CA1322945C - Indicator device - Google Patents
Indicator deviceInfo
- Publication number
- CA1322945C CA1322945C CA000544371A CA544371A CA1322945C CA 1322945 C CA1322945 C CA 1322945C CA 000544371 A CA000544371 A CA 000544371A CA 544371 A CA544371 A CA 544371A CA 1322945 C CA1322945 C CA 1322945C
- Authority
- CA
- Canada
- Prior art keywords
- carbon dioxide
- indicating element
- indicator
- enclosure
- concentration
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Classifications
-
- 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
-
- 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
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
- G01N33/48—Biological material, e.g. blood, urine; Haemocytometers
- G01N33/50—Chemical analysis of biological material, e.g. blood, urine; Testing involving biospecific ligand binding methods; Immunological testing
- G01N33/53—Immunoassay; Biospecific binding assay; Materials therefor
- G01N33/536—Immunoassay; Biospecific binding assay; Materials therefor with immune complex formed in liquid phase
- G01N33/537—Immunoassay; Biospecific binding assay; Materials therefor with immune complex formed in liquid phase with separation of immune complex from unbound antigen or antibody
- G01N33/539—Immunoassay; Biospecific binding assay; Materials therefor with immune complex formed in liquid phase with separation of immune complex from unbound antigen or antibody involving precipitating reagent, e.g. ammonium sulfate
-
- 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
Abstract
A B S T R A C T
A rapid response device for the detection of carbon dioxide in a concentration of more than 2% in a gas mixture comprising an indicator component 9 mounted within an enclosure 1 with a transparent window, said component comprising a carrier having fixedly attached thereto an indicating element formed from an aqueous solution of a colorless base, a hygroscopic, high boiling, transparent, colorless, water-miscible liquid and a pH-sensitive indicator, the enclosure being sealed for storage with sealing means 14.
A rapid response device for the detection of carbon dioxide in a concentration of more than 2% in a gas mixture comprising an indicator component 9 mounted within an enclosure 1 with a transparent window, said component comprising a carrier having fixedly attached thereto an indicating element formed from an aqueous solution of a colorless base, a hygroscopic, high boiling, transparent, colorless, water-miscible liquid and a pH-sensitive indicator, the enclosure being sealed for storage with sealing means 14.
Description
13229~5 Indicator Device This invention relates to an indicator device, more particularly a rapid response device for the detection of carbon dioxide in a gas mixture. The device of the invention is particularly adapted for determining the correct placement of an endotracheal catheter in the trachea of a patient, particularly during apnea.
Devices for the detection of carbon dioxide which rely in part upon the change in color of certain chemical compounds according to the pH of their environment are known in the art. Such chemical indicators change color in solution when the pH of the solution changes.
Numerous examples of chemical indicators which are pH-sensitive, and thereby useful in carbon dioxide indicator systems, have been disclosed in the prior art. Such examples are methyl red, bromcresol green, thymol blue, phenol red, brilliant yellow, meta-cresol purple, cresol red, neutral red, m-nitrophenol and m-dinitrobenzoylene urea.
Although various devices and compositions disclosed in the prior art provide means for detecting or indicating the presence of carbon dioxide under certain circumstances;
the prior art has not directly addressed the problem of determining accurately and rapidly the correct positioning of an endotrarheal catheter in the trachea of an apneic patient.
Introduction of a catheter in the trachea of a human may be re~uired for a number of reasons. For example, in a hospital, an endotracheal catheter, also known as an intratracheal catheter, may be used for general anesthesia;
13229~5 in the field a doctor or paramedic may use an endotracheal catheter to resuscitate an apnoeic patient. In both of these instances, and others, it is critical that the catheter be properly placed in the trachea and not, for example, in the oesophagus. If the catheter is improperly placed and the error is not discovered within a very short time, of the order 5 to 20 seconds, the patient may suffer irreparable harm or even death.
In view of the criticality of the timing when an endotracheal catheter is improperly placed in an apnoeic patient, there is clearly a need for a simple device which will rapidly and reliably give an indication of improper (or proper) placement.
It is known that the concentration of carbon dioxide in the atmosphere is normally about 0.03~, whereas the concentration of carbon dioxide in the gas exhaled by a human being is normally 4.5 to 5.0%. The normal amount of carbon dioxide in the oesophagus of a human being is negligible. Accordingly, a rapid, accurate determination of the presence (or absence) of carbon dioxide in the gas exhaled by a human being will provide a clear indication as to whether the tube carrying said gas is properly placed in the trachea or improperly placed in the oesophagus and it has now been found that the correct placement of an endotracheal catheter can be determined simply and rapidly by attaching to the distal end of said catheter a device embodying a rapid response carbon dioxide indicator.
