Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
  • A61M16/00—Devices for influencing the respiratory system of patients by gas treatment, e.g. mouth-to-mouth respiration; Tracheal tubes
  • A61M16/04—Tracheal tubes
  • A61M16/0488—Mouthpieces; Means for guiding, securing or introducing the tubes
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
  • A61M16/00—Devices for influencing the respiratory system of patients by gas treatment, e.g. mouth-to-mouth respiration; Tracheal tubes
  • A61M16/08—Bellows; Connecting tubes ; Water traps; Patient circuits
  • A61M16/0816—Joints or connectors
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
  • A61M16/00—Devices for influencing the respiratory system of patients by gas treatment, e.g. mouth-to-mouth respiration; Tracheal tubes
  • A61M16/08—Bellows; Connecting tubes ; Water traps; Patient circuits
  • A61M16/0816—Joints or connectors
  • A61M16/0841—Joints or connectors for sampling
  • A61M16/085—Gas sampling
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N31/00—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods
  • G01N31/22—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods using chemical indicators
  • G01N31/223—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods using chemical indicators for investigating presence of specific gases or aerosols
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/08—Detecting, measuring or recording devices for evaluating the respiratory organs
  • A61B5/083—Measuring rate of metabolism by using breath test, e.g. measuring rate of oxygen consumption
  • A61B5/0836—Measuring rate of CO2 production
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
  • A61M16/00—Devices for influencing the respiratory system of patients by gas treatment, e.g. mouth-to-mouth respiration; Tracheal tubes
  • A61M16/04—Tracheal tubes
  • A61M16/0402—Special features for tracheal tubes not otherwise provided for
  • A61M16/0411—Special features for tracheal tubes not otherwise provided for with means for differentiating between oesophageal and tracheal intubation
  • A61M2016/0413—Special features for tracheal tubes not otherwise provided for with means for differentiating between oesophageal and tracheal intubation with detectors of CO2 in exhaled gases
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
  • A61M2230/00—Measuring parameters of the user
  • A61M2230/40—Respiratory characteristics
  • A61M2230/43—Composition of exhalation
  • A61M2230/432—Composition of exhalation partial CO2 pressure (P-CO2)

Definitions

• the present invention relates to novel, improved methods and apparatus for providing an indication if at least a threshold level of carbon dioxide is present or reached in a gas stream or sample of interest.
• the present invention relates to novel, improved methods and apparatus for ensuring that an airway (or endotracheal) tube is properly placed in the trachea of a patient and not in the patient ' s esophagus.
• the present invention relates to novel, improved methods for increasing the shelf life of detectors used for the purposes identified in the two preceding paragraphs and to the resulting detectors.
• Direct visualisation Direct visualization of the vocal cords and observation as the airway tube passes into the trachea is considered by many the "gold standard" of correct tube placement, and this remains one of the more reliable signs.
• direct visualization is impossible to achieve in certain patients, even in the roost experienced hands, due to a multitude of factors.
• Clinicians and medics are thus often called upon to make “blind” intubations in which the position or condition of the patient is such that the progress of the tube cannot be followed visually. For example, it may be dangerous to immediately move an accident victim, or there may be insufficient lighting where a patient has collapsed at home. "Blind" intubations are performed in the hospitals as well, especially in patients who are overweight or have anatomical abnormalities.
• the problem is more common is inexperienced hands and may be associated with haste, poor lighting, or an individual patient's anatomical abnormality.
• the clinician's view may be obstructed by the advancing tube, by acute angulation of the airway in the back of the patient's throat, or by a loss of depth perception with monocular vision.
• the tube may be inadvertently withdrawn fran the trachea before or during securing of the tube or when moving the patient to the lateral or prone position. Additionally, radiographic studies have shown that flexion or extension of the neck can change tube positions as much as five centimeters, resulting in inadvertent extubation which may well not be observed by the clinician.
• Chest Movement Another commonly relied upon method of confirming tracheal intubation is observation of symmetric bilateral movements of the chest wall during ventilation. Some patients, however, have physical conditions in which ventilation is more than usually dependent on diaphragmatic movement as opposed to chest wall movement. Patients with large breasts, obesity, a barrel chest from lung disease, and other conditions tend to develop rigid chest walls. Chest movement can be difficult to evaluate in these circumstances, making assessment of proper tube position by chest expansion unworkable. More importantly, movement of the chest wall simulating ventilation of the lungs can be seen even with the ventilating tube positioned in the esophagus.
• Presence of Exhaled Tidal Volume This method of confirming tracheal intubation can be uncertain because it is possible to have measurable tidal volumes of air moving in the airway tube during spontaneous respiratory efforts with the esophagus intubated and the trachea obstructed.
