Abstract:
A method for taking reflectance oximeter readings within the nasal cavity and oral cavity and down through the posterior pharynx. The method utilizes a reflectance pulse oximeter sensor that preferably is resistant to bodily fluids to contact one of these capillary beds for the taking of readings and then forwarding of these readings to an oximeter for display. The method includes inserting a reflectance pulse oximeter sensor into a cavity within a subject&#39;s skull and contacting a capillary bed disposed in the cavity with the reflectance pulse oximeter sensor.

Description:
This application claims priority from U.S. provisional Application Ser. No. 60/099,579, filed Sep. 9, 1998, U.S. provisional Application Ser. No. 60/101,079, filed Sep. 18, 1999, and U.S. provisional Application Ser. No. 60/101,143, filed Sep. 18, 1998, which are all hereby incorporated by reference. 
    
    
     I. FIELD OF THE INVENTION 
     This invention is directed to a method for measuring blood oxygenation in multiple internal areas of a subject through either the nasal cavity or the oral cavity. More particularly, the invention relates to using pulse oximeter sensors to perform reflective pulse oximetry internal to a subject. 
     II. BACKGROUND OF THE INVENTION 
     With a few exceptions, tradition and technology have favored transillumination pulse oximetry in the operating theater. The principle of operation of the pulse oximeter is fairly simple but is arguably the most important development in anesthesia monitoring in the twentieth century. Two wavelengths of light (usually 660 nm and 940 nm) are used to spectrophotometrically determine the ratio of oxidized to reduced hemoglobin noninvasively as well as to determine the pulsatility of blood plethysmographically. Presently, the most common application of this in the operating theater is via transillumination through the capillary bed of a peripheral digit. However, it is not unusual for multitrauma and thermally injured patients to either have severe peripheral vasoconstriction or to have severely damaged (or missing due to amputation) peripheral vascular beds. Reflectance oximetry rather than transillumination oximetry was the earliest investigative form of the technique. Transillumination pulse oximetry, without question, is the most effective form when oximetry is obtained through skin. However, when skin is not interposed as a barrier to capillary bed access, reflectance pulse oximetry easily can be achieved with very accurate results. The effect is achieved by the backscattering of incident bispectral light that traverses and, on reflection from nonabsorptive collagenous tissues, retraverses formed elements in the blood back to the oximetric detector. Rather than superseding transillumination pulse oximetry, this technique broadens the scope of possible monitoring sites, adding to the clinician&#39;s armamentarium. 
     Conventional pulse oximetry in the severely burned patient can be a significant hallenge, yet this monitoring data is vital in operating room and intensive care settings. Most current oximetric approaches depend upon available peripheral sites permitting transillumination oximetry and indeed, this method is sufficient for most surgical conditions and procedures. Unfortunately, patients with severe burns often have few sites for the effective placement of the transilluminating pulse oximeter sensor. In addition, these patients often have severe circulatory compromise rendering the peripheral pulse oximeter less efficient. A variety of studies have shown that central pulse oximeters are more reliable and rapidly responsive than peripheral pulse oximeters. 
     Reflectance oximetry can be a useful tool where a capillary bed is easily accessible. Indeed, it is used commonly and effectively among intrapartum and neonatal patients whose capillary beds are easily accessed through their skin. The technique has also been applied to adult and pediatric burn patients by placing the reflectance sensor in wounds or over hyperemic sites such as healed partial thickness burns. 
     Prior pulse oximeter sensors inserted through the mouth are usable only when the patient is under general anesthesia. These pulse oximeter sensors are inserted to reach the larynx area, for example, U.S. Pat. No. 5,282,464 to Brain et al. Another known method uses transillumination pulse oximetry of the posterior tongue, but this method may not be used with a patient, who is awake, for example, U.S. Pat. No. 5,205,281 to Buchanan. Also, the posterior tongue is not the most accessible body part to take oximetric measurements. 
     Recent studies indicate that oral pulse oximetry is a superior modality when compared to peripheral transillumination pulse oximetry. A variety of studies have shown that oral pulse oximeters are more reliably and rapidly responsive than peripheral pulse oximeters. However, these studies use oral transillumination pulse oximetry, held in place via complex devices or pieces of improvised malleable metal. Oral secretions, equipment failure, and placement difficulty often render these techniques ineffective. 
     There are other often overlooked capillary beds readily accessible in most adult burn patients that are as amenable to reflectance oximetry as the forehead of the premature infant. The buccal surface, posterior soft palate, hard palate and proximal posterior pharynx of a burned patient are seldom compromised no matter how severe the burn, and the capillary beds are very close to the surface in those areas. Transillumination pulse oximetry of the tongue and cheek has been documented as a viable method of monitoring, but not everyone has the equipment available to place a transilluminating pulse oximeter on the tongue or cheek. A reflectance pulse oximeter sensor has the bispectral emitter and the detector in a side-by-side configuration rather than in opposition. The device may be placed flat upon a suitable capillary bed and it thus becomes a reflectance pulse oximeter sensor. 
