Patent Publication Number: US-2019167171-A1

Title: Aspirators with in-line colorimetric testers

Description:
This invention relates to in-line testers, and in particular, but without limitation, to in-line testers that can be used in conjunction with a nasogastric (hereinafter “NG”) aspirator to test for the correct placement of an NG tube. 
     Aspirators are used in a wide range of medical procedures where fluids need to be drawn from within a body cavity, for example, for diagnostic, sampling and/or therapeutic purposes. 
     An aspirator generally comprises a vacuum source connected to a tube that can be inserted, or fed, into a body cavity. The vacuum source can be of any suitable type, such as a syringe; a syringe-based manual pump (such as that disclosed in published UK patent No: GB2523591B); or an electric vacuum pump (such as that described in published UK patent application No GB2547012). 
     When the vacuum is applied to the free end of the tube, the vacuum draws fluid from the body cavity through the tube, provided, of course, that the tip of the tube is located within the fluid to be aspirated. A liquid trap is usually interposed between the tube and the vacuum source to prevent aspirated liquids from being drawn into the vacuum source, thereby reducing the likelihood of damaging and/or contaminating the vacuum source. 
     One example of a liquid trap is disclosed in published UK patent No: GB2523591B, in which a porous or perforated membrane is used to allow gasses to pass through it, but when wetted by aspirated liquids, blocks the aspirate from passing through it. 
     When using an aspirator, care needs to be taken to ensure that the vacuum is not too high and that the quantity and rate of aspiration is monitored. Monitoring and control circuitry can often be used to facilitate this, as well as the manual interventions of an experienced operator. 
     It is commonplace to use aspirators to assist in determining whether the tip of a NG feeding tube is correctly positioned. When feeding a patient using a NG feeding tube, care must be taken to ensure that the tip of the NG tube is positioned within the patient&#39;s stomach, rather than in his/her lungs. The reason that this is important is that a NG tube is fed into the patient&#39;s throat via his/her nose, and due to the bifurcation of the patient&#39;s throat into the oesophagus and trachea, it is possible for the tip of the NG tube to be fed into the trachea, rather than the oesophagus (i.e. the wrong way) resulting in the tip of the NG tube being positioned within the patient&#39;s lung. If feeding commences with the NG tube positioned in the patient&#39;s lung, the results can be very serious. 
     As such, medical protocols require that before NG feeding commences, correct positioning of the NG feeding tube tip is determined. The only definitive way to determine the correct placement of a NG feeding tube is via a chest X-ray or other imaging procedure. However, chest x-rays have been found, in certain cases, to be less than definitive because the angle of exposure, level of exposure, patient position and the skill of the radiographer are all important in achieving a diagnostic x-ray image that is fit for purpose. Further, the time taken for an x-ray to be booked, carried out, processed and reported can vary considerably—during which time a subject is denied feeding, the subject most likely being in a critical condition. Additionally, for neonates particularly, the subject will be exposed to radiation with the associated potentially negative consequences. 
     Another way to check for the correct positioning of an NG tube is to aspirate and test a sample of fluid via the NG tube prior to feeding. This is indeed the current clinical standard in the UK, whereby fluids are aspirated via the NG tube and are checked for acidity using pH paper. A colour change to indicate acidic pH is considered to be an indicator that the NG tube is in the correct location (it being assumed that the stomach contents are acidic, whereas lung fluids are not) and so feeding may commence. 
     If, however, a basic (alkali or pH&gt;5.5) pH reading is obtained, then the assumption is that the location of the tube is not in the stomach and the NG tube will be withdrawn and reinserted before a further pH test is carried out. 
     However, pH testing has been found to be unreliable insofar as it can yield false negative results, for example, if the patient is taking antacids to prevent reflux. In this case, irrespective of whether the NG tube is in the stomach or not, a basic or neutral pH will be indicated from any sample obtained using the current clinical standard. 
     Therefore, the current guidelines stipulate that if an acidic pH reading is obtained, then it is safe to commence feeding, whereas if a basic (alkali) pH reading is obtained, further investigation is required. The basic “rule of thumb” is therefore: acid=feed; alkali/neutral=do not feed. 
     However, current pH testing protocols fail to take into account the possibility of false positive results (i.e. acid, but not safe to feed), which can prove problematic to patient health, or fatal in extreme cases. False positives can occur when the NG tube tip is located in the lung of a patient, but where the patient is suffering from reflux resulting in some gastric content being inhaled/present in the lung. Clearly, in this case, it is possible for the pH of an aspirated sample to be acidic—indicating, according to current clinical protocols, that the NG tube tip is in the correct location, i.e. in the stomach, and so feeding will commence. However, in this example, the NG tube would not be correctly located, and the consequences of commencing feeding could be very serious. 
     It will be appreciated that the aforesaid protocols, devices and methods are not ideal, and a need therefore exists for an improved and/or an alternative protocol, device and/or method. 
     Various aspects of the invention are set forth in the appended claims. 
     According to a first aspect of the invention, there is provided an in-line tester comprising: an inlet, connectable, in use, to an aspirator tube; an outlet connectable, in use, to a vacuum source; and a chamber interposed between the inlet and the outlet, the chamber comprising: a first tester arranged such that fluids drawn into the chamber by the vacuum source come into contact therewith; a second tester arranged such that fluids drawn into the chamber by the vacuum source pass through it; and a reservoir interposed between the first tester and the second tester; wherein the first tester comprises a first colorimetric substance adapted to exhibit a colour change in the presence of a target substance, and wherein the second tester comprises colorimetric capnometer, which exhibits a colour change in the presence of carbon dioxide, the in-line tester further comprising a liquid-stop device which, when dry, permits the passage of gas from the inlet to the outlet, but when wetted by a liquid, inhibits or prevents the passage of fluids from the inlet to the outlet. 
     According to a second aspect of the invention there is provided an in-line tester comprising: a chamber comprising an inlet, an outlet and a porous or perforated element separating the inlet from the outlet, the porous or perforated element comprising a liquid-absorbent layer comprising a first colorimetric substance adapted to exhibit a colour change in the presence of a target substance and a porous or perforated hydrophobic layer, the porous or perforated element, when dry, permitting the passage of gas from the inlet to the outlet, but when wetted by a liquid, inhibiting or preventing the passage of fluids from the inlet to the outlet, the in-line tester further comprising, a colorimetric capnometer interposed between the porous or perforated element and the outlet. 
     The in-line tester is suitably used in conjunction with an NG aspirator, that is so say, having its inlet connectable, in use, to the outlet of an NG tube, and its outlet connectable, in use, to a vacuum source. Suitably, therefore, the inlet or outlet may comprise connectors for releasably connecting items thereto, such a “Luer lock” connectors, bayonet-type fittings, screw threads, push-fit connectors, being either male or female. Such a configuration suitably facilitates attaching and detaching items to the in-line tester. 
     Suitably, the inlet comprises a connector for connecting the inlet to the connector of enteral or NG tube, such as a female Luer or female Luer-lock connector. Suitably, the outlet comprises a connector suitable for connecting it to an enteral syringe, such as a male Luer, a male Luer-lock or an “EN Fit” connector. 