A
In a broad aspect, the present invention relates to an apparatus for determining whether respiratory gas is present in a gaseous sample, said apparatus comprising an enclosure for collecting the sample and a detector within the enclosure which is adapted to be viewed, said detector comprising a carrier having fixedly attached thereto an indicating element formed from (i) an aqueous solution and (ii) a chromogenic pH sensitive indicator, wherein the nature and concentration of the colourless compound in (i) is correlated to the nature and concentration of indicator (ii) so that no colour change occurs for at least 15 minutes when the indicating element is exposed to an atmosphere having a concentration of 0.03% carbon dioxide, but a colour change is produced within 20 seconds when said indicating element is exposed to an atmosphere containing at least 2% carbon dioxide.
The carrier of the indicating element may be any solid material having no inherent acid or basic properties and to which said indicating element may be fixedly attached either by impregnation or as a coating. As used herein the term "fixedly attached" means that the indicating element is not only impregnated or coated on to the carrier but also that the final reagent solution, from which the indicating element is - ` 13229~5 formed, is incapable of flowing or migrating from the carrier while the device is in use. If necessary, the indicating element is suitably immobilized, for example, by drying to remove excess moisture.
Since the color change providing the required carbon dioxide determination is essentially a surface phenomenon, it is necessary that the carrier provides an appropriate surface area for the indicating layer. Egually important, the carrier should be made from a material which will not produce dust or fumes as these may expose the patient to potentially dangerous conditions.
Accordingly, a particularly preferred carrier is a thin layer of bibulous material, such as filter paper or fibrous synthetic material, and the indicating component is formed by impregnating said bibulous material with said indicating element and drying to remove excess moisture.
Other materials which may be used as the carrier include plastic beads and inorganic crystals.
The use of the device of the invention to determine the correct placement of an endotracheal catheter in the trachea of a patient comprises the steps of opening the sealing means, attaching the inlet of the device to the distal end of an endotracheal catheter, after having placed the proximal end of said catheter through the patient's mouth, and presumably into the patient's trachea, and inflating the sealing cuff, and then visually examining the indicator within said device, after several artificial positive pressure breaths, to ascertain whether a color change thereof indicates correct placement of said catheter 1322~
within the patient's trachea by detection of the presence or absence of a concentration of at least 2% carbon dioxide in the exhaled breath.
The invention will be more particularly described with reference to a preferred embodiment which provides a convenient and comparatively simple device for obtaining a rapid and substantially fool-proof indication of the proper or improper placement of an endotracheal catheter in the trachea of a patient, particularly an apneic patient.
To achieve the desired objective the device includes an indicator element which responds positively and rapidly to the presence of a certain concentration of carbon dioxide, i.e. the amount of carbon dioxide which is present in the exhaled breath of a human bein~. This concentration is 15 ~ normally of the order of 4.5 - 5.0%, but possibly may be as low at 2%.
However, although an extremely rapid response, of the order to 5 to 20 seconds, is crucial for the successful operation of the device, it is equally important that the indicator should not be so sensitvie that it changes color too quickly when exposed to an atmosphere containing some minimal amount of carbon dioxide, for example, ambient air which normally contains about 0.03% carbon dioxide, which minimal amount is substantially less than that present in exhaled breath.
Accordingly, the indicator used in the device according to the invention should have a pK which is lower by 1.0 - 1.5 pH units than the pH of the final solution within which it is dissolved. This means that the indicator will 13229~5 not change color instantaneously upon exposure to an atmosphere which contains a certain minmum amount of carbon dioxide, for example, ambient air, and the resultant delay will provide the operator with ample time to open the seal and connect the device to an endotracheal catheter after having placed the catheter in the patient's throat and having inflated the sealing cuff on the catheter.
It is to be understood that the exposed indicator may eventually change color upon continued exposure to ambient air, or any atmosphere containing minimal amounts of carbon dioxide, since even a slow rate of diffusion of carbon dioxide into the indicator zone will lead, in time, to a sufficient depletion of base to cause a color change.
The hydroxyl ions or amine residues present in the lS alkaline solution from which the indicating element of the device is formed react chemically with carbon dioxide to produce a carbonate and/or bicarbonate or carbamate moiety, respectively, as represented by the following equations: -(i) C02 + 20H- -~ C03-- + H20 (ii) co3 + C02 + H20 --~ 2HC03-(iii) C2 ~ 2R2NH ~ R2NCOO- + R2NH2+
This reaction depletes the hydroxyl ion or amine at the interface and thus lowers the p~ of the surface of the indicating component. The depletion is opposed by diffusion of new base into the surface, a replenishment process which tends to maintain the pH in the surface equal to the bulk solution in the carrier.