     The nasal mucosa and the posterior pharynx contain rich capillary beds ideal for reflectance pulse oximetry. Known pulse oximeters are not suitable for use in the nares as they tend to block the nasal passage thus constricting the patient&#39;s breathing. In addition, they are prone to difficulties when their electrical components are exposed to liquid, moisture, bodily fluids, and/or surgical fluids. Since they rely on transillumination they also tend to be difficult to hold in place. 
     Notwithstanding the usefulness of the above-described devices, and the above-identified recognized viability of transilluminating buccal pulse oximetry, a need exists for a more convenient method for obtaining oximeter readings from a subject. 
     III. SUMMARY OF THE INVENTION 
     The invention while addressing the problems of the prior art obtains advantages that were not achievable with the prior art methods. 
     An object of this invention is to provide an effective method for taking pulse oximetry measurements from nasal, oral, and posterior pharyngeal capillary beds. 
     Another object of the invention is the use of reflectance pulse oximetry via the nasal and/or oral cavities for a variety of surgical, anesthetic, or critical care procedures or situations to include patients that are awake, sedated or undergoing general anesthesia. 
     Another object of the invention is to allow for lingual placement of a pulse oximeter sensor for reflectance readings to provide efficient and clinically accurate pulse oximetry measurements. 
     Another object of the invention is to allow for buccal placement of a pulse oximeter sensor for reflectance readings to provide efficient and clinically accurate pulse oximetry measurements. 
     Still another object of the invention is to monitor oxygen levels in severely burned ICU patients who are difficult to monitor. 
     An advantage of the invention is an improvement in the quality of care resulting from using a straightforward method with easily used devices to take internal oximetry measurements and readings. 
     Another advantage of the invention is that EMS crews and personnel will be able to use this invention easily in the field during, for example, emergency situations. 
     Another advantage of the invention is improved pulse oximetry readings. 
     Another advantage of the invention is reflectance pulse oximetry requires less power to function and thus less heat is produced than transilluminance pulse oximetry. The decrease in produced heat lowers the risk the subject will be burned. 
     The method accomplishes the above objectives and achieves the advantages. The method is easily adapted to a wide variety of situations. 
     Furthermore, intraoral buccal or proximal posterior pharyngeal/palatal placement of a pulse oximeter probe in a configuration relying upon reflectance will provide pulse oximetry measurements comparable to those obtained by peripheral pulse oximetry. Test protocols suggest that buccal and proximal posterior pharyngeal/palatal reflectance pulse oximetry provides a simple, accurate means of monitoring arterial oxygen saturation in the severely burned patient where oximetric monitoring presents a challenge. 
     Furthermore, the method is extremely useful in cases where it is difficult at best or not even possible to attach prior art pulse oximeter sensors with clips or straps to the patient. The types of patients that this method would be useful with are critically ill or injured patients including burn or trauma patients without alternative sites and maxillofacial injuries. 
     Given the following enabling description of the drawings, the method should become evident to a person of ordinary skill in the art. 
     IV. BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a flowchart illustrating the steps for performing the preferred embodiment. 
     FIG. 2 depicts the nasopharyngeal airway oximeter sensor being used in the method against the posterior pharynx. 
     FIG. 3 illustrates the oral airway oximeter sensor being used in the method against the posterior pharynx. 
     FIG. 4 depicts the oral airway oximeter sensor being used in the method against a buccal surface. 
     FIG. 5 illustrates the oral airway oximeter sensor being used in the method against the lingual surface. 
     FIG. 6 depicts the nasopharyngeal airway oximeter sensor. 
     FIG. 7 illustrates a bottom view of the nasopharyngeal airway oximeter sensor. 
     FIG. 8 depicts a radial cross-section view of the nasopharyngeal airway oximeter sensor. 
     FIG. 9 illustrates a rear view of the nasopharyngeal airway oximeter sensor. 
     FIG. 10 depicts a side view of the oral airway oximeter sensor. 
     FIG. 11 illustrates a front view of the oral airway oximeter sensor. 
     FIG. 12 depicts a rear view of the oral airway oximeter sensor. 
     FIG. 13 illustrates a top view of the oral airway oximeter sensor. 
     FIG. 14 depicts a side view of another oral airway oximeter sensor. 
     FIG. 15 depicts a partial front view of the distal end of the oral airway oximeter sensor illustrated in FIG.  14 . 
     FIG. 16 illustrates a top view of a protective cover for a combined protective cover and oximeter sensor. 
     FIG. 17 illustrates a side view of the protective cover depicted in FIG.  16 . 
     FIGS.  18 ( a ) and  18 ( b ) depict alternate geometries of the protective cover depicted in FIG.  16 . 
     FIG. 19 illustrates a top view of the combined protective cover and oximeter sensor that may be used in the method of the preferred embodiment. 
     FIG. 20 depicts a side view of the combined protective cover and oximeter sensor. 