• researchers have documented tidal volumes of up to 180 milliliters and peak flows of greater than fifty liters per minute under these circumstances.
• Reservoir Bag Compliance Another practice commonly employed is noting the characteristic feel of the reservoir bag associated with normal lung compliance during inspiration and the presence of expiratory refilling of the bag during hand ventilation. However, compliance varies widely from one person to another and within the s.ame individual at different times. Repeated filling and emptying of the stomach with esophageal ventilation, leading to inflation and deflation of the breathing bag, can also be mistaken for pulmonary ventilation.
• Airway Tube Cuff Maneuvers - With the cuff deflated, the higher pitched sound of air escaping around a tracheal tube, compared to the more guttural sound of leakage around an esophageal tube, has been used as a distinguishing feature. However, with the cuff of an esophageal tube located near the level of the cricoid cartilage, the distinction in air sounds may not exist. Also, palpation of the airway tube cuff in the neck to verify position has been reported to fail, perhaps because the easily distensible esophagus simply balloons outward with an inflated cuff inside it.
• Air Escape - A less commonly performed procedure involves pressing sharply on the chest while listening over the tube opening to detect "a characteristic feel and sound of expelled air.” This procedure is unreliable because of the inability to distinguish between air expelled from the tracheal tube and: (1) air passing through or around an esophageal tube, or (2) esophageal air present from mask ventilation prior to intubation, or (3) air expelled from the nose.
• Tube Condensation Condensation of water vapor in the tube, although less likely with esophageal intubation, can occur and hence is not a reliable sign. Conversely, the absence of condensation normally seen with a tube positioned in the trachea would be reason to look for further proof of correct tube position.
• Pulse Oximetry Although useful in many situations, pulse oximetry may be an untimely indicator of esophageal intubation for several reasons. researchers have noted normal functioning of a ventilator when connected to an esophageal tube. With the vocal cords relaxed, patients were studied after deliberate intubation of both the esophagus and trachea.
• Ventilation into the esophagus also caused some ventilation of the lungs, as evidenced by carbon dioxide recordings obtained from the open tracheal tube.
• This ventilation could significantly slow the onset of oxygen desaturation of the blood after esophageal intubation and could delay recognition of esophageal tube placement until surgery is in progress.
• the practice of preoxygenation of patients prior to intubation can slow the recognition of an improper tube position using pulse oximetry because the patients' blood is highly saturated with oxygen at the start of the surgical procedure.
• End-tidal carbon dioxide measurement offers perhaps the most reliable and simplest determination of proper tube placement. It involves the measurement of carbon dioxide concentration during the respiratory cycle. The reliability of carbon dioxide monitoring is based on the assumption that carbon dioxide can be reliably detected in patients with an intact pulmonary circulation and an intubated trachea whereas no carbon dioxide is present in gases exiting from an esophageal tube. Carbon dioxide can be detected initially with esophageal intubation when carbon dioxide has been forced into the stomach during prior mask ventilation. However, the end-tidal carbon dioxide is low in such cases; the wave pattern is irregular; and the carbon dioxide levels rapidly diminish with repeated ventilation, making it easy to distinguish between carbon dioxide from the trachea and that from the esophagus.
• Ease of use - The device must be easy to connect to the airway tube, require no more than minimal interpretation of the indication, and require no electrical power.
• Sensitive - The device must display an obvious indication of carbon dioxide expired from the lung within thirty seconds.
• the indicator must not give false-positive readings but may show transitory readings from a limited volume of carbon dioxide or other materials from the stomach.
• inexpensive The device should desirably sell for less than $1.00 U.S. in large quantities.
• the device should be designed for single patient use. Clean - The device should be designed to be cleaned during assembly in accordance with ANSI Code 279.2 for tracheal tube connectors and adapters.
• Storable - The device must have a shelf life of twenty-four months prior to use without loss of effectiveness.
• novel devices disclosed herein, and the methods in which they are employed, operate on the principles that: (1) after a few breaths, at most, carbon dioxide will appear in the intubated patient' s exhalations at a threshold level (typically three percent) commensurate with tracheal intubation only if the airway tube has been placed in the patient's trachea and not his or her esophagus, and (2) this end-tidal carbon dioxide in a concentration which equals or exceeds the threshold value can be employed to effect an easily observed change in a characteristic of an appropriate indicator.
• a threshold level typically three percent
• One embodiment of the invention which takes advantage of and can be employed to effect such a change in an indicator characteristic and which operates on the principles just described consists of a molded plastic housing, a reservoir of unreacted indicator solution, a reaction medium (or wick), and a sink for the reacted solution.