1322~
This is a dynamic process, constantly changing with time and the balance at any given time depends upon the following theoretical scheme:-(l) the concentration of OH- or amine in the bulk of the solution impregnated in or coated on the carrier. This determines the rate of diffusion into the surface of the indicating element which, for this purpose, may be considered as a "reaction zone";
Devices for the detection of carbon dioxide which rely in part upon the change in color of certain chemical compounds according to the pH of their environment are known in the art. Such chemical indicators change color in solution when the pH of the solution changes.
Numerous examples of chemical indicators which are pH-sensitive, and thereby useful in carbon dioxide indicator systems, have been disclosed in the prior art. Such examples are methyl red, bromcresol green, thymol blue, phenol red, brilliant yellow, meta-cresol purple, cresol red, neutral red, m-nitrophenol and m-dinitrobenzoylene urea.
Although various devices and compositions disclosed in the prior art provide means for detecting or indicating the presence of carbon dioxide under certain circumstances;
the prior art has not directly addressed the problem of determining accurately and rapidly the correct positioning of an endotrarheal catheter in the trachea of an apneic patient.
Introduction of a catheter in the trachea of a human may be re~uired for a number of reasons. For example, in a hospital, an endotracheal catheter, also known as an intratracheal catheter, may be used for general anesthesia;
13229~5 in the field a doctor or paramedic may use an endotracheal catheter to resuscitate an apnoeic patient. In both of these instances, and others, it is critical that the catheter be properly placed in the trachea and not, for example, in the oesophagus. If the catheter is improperly placed and the error is not discovered within a very short time, of the order 5 to 20 seconds, the patient may suffer irreparable harm or even death.
In view of the criticality of the timing when an endotracheal catheter is improperly placed in an apnoeic patient, there is clearly a need for a simple device which will rapidly and reliably give an indication of improper (or proper) placement.
It is known that the concentration of carbon dioxide in the atmosphere is normally about 0.03~, whereas the concentration of carbon dioxide in the gas exhaled by a human being is normally 4.5 to 5.0%. The normal amount of carbon dioxide in the oesophagus of a human being is negligible. Accordingly, a rapid, accurate determination of the presence (or absence) of carbon dioxide in the gas exhaled by a human being will provide a clear indication as to whether the tube carrying said gas is properly placed in the trachea or improperly placed in the oesophagus and it has now been found that the correct placement of an endotracheal catheter can be determined simply and rapidly by attaching to the distal end of said catheter a device embodying a rapid response carbon dioxide indicator.
A
In a broad aspect, the present invention relates to an apparatus for determining whether respiratory gas is present in a gaseous sample, said apparatus comprising an enclosure for collecting the sample and a detector within the enclosure which is adapted to be viewed, said detector comprising a carrier having fixedly attached thereto an indicating element formed from (i) an aqueous solution and (ii) a chromogenic pH sensitive indicator, wherein the nature and concentration of the colourless compound in (i) is correlated to the nature and concentration of indicator (ii) so that no colour change occurs for at least 15 minutes when the indicating element is exposed to an atmosphere having a concentration of 0.03% carbon dioxide, but a colour change is produced within 20 seconds when said indicating element is exposed to an atmosphere containing at least 2% carbon dioxide.
The carrier of the indicating element may be any solid material having no inherent acid or basic properties and to which said indicating element may be fixedly attached either by impregnation or as a coating. As used herein the term "fixedly attached" means that the indicating element is not only impregnated or coated on to the carrier but also that the final reagent solution, from which the indicating element is - ` 13229~5 formed, is incapable of flowing or migrating from the carrier while the device is in use. If necessary, the indicating element is suitably immobilized, for example, by drying to remove excess moisture.
Since the color change providing the required carbon dioxide determination is essentially a surface phenomenon, it is necessary that the carrier provides an appropriate surface area for the indicating layer. Egually important, the carrier should be made from a material which will not produce dust or fumes as these may expose the patient to potentially dangerous conditions.
Accordingly, a particularly preferred carrier is a thin layer of bibulous material, such as filter paper or fibrous synthetic material, and the indicating component is formed by impregnating said bibulous material with said indicating element and drying to remove excess moisture.
Other materials which may be used as the carrier include plastic beads and inorganic crystals.
The use of the device of the invention to determine the correct placement of an endotracheal catheter in the trachea of a patient comprises the steps of opening the sealing means, attaching the inlet of the device to the distal end of an endotracheal catheter, after having placed the proximal end of said catheter through the patient's mouth, and presumably into the patient's trachea, and inflating the sealing cuff, and then visually examining the indicator within said device, after several artificial positive pressure breaths, to ascertain whether a color change thereof indicates correct placement of said catheter 1322~
within the patient's trachea by detection of the presence or absence of a concentration of at least 2% carbon dioxide in the exhaled breath.