     The liquid-stop device suitably comprises a porous of perforated disc, which is at least partially manufactured from, or coated with, a hydrophobic material; or which has a hydrophobic layer on it. The function of such a liquid-stop device is essentially that; when it is dry, gasses (including air) are able to pass through the pores or perforations therein, thus permitting the passage or transduction of gases/air through the liquid-stop device. However, when the liquid-stop device is wetted by a liquid, in this case an aspirated liquid, the hydrophobicity of the liquid-stop device repels the liquid from its surface—towards the pores/perforations, which are not hydrophobic. This results in liquid preferentially covering the liquid-stop device&#39;s pores/perforations, thereby preventing gas/air from passing through it. As such, when the liquid-stop device is dry, for example, during the initial stage of an aspiration, where air is primarily drawn up through the NG tube, the aspirated air is able to pass through the liquid-stop device. However, subsequently, when liquid is aspirated, when that liquid eventually reaches the liquid-stop device, it will wet it, thereby preventing any further passage of fluid (that is to say liquids or gases) through the liquid-stop device. 
     In one possible embodiment of the invention, the liquid-stop device comprises a porous or perforated element, which separates the inlet from the outlet at some point along the fluid flow path. Therefore, fluids (liquid or gases) drawn into the in-line tester must come into contact with the porous or perforated element at some point. In one possible embodiment, the liquid-stop device comprises a small piece of pH indicator paper with a hydrophobic plastics backing layer. Thus, liquids drawn into the in-line tester can be tested for pH by the pH paper, but when the pH paper is wetted, the liquid also wets the hydrophobic layer behind it, thereby closing-off the fluid pathway. In other embodiments, the pH paper can be substituted for capnometry indicator paper, which changes colour in the presence, or otherwise, of carbon dioxide. 
     The test trip (pH or CO2) and hydrophobic layer can be integrally formed, for example by laminating or bonding the test strip to the hydrophobic layer; in other cases, they can be separate components, which are simply placed together; or in yet further embodiments, they can be entirely separate, that is to say, with a finite gap, of any size, between the test strip or tester and the liquid-stop device. 
     The liquid-stop device inhibits or prevents the passage of fluids from the inlet to the outlet, thereby effectively acting as a valve, which automatically closes the fluid passageway between the inlet and the outlet upon coming into contact with a liquid. 
     This is particularly beneficial in NG aspirator applications, where gasses (air/gas from the stomach/lung) are usually aspirated before liquids. Thus, by placing the colorimetric capnometer downstream of the liquid-stop device and before the outlet, sequential testing may be possible. Specifically, when the in-line tester of the invention is used in conjunction with an NG aspirator, typically gasses will be aspirated before liquids are drawn-up through the NG tube. Initially, the liquid-stop device will be dry, which enables the aspirated gasses to pass through it to then come into contact with the colorimetric capnometer, and so test for carbon dioxide in the aspirate. Later, liquids may then be aspirated, and when this happens, the liquids come into contact with the first element, and are tested for the target substance thereby. When, eventually, the liquid-stop device is wetted by an aspirated liquid, it inhibits or prevents the passage of liquids through it, thereby keeping the colorimetric capnometer dry. 
     Suitably, a one-way valve is provided at, or downstream of the outlet of the in-line tester, and where such is provided, a sample of aspirated gas can be trapped/retained within the chamber between the (now wetted) liquid-stop device and the one-way valve. This is particularly beneficial when using colorimetric capnometry because colorimetric capnometers tend to revert to their initial colour after a relatively short period of time. However, by effectively trapping a sample of aspirated gas in the chamber between the liquid-stop device and a one-way check valve, reversion of the colour of the colorimetric capnometer back to its initial state is slowed or inhibited. 
     The first tester is adapted to exhibit a colour change in the presence of a target substance. The target substance is suitably a substance found in the stomach of a patient. 
     The target substance can be stomach acid (e.g. HCl), in which case, the first tester may comprise, e.g. on a liquid-absorbent layer thereof, a colorimetric substance that is an acid-base indicator, such as litmus paper or paper comprising Bromothymol sulfonephthalein. 
     Additionally or alternatively, the target substance can be a stomach-related marker, which may comprise any compound or biological structure, such as a cell or a cell fragment, an enzyme, a chemical etc., which is found within the stomach of a patient, but preferably not the lung of a patient. 
     In certain embodiments of the invention, the stomach-related marker may comprise any one or more of the group comprising: gastric enzyme (or substrate thereof); gastric hormone; pepsin; pepsinogen; intrinsic factor (IF); vitamin B12-IF complex; mucin; gastrin; gastric lipase; and trypsin. 
     In an embodiment, the in-line tester comprises detection means for gastric lipase. The detection means for gastric lipase may comprise tributyrin. 
     The device may contain means for detecting the presence of two or more stomach-related compounds. Advantageously, the device comprises means for detecting two stomach-related markers. 
     Suitably, therefore, the in-line tester may comprise a further tester having a further colorimetric substance adapted to exhibit a colour change in the presence of a second target substance. In certain embodiments, the first and further testers may be incorporated into a single device, that is to say being is divided into discrete regions, each discrete region comprising a different colorimetric substance adapted to exhibit a colour change in the presence of different target substances. 
     Suitably, the outlet of the porous or perforated element sealingly separates the inlet from the outlet. 
     Suitably, the liquid-stop device comprises a hydrophobic layer that comprises pores or perforations that enable, when dry, air to pass through them, but when wetted by liquid, the hydrophobicity of the hydrophobic layer repels the liquid from its surface and is forced towards the openings of the pores or perforations. 
     The colorimetric capnometer is adapted to detect carbon dioxide, and this may be by using a specially adapted form of indicator paper, impregnated with a dye that changes colour from, say, purple to yellow in the presence of carbon dioxide. Carbon dioxide monitoring to check NG tube position has been suggested (Thomas and Falcone, J Am Coll Nutr 1998, 17(2):195-7). Various trials have used either capnography (direct carbon dioxide measurement) or colorimetric capnometry (based on colour change of adapted pH paper with sulfonephthalein). It has already been shown that that there is a higher concentration of carbon dioxide in exhaled air from the lungs compared to any air obtained from a gastric aspirate. However, the use of measuring carbon dioxide provides no information about tube placement within the gastrointestinal tract and administration of enteral nutrition may be delivered into the oesophagus which would increase the risk of aspiration to the lung. 
     The Applicants have identified the problems associated with the prior art and surprisingly discovered that a combination of being able to detect at least one stomach-related marker and carbon dioxide provides a much more reliable means for determining the location of, for example, a NG feeding tube in a subject. 
     The detection means for carbon dioxide and at least one detection means for a stomach-related marker may be disposed on at least one substrate. 
     The substrate may comprise a matrix. Advantageously, the substrate comprises a cellulose-based matrix. The substrate may be porous and/or perforated to permit the flow of fluid therethrough. 
     In an embodiment, the device comprises two or more detection means for a stomach-related marker. The two or more detection means may be disposed on the same substrate or different substrates. 
     The substrate may be an adapted form of pH filter paper, impregnated with a dye which changes colour from purple to yellow in the presence of carbon dioxide. Alternatively, the substrate may comprise adapted pH paper carrying sulfonephthalein or Bromothymol sulfonephthalein, which is an acid-base indicator. 
     The detection means for carbon dioxide may be capable of distinguishing the level of carbon dioxide present. A known carbon dioxide detector (available form Mercury Medicalhttp://www.mercurymed.com/catalogs/ADR_CarbonDioxideDetector.pdf) changes colour depending upon the level of carbon dioxide present. 5% carbon dioxide detected in a sample is indicative of normal exhalation value and would indicate that the NG tube is located in the lung of a subject. Levels below that would indicate that the NG tube is either not in the lung or that the subject may be experiencing other medical problems, particularly where a stomach-related marker is not detected, indicating that the tube may possibly be in the lung. 
     The subject may be a mammal. Advantageously, the subject is a human. 
    
