Abstract:
A method and system for determining the residual volume within a patient having a naso-enteral feeding tube. A collection container is coupled to the naso-enteral feeding tube and a physical force is applied to the collection container to prevent stomach fluid from flowing into the collection container. The physical force is removed from the collection container and the stomach fluid is allowed to flow into the collection container. The volume of fluid within the collection container is determined, which represents the gastric residual volume of the patient. At least a portion of the collected volume of stomach fluid is returned to the patient from the collection container.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on and claims priority from U.S. Provisional Patent Application Ser. No. 61/119,583 filed on Dec. 3, 2008 
    
    
     FIELD OF THE INVENTION 
     The present disclosure generally relates to a method and apparatus for measuring residual volume in patients receiving enteral nutrition. More specifically, the present disclosure relates to a method and apparatus for measuring residual volume in which the residual volume is removed from the patient, evaluated, and returned to the patient or discarded, as deemed appropriate. 
     BACKGROUND OF THE INVENTION 
     Enteral nutrition is generally preferred over parenteral nutrition because of its lower cost, lower rate of complications, and effective preservation of gut structure and function. Many critically ill patients cannot tolerate naso-gastric tube feeding, developing manifestations of intolerance including nausea, vomiting, and abdominal distension and aspiration. Gastric residual volumes are widely used to evaluate feeding tolerance and gastric emptying. High gastric residual volumes raise concern about intolerance to gastric feeding and the potential risk for regurgitation and aspiration pneumonia. Furthermore, high gastric residual volumes may be one of the key contributing factors to intra-abdominal hypertension. Values of gastric residual volumes cited as being high in patients receiving naso-gastric feeding typically range from 75 to 500 ml. 
     Conventional use of gastric residual volume measurement obtained by aspiration via a syringe is a time consuming procedure. The size of standard syringes for this purpose is limited to 100 ml, which means that a residual volume of e.g. 300 ml will require three aspiration cycles. The aspirated volume must be stored temporarily in a container because a residual volume lower than a critical volume should be returned to the patient&#39;s stomach, using the syringe for the re-injection of the aspirated volume. If the total aspirated volume is higher than the critical volume, it will be discarded in its entity. The critical volume varies from hospital to hospital, but is typically 100-499 ml. The procedure of aspirating a patient&#39;s stomach will often be delayed because the naso-gastric tube may collapse in response to the negative pressure created when aspirating with the syringe. 
     SUMMARY OF THE INVENTION 
     The present disclosure relates to a method and system for determining the gastric residual volume of a patient. Specifically, the present disclosure relates to a system and method that determines the gastric residual volume of a patient by collecting stomach fluid from the patient in a collection container, measuring the volume of the collected fluid and returning the collected stomach fluid to the patient after the gastric residual volume has been measured. 
     In one embodiment of the present disclosure, a collection container is connected to a naso-gastric feeding tube already inserted into the patient through a collection conduit. The collection container is preferably a clear, flexible container that includes a series of volume markings, preferable on the exterior surface of the collection container. During normal feeding of the patient through the naso-gastric feeding tube, the collection container is elevated 50-100 cm above the mid-axillary line of the patient to prevent the flow of stomach fluid from the patient into the collection container. 
     When it is desired to determine the gastric residual volume of the patient, the collection container is lowered to a level below the mid-axillary line of the patient such that stomach fluid from within the patient&#39;s stomach flows (siphons) into the collection container. The volume of stomach fluid within the collection container can be determined by the volume markings on the exterior of the collection container. Excess fluid or air may be drained through a valve placed in the bottom of the collection container. 
     Once the gastric residual volume within the collection container is determined, the collection container is again elevated above the patient such that the contents of the collection container flows (siphons) back into the patient&#39;s stomach. 
     In one embodiment of the disclosure, the collection conduit extending between the naso-gastric feeding tube and the collection container is clear and includes a series of pressure markings, including a zero marking. In accordance with the method of the present disclosure, the collection container is elevated above the patient until the zero marking on the collection conduit is aligned with the mid-axillary line of the patient. When the zero marking is aligned with the mid-axillary line of the patient, a column of fluid, which may be feed solution or stomach fluid, is pushed into the collection conduit by the intra-gastric pressure (IGP) of the patient. The height of the column of fluid within the collection conduit is compared to the pressure markings on the collection conduit to determine the IGP of the patient. 
     In yet another alternate embodiment of the disclosure, a pressure transducer is placed in fluid communication with the collection conduit leading from the collection container to the naso-gastric feeding tube. A supply of flushing fluid flows at a low rate through the pressure transducer and into the collection conduit. The pressure transducer is operable to measure the pressure within the collection conduit, which in turn determines the IGP of the patient. 