The invention will be more particularly described with reference to a preferred embodiment which provides a convenient and comparatively simple device for obtaining a rapid and substantially fool-proof indication of the proper or improper placement of an endotracheal catheter in the trachea of a patient, particularly an apneic patient.
To achieve the desired objective the device includes an indicator element which responds positively and rapidly to the presence of a certain concentration of carbon dioxide, i.e. the amount of carbon dioxide which is present in the exhaled breath of a human bein~. This concentration is 15 ~ normally of the order of 4.5 - 5.0%, but possibly may be as low at 2%.
However, although an extremely rapid response, of the order to 5 to 20 seconds, is crucial for the successful operation of the device, it is equally important that the indicator should not be so sensitvie that it changes color too quickly when exposed to an atmosphere containing some minimal amount of carbon dioxide, for example, ambient air which normally contains about 0.03% carbon dioxide, which minimal amount is substantially less than that present in exhaled breath.
Accordingly, the indicator used in the device according to the invention should have a pK which is lower by 1.0 - 1.5 pH units than the pH of the final solution within which it is dissolved. This means that the indicator will 13229~5 not change color instantaneously upon exposure to an atmosphere which contains a certain minmum amount of carbon dioxide, for example, ambient air, and the resultant delay will provide the operator with ample time to open the seal and connect the device to an endotracheal catheter after having placed the catheter in the patient's throat and having inflated the sealing cuff on the catheter.
It is to be understood that the exposed indicator may eventually change color upon continued exposure to ambient air, or any atmosphere containing minimal amounts of carbon dioxide, since even a slow rate of diffusion of carbon dioxide into the indicator zone will lead, in time, to a sufficient depletion of base to cause a color change.
The hydroxyl ions or amine residues present in the lS alkaline solution from which the indicating element of the device is formed react chemically with carbon dioxide to produce a carbonate and/or bicarbonate or carbamate moiety, respectively, as represented by the following equations: -(i) C02 + 20H- -~ C03-- + H20 (ii) co3 + C02 + H20 --~ 2HC03-(iii) C2 ~ 2R2NH ~ R2NCOO- + R2NH2+
This reaction depletes the hydroxyl ion or amine at the interface and thus lowers the p~ of the surface of the indicating component. The depletion is opposed by diffusion of new base into the surface, a replenishment process which tends to maintain the pH in the surface equal to the bulk solution in the carrier.
1322~
This is a dynamic process, constantly changing with time and the balance at any given time depends upon the following theoretical scheme:-(l) the concentration of OH- or amine in the bulk of the solution impregnated in or coated on the carrier. This determines the rate of diffusion into the surface of the indicating element which, for this purpose, may be considered as a "reaction zone";
(2) the rate of the chemical reaction, determined by the nature of each specific reacting species.
This rate R may be expressed by the eguation R = KA [CO2][A]
where: [ ] represents the concentration of the i species in mole/liter.
KA is a constant, specific for the reactant species A;
This rate R may be expressed by the eguation R = KA [CO2][A]
where: [ ] represents the concentration of the i species in mole/liter.
KA is a constant, specific for the reactant species A;
(3) The contact time between the surface of the indicating component and the gas to which it is exposed;
(4) the composition of the specific bibulous carrier which will determine the diffusivity constant for A in the carrier and therefore the rate of diffusion of A into the reaction zone; and ~5) the concentration of carbon dioxide in the gas. This determines the rate of diffusion of carbon dioxide into said reaction zone.
Items (l), ~2), ~3) and ~4) ç~ill be predetermined by the manner in which the device is constructed and the manner in which it is used in practice. Thus, in the medical application discussed ~3229~5 above, the contact time is predetermined to correspond with the time the indicator will change color rapidly when subjected to artificial positive pressure exhaled breath, e.g. 5 to 20 seconds. Only item (5), the concentration of carbon dioxide, S is the variable parameter in the scheme.
For the particular device of the invention, items (1) and (2) are carefully selected such that the pH in the reaction zone decreases sufficiently to cause a color change in the indicator only if the concentration of carbon dioxide is greater than 2.0%
for an exposure time of 5 to 20 seconds. For the proposed embodiment the concentration of OH- necessary for these kinetic performance characteristics will produce a pH of 9.6 ~ 0.2 in the final indicator element solution which is impregnated into Whatman No. 1 filter paper.
As stated above, if the contact time is substantially prolonged, a color change may occur eventually upon exposure to air, i.e. when the carbon dioxide concentration is only 0.03%.
That is why it is desirable that the device be sealed under an atmosphere devoid of carbon dioxide, preferably by being packaged in a gas-impermeable metallic foil, until just before it is reguired for use.