    
     
       Preferred embodiments of the invention shall now be described, by way of example only, with reference to the accompanying examples and drawings in which: 
         FIG. 1  is a perspective view of first embodiment of an in-line tester in accordance with the invention; 
         FIG. 2  is an exploded view of the in-line tester of  FIG. 1 ; 
         FIG. 3  is a sectioned view of the in-line tester of  FIG. 1 ; 
         FIGS. 4 and 5  are plan views of decals suitable for use with the in-line tester of  FIG. 1 ; 
         FIG. 6  is a schematic plan view of a second embodiment of an in-line tester in accordance with the invention; 
         FIG. 7  is a schematic sectional view of  FIG. 6  on VII-VII; 
         FIG. 8  is a schematic sectional view of  FIG. 6  on VIII-VIII; 
         FIG. 9  is a schematic sectional view of  FIG. 6  on IX-IX; 
         FIG. 10  is an exploded view of  FIG. 9 ; 
         FIG. 11  is a schematic circuit diagram of the embodiment of the in-line tester of  FIGS. 1 to 3 ; 
         FIG. 12  is a schematic circuit diagram of the embodiment of the in-line tester of  FIGS. 6 to 9 ; 
         FIG. 13  is a schematic exterior view of the in-line tester shown in  FIG. 6 ; and 
         FIG. 14  is a schematic circuit diagram showing a variation of the circuit of  FIG. 12 , incorporating a coarse liquid-stop device. 
     
    
    