     FIG. 21 illustrates an end view of the combined protective cover and oximeter sensor. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Like reference numerals in the figures represent and refer to the same element or function. 
     a. Overview 
     In accordance with the present invention, there is a method to take oximeter readings from different sites within a subject, which may be either human or animal, for the purposes of determining the amount of oxygen within the blood of the subject. The oximeter readings are accomplished using reflectance oximetry from capillary beds that are readily accessible within the subject. The capillary beds include, for example, the nasal mucosa, the nasal passageway, the posterior pharynx, the hard palate, the soft palate, the superior lingual surface, the inferior lingual surface, the gingivae, the mouth floor, and the buccal surface. Each of these capillary beds is accessible through at least one opening in the subject&#39;s head leading to an intrahead cavity, which includes an oral cavity and a nasal cavity. The oral cavity extends from the lips to the oral portion of the pharynx, i.e., pars oralis. The nasal cavity extends from the nostrils to the nasal portion of the pharynx, i.e., pars nasalis. The nasal cavity and the oral cavity together form what is known as the nasal oral pharynx region of an individual. 
     FIG. 1 illustrates a flowchart showing the common steps for taking oximeter readings from the previously mentioned capillary beds. In the first step  110 , which may actually occur at a later point but no latter then the initiation of taking pulse oximeter readings, the pulse oximeter sensor elements are connected to an oximeter device such as a spectrophotometer. In step  115 , the oximeter sensor device is inserted into the subject through an available opening such as the mouth or the nose. In step  120 , the pulse oximeter sensor is positioned adjacent the relevant capillary bed such that the pulse oximeter sensor elements are facing and preferably in contact with the capillary bed to allow for reflectance pulse oximetry. The placement of a device with a pulse oximeter sensor is illustrated, for example, in FIGS. 2-5. In step  130 , reflectance pulse oximeter readings are taken from the relevant capillary bed. While taking the pulse oximeter readings, the pulse oximeter sensor elements preferably remain in contact with the relevant capillary bed to continue the flow of accurate oximeter readings. 
     In the case where the capillary bed is the nasal mucosa, the opening through which the pulse oximeter sensor is inserted is one of the nostrils as shown in FIG.  2 . In the case where the capillary bed is the posterior pharynx, the pulse oximeter sensor may be inserted through either the nasal cavity or orally depending of the type of device used as exemplified by the devices shown in FIGS. 2 and 3. If the capillary bed is the soft or hard palate, the superior lingual, or the buccal surface, then the pulse oximeter sensor preferably is inserted into the mouth as shown, for example, in FIGS. 3-5. 
     The readings may be taken with a variety of devices, some of which are discussed below and shown in FIGS. 2-21. Suitable devices for performing the method preferably include at a minimum, the following: pulse oximeter sensor elements, including a light source and a light detector, and a support surface or structure. In addition, the devices may include wiring and an external cord, both of which may be connected to the pulse oximeter sensor elements. 
     More particularly, in an exemplary device, the pulse oximeter sensor elements include a light source  20 , which preferably emits light with wavelengths of 660 nm (red) and 940 nm (near infrared), and a light detector  22 . The placement and location of the light source  20  and the light detector  22  depicted in the Figures may be switched with respect to each other. 
     The light source  20  emits at least two frequencies of light at, for example, about 660 nm and about 940 nm. The light source  20  preferably is one or more of the following: two light emitters such as light emitting diodes (LED), a bispectral emitter, a dual spectral emitter, a photoemitter, or a semiconductor die. However, any light source that facilitates reflectance pulse oximetry may be employed. Typically, the two emitter arrangement will include a red LED around or at 660 nm and a near-infrared LED emitting in the range of 890 to 950 nm and more particularly at about 940 nm. The light source  20  may emit light having a bandwidth, for example, in the range of 20 to 50 nm. 
     The light detector  22  detects light emitted by the light source  20 . Electrical signals representing the detected light are transmitted by the light detector  22  to a spectrophotometer, or other similar oximeter device, that discriminates between the relative intensity of these emissions and provides an index as to the degree of oxygen saturation of hemoglobin in blood. Preferably, the light detector  22  may be one of the following: a photoelectric receiver, a photodetector, or a semiconductor die. 
     Wiring  24  includes conductive lines and contact electrodes. An external cord  26  preferably is insulated and connects to the wiring  24  at the proximal end of the support structure so that the external cord  26  preferably is either outside the subject or near the opening in which the device was inserted. The external cord  26  has a standard plug design to interface with a pulse oximetry spectrophotometer, a pulse monitor such as a plethysmograph, or other external device. The spectrophotometer provides the electrical signals for controlling the pulse oximeter elements  20  and  22 . The light source  20  and the light detector  22  may be in wireless communication with the external device instead of connected with the external cord  26  shown, for example, in FIGS. 3,  14 , and  15 . 
     The method according to the invention may be used in a variety of surgical, anesthetic, combat or critical care procedures or situations that include patients that are awake, sedated or undergoing general anesthesia. In particular, the method may be used throughout the pre-induction, throughout induction, during, upon emergence from, and after anesthesia without switching devices. This advantage is accomplished while avoiding uncomfortable stimulation deep in the throat, thus minimizing the possibility of gagging, vomiting, aspiration, and impingement of the teeth upon the endotracheal tube prior to extubation. 