• the user pulls an activator tab or lanyard, breaking a reservoir seal and exposing the solution to the reaction medium.
• the solution thereupon immediately begins to wick (or migrate) across the reaction medium toward the sink.
• the clinician then connects the detector to the exposed end of an endotracheal tube just previously placed in the patient's airway.
• a ventilator is then connected to the other end of the detector to complete the patient's breathing circuit.
• any carbon dioxide in the patient's breath over or a three percent or other threshold concentration reversibly hydrates in the indicator solution and brings about a change in the color of the indicator solution migrating across the reaction medium toward the sink. This color change is monitored by the clinician. If the endotracheal tube were misplaced in the esophagus, carbon dioxide trapped in the stomach or the esophagus might cause a color change in the indicator solution on the reaction medium. As the carbon dioxide in the breath decreases, however, and more solution migrates across the medium from the reservoir, the color would tend to change back to its initial hue.
• Another important and representative embodiment of the invention employs a thin body of indicator solution trapped between a housing and a liquid-tight membrane of a material which is permeable to uncharged molecules but not to charged molecules or ions.
• a material which is permeable to uncharged molecules but not to charged molecules or ions.
• Teflon tetrafluoroethylene polymer.
• Carbon dioxide in expired gases flowing through the detector diffuses across the permeable membrane and then undergoes reversible hydration in the indicator solution, generating excess hydrogen (H + ) ions and thus reducing the pH of the solution. This causes the indicator to change color, provided that the concentration of carbon dioxide in the expired gases has reached the threshold level and the pH of the solution has consequently been reduced to a level at which the indicator will change color.
• the indicator tends to revert to its original color. Sustained periodic changes of color are an indication of successful tracheal intubation. If esophageal intubation has instead been achieved, the indicator may change color once or a very few times. Thereafter, however, it will tend to revert to and remain its initial color.
• the membrane employed in detectors constructed as disclosed herein passes only uncharged molecules (in this case carbon dioxide), and not hydrogen ions or other charged particles, the membrane keeps charged particles not attributable to the reversible hydration of carbon dioxide from triggering an indicator color change and thereby perhaps providing a false indication of proper endotracheal tube placement.
• uncharged molecules in this case carbon dioxide
• hydrogen ions or other charged particles the membrane keeps charged particles not attributable to the reversible hydration of carbon dioxide from triggering an indicator color change and thereby perhaps providing a false indication of proper endotracheal tube placement.
• the indicator solutions employed in the practice of the present invention may include an oxidation sensitive constituent such as a carbonic anhydra.se catalyst. If incorporated in the solution, it can prove difficult, and expensive, to keep the oxidation sensitive material from deteriorating over a storage period of acceptable length. However, at least in the case of carbonic anhydrase, the perishable material is also available as a freeze, dried powder and, in that form, can be stored indefinitely without deterioration.
• an oxidation sensitive constituent such as a carbonic anhydra.se catalyst.
• selected components of the indicator solution are therefore supplied in a dry, more stable form and are mixed with the fluid phase of the solution only as the carbon dioxide detector is readied for use.
• This can be accomplished by placing the dry and liquid components of the indicator solution in separate, communicable, detector compartments; rupturing a seal between those compartments to establish communication therebetween when the detector is readied for use; and then shaking the detector to disperse the dry components of the solution (the solute) in the fluid carrier. As this dispersion proceeds, the color of the solution will develop, providing a clear indication to the user of the detector that it is ready to be used.
• the material to be protected can be stored on a wick and a fluid phase containing the remaining constituents of the indicator solution put in a capsule.
• the capsule is loaded in a cavity having fluid communication with the wick.
• the capsule is ruptured; and its contents are transferred to the wick, preferably under pressure.
• the fluid phase of the solution then migrates across the wick, incorporating into the indicator solution the relatively perishable material theretofore separately stored on the wick.
• detectors employing the principles of the present invention are rugged, reliable, and easy to use; and they are sensitive to changes in the concentration of carbon dioxide in the gases being monitored. These detectors are simple to use because they employ easily made connections to an airway (or endotracheal) tube or adapter and to the ho.se of a mechanical ventilator, do not require any electrical connections, and require only minimal interpretation of the indications the device provides.
• Monitoring devices employing the principles of the invention are also safe because they are designed to provide secure connections between the device and the components to which it is attached -- typically, as indicated above, an adapter at the exposed end of the airway tube and one end of the ventilator hose tube. There is consequently little chance that the airway tube will come loose and be lodged in the patient's trachea or interfere with the ventilation of the patient or the administration of anesthetics or other gases, etc. or that the ventilator hose will be detached and pose similar problems.