Although a color change may occur eventually upon prolonged contact with ambient air, when the sealed package is opened it is desirable that no color change takes place for at least fifteen minutes. While this could be arranged by increasing item (1) while keeping all other parameters constant, such a change would alter the entire kinetics of the reaction and a color change would not occur within S to 20 seconds at a minimum 2% car~on dioxide level. Thus, the initial pH would ~e 132294~
too high and the device would be out of calibration for its intended use.
Accordingly, to overcome the problem of providing a suitable delayed reaction in ambient air and yet a rapid response when desired, the device of the present invention uses an indicator with a pK value sufficiently lower than the pH of the final solution, so that a color change does not occur upon fifteen minutes of exposure to ambient air.
Under such exposure, the pH in the reaction zone will be decreasing, but too slowly to cause a color change in the indicator in the stated contact time.
Since none of the items (1), (2), (3) or (4) have been altered, the device according to the invention will behave in the desired manner when exposed for S to 20 seconds to a gas mixture containing a minimum of 2% carbon dioxide. Thus the device is still in calibration for its intended use.
It is to be understood that a change in any one of the parameters of the scheme will necessitate a change in the others if the performance characteristics of the device are to remain unchanged.
Thus, it is to be noted that the selection of the indicator will also affect the choice of base to provide the alkaline solution. If the pK of the indicator is low for the reasons stated above~ it is possible, with certain bases, that the pH of the indicating element will not drop low enough to cause a color change, even in the presence of a 5%
concentration of carbon dioxide.
For example, with sodium hydroxide the carbonate reaction product is water soluble and a base itself. This tends to buffer the decrease in pH and the latter may never reach the transition pH for an indicator of low pK.
Consequently, the choice of compound which provides an alkaline solution has to be correlated with the selection of pH-sensitive indicator.
Calcium hydroxide provides a particularly suitable source of hydroxyl ions for use in a device according to the invention. This compound is soluble enough in water to p~ovide an appropriate concentration of hydroxyl ions in item (i) to calibrate the device for medical use, but its carbonate reaction product with carbon dioxide is insoluble and therefore unable to buffer the decrease in pH. This makes possible the use of an indicator with a lower pK, such as metacresol purple, rather than, for example, thymol blue or phenol phthalein. This in turn allows for a longer exposure time in air.
While barium hydroxide has a similar chemical profile to calcium hydroxide, because of its toxicity, it cannot be used in a medical device unless very strict precautions are taken to avoid any possible contact with the patient and user.
Since an object of the present invention is to provide a device which is not only simple to use but also relatively cheap to produce, a device utilizing a potentially toxic material is impracticable. Furthermore, disposal of such material is subject to strict government regulatory guidelines.
Examples of suitable colorless compounds which provide an alkaline solution and which may be used in the device according to the invention~ subject to the selection of accompanying indicator, are calcium hydroxide, sodium carbonate, 13229`1S
lithium hydroxide, sodium hydroxide, potassium hydroxide, magnesium hydroxide, potassium carbonate, sodium barbital, tribasic sodium phosphate, dibasic sodium phosphate, potassium acetate, monoethanolamine, diethanolamine and piperidine.
Calcium hydroxide and sodium carbonate are particulary preferred.
Examples of suitable pH-sensitive indicators for use in the device of the invention are metacresol purple, thymol blue, c~esol red, phenol red, xylenol blue, a 3:l mixture of cresol red and thymol blue, bromthymol blue, neutral red, phenolphthalein, rosolic acid,~-naphtholphthalein and orange I
Metacresol purple is particulary preferred and a particularly preferred combination of carrier, base and indicator is Whatman No. 1 filter paper, calcium hydroxide and metacresol purple.
By using a different carrier, for example Whatman No. 3, all the other parameters must be adjusted to maintain the same kinetic performance characteristics. Whatman No. 3 has a lower diffusivity constant for OH- than Whatman No. l. Therefore, the concentration of OH- must be higher in the final solution producing a higher pH in the indicating component. This in turn, requires the selection of a matchinq pH indicator havinq a correspondingly higher pK, for example thymol blue.
A 3:l mixture of thymol blue and cresol red has a pK
very similar to metacresol purple and also may be used in a device according to the invention. However, this mixture adds complexity and the orange tinted yellow color achieved upon transition is not aesthetically pleasing.
Cresol red along has a pK even lower than metacresol 132'~9~
purple, but the red to yellow transition is less visually dramatic than the purple to yellow of metacresol purple.
The other ingredient of the aqueous solution which forms the indicating element of the invention is a hygroscopic, high-boiling, transparent, colorless, water-miscible liquid.
The purpose of this ingredient is to entrap sufficient water in the indicating element, for example when it is absorbed in a bibulous materlal and then dried in a hot air stream, to enable the exposed surface of the element to act as a reaction zone with the surrounding gas.