     The following devices are capable of being used in conjunction with the method for at least one of the previously discussed capillary beds. Each of the discussed devices are more fully described in co-pending patent applications filed by the inventors as well be referenced below. With each device there is an explanation as to how the device is utilized in conjunction with the method. 
     b. Nasopharyngeal Airway Oximeter Sensor 
     The first device is a nasopharyngeal airway with a reflectance pulse oximeter sensor described in a co-pending patent application claiming priority from U.S. provisional Application Ser. Nos. 60/099,579 and 60/101,143. FIGS.  2  and  6 - 9  illustrate this device. This device includes a nasopharyngeal airway  100  in combination with pulse oximeter elements  20  and  22 , wiring  24 , and external cord  26 . The pulse oximeter sensor elements  20  and  22  and wiring  24  are preferably disposed within the wall of the nasopharyngeal airway  100 . 
     As depicted in FIG. 6, the nasopharyngeal airway  100  is preferably a hollow, elongated member defining a passageway, e.g., a cylindrical tubular member, having an insertion end  114  and a base end (or proximal end)  116 . The insertion end  114  preferably is angled. The base end  116  may be flat and disposed substantially perpendicular to the rest of the nasopharyngeal airway or angled. The base end  116  may include a notch or other marking corresponding to the tip of the nasopharyngeal airway  100  to assist the user in further positioning the device in the patient after insertion of the device. 
     Preferably, the wall of the nasopharyngeal airway  100  is made of a clear polymer. Furthermore, it is preferable that the wall may include a thickened section  112  around approximately one-third of the cross-sectional circumference to house the pulse oximeter sensor elements  20  and  22  and wiring  24 . Alternatively, the thickened section  112  may be around just the elements and not run the length of the nasopharyngeal airway  100 . The pulse oximeter sensor elements  20  and  22  and wiring  24  are preferably embedded and sealed in the wall of the nasopharyngeal airway with a cover, which may be integrally formed with the nasopharyngeal airway  100 , protecting them. Preferably, the cover is a clear, fluid impermeable plastic. 
     Alternatively, the pulse oximeter sensor elements  20 ,  22 , and  24  may be disposed within the passageway of the nasopharyngeal airway  100 . A disposable pulse oximeter like the Nellcor® Oxisensor® II N-25 or D-25 (Nelicor Puritan Bennett®, Inc., Pleasanton, Calif.) may be stripped of its surroundings to leave only the pulse oximeter sensor elements. The pulse oximeter elements may then be fed into the nasopharyngeal airway  100  along one side of the passageway. Even though the pulse oximeter sensor elements and wiring may be present in the passageway, there is sufficient airflow capacity to supply adequate oxygen to the patient. 
     Preferably, the pulse oximeter sensor elements  20  and  22  are located near the angled end  114  to facilitate readings being taken from the proximal posterior pharynx as shown in FIG.  2 . This arrangement provides for easy access and a reliable contact point. However, if the pulse oximeter sensor elements  20  and  22  are located near the base end  116 , then the readings will be taken from within the nasal cavity. The nasal cavity, while adequate, provides less reliable and accurate pulse oximetry readings than the posterior pharynx. 
     The nasopharyngeal airway preferably is manufactured using polypropylene, polyvinyl chloride, silicones, epoxies, polyester, thermoplastics, rubber, similar flexible material, etc. The material should be sufficiently flexible that it freely bends in accordance with the contour of the nasal passageway. The thickened area is preferably formed from a clear or semi-translucent material to allow for the passage of light from the light source  20  and to the light detector  22 . 
     In use, the nasopharyngeal airway  100  preferably takes measurements from a central measurement site, namely the proximal posterior pharynx, posterior soft palate or nasal mucosa. The data collected from these locations has proven more reliable then data attainable from periphery locations. The increased reliability is believed to be due to the centrality of the measurement location and the stability of the measurement surfaces. 
     This device is particularly useful when the patient is awake but sedated. However, the device may be used while the patient is fully awake, during induction of anesthesia, during general anesthesia, on emergence from anesthesia and during recovery. This device will allow pulse oximeter measurements to be taken in very wet environments as the oximetric components and wiring are sealed within the polymeric envelope of the nasopharyngeal airway. This device is useful for taking pulse oximeter measurements in the field and in emergency medical areas, because the device is capable of both establishing an airway and providing pulse oximetry monitoring in a single device. 
     C. Oral Airway/Bite Block Pulse Oximeter Sensor 
     Another device suitable for performing the method according to this invention is a pulse oximeter sensor combined with a combination oral airway and bite block as illustrated in FIGS. 3-5 and  12 - 15  and described in a co-pending patent application entitled Pulse Oximeter Sensor Combined with a Combination Oropharyngeal Airway and Bite Block claiming priority from U.S. provisional Application Ser. Nos. 60/099,579 and 60/101,079 filed concurrently herewith. 