     Referring to  FIGS. 1 to 5  of the drawings, the in-line tester  10  comprises a main body  12  manufactured via a plastics injection moulding process from a transparent material, such as ABS. The main body  12  defines a hollow interior chamber  14  and has an inlet  16  connectable, in use, to an NG tube  18 , and an outlet  20 , connectable in use to a vacuum source (e.g. a vacuum pump; or a syringe  22 —as shown in  FIG. 1 ). A vacuum is applied to the outlet  20  of the in-line tester  10  to draw a sample of aspirate (gas and/or liquid) from within a patient via the NG tube  18 , and the aspirate enters the hollow interior chamber  14  of the in-line tester  10  via the inlet  16 . 
     Referring to  FIGS. 2 and 3  in particular, the main body  12  is formed by three main parts, namely: a generally dish-shaped first part  30 ; an annular back plate disc  32 ; and an insert  34 . 
     The inlet  16  is formed as a tubular spigot extending concentrically from the outer face  36  of the generally dish-shaped first part  30 . The inlet  16  has a through hole  38  that provides a fluid communication pathway into the interior of the main body  12 , and also has external screw thread formations  40  for engaging complementary internal thread formations of a Luer-type connector  42  at the end of the NG tube  18 . 
     The insert  34  is mostly located within the generally dish-shaped first part  30 , but has an outlet spigot  20  formed integrally therewith, which sealingly extends through a tapered central through hole  42  in the annular back plate disc  32 . The outlet spigot has a blind hole  33  in it (explained in greater detail below) and a plain outer surface, which can connect to the inlet of a syringe  22 , or to a vacuum pump (not shown). 
     As can be seen by comparing  FIGS. 2 and 3 , the generally dish-shaped first part  30  has a planar peripheral edge  44 , which is sealingly connected (for example by gluing or welding) to the outer periphery of the annular back plate disc  32 . The insert  34  is thus retained in-situ. 
     The insert  34  has a generally circular dish-shaped profile, with an internally-rebated lip  46 , which retains, by frictional engagement, a circular porous or perforated element  48  (first tester incorporating a liquid-stop device). The dimensions of the lip  46  are sized so as to form a valve seat against which the porous or perforated element sealingly seats. A seal can be perfected, if necessary, using a bead of sealant or adhesive (not shown). 
     As can be seen from the drawings, the porous or perforated element  48  comprises an air-permeable membrane, which permits air to pass through it, but not fluids. In the illustrated embodiment, the porous or perforated element  48  is both a pH tester and a liquid-stop device, and thus comprises two components, namely a liquid-absorbent layer  50 , such as paper (located closest to the inlet  16 ), and a porous or perforated hydrophobic layer  52  (downstream of the liquid-absorbent layer  50 ). The two layers  50 ,  52  are conjoined to form a laminated structure, although they may equally be just clamped or otherwise held together. The main advantage of putting the two layers in close proximity, or touching one another, is that the wetting of the liquid-absorbent layer  50  very quickly, if not immediately, also wets the liquid-stop device, i.e. porous or perforated hydrophobic layer  52 . Thus, the wetting of the first layer  50  causes the liquid-stop layer  52  to automatically close off almost immediately. However, in other embodiments, there may be a separation between these two layers  50 ,  52 , or indeed, they may be located in entirely different regions of the in-line tester  10 . 
     In this embodiment, the liquid-stop device, i.e. the hydrophobic layer  52 , comprises pores or perforations that enable, when dry, air to pass through them (i.e. through the hydrophobic layer  52 ). However, when wetted by liquid, e.g. liquid absorbed by the liquid-absorbent layer  50 , the liquid is repelled from the surface of the hydrophobic layer  52  and forced to overlie the less hydrophobic regions, that is to say, the openings of the pores or perforations. Provided the pores or perforations of the hydrophobic layer  52  are small enough (i.e. significantly smaller than the size of a liquid droplet), the liquid that overlies the pores or perforations effectively blocks the pores or perforations, thus inhibiting or preventing the passage of air or liquid through them. 
     Most preferably, the size of the pores and/or perforations is selected to permit the passage of vapour through the liquid-stop device, but not larger liquid drops. The reason for this is that certain CO2 test papers require the CO2 to be a “wet sample” in order create the reaction that causes a colour change. Thus, many CO2 test papers are configured to detect CO2 in a “breath” sample, that is to say, a gas sample comprising CO2, plus a small amount of water vapour. This, the liquid-stop device of the invention is suitably configured such that water vapour (such as that found in a patient&#39;s breath sample) can pass therethrough, but not liquid droplets above a certain size, as would be the case where an actual liquid sample (e.g. saline, liquid water, liquid feed, stomach acid, bile etc.) has been aspirated. 
     The aforesaid configuration conveniently converts the in-line tester  10  into a self-closing valve that permits air or gasses (including, in certain cases, water vapour) to pass through it when the porous or perforated element  48  is dry, but which when the porous or perforated element  48  is wetted, self-seals to prevent fluids from passing through it and further downstream. 
     It will be appreciated that once the liquid-stop device has been wetted-out by an aspirated liquid sample, the device hydraulically locks, thereby preventing further aspiration of liquid or gas. Therefore, it is preferable that the liquid-stop device comprises a “coarse filter” and a “fine filter”, the latter being, in many cases, the porous or perforated, hydrophobic membrane/element/disc described herein. The coarse liquid stop device could be a baffle arrangement, or a tortuous fluid pathway, which prevents or inhibits the fine filter from being inadvertently splashed with aspirated liquid. A detailed description of this is provided hereinbelow, with reference to  FIG. 14  of the accompanying drawings. 
     The liquid-absorbent layer  50  is coated or impregnated, in the illustrated embodiment, in two discrete areas  54 ,  56 , by different colorimetric substances adapted to exhibit a colour change in the presence of different target substances. 
     In one embodiment, the first area  54  is adapted to change colour according to the pH of an aspirated liquid, and the second area  56  is adapted to change colour in the presence of a target stomach-related marker, as described herein. The colour of the two regions  54 ,  56  can be viewed from without the tester  10  via the transparent generally dish-shaped first part  30 . A generally C-shaped decal  56 , comprising a colour chart corresponding to the or each colorimetric substance is affixed to the outer surface  36  of the generally dish-shaped first part  30 . In the illustrated embodiment, the generally C-shaped decal  56  surrounds, and slightly overlaps, the porous or perforated element  48  so that a visual comparison of colour of the porous or perforated element  48  to the decal  56  can be made. 
     In one embodiment, the liquid-absorbent layer is manufactured of litmus paper, and this forms the first area  54 , such that the acidity/alkalinity of the aspirate can be tested. However, the second area  56  is a stomach-related marker detector, which is coated, or impregnated, with tributyrin, which tests for gastric lipase. Tributyrin will produce alcohol and butyric acid on contact with gastric lipase, and the butyric acid will lower the pH on the litmus paper, giving an acidic pH reading. This method can effectively correct the “false negatives” of relatively high pH in gastric aspirates from patients on antacids. 
     Below (downstream of) the porous or perforated element  48 , the insert  36  comprises an internal chamber  58  into which aspirated gasses are vented after having passed through the porous or perforated element  48 . The side wall of the insert  34  comprises one or more through apertures  60 , through which the aspirated gasses are vented, in use. The apertures are located slightly above a shelf part  62  of the insert  34 , upon which is located a colorimetric capnometer  64  in the form of a paper test strip impregnated with a substance that undergoes a colour change in the presence of greater than 5% CO2. The shelf part  62  has a base  63  and two side walls  65 , which serve to frictionally retain the colorimetric capnometer test strip  64  when the device is assembled. This particular configuration usefully causes the aspirated gasses to be concentrated, and to vent over the surface of, the colorimetric capnometer test strip  64 , thus enabling the colorimetric capnometer  64  to test more effectively for the presence of relatively low concentrations of CO2 in the aspirated gas. 