• monitoring devices employing the principles of the invention have a long shelf life.
• novel monitoring devices disclosed herein is such that they are clean at the end of the manufacturing process, and their design also minimizes the possibility of foreign matter being introduced into the device from the ambient surroundings and subsequently entering a patient's lungs.
• the indicator characteristic will consequently change repeatedly (viz., with each exhalation) if the airway tube is placed in the patient's trachea. In contrast, there will be only a single cycle of change or a very few such cycles if the tube is improperly placed in the patient's esophagus as the expelling of the carbon dioxide from the patient's stomach and esophagus is a very short time phenomenon.
• the change in indicator character indicative of a threshold level of carbon dioxide in the gases being monitored is brought about by the reversible hydration of carbon dioxide in an indicator solution to produce excess hydrogen (H + ) ions and a consequent reduction in the pH of .the indicator solution.
• the reversible hydration of carbon dioxide proceeds slowly; and the hydration is preferably catalyzed -- as with the above-mentioned carbonic anhydrase -- so that the indicator will react fast enough to be acceptable to the medical profession; viz. , provide an indication commensurate only with proper tube placement in 30 seconds or less. Buffering can be employed to alter the threshold concentration of carbon dioxide required to trigger a change in the character of the indicator.
• Another important and related, but more specific, object of the invention resides in the provision of methods and devices in accord with the preceding object which employ: (1) the reversible hydration, in an indicator solution, of carbon dioxide in the gases being monitored to produce excess H + ions and reduce the pH of the solution, and (2) the use of an indicator which changes character (typically color) when the concentration of such ions reduces the pH in a solution containing the indicator to a level commensurate with a threshold level of carbon dioxide to provide an indication that that level of carbon dioxide has been reached in the gases being monitored.
• Another important and primary object of the present invention is the provision of novel, improved methods and devices for ensuring that an airway tube has been placed in the trachea of an intubated patient.
• a related, also primary and important object of the invention resides in the provision of devices and methods as characterized in the preceding object in which the concentration of carbon dioxide in the gases flowing through the airway tube is monitored to insure that the airway tube has been properly placed.
• a related and also important and primary object of the invention is the provision of methods and devices in accord with the preceding object in which the carbon dioxide expired by the patient is monitored in a manner that clearly distinguishes between: (1) the reaching of threshold levels of carbon dioxide due to proper placement of the airway tube in the patient's trachea, and (2) the reaching of that same level due to the presence in the monitored gases of carbon dioxide expelled from the patient's stomach and/or esophagus.
• FIG. 1 is a pictorial view of a supine patient with an airway tube placed in his trachea and connected to a mechanical ventilator by way of a carbon dioxide detector as disclosed herein to confirm tracheal intubation in accord with the principles of the present invention
• FIG. 2 is a perspective view of the carbon dioxide detector with part of the detector casing broken away to show its internal construction
• FIG. 3 is a longitudinal section through the detector
• FIG. 4 is an exploded view of a second form of carbon dioxide detector which embodies, and can be employed in methods embodying, the principles of the present invention
• FIG. 5 is a bottom view of the carbon dioxide detector of FIG. 4;
• FIG. 6 is a longitudinal section through the detector of FIG. 4, taken substantially along line 6-6 of FIG. 5;
• FIG. 7 is a longitudinal section through a third type of carbon dioxide detector which can also be employed in methods embodying the principles of the invention and is designed to have a long shelf life;
• FIG. 8 is a fragment of FIG. 7 to a larger scale
• FIG. 9 is a pictorial view of a fourth type of carbon dioxide detector which employs the principles of the present invention and is also designed to have an extended shelf life;
• FIG. 10 is a longitudinal section through the detector of FIG. 9; and FIG. 11 is a transverse section through that detector.
• novel detectors disclosed herein provide a visual indication, typically by effecting a color change in an appropriate indicator, if the carbon dioxide concentration in a .sample of gases supplied to the detector is at, or above, a threshold level.
• pH sensitive indicators are employed. Among those suitable for the purposes of the present invention are :
• the gases flowing through the monitoring device are substantially devoid of carbon dioxide; and those gases are therefore not capable of causing the indicator to change color or causing it to retain the color it assumes when the pH in its environment is reduced.
• the indicator tends to revert to its original color. Therefore, by contacting aliquots of the indicator solution alternately with exhaled and then inspired breaths, the indicator solution will alternately change color and revert to its orginal color. A sustained series of these color change cycles indicates that the airway tube has been placed in the patient's trachea.
• the presently preferred catalyst is the zinc metalloenzyme, carbonic anhydrase.