     In another embodiment of the disclosure, the collection container is positioned within a pressure chamber. The height of the pressure chamber is fixed relative to the patient such that the collection container is generally aligned with the mid-axillary line of the patient. A supply of pressurized air enters into the pressure chamber to elevate the pressure of the collection container above the IGP of the patient. The elevated pressure on the collection container prevents the flow of stomach fluid into the collection container. 
     When it is desired to determine the gastric residual volume of the patient, the pressurized air within the pressure chamber is vented to atmosphere through a flow meter. As the pressurized air flows through the flow meter, a control unit monitors the amount of flow and the pressure within the pressure chamber to determine the gastric residual volume for the patient. Once the gastric residual volume has been determined, the control unit re-pressurizes the pressure chamber to return the volume of stomach fluid to the patient. 
     Various other features, objects and advantages of the disclosure will be made apparent from the following description taken together with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings illustrate the best mode presently contemplated of carrying out the invention. In the drawings: 
         FIG. 1  is an illustration of a system to measure the gastric residual volume of a patient with a collection container in an elevated position; 
         FIG. 2  is an illustration of the system of  FIG. 1  with the collection container in the lowered, collection position; 
         FIG. 3  is a first, alternate configuration of the system shown in  FIG. 1  in which the collection tube includes markings to determine the intra-gastric pressure (IGP) of the patient; 
         FIG. 4  is a second, alternate embodiment in which a supply of liquid is coupled to the collection conduit through a pressure sensor to determine the IGP of the patient; 
         FIG. 5  is a third, alternate embodiment in which the naso-gastric feeding tube is not connected to a supply of feed solution; and 
         FIG. 6  is a fourth, alternate embodiment in which the collection container is pressurized using a supply of pressurized air. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates a system  10  to be used in measuring the gastric residual volume of a patient  12 . As illustrated in  FIG. 1 , the patient  12  is in the supine position with a naso-gastric feeding tube  14  extending through the patient&#39;s nose  16  and being received within the stomach  18  or the jejunum. The naso-gastric feeding tube  14  allows a supply of liquid feed solution  20  to be fed into the patient&#39;s stomach  18  from a supply bag  22 . The method and apparatus may be used for patients receiving enteral nutrition in the stomach, duodenum, or jejunum. The gastric route is most commonly used for enteral feeding and will be used in the present disclosure, to describe the invention. 
     In the embodiment shown in  FIG. 1 , the supply bag  22  is connected to a supply conduit  24  that includes a second end with a male connector  25  that is received by female connector  26 . The female connector  26  is in fluid connection with male connector  36  that is received by a female connector  28  formed as part of the feeding tube  14 . 
     In the embodiment illustrated, the supply of liquid feed solution from the supply bag  22  is pumped into the patient&#39;s stomach  18  by an enteral feeding pump  30 , such as the Kangaroo Pump available from the Kendall Medical Company. The feeding pump  30  operates to push the liquid feed solution  20  through the supply conduit  24  and into the stomach  18  of the patient  12 . Although a feeding pump is illustrated in the drawing figures, a gravity set placed well above the patient&#39;s mid-axillary line could also be used to supply the feed solution to the patient. In such an embodiment, a roller clamp and a drip counter chamber are used to supply the feed solution to the patient. 
     In addition to the supply of feed solution  20  and the supply bag  22 , the naso-gastric feeding tube  14  is also coupled to a collection container  32  through a collection conduit  34 . One end of the collection conduit  34  includes the female connector  26  and a male connector  36  that is received within the female connector  28  formed on the naso-gastric feeding tube  14 . 
     When the patient  12  is receiving the supply of liquid feed solution  20  from the supply bag  22 , the collection container  32  is elevated above the patient, as illustrated in  FIG. 1 . When the collection container  32  is elevated above the patient, the intra-gastric pressure (IGP) within the patient forces stomach fluid, which may be the feed solution, into the collection conduit  34  to a level  38  shown in  FIG. 1 . Since the collection container  32  is elevated well above the patient, the IGP of the patient is not sufficient to cause the stomach fluid from the patient  12  to flow against the force of gravity and into the open interior of the collection container  32 . 
     In the embodiment shown in  FIG. 1 , the collection container  32  is a flexible, clear container that includes a series of volume markings  40  that can be labeled with volume indicators  42 . The combination of the volume markings  40  and volume indicators  42  allows the volume of the collection container  32  to be determined without emptying the contents of the collection container  32 . 