     The colorimetric capnometer test strip  64  comprises a dye carrying substrate (such as used in Mercury Medical carbon dioxide detector http://www.mercurymed.com/catalogs/ADR_CarbonDioxideDetectorpdf), which functions by detecting acid formed in exhalation of carbon dioxide form a subject. Indicator colour is indicative of the following conditions: Blue—No CO2 is present; Green—Between 1%-2% CO2 is present; Yellow 5% or more CO2 is present. 
     The aspirated gas then flows out of the in-line tester  10 , via the outlet  20 , and this is accomplished by the provision of through holes  66  extending through the side wall of the outlet spigot  20  upstream of the annular back plate disc  32 . 
     The flow path of aspirate is indicated schematically, in  FIG. 3 , by the chain-dash arrow  70 , that is to say, in via the inlet  16 , through the porous or perforated element, out through the apertures  60  and over the colorimetric capnometer  64 , under the insert  34 , through holes  66  and out through the outlet  33 ,  20 . 
     In use, the inlet  16  is connected to an NG tube  18  and an aspirate is drawn up the NG tube  18  and into the device  10 . Initially, gas containing carbon dioxide will flow form the patient into the device, passing through the porous pH indicator  260  substrate, through the bores  223  and contact the carbon dioxide detecting substrate  280 . If the carbon dioxide level is above a predetermined threshold to indicate exhaled air, then a colour change occurs in the carbon dioxide detecting substrate which if positive is indicative of the NG tube being located in the lung of a patient. 
     Subsequent aspiration results in liquid entering the device which is absorbed by liquid absorbent layer. If stomach acid is present, the pH detector will change colour to indicate the presence of acid, and if stomach enzyme or another target stomach-related substance is present, then an acid will be catalysed causing a pH indicator to show the presence of an acid. 
     The decal  56  referred to previously, has different colour comparison areas, as shown in  FIG. 4  of the drawings, against which the respective colorimetric test strips can be compared, in use, by a medical practitioner. In the example shown in  FIG. 4 , there are four areas. A first area  80  comprises a colour chart corresponding to the first area  54  of the porous or perforated element  48 ; a second area  82  comprises a colour chart corresponding to the second area  56  of the porous or perforated element  48 ; and a third area  84  (located either side of a cut-out  86 ) corresponding to the colorimetric capnometer. Thus, a practitioner can compare each of the three colorimetric test strips/areas against their corresponding colour charts. An outer peripheral region  88  is also provided, for displaying text, logos, instructions, CE markings etc. 
     In an alternative embodiment, as shown in  FIG. 5 , the decal  56  is adapted to cover most/all of the upper surface of the main body. In this embodiment, its colour corresponds to a “fail” colour for each of the tests (which may be a different colour in different areas of the decal  56 ). The decal  56  has tick-shaped through apertures cut into it, such that if a “positive” test result is confirmed using each of the thee colorimetric tests, the respective test trip/area will become visible, due to a difference in colour, compared with the regions of the decal  56  surrounding each cut out  90 . 
     The aforedescribed embodiment of the invention has been found, in clinical trials, and tests, to provide a solution to one or more of the problems outlined in the introductory part of this disclosure, namely providing a double—or triple check for the correct positioning, or otherwise, of the tip of an aspirator tube in a patient. However, in certain situations, practice/protocols dictate other NG tube use methodologies. For example, in certain hospitals/environments, patients are intubated each time a feed is to be given. In this case, a clean, empty NG tube is inserted into the patient immediately prior to each feed, and after each feed, the NG tube is withdrawn and then discarded. In these situations, the NG tube is empty prior to aspiration of gases/liquids, in which case the aforedescribed embodiment of the invention has been shown to work satisfactorily. 
     In other hospitals/environments, however, the feed protocols can be somewhat different. By way of an example, in certain hospitals, where a patient is receiving ongoing nasogastric feeding, the NG tube is kept in place and is only withdrawn/replaced at certain intervals. As such, the same NG tube may be used to feed a patient several times before it is eventually discarded and replaced. In these situations, except for the first time the NG tube is used, the NG tube will inevitably contain some liquid—be that stomach liquid, residual feed from the previous feed, or a saline flush solution. As such, when the NG tube is used subsequently and an aspirate taken, the first few drops of aspirate may not be representative of the liquid surrounding the tip of the NG tube, but rather may be representative of the residual contents of the NG tube. When the previously-described embodiment of the invention is used, in these situations, it can result in the aspiration test procedure being stopped prematurely, for example when a drop of saline flush liquid, or residual feed from within the tube, is aspirated onto the pH test strip, which according to the afore described embodiment, would result in the in-line tester being “hydraulically locked” by the liquid-stop device becoming wet. As such, in these situations, the aforedescribed in-line tester may be somewhat ineffective because, by virtue of its self-closing feature, it is unable to test a sample of aspirate from the region surrounding the NG tube&#39;s tip, but rather simply tests an aspirate that was already in the NG tube prior to the test commencing. A need therefore exists for a further embodiment of the invention, which addresses this particular issue. 
     Referring now to  FIGS. 6 to 10  of the drawings, another embodiment of an in-line tester  100  in accordance with the invention is shown. In this embodiment, the in-line tester  100  comprises a main body  12 , again manufactured via a plastics injection moulding process, from a transparent material, such as ABS. The main body  12  defines a hollow interior chamber  14  as shall be described herein below. 
     The in-line tester has an inlet  16 , which is connectable, in use, to an NG tube  18  via a luer connector  102 . The inlet  16  connects the NG tube  18 , to a first portion  104  of the chamber  14 . The first portion  104  of the chamber  14 , which is shown in cross section in  FIG. 7 , comprises a base wall  106 , which supports a small strip of pH indicator paper  108 . A cavity  110  is provided on one side of the pH test strip  108 , such that fluid entering the in-line tester  100 , via the inlet  16  is able to come into contact with at least one surface or part thereof. 
     The first chamber part  104  has an outlet  112 , which leads to a reservoir part  114  of the chamber  14 . 
     The inlet  16  comprises a restriction, in the form of a Venturi  116  in a preferred embodiment, which causes liquid drawn up through the NG tube  18  to be “sprayed” over the exposed surface of the pH test strip  108 . The provision of a constriction or Venturi  116  serves to cause the incoming liquid to “fan-out” as it enters the first chamber part  104 , thereby ensuring that an adequate area of the pH test strip  108  is wetted by the incoming liquid. 
     The outlet  112  of the first chamber part  104  leads to a reservoir portion  114  of the chamber  14 . In the illustrated embodiment, the reservoir  114  comprises a serpentine pathway within the main body  12 , which can retain approximately 4 ml of liquid, when full. The volume of the reservoir  114  is ideally selected to be slightly larger than the internal volume of the NG tube  18  and so the exact volume of the reservoir is not fixed. The reason for providing a reservoir  114  is to enable a quantity of liquid within the NG tube  18  to be accumulated within the main body  12  of the in-line tester  110 , for reasons that shall become apparent later. 
     The reservoir part  114  of the chamber  14  comprises an outlet  118 , which feeds into a further test chamber part  120  of the chamber  14 . The further test chamber part  120  is shown in cross section in  FIG. 8  of the drawings, from which it can be seen that the outlet  118  of the reservoir is in fluid communication with a small disc tester  122  trapped, by its peripheries, between an upper part and a lower part of the main body  12 . The test disc  122  is a CO2 tester, which exhibits a colour change in the presence of carbon dioxide. 
     The test disc  122  can be manufactured from a perforated, hydrophobic material, which enables gases exiting the reservoir  114  via its outlet  118  to pass through the test disc  122  and into a lower part  124  of the second test chamber  120 , before exiting via an outlet  126  into a further pathway  128 . 
     As gases are aspirated through the NG tube  18 , they pass through the first chamber part  104 , through the reservoir part  114  and eventually into the second test chamber  120 , where they interact with the test disc  122 . If the gas contains carbon dioxide, it will cause the test disc  122  to change colour, which will be visible to a user (not shown) observing the in-line tester  110 , through its transparent main body portion. The aspirated gas can be drawn into a connected vacuum source, in the illustrated example, a syringe  22 , and the aspirated gas can, therefore, be tested for the presence or otherwise of carbon dioxide. 