     As depicted, the device includes a base  210 , a straight portion  220 , and a palatal and proximal pharyngeal contour portion  230  preferably arched to be physiologically compatible with the palate and pharynx. The airway also includes oximeter elements  20  and  22 , which reside in the posterior distal curvature of the device. As represented in the figures, the optional wiring  24  and external cord  26  are represented, but as discussed above may be removed in a wireless configuration. The contour portion  230  includes arched section A having an outer distal curve  234  and a distal end  236 . The contour portion  230  is preferably integrally formed with straight portion  220 , which includes a proximal end abutting the base  210 . The base  210  preferably is large enough to allow the device to be manipulated by the user. 
     A central passageway or channel  240  may be formed within the device to extend from the distal end  236  to the base  210 . As is apparent to one of ordinary skill in the art in view of the present disclosure, the cross-section and dimensions of the passageway  240  may be selected to maximize the airflow through the passageway without reducing the integrity of the device. 
     Preferably, the light source  20  and the light detector  22  are embedded in the body of the device along the outer distal curve  234  facing radially outward with a cover, which may be integrally formed with the airway, protecting them. Preferably the cover is a clear, fluid impermeable plastic. Alternatively, the pulse oximeter elements  20  and  22  may be disposed within passageway  240  adjacent the outer distal curve  234 . FIGS.  3  and  10 - 13  depict wiring  24  connecting the pulse oximeter elements  20  and  22  to the external cord  22 . The wiring  24  is preferably also embedded in the body of the contour portion  230 . 
     The pulse oximeter elements  20  and  22  may be disposed in a variety of locations along the passageway in accordance with the desired application. Preferably, the pulse oximeter elements  20  and  22  are placed closer to the distal end  236  of the device so that the readings may be taken from the posterior pharynx area, the buccal surface, the lingual surface, the gingiva surfaces, or the mouth floor of the patient. As the pulse oximeter elements  20  and  22  are moved towards the apex of the arched section A, the readings more likely will be taken from the soft palate of the patient. The dividing line between these regions is highly dependent on the internal dimensions of the patient. However, the readings obtained from each area work equally well in terms of accuracy. Also, the closer to the apex of the arched section A the pulse oximeter elements  20  and  22  are, the more difficult it is for the device to contact the buccal surface or the lingual surface when the device is used as a bite block. When the pulse oximeter elements  20  and  22  are positioned away from the apex of the arched section A towards the proximal end abutting the base  210 , the readings will be taken from the hard palate, which also will provide accurate pulse oximetry readings. 
     To facilitate operation of the device as a bite block, bilateral grooves (or recesses)  250  into which the teeth may fit are preferably disposed in opposing relationship to each other and formed in the contour portion  230 . More preferably, the bilateral grooves extend from the distal end  236  to a point along the outer distal curve  234 . The bilateral grooves  250  may be filled with a sponge-like or soft material, e.g., foam or rubber to protect the teeth. The bite block groove/recess feature is not necessary for this device to be used for monitoring arterial oxygen saturation pursuant to the preferred method. 
     Alternatively, the pulse oximeter elements may be disposed in the passageway. A disposable pulse oximeter sensor like the Nellicor® Oxisensor® II N-25 may be stripped of its surroundings to leave only the pulse oximeter elements. The pulse oximeter elements are then fed along the topside of the passageway  240 . Although the pulse oximeter elements and wiring may be present in the passageway  240 , there will be sufficient airflow capacity in the passageway to supply oxygen to the patient. The N-25 pulse oximeter sensor when installed in this manner does not overdrive as a result of the emitted brightness from the light source, because of the optical effects provided by the oropharyngeal airway. 
     To facilitate operation of the device as a pulse oximeter sensor, a plastic bag, protective cover or similar item may be placed around the distal end  236 . This addition is particularly useful when there is excess moisture that might interfere with the operation of the pulse oximeter sensor elements. 
     Alternatively the oral airway/bite block oximeter sensor may have an I-beam construction as shown in FIGS. 14 and 15. The I-beam structure includes a first wall  260 , a second wall  270 , and a third wall  280 . The first wall  260  runs parallel to the second wall  270  and the third wall  280  runs perpendicular to and between the first and second walls  260  and  270 . Each wall preferably includes a straight portion  262 ,  272 , and  282  and a distal curve portion  264 ,  274 , and  284  configured to fit the contour of the palatal and proximal pharyngeal. At the end opposite the distal end  236  is a base  210 . A passageway  240 ′, as shown in FIG. 14, is formed on either side of the third wall  280  and is framed by the first and second walls  30  and  40 . A groove  25 ′ may be provided in the first wall  260  to provide a recess for the teeth to pass through to facilitate operation as a bite block. 