An essential criterion of the device is that the indicating element be immobilized in or on the carrier. This requires active drying of the impregnated carrier to achieve minimal moisture reten~ion so as to prevent migration or flow i of material while in use. However, since carbon dioxide will not react with the base without water, the presence of a certain minimum amount of water is necessary for the device to work. The hygroscopic liquid ensures that the required minimum amount of water is present in the indicating element when exposed to humid air or exhaled breath.
Examples of suitable hygroscopic liquids for use in the device of the invention are glycerol, propylene glycol, monothylene glycol, diethylene glycol, polyethylene glycol and various aliphatic alcohols. Because they are non-toxic and have antiseptic properties which inhibit bacterial and fungal growth, glycerol and propylene glycol or mixtures thereof are particularly preferred.
The following Examples illustrate the preparation of the indicating element used in the device according to the inventîon.
1322~
A 0.003 M aqueous solution of calcium hydroxide was prepared by dissolving calcium hydroxide in 5 ml. of freshly boiled, distilled water. The pH of the resulting solution was 11.6 to 11.7.
Metacresol purple sodium salt was added to the solution so that the concentration of the indicator was 0.12%. An equal volume of propylene glycol was added and the solution stirred to obtain a homogeneous mixture. A 10% additional volume of glycerol was added to the mixture. The glycerol improves penetrability and diffusion into the filter paper.
The resulting solution, having a pH of about 9.6, was applied to a double layer of Whatman No. 1 filter paper and the surface of the paper was then dried by passing a stream of heated air over it for several seconds.
The impregnated paper may be cut into strips and immediately used in a device according to the invention, as described hereinafter, or, if stored for future use, should be protected from prolonged exposure to ambient atmosphere by being stored in a sealed container under an atmosphere of nitrogen or over soda-lime ~ranules.
When the impregnated strip is incorporated in a device according to the invention, said device is packaged in a gas impermeable metallic foil. Said package is sealed after the atmosphere therein has been purged from carbon dioxide by nitrogen gas or by air which has been passed over soda-lime granules The impregnated strip made in accordance with this Example stays purple for more than two hours in an atmosphere containing 0.03% carbon dioxide. Upon exposure to an atmosphere 13229~
containing 5% carbon dioxide, the strip turns bright yellow within three to five seconds. In 2% carbon dioxide the yellow color is achieved in 7 to 10 seconds.
(a) A 0.0065 M aqueous solution of sodium carbonate was prepared by dissolving sodium carbonate in 5 ml. of carbon dioxide-free, distilled water. The pH of the resulting solution was approximately 11Ø 0.005% w/v of thymol blue was added to the solution. An egual volume of glycerol was added and the solution stirred to provide a homogeneous mixture having a pH
of about 9.4.
The resultant mixture was absorbed on a strip of Whatman No. 1 filter paper and the impregnated paper was dried in a stream of hot air.
lS When exposed to varying concentrations of carbon dioxide, the impregnated strip responded as follows:-C2 Concentration Contact Time Color of Strip oO blue 0.03% (ambient air) 10 minutes blue-green 0.03% 15 minutes green 2.0% 5 seconds yellow 5.0% 1 second yellow This chemical system is slightly too sensitive, since some color change occurs in ambient air within 15 minutes.
~ b) Example 2(a) above was repeated except that propylene glyc~l was substituted for the glycerol. The performance characteristics of the impregnated strip were 13 2 2 9 ~ ~
substantially similar to those of the strip of (a~ above.
A solution of sodium carbonate, water and glycerol was made as in Example 2(a) but instead of thymol blue, the indicator was metacresol purple (sodium salt). Metacresol purple has a lower pK than thymol blue. The substitution of metacresol purple solves the sensitivity problem in ambient air but produces a very slight greenish tint to the yellow color after 5 seconds exposure to 5% carbon dioxide. This slightly incomplete transition is the result of buffering by the bicarbonate reaction product.
An interesting property of this system is its extremely rapid return to the original purple color when returned to ambient air. Accordingly, this pH 9.4, sodium carbonate, 15 , glycerol, metacresol purple indicator system is a useful alternative to the preferred calcium hydroxide system illustrated in Example 1.
The response characteristics of a strip of Whatman No. 1 filter paper impre~nated with the solution of this Example are as follows:-C2 Concentration Contact Time Color of Strip O oo bright purple 0.3%2 hours bright purple 2.0%10 seconds greenish yellow 5.0%5 seconds greenish yellow ComParati~e ~xamPle 4 This Example is included to illustrate the importance 132294~
of balancing the parameters of the scheme used in theinvention.