     In other embodiments of the invention, the test disc  122  is formed from two parts, namely a downstream colorimetric test disc  122 , and an upstream porous or perforated element comprising a hydrophobic material  52 . In this embodiment of the invention, the two parts work together as previously described, namely with the colorimetric test disc  122  being able to test for the presence of CO2, with the porous or perforated, hydrophobic layer  52 , acting as a liquid-stop device  52  upstream of the colorimetric capnometer. Again, the two layers  122 ,  52  need not necessarily be in intimate contact with each other, although this may be beneficial in certain circumstances. Nevertheless, there is a liquid-stop device  52  located upstream of the CO2 tester, which means that when the test is complete, that is to say when a sample of aspirated liquid comes into contact with the porous or perforated, hydrophobic layer  52 , the in-line tester  100  is essentially hydraulically locked, thereby preventing further aspiration. Meanwhile, a sample of aspirated gas will be trapped downstream of the liquid-stop device  52 , thereby inhibiting or slowing the reversion of any colour change in the colorimetric capnometer for a certain period of time. 
     It is possible to connect the outlet of the in-line tester to a vacuum pump, or, in a preferred embodiment to a syringe  22 . 
     Where a small syringe  22  is used, it may be necessary to repeatedly withdraw the syringe plunger (not shown) to obtain a sufficient test volume via the NG tube  18 . To accomplish this, the in-line tester  110  is provided with a secondary outlet  128 , to which is connected a one-way valve  130 . The syringe  22  and one-way valve  130  are operatively interconnected via a chamber  132  formed in the main body  12  of the in-line tester  100 . The one-way valve  130  has a particular “cracking pressure”, above which, the valve will open to allow gas to be expelled  134  from the in-line tester. The cracking pressure of the one-way valve  130  is designed to be lower than the permeability of the liquid-stop device such that upon depression of the syringe plunger (not shown) fluid is forced from the syringe  22 , via the chamber  132  and out via the one-way check valve  130 , as indicated by arrow  134  in  FIG. 6 . However, upon withdrawing the plunger, the one-way check valve  130  closes, thus enabling fluid to be drawn up through the NG tube, through the in-line tester  100 , and, ultimately, into the syringe, as indicated by arrow  136 . 
     The benefits of this particular configuration of the invention are manifold. 
     In particular, because the main body  12  of the in-line tester  100  is manufactured from a transparent plastics material, it is possible for a user (now shown) to observe the progression of aspirated fluids through the tester  100 . This usefully enables a user of the device to “see” when e.g. saline flush has been aspirated, followed by stomach content, for example, by a colour change in the reservoir. 
     In a first example, where the NG tube  18  is initially empty, upon repeated withdrawal and compression of the syringe  22  plunger, fluid will be “pumped” up through the NG tube in the manner previously described. Because the NG tube  18  is initially empty, the first fluid that will be drawn into the in-line tester  100  will be gas/air from within the NG tube itself or the patient&#39;s stomach/lung. This gas/air will simply flow through the first chamber part and over the pH test strip  108 , through the reservoir  114 , where it will eventually come into contact, and pass through the CO2 test disc  122 . 
     The user, by observing the colour of the CO2 test disc  122  will be able to ascertain whether it is an air/stomach gas sample, or whether it is a “breath” sample of air aspirated from the patient&#39;s lung, for example. 
     Eventually, liquid (hopefully gastric juice) will be aspirated up the NG tube  18 , where it will enter the in-line tester  100  via the inlet  16 . The aspirated liquid will be “sprayed” by the Venturi  116  at the tester inlet  116 , and the design of the Venturi  116  is such that aspirated liquid is sprayed/dispensed over the exposed surface of the pH test strip  108 . By observing a colour change in the pH test strip  108 , a user (not shown) will be able to determine whether an acidic, (e.g. a gastric juice) sample has been aspirated, or whether something else has been aspirated. 
     Liquid will then be drawn into the reservoir  114 , where it will gradually fill the reservoir and the user will be able to observe the progress of the liquid as it is drawn into the reservoir. 
     In a second situation, for example where the NG tube  18  has been flushed with water or saline prior to use, it will initially contain a quantity, typically 4 ml, of saline solution or water. In this situation, the “first liquid” to come into contact with the pH test strip  108  ought to be neutral, which might, ordinarily, indicate incorrect placement of the NG tubes tip in the patient&#39;s stomach. However, this could be a simple “false negative” because the first liquid aspirated is, in fact, saline solution rather than gastric juice. The test therefore needs to continue until such time as the flush liquid within the NG tube  18  has been recovered, which will, hopefully, be followed by a sample of gastric juice. 
     Therefore, the invention comprises a reservoir  114 , into which this initial liquid may be accumulated. Here, the volume of the reservoir  114  is slightly greater than the internal volume of the NG tube  18  such that when the reservoir is full, the user knows that what is being tested ought to be gastric juice, rather than flush liquid. The user (not shown) is therefore able to observe the progression of the flush liquid through the system, by observing the reservoir, which is visible from outside the in-line tester  100  by virtue of it being manufactured from a transparent plastic, and, ultimately, to test the pH of a gastric juice sample thereafter. 
     Although not shown in  FIG. 6  for clarity, the in-line tester  100  suitably comprises one or more decals, each comprising a colour chart corresponding to the or each colorimetric substance. The decal or decals are suitably affixed to an outer surface of the in-line tester  100 , adjacent to, but preferably slightly overlapping the testers  108 ,  122 —so that a visual comparison of colour of the testers  108 ,  122  to the colours or other indications on the decal can be made. 
     The in-line tester  100 , shown in  FIGS. 6, 7 and 8  of the drawings, is shown, schematically, in cross section in  FIG. 9 , which is a cross section of  FIG. 6  on IX-IX. 
     In a preferred embodiment of the invention, the main body  12  of the in-line tester  100  is manufactured from two plastics injection moulded components, which fit together to form the device shown, schematically, in  FIG. 6 . The various chambers  104 ,  120 ,  132  can be formed simply by providing recesses or grooves in the mating surfaces of the two components. 
     Referring to  FIGS. 9 and 10  of the drawings— FIG. 10  being an exploded view of  FIG. 9  the inlet  16  is formed in two halves from each of the main body pieces  160 ,  162 . The two parts  160 ,  162  have a flat mating surface  164 , which when pushed together, form a fluid-tight seal between the two pieces  160 ,  162 . Channels or cavities within the in-line tester  100  can be formed by providing recesses or cavities in each of those mating surfaces  164 . 
     Referring to  FIGS. 9 and 10 , it can be seen that the Venturi  116  is formed by a pair of opposing inclined surfaces  166  formed in each of the main body pieces  160 ,  162 . The first cavity  104 , which houses the pH test strip  108  is likewise formed with an additional recess part  168  formed in one of the pieces  162 , for locating and retaining the pH test strip  108 . 
     The outlet  112  of the first chamber part  104  is formed by complimentary recesses formed in each of the pieces  160 ,  162 . 
     The serpentine reservoir  114  is formed by a correspondingly shaped serpentine groove formed in one of the main body pieces  162 . 
     Likewise, the second chamber  120  is formed by a relatively deeper depression in the second main body part  162  and that enables the cot test disc  122  to be housed therein. Further recesses formed in the main body pieces  160 ,  162  form the various other channels/cavities as indicated, schematically in  FIGS. 9 and 10 . 
     The two main body pieces  160 ,  162  can either be glued together, for example, by using an adhesive or welding along the shut line to form fluid-tight cavities/channels within the main body  12 , or, where the mating surfaces  164  are sufficiently flat and/or intimate, such sealing may be accomplished by simply clamping, clipping, or otherwise holding together, the two main body pieces  160 ,  162 . 