     Preferably, the pulse oximeter elements  20  and  22  are located within the first wall  260  in the distal curve portion  264 . Preferably, the first wall  260  is thickened in the area around the pulse oximeter elements  20  and  22  slightly relative to the second wall  270  to better house the pulse oximeter elements  20  and  22 . This area may include translucent material to allow for light to travel through the first wall  260 . As one of ordinary skill in the art will appreciate, the pulse oximeter elements  20  and  22  may be placed within the third wall  280  in the distal curve portion  284  (not shown). The pulse oximeter elements  20  and  22  are positioned to perform reflectance pulse oximetry. The pulse oximeter elements  20  and  22  may be placed anywhere along the length of the first and third walls  260  and  280  in a manner similar to the first oral airway/bite block oximeter sensor discussed above. The wiring  24  connected to the pulse oximeter elements  20  and  22  preferably are within the same wall as the pulse oximeter elements  20  and  22 . 
     The base oral airway/bite block structure is preferably manufactured using polypropylene material that is either molded or extruded. Molding will produce a more rigid structure than extrusion. The sponge-like material, e.g., foam or rubber in the recesses may be added after forming the base oral airway/bite block. Both molding and extrusion will allow the pulse oximeter sensor elements to be embedded in the oral airway/bite block structure. 
     To accomplish a change between the two modes, this device only needs to be repositioned within the patient thus avoiding the need to exchange devices as required with present devices. For example, during anesthesia, it may be desirable to use the device as an oral airway to establish a ventilatible airway for the patient. When used as such, the device is preferably inserted into the patient&#39;s mouth such that it impinges upon the posterior soft palate and/or the posterior pharynx along the outer distal curve  234 . 
     In addition, before, on induction of, during, on emergence from and after anesthesia, it may be desirable to employ the device as a bite block. When used as such, the device is preferably inserted into the patient&#39;s mouth such that the bilateral grooves  250  on the sides of the contour portion  230  may be inserted between the molars and/or bicuspids on one side of the mouth. The outer distal curve  234  in this mode abuts the buccal mucosa, as shown in FIG.  4 . The alternative preferred insertion method is to place the device such that the bilateral grooves  250  are inserted between the molars and/or bicuspids on the other side of the mouth so that the outer distal curve  234  will abut the lingual surface of the tongue, as shown in FIG.  5 . Neither mode will stimulate the posterior tongue/pharynx. 
     d. Combination Protective Cover and Oximeter Sensor 
     A further device suitable for performing the method in accordance with the invention is a combination pulse oximeter sensor and protective cover as illustrated in FIGS. 16-21 and described in a co-pending patent application entitled Disposable Pulse Oximeter Assembly and Protective Cover Therefor claiming priority from U.S. provisional Application Ser. Nos. 60/099,579 and 60/101,079. 
     Referring to FIGS. 16 and 19, the protective covering  310  may include a condom, a shield or a protective sheath made from polypropylene, translucent rubber, or a similar material. Preferably, the protective covering  310  includes a substantially transparent section to be disposed adjacent to a light source  20  and a light detector  22  of a pulse oximeter sensor  320  that preferably includes wiring  24 , an external connector  26 , and plastic tape covers  322  providing the support structure. The protective covering  310  preferably includes a top surface  311  and a bottom surface  312 . The protective covering  310  further includes a proximal end  314  and a distal end  313  having a pocket formed therebetween. The distal end  313  preferably is sealed while the proximal end  314  includes an opening to allow insertion of the pulse oximeter sensor  320 . 
     The pulse oximeter sensor  320  may be disposed within the protective covering  310 . To facilitate insertion, removal and storage of the pulse oximeter sensor  320  in the protective covering  310 , the proximal end  314  of the protective covering  310  preferably is wider than the distal end  313 . Preferably, the width of the pocket formed between the distal and proximal ends  313  and  314  increases along the length of the protective covering  310 . In accordance with a particularly preferred feature of this device, the change in width of the opening along the length of the protective covering  310  is approximately one-half centimeter. 
     As one of ordinary skill in the art will realize from this description, the protective covering  310  may be implemented in a variety of geometries. For example, in accordance with an aspect of this device, the protective cover  10  may include first and second edges  315  and  317 . As shown in FIG. 16, the first edge  315  may be angularly displaced relative to the axis of the protective covering  310 . In another geometry, each of the first and second edges  315  and  317  may be angularly displaced from the axis of the protective covering as depicted in FIG.  18 ( a ). In still another geometry, as illustrated in FIG.  18 ( b ), the first edge  315  may include a first section that is angularly displaced from the axis of the protective covering  310  near the distal end  313  and a second section that is substantially parallel to the axis of the protective covering  310  near the proximal end  314 . The second edge  317  may be a mirror image of the first edge  315  or the second edge may be parallel to the axis of the protective covering  310  along the entire length of protective covering  310  (not shown). One of ordinary skill in the art will appreciate that the forgoing constitutes only a representative sample of suitable geometries for the protective covering. Angularly displaced edges increase the convenience of using off-the-shelf pulse oximeter sensors, because the adhesive portions  322  can be folded inward without mutilating the pulse oximeter sensor by removing or excising the adhesive portions. 
