-change indicator and is adhered or affixed to an inside face of the test tube. A reference indicator  6206  is coupled with an outer surface of the test tube adjacent to the detection indicator  6202 . Turning to  FIG. 63 , the housing in another example comprises a vacutainer  6300 . The vacutainer has a small level of vacuum held by a membrane  6302  that is sealed against a tube  6304 . A first end of a dual-ended needle (not shown) is inserted into the patient, then a second end of the dual-ended needle punctures the membrane  6302 . The vacuum within the test tube then pulls blood or other fluid into the test tube where it contacts the detection indicators  6306 . A reference indicator  6308  is affixed to an outer surface of the tube  6304 . In the implementation shown in  FIG. 63 , the detection indicators  6306  are wrapped around a perimeter of the tube  6304  (e.g., wraparound configuration), as opposed to lengthwise as shown in  FIGS. 61 and 62 . The orientation of the detection indicator  6306  may be selected based on various design considerations. With the detection indicator  6306  located at one end of the tube  6304  in the wraparound configuration, a smaller fluid sample will be sufficient to saturate the various levels of the detection indicator  6306 , as will be appreciated by those skilled in the art. 
     Turning to  FIG. 64 , another implementation of a housing  6400  has a detection indicator  6402  that is molded or partially encapsulated in a wall  6404  of the housing  6400 . One or more passageways, capillaries, or openings  6406  allow the fluid sample to reach the detection indicator  6402 . Turning to  FIG. 65 , in yet another implementation, a housing  6500  comprises an interior chamber  6502  with a divider  6504 . The divider  6504  creates a separate channel  6506  where the detection indicator  6508  is located. The detection indicator in this example may be applied to an inner surface of the housing  6500 , to a surface of the divider  6504 , or placed in the separate channel  6506 . An opening  6510  in the divider  6504  allows the fluid sample to reach the detection indicator  6508 . 
     Turning to  FIGS. 66 and 67 , one implementation of the housing  6600  comprises detection indicators  6602 ,  6604 , and  6606 . The detection indicators  6602 ,  6604 , and  6606  are configured to change from the first visual indicator ( FIG. 66 ) to a second visual indication based on a pH of the fluid sample, for example, at pH levels of 3, 4, and 5, respectively. Referring to  FIG. 67 , upon contact with a fluid sample with a pH of 3, the detection indicator  6602  has changed to a second visual indication (i.e., a darker color relative to the first visual indication) to indicate the pH of the fluid sample. 
     Turning to  FIGS. 68 and 69 , another implementation of the housing  6800  comprises detection indicators  6802 ,  6804 , and  6806 . Each detection indicator is configured to respond to a characteristic of the fluid sample. However, the detection indicators may be configured for the same characteristic to provide redundancy or for separate characteristics. Referring to  FIG. 69 , detection indicator  6804  has changed from a first visual indication that is clear ( FIG. 68 ) to a second visual indication with a darkened “X”. 
     Turning to  FIG. 70 , a process flow shows one example of use for the apparatus  5500 . The first opening of the removable housing is engaged with a proximal end of a lumen, such as a nasogastric tube. This may include engaging an adapter between the lumen and the first opening. Engagement of the first opening, the adapter, and the lumen creates a sealed channel between an interior of the lumen and an interior of the housing. Optionally, a second opening of the removable housing is engaged with the fluid retrieval component. 
     A transfer of a fluid sample from a distal end of the lumen, through the lumen, and into the removable housing through the first opening is then performed such that the fluid sample contacts the detection indicator  5504 . For example, the practitioner activates the syringe or suction device to bring fluid from the distal end of the lumen (e.g., aspirate from the stomach) up through the lumen and into the interior chamber of the housing. The practitioner can then perform a visual comparison of the detection indicator  5504  with the reference indicator  5530  for determination of the characteristic of the fluid sample. For example, the practitioner observes the detection indicator  5504  for a change from a first visual indication to a second visual indication (e.g., from red to blue). After the observation, the practitioner disengages the removable housing by removing the first opening of the removable housing from the proximal end of the lumen. Optionally, the practitioner may dispose of the housing. 
     Turning to  FIG. 71 , a process flow for determining placement of a lumen into the small intestine is shown. A first housing is engaged with the lumen, along with any necessary adapters or fluid retrieval component, as described above. Placement of the distal end of the lumen in the stomach is confirmed, for example, by reading a pH level of less than or equal to approximately 4.5 on the detection indicator  5504 . The first housing is disengaged from the lumen and the distal end of the lumen is then advanced further into the patient, from the stomach into the small intestine. A second housing is engaged with the lumen. The pH of the small intestine is known to be approximately 6 and above and accordingly, placement of the distal end of the lumen in the small intestine can be confirmed with a second reading of the pH in or near this range. The second housing is then disengaged and optionally discarded. Additional readings or comparisons may be performed as needed to determine correct placement in alternate locations or to confirm that the lumen has not shifted or moved away from the desired location over a period of time. 
     While reference has been made to measuring pH of stomach aspirate, the detection indicator  5504  can be configured for alternate measurements. Examples include carbon dioxide, alkalinization, proteins, enzymes, chemicals, other biological agents or detectable components that may be present in air, blood, urine, or other bodily fluids or tissue. In one example, the detection indicator  5504  is configured to respond to the presence of a protein such as kinase, myoglobin, troponin, or other cardiac muscle proteins which may indicate that the patient is suffering from a heart attack or other heart muscle injuries (e.g., microinfarctions). 
     While the principles of the invention have been described above in connection with specific apparatus and applications, it is to be understood that this description is only an example and is not intended as a limitation on the scope of the invention. The above-described embodiments of the invention are merely examples of ways in which the invention may be carried out. Other ways may also be possible, and are within the scope of the following claims defining the invention.