• This enzyme has at least three distinct isozymes, which can be obtained from a wide variety of human, other animal, and vegetable sources. Carbonic anhydrase obtained from bovine erythrocytes has proven suitable. However, the catalytic mechanism of the different isozymes of carbonic anhydrase appears to be the s»ame (see Silverman et al. , The Catalytic Mechansim of Carbonic Anhydrase: Implications of a Rate-Limiting Protolysis of Water, 21 Accounts of Chemical Research, The Merican Chemical Society, January, 1988 , pp. 30 et seq.) . Consequently, it is not intended to exclude from the patent coverage sought herein the use of carbonic anhydrase isozymes obtained from other sources -- parsley or spinach, for example -- or synthetic isozymes of the carbonic anhydrase.
• a stabilizer for the catalyst may be required.
• Glycerol and propylene glycol are examples of appropriate stabilizers.
• a preservative will typically be required to protect the carbonic anhydrase enzyme against attack by fungi and bacteria.
• Parabens methyl, propyl, butyl, and ethyl esters of para-hydroxybenzoic acid are suitable for this purpose.
• the selected catalyst can be mixed with the indicator solution.
• the carbonic anhydrase can be provided in the form of a freeze-dried powder, a form in which that enzyme is very stable, and mixed with the indicator solution in which the carbon dioxide is reversibly hydrated only when the carbon dioxide detector is readied for use.
• buffers may be added to the indicator solution, as appropriate.
• These compositions alter the concentration of hydrogen ions required to lower the pH of the solution to the level at which the indicator will change color.
• this parameter one can define the threshold concentration of carbon dioxide required to effect a change in the color of the indicator. This allows one to structure the monitoring device so that: the indicator will change color with each exhalation even if the intubated patient is hyperventilating or the concentration of carbon dioxide in his expired breaths is otherwise relatively low and to otherwise adjust the response of the indicator to specified concentrations of carbon dioxide and define its sensitivity to specified concentrations of carbon dioxide.
• Buffers that have been employed for the foregoing purposes include aqueous solutions of: (1) sodium barbital and HCl, (2) NaHCO 3 , and (3) NaOH.
• FIG. 1 depicts the head 20 and upper body 22 of a supine patient 24 and an airway or endotracheal tube 26 placed in the patient's trachea 28.
• the exposed or outer end 30 of the endotracheal tube 26 is connected by an adapter 32 to a detector 34: (1) embodying the principles of the present invention, and (2) provided to detect threshold levels of carbon dioxide in the breaths exhaled by patient 24.
• the carbon dioxide detecting device 34 is connected in line between endotracheal tube 26 and the hose 36 of a mechanical ventilator (not shown).
• a human's esophagus (identified by reference character 38) lies immediately adjacent the patient's trachea 28.
• an endotracheal tube such as that identified by reference character 26 and introduced through the patient's mouth 40 can easily be placed in esophagus 38 rather than trachea 28, even if care is exercised in placing the tube and the conditions under which the tube is placed are optimal.
• carbon dioxide detector 34 substantially eliminates this hazard, even when an endotracheal tube is placed under adverse conditions or by a less than highly trained or skilled individual, because it provides an unmistakable differentiation between tracheal and esophageal intubation.
• an indicator of the character discussed above changes color each time the patient 24 exhales; and the indicator tends to revert to its original (or initial) color between exhalations. If tracheal intubation has been achieved, these changes in color will continue over an extended period of time.
• carbon dioxide detector 34 includes an elongated, hollow, cylindrical, circularly sectioned housing 42 molded or otherwise fabricated from a clear synthetic polymer such as a polyethylene.
• a typical detector of this character is one and one-half inches long and 15 millimeters in diameter.
• Tabs 49 extend radially and in opposite directions from detector housing 42. Rubber bands (not shown) can be trained over these tabs to ensure that the connections of the monitoring device 34 to the endotracheal tube 26 and ventilation hose 36 are maintained.
• a central section 50 Midway between the end sections 44 and 48 of housing 42 is a central section 50.
• An annular groove 52 is formed in this central section 50 of housing 42, and this groove opens onto the bore 54 through housing 42.
• a cylindrical membrane 56 and circular seals 58 and 60 cooperate with the groove 52 in the central section 50 of housing 42 to define a sealed, annular plenum or cavity 62.
• Seals 58 and 60 have annular recesses 64 and 66 in which the opposite ends 68 and 70 of membrane 56 are seated. The resulting assemblage of that membrane with seals 58 and 60 is installed in housing 42 in spaced relation to the inner end of groove 52 and with seal 60 butting against an internal, annular flange 72 in housing 42.