By using a similar system to that illustrated in Example 2 but increasing the concentration of sodium carbonate to produce a O.lM aqueous solution having a pH of 11.6 before addition of the hygroscopic liquid, the system behaves as follows:- -C2 ConcentrationContact Time Color of Strip lo 0.03%3 hours blue 0.3%10 minutes blue 5.0~20 seconds blue 100%1 second yellow Since the strip did not change color in less than 20 l~ seconds in the presence of S.0% carbon dioxide, it lacks the rapid response required and therefore is not suitable for a device according to the invention.
In contrast, a thymol blue system using a 0.00016 aqueous solution of sodium carbonate having a pH of approximately 10.0 ~efore addition of the hygroscopic liquid also is not suitable for a device according to the invention because, in this case, the contact time for a color change in thc presence of 0 03% or 0.3% carbon dioxide is too shor~, accentuating the problem discussed in Example 2.
2s EXAMPLE S
A 0.1 ~ aqueous solution of sodium hydroxide was prepared by dissolving sodium hydroxide in 5 ml. of carbon dioxide-free distilled water. 0.OOS~ w/v thymol blue was added followed by an equal volume of propylene glycol. The 1h 1322~
resultant solution was absorbed on Whatman No. 1 filter paper.
The impregnated paper strip was exposed to varying concentrations of carbon dioxide and performed as follows:
C2 Concentration Contact Time Color of Strip 0.03% 45 minutes blue 0.3% 50 seconds blue ~ S.0% 1 second green Lithium hydroxide was substituted for sodium hydroxide with similar results.
An a~ueous solution containing 0.67~ monoethanolamine was prepared by dissolving the monoethanolamine in 5 ml. of 15' carbon dioxide-free, distilled water. 0.005% w/v metacresol purple was added to the solution followed by an equal volume of propylene glycol.
The resultant mixture was absorbed on filter paper in a similar manner to that illustrated in previous Examples.
Exposure to various concentrations of carbon dioxide gave the following results:-C2 Concentration Contact Time Color of Strip 0% oo deep purple 0.03% 0.5 second light purple 0.03% 1 hour light purple 0.3% 3 minutes light purple 2.0% 8 seconds greenish yellow ~7 1322~
5.0% rJ 1 second yellow Exàmple 6 was r~peated using a 2.5% solution ofmonoethanolamine and thym~l blue as indicator. The following results were obtained:-C2 Concentration Contact Time Color of Strip _ % CO blue 0.03% 1 second blue-green 0.03% 3 hours blue-green 2.0% 8 seconds green 5.0% 2 seconds yellow-green Within one second of exposure to ambient air the surface pH drops from 12.4 to approximately 9.2 ~blue-qreen lS color) ~ut does not change thereafter to any measureable degree from this steady state value. However, exposure to 5%
carbon dioxide rapidly causes a kinetic transition (yellow color) to occur, i.e. within one to two seconds.
The preferred embodiment of the invention is a device for determining the placPment of an endotracheal catheter in a patient and, conse~uently, the configuration of th~ devic~, particularly the enclosure, is such that it is adapted to be connected to a standard endotracheal catheter. The invention will now be particularly described with reference to such pref~xred embodiment as illustrated in the accompanying drawings in which:-Fisure 1 ls an exploded view of thc device showing therelative position of the component parts;
1322~
Figure 2 is a side cross-section of the device fully assembled;
Figure 3 is an end elevation of the inlet end of the device;
Figure 4 is a plan of one of the spool supports;
Figure 4a and 4b illustrate alternative configurations for the spool supports; and Figure 5 is a side elevation of the support of Figure 4.
The preferred embodiment illustrated in Figures l and 2 of the drawings comprises a cylindrical housing l having at its proximal end a cone-shaped coupling 2 terminating in a cylindrical connector 3 and at its distal end a cone-shaped coupling 4 terminating in a cylindrical connector 5.
In this embodiment the proximal cone-shaped coupling 2 is integral with the cylindrical connector 3 and is made from a transulucent white plastic, for example, polyethylene or polypropylene. The integral coupling/connector unit is separate fxom the housing l (Figure 2) but is secured thereto by a screw thread 6.
Likewise, the distal cone-shaped coupling 4 is - integral w~th the cylindrical connector 5, is made from a similar translucent plastic and is secured to the housing by a screw thread ?
The cylindrical housing l is made from a clear, colorless, transparent plastic, for example, an acrylic polymcr, such as that available under the Trademark PLEXIGLAS, poly~ethyl acrylate, polymethyl methacryla~e, polycarbonate, polystyrene or styrene-acrylonitrile I ~
1322~
copolymer.
When the housing and coupling/connector units are connected to each other they effectively form an enclosure having an inlet formed by proximal connector 3 and an outlet formed by distal connector 5.