     As described previously, many critically ill patients cannot tolerate naso-gastric tube feeding. When monitoring these patients, gastric residual volumes are widely used to evaluate the feeding tolerance and gastric emptying. Specifically, when a patient is properly absorbing nutrients and feed solution, the feed solution is passed from the patient&#39;s stomach  18  into the intestinal tract. To conduct an evaluation of the gastric residual volumes, the volume of fluid within a patient&#39;s stomach  18  is determined and compared to the amount of feed solution directed to the patient through the supply conduit  24 . 
     Referring now to  FIG. 2 , when a gastric residual volume measurement is to be made, the collection container  32  is lowered from the elevated hanger  44  to a lower hanger  46  such that the collection container  32  is positioned below the mid-axillary line  48  of the patient. 
     When the collection container  32  is positioned below the mid-axillary line  48 , the stomach fluid from within the patient&#39;s stomach  18  will flow (siphon) into the collection container  32  through the naso-gastric tube  14  and the collection conduit  34 . 
     When the collection container  32  is positioned as shown in  FIG. 2 , the stomach fluid from the patient  12  begins to fill the open interior of the collection container  32 . As the stomach fluid fills the collection container  32 , the exterior markings  40  allow a user to determine the volume of fluid within the collection container  32 . Preferably, the volume of the collection container  32  is selected to insure that the stomach fluid from the patient  12  will not overfill the collection container  32 . In the case of overfilling, a drainage valve  33  may be activated and excess fluid or air may be drained from the collection container  32  into an external open container and subsequently discarded. 
     Once the stomach fluid from the patient  12  has been collected within the collection container  32 , the gastric residual volume can be determined using the volume markings  40 . If the gastric residual volume is below a critical volume, such as 400 ml, the stomach fluid can be returned to the patient. Stomach fluid is returned to the patient by once again elevating the collecting container  32  to the position shown in  FIG. 1 . In this position, the force of gravity causes the collected stomach fluid to flow (siphon) back into the patient&#39;s stomach through the collection conduit  34  and the naso-gastric tube  14 . 
     If the gastric residual volume collected within the collection container  32  exceeds a critical volume, a portion of the stomach fluid can be withdrawn from the collection container through drainage valve  33  and discarded. 
     In the embodiment shown in  FIGS. 1 and 2 , the collection container can either be a soft-sided bag or a stiff-sided container that includes a vent to atmosphere. The venting to atmosphere allows the stiff-sided collection container to fill with the stomach fluid when the collection container is lowered to its collection position shown in  FIG. 2 . 
     Referring now to  FIG. 3 , thereshown is an alternate embodiment of the system for measuring the gastric residual volume of a patient. In the embodiment shown in  FIG. 3 , the collection conduit  34  is a transparent manometer tube that includes a series of pressure markings  50 . Alternatively, a separate printed pressure scale (not shown) can be positioned adjacent to the collection conduit  34 . Since the collection container  32  is either made form a flexible material or vented to atmosphere, the feeding solution and/or stomach fluid will enter the collection conduit  34  when the collection container  32  is elevated above the patient. The height of the fluid column in the collection conduit  34  reflects the intra-gastric pressure (IGP) of the patient  12 . 
     When the user desires to make an IGP measurement for the patient, the collection container  32  is elevated above the patient until a zero marking  54  contained on the collection conduit  34  is aligned with the mid-axillary line  48  of the patient. Once the collection container is in this elevated position, the height of the fluid column  52  above the mid-axillary line  48  is indicative of the IGP. 
     In the embodiment shown in  FIG. 3 , the series of pressure markings  50  are used to determine the IGP. In the alternate embodiment employing the separate printed pressure scale, a zero marking on the printed pressure scale is aligned with the zero marking on the collection conduit  34 . The level of fluid in the collection conduit is compared to the markings on the printed pressure scale to determine the IGP of the patient. The system shown in  FIG. 3  can also be used as described in the discussion of  FIGS. 1 and 2  to determine the gastric residual volume of the patient. 
     In another embodiment shown in  FIG. 4 , the system includes an IGP sensing system  56 . The IGP sensing system  56  includes a pressure transducer  58  generally aligned with the mid-axillary line  48  of the patient. The pressure transducer is of the type normally used for measurement of blood pressure, and includes a flow-resistance that limits the flow trough the transducer. The pressure transducer  58  is connected to a flushing conduit  60  extending between a supply  62  of a flushing fluid  64 . Preferably, the flushing fluid  64  is sterile saline. The volume of the flushing fluid  64  flows through the pressure transducer  58  and into the collection conduit  34  through sensing conduit  61  and an inline connector  59 . The flushing fluid flows through the collection conduit  34  and into the patient. Preferably, the flushing fluid  64  has a continuous flow rate of approximately 3 ml per hour or less to create continuous flushing of the pressure transducer  58 . 