• the sealed chamber thus provided by the cooperation among housing 42, membrane 56, and circular seals 58 and 60 is filled with an indicator solution of the character described above. This may be done by injecting that solution with a hypodermic needle through a port 74 in detector housing 42.
• the injection port is thereafter sealed in any convenient fashion (sealing may be unnecessary, especially if housing 42 is made from a self-sealing material).
• membrane 56 is preferably fabricated from a liquid-tight material which is permeable to uncharged compounds such as carbon dioxide but impermeable to charged particles such as hydrogen ions. Twelve micrometer thick Teflon is satisfactory.
• the concentration of carbon dioxide in the exhalations flowing through detector 34 is at or above a threshold level, the reversible hydration of the carbon dioxide and the resulting build-up of hydrogen ions in the indicator solution will lower the pH of that solution to a level at which the indicator in the solution will change color. Thereafter, and until the next exhalation of patient 24, the hydration reactions will reverse when carbon dioxide comes out of the indicator solution, decreasing as the concentration of that compound in the detector decreases. This carbon dioxide diffuses across membrane 56 back into the bore 54 through detector 34. As this occurs, the concentration of hydrogen ions in the indicator solution will decrease, the pH of that solution will rise, and the indicator will consequently tend to revert to its original color.
• the indicator in the solution trapped in cavity 62 will change color with a frequency approaching that with which patient 24 breaths. If these reversals in color occur for more than a very few breathing cycles, it can safely and reliably be assumed that tracheal intubation has been achieved. This is because, if esophageal intubation has instead been achieved, indicator color changes will not occur after whatever carbon dioxide might be present has been expelled from the patient' s stomach and esophagus; and this occurs, at the latest, after only a very few exhalations. Thereafter, the indicator will tend to revert to its initial color and will remain the color to which it reverts, clearly indicating to the observer that esophageal rather than tracheal intubation has been achieved.
• detector housing 42 is fabricated from a clear material, the just-described visual indications will be clearly evident to the individual monitoring the placement of airway tube 26.
• Bands of color 78 and 79 shown in exaggerated form in FIG. 3, circle detector housing 42 at locations corresponding to the ends of the cavity 62 in which the indicator solution is trapped.
• One of these bands matches the initial color of the indicator; i.e. , the color the indicator has when the carbon dioxide in the gases being monitored is below the threshold limit required to trigger a color change.
• the other band is matched to the color the indicator has when the threshold concentration is reached and the color change effected.
• Indicia associated with the bands (not shown) identify the association of those bands with the initial and changed colors, respectively. Thus, by merely looking at the indicia associated with the band matched by the indicator, the individual monitoring the detector can ascertain whether carbon dioxide is present in a threshold amount.
• FIGS. 4-6 depict a second carbon dioxide detector 80 which also operates in accord with the principles of the present invention but in a somewhat different manner than the just-described detector 34 does.
• carbon dioxide detector 80 includes a housing or casing 82 having a main, boxlike member 84.
• a lid 86 can be sealed to casing member 84 after the internal components of the detector are installed to isolate the interior 88 of housing 82 from the ambient surroundings. This keeps the casing interior from being contaminated by foreign substances in the surrounding environment.
• Integra bosses 90 and 92 at the opposite ends of main casing member 84 have external and internal tapers 94 and 96 which, like their counterparts 44 and 46 in adapter 34, provide reliable and secure connections between: (1) the carbon dioxide detector 80, and (2) the airway adapter 32 and mechanical ventilator hose 36 to which that detector is attached.
• Supported in parallel, spaced apart recesses 98 and 100 in main casing member 84 are: (1) a reservoir capsule 102 filled with an indicator solution of the character described above, and (2) a member 104 which functions as a sink for the indicator solution. Encapsulation or other packaging is employed to prevent evaporation and to keep the indicator solution from being contaminated.
• Window 114 may be provided by molding main casing member 84 from a clear plastic or by installing a window of such material in a casing member otherwise formed from a different material. Appropriate clear polymers are identified above and hereinafter.
• Wick 112 will typically be fabricated from a conventional, commercially available, non-woven, Nylon paper. Other materials with wicking capabilities may instead be employed; but it is, however, important that the wicking medium not be acidic. Otherwise, it might affect a change in the indicator solution not attributable to the presence of a threshold level of carbon dioxide, consequently keeping the carbon dioxide detector from working properly.
• Member 104 can be made from an absorbent material such as a gauze sponge.
• a lanyard 116 (see FIGS. 4 and 6) is pulled before the connection between detector 80 and endotracheal tube adapter 32 is effected. This ruptures reservoir 102 over a span indicated by reference character 118 in FIG. 4, allowing the indicator solution to flow onto and saturate that end 108 of wick 112 at reservoir 102. If tracheal intubation of patient 24 has been achieved, carbon dioxide in the exhalations flowing through detector 80 in the direction indicated by arrow 120 in FIG. 4 will reversibly hydrate in the indicator solution migrating along wick 112 and effect an indicator color change as discussed above.