     Furthermore, the protective covering  310  preferably is bilaminar in nature providing increased strength to contain a substantially rectangular pulse oximeter sensor  320  with probe fixing tape and/or plastic tape covers  322  folded back. The proximal end  314  may include a flap extending from either the top surface  311  or the bottom surface  312  to fold back and seal the protective covering  310  or some type of adhesive inside the pocket near the proximal end  314  to seal the protective covering  310 . The protective covering  310  preferably covers and encases the pulse oximeter sensor  320  and a portion of the connector cable  24  extending from the pulse oximeter sensor  320 . 
     In commercial applications, it is expected that the protective covering  310  will be disposable. The protective covering  310  may serve as an envelope like structure for the pulse oximeter sensor  320  to be inserted into for use. In particular, the structure of the protective covering  310  may be a blind flat bilaminar bag. As a result, the protective covering  310  insulates the pulse oximeter sensor  320  from direct contact with bodily or surgically related fluids, consequently, protecting the electrical components of the pulse oximeter sensor  320  from fluid. 
     The protective covering  310  is easily manufactured. Two sheets of polypropylene or similar non-reactive material may be laid out, on a substantially flat surface such that the two sheets overlap in the area where the protective covering(s) will be formed. Then, using a heat sealer or gun, the sheets may be subdivided into individual protective coverings. The heat sealer or gun allows the manufacturer to subdivide the sheets&#39; surface area into individual protective coverings that will have their sides formed by melting together the two sheets into seams. In keeping with the invention, the two sheets of polypropylene may be replaced with a large polypropylene, or similar material, bag. In further keeping with the invention, two sheets of polypropylene may be replaced with one polypropylene, or similar material, sheet folded over such that the fold line forms the side of the protective coverings formed along the fold line. 
     The protective covering  310  will allow off-the-shelf disposable pulse oximeter sensors  320  to be used in a greater number of locations within patients or animals. In particular, oximetry will be able to be performed according to the invention with this device in the oral cavity on the lingual or buccal mucosa, the mouth floor, the gingiva, the hard or soft palate, or the posterior pharynx. According to this invention, the device will also be able to take oximeter readings from within the nasal cavity. An example of a disposable pulse oximeter sensors that will have increased use is the Nellcor® Oxysensor® II line of pulse oximeter probes and sensors. 
     The insulation aspects of the protective covering  310  will allow for use of pulse oximeter sensors  320  for peribuccal, perilingual, sublingual, peripalatal, and peripharyngeal pulse oximetry. To take readings from the buccal surface, the patient&#39;s jaw should be opened to allow access to the buccal surface. The protective covering  310  with inserted pulse oximeter sensor  320  disposed therein may be placed against the buccal surface. As the jaw closes, the muscles will contract and close around the protective covering  310 , thus holding the protective covering  310  and the pulse oximeter sensor  320  against the buccal surface. A much tighter fit is possible, because of the flexible nature of the combination of the protective covering  310  and the pulse oximeter sensor  320 . 
     e. Testing 
     The method of taking pulse oximeter readings from different surfaces within a patient has been submitted to actual testing in the below-described population and according to the following protocols. 
     Reflectance Oximetry from the Buccal Surface 
     The first protocol involved taking readings from the buccal surface. Nine patients were monitored via buccal reflectance pulse oximetry over  20  consecutive surgical procedures, which procedures consisted of burn excision and grafting. Patients ranged in age from 23 to 56 years (Mean=264.8, Standard Deviation (SD)=11.2) and ranged from 17 to 75 percent total body surface area (%TBSA) burned (Mean=274.3%, SD=28.9). Each patient received from one to eight operations (Mean=4.01). Five of these nine patients arrived at the operating room intubated for all of the operations in this study. Four patients were induced and intubated in a standard fashion for all surgical procedures. 
     A Nellcor® Oxisensor® II D-25 was placed intraoraly between the lower teeth and the left or right buccal surface of the cheek and lip, with the bispectral emitter and detector facing the buccal surface. This pulse oximeter sensor orientation was used for the duration of each case. In addition, a similar disposable oximetric probe was placed on a peripheral digit in the commonly accepted transillumination configuration. At five minute intervals throughout the case, values for both oximetric probes were coded on the anesthesia record. 
     The differences between the peripheral and buccal SpO 2  (oxygen saturation of hemoglobin) values were insignificant by t-tests for correlated means. Concordance rates as percent agreements were calculated for all cases. Average percent agreement was 84% ranging from 25% to 100%. Three of the 20 samples had percent agreements less than 91%. In each of these cases, the peripheral pulse oximeter sensor appears to have failed, in two cases secondary to sepsis, and in another secondary to peripheral vasoconstriction in the face of a norepinepherine infusion. Buccal SpO 2  readings in all three cases continued to be 97% or greater. 
     This data suggests that buccal reflectance oximetry is a simple, accurate means of monitoring arterial oxygen saturation in the severely burned patient where oximetric monitoring presents a challenge. Given that central oximetry has been shown in numerous studies to be more rapidly responsive to oxygen saturation variability than peripheral oximetry, as well as more directly reflective of central oxygen saturation, there are few drawbacks and considerable benefit from this method. Indeed, in the three examples in this study where percent agreements were low, the peripheral oximetric probes were returning apparently erratic and/or generally low values while buccal oximetric readings remained at 97% or higher. All three of these patients had peripheral vascular compromise secondary to sepsis and/or a vasoconstricting agent (norepinepherine infusion). 