     By way of example, an in-line tester  100  similar to that described above with reference to  FIGS. 6 to 10  of the drawings, is shown in  FIG. 13 , in which a partially transparent decal  56  covers a front face of the in-line tester  100 . The decal  56  has a first part  562 , which surrounds the pH test strip  108  viewing window. The first part  562  is divided into two differently-coloured regions  564 ,  566 , which are colored to match the colour of the pH paper  108  when a “fail”/“do not feed”; or a “pass” condition is detected, respectively. The two regions are indicated, for the avoidance of doubt by “X” and “stomach” indicia, respectively. 
     The reservoir  114  part of the in-line tester  100  is visible through a transparent  568  part of the decal  56 . Graduations  570 , indicating the volume of aspirated liquid, are optionally provided. 
     A third part  572  of the decal  56 , which surrounds the CO2 test strip  122  viewing window. The third part  572  is divided into two differently-coloured regions  574 ,  576 , which are colored to match the colour of the CO2 paper  122  when a “fail”/“do not feed”; or a “pass” condition is detected, respectively. The two regions  574 ,  576  are indicated, for the avoidance of doubt by “tick” and “lung” indicia, respectively. 
     Referring now to  FIGS. 11 and 12  of the drawings, which are schematic circuit diagrams for the in-line testers  10 ,  100  shown in  FIGS. 1 to 3 and 6 to 9  above, respectively. 
     In  FIG. 11 , the in-line tester  10  is fitted to an NG tube  18  at its inlet  16 , and to a syringe  22  at its outlet  20 . The tip of the NG tube is placed in the stomach  13  of a patient (not shown). 
     The in-line tester  10  comprises a chamber  14 , which houses a first tester, namely a disc of pH test paper (e.g. litmus paper)  50 , which is backed by a liquid-stop device, namely a perforated plastics, hydrophobic disc  52 , which when wetted by aspirated liquids, closes-off and stops/inhibits further aspiration. A fluid passageway  15  connects the chamber  14  to a further chamber that houses a colorimetric capnometer  64 , in this case, a strip of CO2-sensitive indicator paper that changes colour in the presence of CO2. 
     The syringe&#39;s plunger can be withdrawn to aspirate a sample of fluid from the stomach, via the NG tube  18  and into the in-line tester  10 . 
     Aspirated gas passes through the pH test paper  50  and the liquid-stop device  52 , where it then comes into contact with the colorimetric capnometer  64  to indicate the presence or otherwise of CO2 in the aspirated gas sample. 
     Thereafter, liquids may be aspirated from the stomach  13 , via the NG tube  18 , where they come into contact with the first tester  50  and indicate the presence, or not, of a target substance, e.g. stomach acid and/or a substance (e.g. a protein) only found in the stomach  13 . The aspirated liquid contacts the liquid-stop device  52 , causing the in-line tester  10  to hydraulically lock, thereby signifying the end of the procedure. 
     A one-way valve  130  may optionally be provided in a branch spurred-off between the syringe  22  and the outlet  20 . This enables the syringe plunger to be depressed, and fluid within the syringe  22  to be vented via the one-way valve  132 . This configuration permits a relatively small syringe  22  to be used as part of a pump, rather than having to use a relatively large syringe to obtain an adequate quantity of aspirate. 
     Referring now to  FIG. 12 , the in-line tester  100  is fitted to an NG tube  18  at its inlet  16 , and to a syringe  22  at its outlet  20 . The tip of the NG tube is placed in the stomach  13  of a patient (not shown). The in-line tester  100  comprises a chamber  14 , which has several parts. 
     A first chamber part  104  houses a first tester, for example a strip of pH test paper (e.g. litmus paper)  108  and/or a strip of other indicator paper, which changes colour in the presence of a target substance. 
     The first chamber part  104  is connected to a reservoir  114 , which can accumulate a quantity of aspirated liquid. 
     The reservoir  114  connects to a further chamber  120 , which houses a liquid-stop device  52 , namely a perforated plastics, hydrophobic disc, which when wetted by aspirated liquids, closes-off and stops/inhibits further aspiration. 
     Downstream of the liquid-stop device  52 , there is provided a colorimetric capnometer  122 , in this case, a disc of CO2-sensitive indicator paper that changes colour in the presence of CO2. 
     A one-way valve  130  is provided in a branch spurred-off, e.g. via a chamber  132 , between the syringe  22  and the outlet  20 . 
     The syringe&#39;s plunger can be withdrawn to aspirate a sample of fluid from the stomach, via the NG tube  18  and into the in-line tester  10 . Aspirated gas passes through the first tester  108  and the liquid-stop device  52 , where it then comes into contact with the colorimetric capnometer  122  to indicate the presence or otherwise of CO2 in the aspirated gas sample. 
     Thereafter, liquids may be aspirated from the stomach  13 , via the NG tube  18 , where they come into contact with the first tester  104  and indicate the presence, or not, of a target substance, e.g. stomach acid and/or a substance (e.g. a protein) only found in the stomach  13 . The aspirated liquid then fills the reservoir  114  until it eventually contacts the liquid-stop device  52 , causing the in-line tester  10  to hydraulically lock, thereby signifying the end of the procedure. 
     By virtue of the one-way valve  130 , the syringe plunger to be depressed, and fluid within the syringe  22  can be vented via the chamber  132  and the one-way valve  132 . This configuration permits a relatively small syringe  22  to be used as part of a pump, rather than having to use a relatively large syringe to obtain an adequate quantity of aspirate. 
     Referring now to  FIG. 14  of the drawings, a slight variation of the circuit diagram shown in  FIG. 12  is described. Identical reference signs have been used to identify identical features, for the avoidance of repetition, and for clarity. In  FIG. 14 , it can be seen that the in-line tester  100  has been modified by the addition of a coarse liquid-stop device  520  locate upstream of the previously-described porous or perforated, hydrophobic membrane/disc  52 . The coarse liquid-stop device  520  comprises a chamber  522 , having an inlet  524  connected to the outlet of the reservoir  114 , and an outlet  526  connected to the inlet of the chamber  120 . Baffling  526  is provided within the chamber  522 , to prevent liquid drops from being inadvertently splashed onto, or reaching the outlet  526 . Here, liquids and gasses can be drawn into the coarse liquid-stop device  520 , as may happen when the reservoir  114  is full, and the coarse liquid-stop device  520  provides a further means for preventing the porous or perforated, hydrophobic membrane/disc  52  from wetting out, as liquid droplets will be collected in the chamber  522 , rather than passing through the coarse liquid-stop device  520  to the porous or perforated, hydrophobic membrane/disc  52  downstream of it. 
     The main purpose of the coarse liquid-stop device  520  is that it enables, where the reservoir  114  is full of aspirated liquid, say saline flush, to nevertheless permit the passage of air/gas bubbles to the CO2 test strip  122 , via the porous or perforated, hydrophobic membrane/disc  52 . This may occur where an NG tube has been used previously and thus contains a saline flush liquid. However, if, somehow, the NG tube has become misplaced, as may happen where the patient “wretches” the NG tube back up their oesophagus, then the next time the NG tube needs to be used, it will be checked for correct placement. Now, the first few ml of aspirate will be saline flush, or residual feed within the NG tube, and this liquid will fill, or partially fill the reservoir  114 . Subsequent aspiration eventually empties the NG tube  18 , such that gas is now, finally, aspirated. This aspirated gas will bubble through the liquid already in the reservoir, and without a coarse liquid-stop device  520  present, the liquid would tend to be splashed onto the porous or perforated, hydrophobic membrane/disc  52 , thereby wetting it, and causing the in-line tester  100  to hydraulically lock. However, by placing a coarse liquid-stop device  520  upstream of the porous or perforated, hydrophobic membrane/disc  52 , the aspirated gas is able to pass through the reservoir, and the porous or perforated, hydrophobic membrane/disc  52  before it reaches the CO2 paper  122 , with the splashed liquid effectively being filtered-out by the coarse liquid-stop device  520 . This enables a user to reliably test an aspirated gas sample—even after already having aspirated a liquid sample. 
     The coarse liquid-stop device  520 , where provided, can be incorporated into the reservoir  114 , or into the chamber  120 , as desired. 
     EXAMPLE 1 
     Samples were used to generate the following truth table comparing a device in accordance with the present invention having means for pH detection, enzyme detection and carbon dioxide detection with the current clinical standard (pH paper). 
     There were three scenarios: 1) Normal pH content in stomach; 2) Patient on antacid medication; and 3) Stomach content in the lung. Each method and device was used and the results set out below. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 DEVICE IN 
                   