• the indicator solution will migrate to the left .along wick 112 as indicated by arrow 122 once it has been released from reservoir 102, typically for a period of approximately fifteen minutes. If tracheal intubation has been achieved, the indicator on wick 112 will tend to revert to its original color between exhalations, a change promoted by air flowing through the detector to the patient and flushing carbon dioxide from the indicator solution as the air traverses detector casing 82. That part of the wick subsumed by the color change will increase with each successive exhalation. This clearly indicates that tracheal intubation has been achieved.
• FIGS. 7 and 8 depict yet another carbon dioxide detector 130 embodying the principles of the present invention.
• This detector resembles the carbon dioxide detector 34 illustrated in FIGS. 2-4 and discussed above. To the extent that this is true, like components of detectors 34 and 130 have been identified by the same reference characters.
• the carbon dioxide detector 130 illustrated in FIGS. 7 and 8 is furthermore like detector 34 in that an indication commensurate with a threshold level of carbon dioxide having been reached in a sample being monitored is produced by: (1) that carbon dioxide diffusing across a permeable membrane and undergoing reversible hydration in an indicator solution behind the membrane, and (2) a consequent generation of an excess of hydrogen ions in the indicator solution to trigger a change in the color of the indicator.
• Indicator 130 does differ in a major respect frcm indicator 34 in that the solute (dry components, typically a pH sensitive indicator and a carbonic anhydrase catalyst) and solvent (typically water plus a buffer) of the indicator solution are not mixed until carbon dioxide detector 130 is readied for use. As discussed above, this is important with respect to the storage life prior to use of the detector because the indicator solution will typically contain one or more constituents which are much more stable in dry form then in aqueous solution.
• solute dry components, typically a pH sensitive indicator and a carbonic anhydrase catalyst
• solvent typically water plus a buffer
• indicator 130 the typically but not necessarily aqueous, fluid phase of the indicator .solution is injected into the sealed cavity 62 behind permeable membrane 56 through injection port 74.
• the remaining constituents of the indicator solution are furnished in a dry form and placed in a compartment 132.
• This compartment lies between a seal 134 located in a depression 135 in the central section 50 of casing 42 and a flexible push tab 136 fixed to that seal.
• a communicating channel 138 is provided through detector housing 42 between sealed compartment 132 and the sealed cavity 62 behind membrane 56.
• FIGS. 9-11 depict a novel carbon dioxide detector 144 which embodies the principles of the invention and which, like the detector 130 illustrated in FIGS. 7 and 8, is designed for increased shelf life.
• detector 144 components of detector 144 which are like those of previously disclosed embodiments of the invention will be identified by the same reference characters. As in the case of carbon dioxide detector 130, detector 144 has an increased shelf life because constituents of the indicator solution such as the above-discussed carbonic anhydrase catalyst are stored in their most stable, dry form until the detector is readied for use.
• the deterioration susceptible component (or components) of the indicator solution are placed on a porous wick 146; and the remaining constituents of the indicator solution 148, including one of the indicators identified above or a comparable one, are confined in a capsule 150.
• an opening 152 is formed in the center section 50 of the detector housing or casing 42 (in this case generally ⁇ -sectioned, see FIG. 11).
• the flanges 154 and 156 of this detector component are seated on end section 48 and shoulder 44 of detector casing 42 at the opposite ends of opening 152.
• Membrane 56 is trapped against the bottom wall 160 of support 158 by a combined lens and actuator support 162. This component fits in a recess 164 in membrane/wick support 158 (see FIG. 10) and is frictionally retained in that recess.
• An aperture 166 is formed through the center section 50 of detector casing 42 opposite membrane 56 . In a manner akin to that discussed above in conj unction with detectors 34 and 130 , this allows carbon dioxide in exhaled breaths or other gases traversing the bore 54 in detector casing 42 to flow into contact with, and migrate through, the permeable membrane.
• the wick 146 which serves as a carrier or support for a carbonic anhydrase catalyst (or other "dry" phase) in the illustrated, representive embodiment of the invention is seated in, and extends at both ends beyond, a recess or enclosed space 168 opening onto the lower side 170 of the lens/actuator support 162 immediately adjacent membrane 56 .
• the membrane therefore traps wick 146 in recess 168.
• Wick 146 of detector 144 will typically be fabricated f rom a 2-4 mil thick, porous Nylon. Other materials may instead be used with the caveat that the material must facilitate the rapid migration of the indicator solution across the wick.