     It may appear from the study results, at first blush, that a full range of SpO 2  values was not tested and that the continuously high SpO 2  readings are spurious to the technique. On the contrary, in order to obtain a SpO 2  value greater or less than 85% a very specific set of relationships must be present relative to the bispectral emitter and light sensing oximetric elements. Thus, spuriously high values in particular do not consistently occur. High SpO 2  values require the presence of saturated hemoglobin. Unlike lingual oximetry, this technique is not necessarily limited to intubated patients as a flat disposable oximetric probe could be placed between the cheek and teeth of an awake patient. In addition to operating room considerations, ventilated patients in intensive care settings could benefit from this technique, especially given the more rapid response of a centrally placed pulse oximeter over a peripheral one. 
     Posterior Pharyngeal Reflectance Oximetry 
     The second protocol involved comparing posterior pharyngeal reflectance pulse oximetry to conventional peripheral transillumination pulse oximetry in difficult to monitor burn patients. Eight patients&#39; records were reviewed over fourteen consecutive surgical procedures, all consisting of excision and grafting. Patients ranged in age from 9 to 43 years and ranged from 14.5% to 77.5% TBSA burned (Mean=30.4, SD=22.1). The number of operations per patient ranged from one to four. 
     A Nellcor® Oxisensor® II pulse oximeter probe was placed in the distal lumen of an appropriately sized oropharyngeal airway with sensor and emitter facing the posterior pharynx. A similar probe was placed on a peripheral digit as a transilluminating pulse oximeter. SpO 2  values were noted at five-minute intervals. Concordance statistics as well as a t-test for correlated means were calculated between the simultaneously obtained SpO 2  values. 
     The mean differences between pharyngeal reflectance and peripheral digital transillumination SpO 2  values were insignificant for all cases. Concordance statistics were as follows: 0.75 (n=1) and 1.0 (n=12). 
     Given the near perfect concordance statistics in this study, this data suggests that posterior pharyngeal reflectance oximetry is a simple, highly accurate means of monitoring arterial oxygen saturation in the severely burned patient where oximetric monitoring presents a challenge. 
     Lingual Surface Reflectance Oximetry 
     The third protocol involved taking readings from the lingual surface. Data was reviewed for eight difficult to monitor patients who were monitored via lingual reflectance pulse oximetry over twenty-five consecutive surgical procedures, all consisting of burn excision and grafting. Patients ranged in age from 26 to 57 years (Mean=36.0, SD=10.3). Patients ranged from 20% to 92% TBSA burned (Mean=66.75%, SD=26.42). Number of operations per patient ranged from one to five (Mean 3.13, SD=1.55). Six of these eight patients arrived at the operating room intubated for all of the operations in this study. Two patients were induced and intubated in a standard fashion. 
     In each case, a Nellcor® Oxisensor® II D-25 was centered flat on the superior lingual surface with the detector and the bispectral emitter facing the lingual surface. This pulse oximeter configuration was used for the duration of each case. When clinically indicated, an arterial blood gas (ABG) sample was drawn and the SpO 2  noted for clinical monitoring and prior to transfusion in every case. All had multiple ABG&#39;s drawn and all patients were transfused. The ABG SaO 2  (oxygen saturation of arterial blood) was noted in each case. 
     Descriptive statistics and a concordance rate as well as a t-test for correlated means were calculated between the simultaneously obtained SpO 2  and SaO 2  values. The difference between the SpO 2  and SaO 2  values was insignificant by t-test for correlated means (t=1.25, df=24, NS). Upon inspection, the means were very close and the standard deviations were very small, as were the SEM&#39;s, all suggesting very little difference or variability between these two measures of oxygen saturation. A concordance rate of 92% was calculated (+1.5%) showing a high degree of relationship between lingual and ABG SaO 2 . 
     This data suggests that lingual reflectance oximetry is a simple, accurate means of monitoring arterial oxygen saturation in the severely burned patient where oximetric monitoring presents a challenge. An existing disposable pulse oximeter sensor was utilized in this study saving the cost of specially designed equipment. Given that central oximetry has been shown to be more rapidly responsive to oxygen saturation variability than peripheral oximetry, there are few drawbacks and considerable benefit from this method. As a practical matter, the foregoing technique is probably limited to intubated patients, as awake, extubated patients could find the presence of a lingual pulse oximeter sensor irritating. However, this limitation would hold with lingual transillumination pulse oximetry as well. In addition to operating room considerations, ventilated patients in intensive care settings could benefit from this technique, especially given the more rapid response of a centrally placed pulse oximeter over a peripheral one. 
     Those skilled in the art will appreciate that various adaptations and modifications of the above-described devices and steps can be configured without departing from the scope and spirit of the their use in the method. Therefore, it is to be understood that, within the scope of the appended claims, the method may be practiced and arranged other than as specifically described herein.