     As illustrated in  FIG. 4 , when the pressure transducer  58  is positioned aligned with the mid-axillary line  48  of the patient, the pressure of the fluid within the collection conduit  34  is directly related to the IGP of the patient. The pressure determined by the pressure transducer  58  can then be displayed on the display screen  66  of a patient monitor  68 . 
     In yet another embodiment shown in  FIG. 5 , the system of the present disclosure is shown being utilized with a patient  12  that is not yet receiving enteral feeding. In such an embodiment, the naso-gastric feeding tube includes a stopper  70  in a location where the supply conduit would typically be connected during enteral feeding. As shown, the collection container  32  is positioned below the patient with a clamp  72  preventing the flow of fluid into the collection container  32 . In this embodiment, all of the conduits, including the naso-gastric tube  14  and the sensing conduit  60 , are primed with sterile water or saline. When the pressure transducer  58  is positioned even with the mid-axillary line  48  of the patient, the pressure transducer can determine the IGP of the patient and relay this information to the display  66  of the patient monitor  68 . 
       FIG. 6  illustrates yet another embodiment of the system of the present disclosure. In the embodiment shown in  FIG. 6 , the collection container  32  is positioned within a pressurizing chamber  74 . The collection container  32  is coupled to the naso-gastric feeding tube  14  through the collection conduit  34  as in the past embodiments. However, in the embodiment shown in  FIG. 6 , the collection container  32  is stationarily mounted to the stand  76  at a fixed location generally in line with the mid-axillary line  48 . Although not illustrated in  FIG. 6 , the air-tight chamber  74  includes a door that can be opened to remove the collection container  32  as desired. 
     The air-tight chamber  74  is connected to an output  76  of an air pump  78  which is operable to pressurize the open interior  80  of the chamber  74 . Pressure transducer  58  is also connected to the open interior  80  of the chamber  74  through a pressure conduit  82 . Finally, an air flow meter  84  is connected to the open interior  80  through an air flow conduit  86 . The control unit  87  is in communication with the feeding pump  30  through a communication cable  88 . 
     During normal conditions, the air pressure within the open interior  80  of the chamber  74  is elevated above the IGP of the patient by operating the air pump  78 . When the pressure within the open interior  80  is above the IGP for the patient, no fluid from the patient flows through the collection conduit  34  and into the empty collection container  32 . 
     When it is desired to measure the gastric residual volume of the patient, a valve is opened in the air flow meter  84 , thereby providing an air flow path to atmospheric pressure through the flow meter. The pressure transducer  58  measures the pressure drop within the open interior  80  and when the pressure within the open interior  80  has fallen to a steady value, which is equivalent to the patient&#39;s IGP, the air flow out of the pressure chamber  74  is calculated in the control unit  87  as the patient&#39;s stomach fluid fills the collection container  32 . The air flow is calculated until the air flow drops to zero, indicating that the stomach is empty. At this time, the gastric residual volume has filled the flexible collection container  32  and the total air volume escaping the chamber  74  as the flexible collection container  32  fills with stomach fluid equals the gastric residual volume. The gastric residual volume may be calculated by associated electronic circuitry and software in control unit  87  by integrating the flow signal from the flow meter  84 . Although not illustrated, the gastric residual volume and IGP can be displayed digitally on a patient monitor. 
     In addition to the display of the gastric residual volume, the gastric residual volume signal may be routed to the feeding pump  30  over the communication line  88  in order to adjust the rate of feeding. A high gastric residual volume may reduce the rate at which the feeding solution is supplied while a low gastric residual volume may justify an increase in the rate of feeding. 
     In addition to calculating the gastric residual volume, the system shown in  FIG. 6  can also be used to determine the compliance of the stomach or the abdominal compartment. As discussed above, the pressure transducer  58  can determine the pressure within the open interior from when the collection container  32  begins to fill with the stomach fluid from the patient to a time when the collection container has filled with the entire contents of the patient&#39;s stomach. The pressure difference between the beginning and the end of the air flow out of the open interior  80  due to the filling of the collection container, together with the calculated gastric residual volume, can be used to calculate the compliance of the stomach or the abdominal compartment. 
     In accordance with the embodiment shown in  FIG. 6 , when the stomach contents have emptied completely into the collection container  32 , the air pump  78  can be reactivated to pressurize the box and return the container&#39;s contents to the stomach of the patient. In one embodiment, it is contemplated that the gastric residual volume, IAP and compliance may be determined by the control unit  87  at regular intervals, such as once an hour, and displayed on a patient monitor or on a dedicated display module  90 . 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.