• the capsule 150 containing the liquid or fluid phase of the indicator solution is fabricated from a thermoplastic polymer such as polyvinyl chloride .
• the capsules may conveniently be made by filling an elongated tube of the selected polymer with the solution, heat sealing the tube from edge to edge at intervals therealong, and subsequently separating the thus provided, filled capsules.
• the lens/actuator support 162 has a vertically oriented, integral section 172 with a rectangularly sectioned cavity 174 extending from top to bottom thereof.
• a passage 176 in component 162 provides fluid communication between the bottom end of cavity 174 and that enclosed space 168 in component 162 which houses membrane 146.
• an integral, vertically extending pin 180 with a point or knife edge 182 at its upper end is formed in detector component 162 at the bottom of cavity 174.
• the indicator solution filled capsule 150 is installed in cavity 174 with the lower edge 184 of the capsule resting on the pointed, upper end 182 of pin 180.
• a frictionally retained plunger 186 with an operator-engageable button 188 and an integral, depending main body section 190 configured to match the contour of cavity 174 is installed in the latter above the indicator solution-containing capsule 150.
• the capsule is seated in an arcuate recess 192 in the lower end of the plunger section with the plunger resting on the capsule 190 and thereby restrained against side-to-side movement in the cavity.
• plunger 186 is displaced by button 188 in the direction indicated by arrow 193 in FIG. 10 until detents 194 and 195 at the opposite sides of the plunger main section 190 click into cooperating recesses 196 and 197.
• These recesses are formed in vertically oriented, lens/plunger support component 162 at the opposite sides 198 and 200 of the vertical, rectangularly sectioned cavity 174 in section of that component and toward the upper end of the cavity.
• the cavity surrounding end walls 202 and 204 of section 172 have recesses 206 and 208 at the upper ends thereof.
• the fluid phase of the indicator solution released from capsule 150 by rupturing the latter and pumped through the communicating passage 176 into the cavity 168 in which wick 146 is housed dissolves the "dry" indicator constituent or constituents on that wick as it migrates thereacross. Because of the wicking capabilities of support 146, this occurs within a few seconds, resulting in color being developed in the indicator solution. This development of color clearly indicates to the user of the device that the carrier supported and capsule contained components of the solution have been intimately mixed and that the carbon dioxide detector 144 is therefore ready for use.
• plunger main section 190 the opposite sides 212 and 214 of plunger main section 190 are relieved as with the illustrated, vertically extending slots 216 and 218. These slots allow air to escape from that part 220 of the cavity 174 in lens/plunger support component 162 beneath plunger 186 as the latter is depressed. This ensures that the plunger can readily be fully displaced to the click stop position discussed above.
• At least the lens/plunger supporting component 162 of detector 144 is fabricated from a clear polymer and with an integral, convex lens 210 opposite indicator solution-filled space 168 (see FIGS. 9 and 10) so that the development of color in the indicator solution and subsequent changes in that color can be readily seen by the user of the device.
• This component of carbon dioxide detector 144, as well as the other components of that device may be made from a number of clear, thermoformable polymers -- for example, the styrene-butadiene copolymers marketed by Phillips Petroleum Company under the trade name K-RESIN. It is not essential, in fabricating a carbon dioxide detector of the type illustrated in FIGS.
• the carbon dioxide is reversibly hydrated in the indicator solution to produce excess hydrogen ions and lower the pH of the indicator solution. If the carbon dioxide is at, or reaches, a threshold level, the pH of the solution will decrease to a level capable of triggering an indicator color change and providing a visual indication that the concentration of carbon dioxide is at or has reached the threshold level.
• original and changed colors are clear visual indications of, respectively, the absence and presence of a threshold level of carbon dioxide in gases being sampled and passing through the bore 54 in carbon dioxide detector 144.
• the constituents of the indicator solution will be the following:
• the carrier of the indicator solution be an aqueous one.
• the reversible hydration of carbon dioxide in ethanol is a well-documented phenomenom.
• the use of this compound and other fluids in which the reversible hydration of carbon dioxide can be carried out in the indicator solutions of the present invention is therefore intended to be covered in the appended claims unless expressly excluded therefrom.
• a catalyst preferably a "dry" carbonic anhydrase isozyme or a mixture of such isozymes -- can be added to the indicator solution to increase the speed with which the detector employing the indicator solution reacts to a change in carbon dioxide concentration. Storage of this catalyst and/or other perishable indicator solution constituents is optionally employed to increase the shelf life of the detector.

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• 1989
  • 1989-02-24 AU AU33471/89A patent/AU3347189A/en not_active Abandoned
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