               
               
                   
                 ACCORDANCE 
               
               
                   
                 WITH PRESENT 
                 CURRENT CLINICAL STANDARD 
               
               
                 SCENARIO 
                 INVENTION 
                 (PH PAPER) 
               
               
                   
               
             
            
               
                 Normal pH 
                 Confirmed 
                 Confirmed 
               
               
                 content in 
               
               
                 stomach 
               
               
                 Patient on 
                 Confirmed 
                 False negative confirmation tube not in 
               
               
                 antacid 
                   
                 stomach, patient has delayed feed 
               
               
                 medication 
               
               
                 Stomach 
                 Confirmed 
                 False negative confirmation tube not in 
               
               
                 content in 
                   
                 stomach, patient has delayed feed 
               
               
                 the lung 
               
               
                   
               
            
           
         
       
     
     EXAMPLE 2 
     Samples were used to generate the following truth table comparing a device in accordance with the present invention having means for pH detection, enzyme detection and carbon dioxide detection with the current clinical standard (pH paper). In this example, the three markers tested for in the device according to the present invention are separated out to give a clearer demonstration of the advantages of a device in accordance with the present invention. 
     There were three scenarios: 1) Normal pH content in stomach; 2) Patient on antacid medication; and 3) Stomach content in the lung. The presence or absence of three markers was known and each method and device was used and the results set out below. 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                   
                   
                 DEVICE 
                 CURRENT 
               
               
                   
                 1 ST   
                 2 ND   
                 3 RD   
                 ACCORDING TO 
                 CLINICAL 
               
               
                   
                 MARKER 
                 MARKER 
                 MARKER 
                 PRESENT 
                 STANDARD 
               
               
                 SCENARIO 
                 PH 
                 ENZYME 
                 CO 2   
                 INVENTION 
                 (PH) 
               
               
                   
               
             
            
               
                 Normal pH content 
                 Positive 
                 Positive 
                 Negative 
                 1 st , 2 nd  and 3 rd   
                 1 st  marker 
               
               
                 in stomach 
                   
                   
                   
                 markers 
                 confirmed only 
               
               
                   
                   
                   
                   
                 confirmed 
               
               
                 Patient on antacid 
                 Negative 
                 Positive 
                 Negative 
                 1st, 2nd and 3rd 
                 None or 
               
               
                 medication 
                   
                   
                   
                 markers 
                 confirmed 
               
               
                   
                   
                   
                   
                 confirmed 
               
               
                 Stomach content in 
                 Positive 
                 Positive 
                 Positive 
                 1st, 2nd and 3rd 
                 1 st  confirmed 
               
               
                 the lung (or  M. Cattarhalis   
                   
                   
                   
                 markers 
                 only - 
               
               
                 infection 
                   
                   
                   
                 confirmed 
                 dangerous 
               
               
                 in lung) 
               
               
                   
               
            
           
         
       
     
     In complicated situations where for example, a patient is taking antacids or there is stomach content in the lung, only devices in accordance with the present invention will confirm the actual location of the NG tube for enteral feeding. Known devices and methods will only give an accurate indication of location when a patient has a normal stomach pH. In all other scenarios, the result from using known devices can be dangerous and has potentially fatal consequences should feeding via the tube be initiated where an incorrect placement of the tube is mistakenly indicated as being in the stomach. 
     The invention is not restricted to the details of the foregoing embodiments, which are merely exemplary of the invention. For example, any shapes, sizes, relative dimensions etc. are illustrative, and not limiting, as are any material selections and/or design choices (e.g. type of check valve).