The clear transparen~ plastic used for the cylindrical hcusing provides an effective window 8 for viewing the indicator component 9, which comprises a strip of filter ' paper impregnated with an indicator element such as that illustrated in Example 1 herein. Fogging of said window by the humidity in exhaled breath is prevented by coating thc inner surface of the window with a suitable anti-fogging surfactant, such as dioctyl sodium sulfosuccinate.
The indicator strip 9 is securely wrapped around the center of a cylindrical spool which is made from a rigid plastic, such as polyethylene. The spool 10 is mounted at each end on an inwardly facing flange 11 of a support 12.
The supports 12 are substantially circular in shape and have a plurality of apertures 13 which allow su~stantially unrestricted flow of gas through the d~vice when in use.
Said apertures may be a series of circular holes, as illustrated in Figure 4, or may be a different arrangement of holes as illustrated in Figures 4a and 4b.
Th~ spool supports 12 are preferably made from a clear 2s plastic, similar to that used for the cylindrical housing.
Each of the spool supports is mounted in a groovc between each cone-shaped coupling and each end of the cylindrical housing, and is secured in place when each coupling is screwed to the housing, as illustrated in Figure 13229~
2.
The device containing the indicating component mounted on the spool within the transparent cylindrical housing should be assembled under a carbon dioxide-free atmosphere S and then sealed within a gas-impermeable metallic foil 14 until re~ui.red for use.
A device such as that described above having an indicator component as illustrated in Example 1 provides a . rapid response and reliable means for visually detecting the 1~ presence of more than 2~ carbon dioxide in exhaled breath passing through a catheter placed in the trachea of an apneic patient, in accordance with the method described herein.
~1 ~ .
Items (l), ~2), ~3) and ~4) ç~ill be predetermined by the manner in which the device is constructed and the manner in which it is used in practice. Thus, in the medical application discussed ~3229~5 above, the contact time is predetermined to correspond with the time the indicator will change color rapidly when subjected to artificial positive pressure exhaled breath, e.g. 5 to 20 seconds. Only item (5), the concentration of carbon dioxide, S is the variable parameter in the scheme.
For the particular device of the invention, items (1) and (2) are carefully selected such that the pH in the reaction zone decreases sufficiently to cause a color change in the indicator only if the concentration of carbon dioxide is greater than 2.0%
for an exposure time of 5 to 20 seconds. For the proposed embodiment the concentration of OH- necessary for these kinetic performance characteristics will produce a pH of 9.6 ~ 0.2 in the final indicator element solution which is impregnated into Whatman No. 1 filter paper.
As stated above, if the contact time is substantially prolonged, a color change may occur eventually upon exposure to air, i.e. when the carbon dioxide concentration is only 0.03%.
That is why it is desirable that the device be sealed under an atmosphere devoid of carbon dioxide, preferably by being packaged in a gas-impermeable metallic foil, until just before it is reguired for use.
Although a color change may occur eventually upon prolonged contact with ambient air, when the sealed package is opened it is desirable that no color change takes place for at least fifteen minutes. While this could be arranged by increasing item (1) while keeping all other parameters constant, such a change would alter the entire kinetics of the reaction and a color change would not occur within S to 20 seconds at a minimum 2% car~on dioxide level. Thus, the initial pH would ~e 132294~
too high and the device would be out of calibration for its intended use.
Accordingly, to overcome the problem of providing a suitable delayed reaction in ambient air and yet a rapid response when desired, the device of the present invention uses an indicator with a pK value sufficiently lower than the pH of the final solution, so that a color change does not occur upon fifteen minutes of exposure to ambient air.
Under such exposure, the pH in the reaction zone will be decreasing, but too slowly to cause a color change in the indicator in the stated contact time.
Since none of the items (1), (2), (3) or (4) have been altered, the device according to the invention will behave in the desired manner when exposed for S to 20 seconds to a gas mixture containing a minimum of 2% carbon dioxide. Thus the device is still in calibration for its intended use.
It is to be understood that a change in any one of the parameters of the scheme will necessitate a change in the others if the performance characteristics of the device are to remain unchanged.
Thus, it is to be noted that the selection of the indicator will also affect the choice of base to provide the alkaline solution. If the pK of the indicator is low for the reasons stated above~ it is possible, with certain bases, that the pH of the indicating element will not drop low enough to cause a color change, even in the presence of a 5%
concentration of carbon dioxide.
For example, with sodium hydroxide the carbonate reaction product is water soluble and a base itself. This tends to buffer the decrease in pH and the latter may never reach the transition pH for an indicator of low pK.
Consequently, the choice of compound which provides an alkaline solution has to be correlated with the selection of pH-sensitive indicator.
Calcium hydroxide provides a particularly suitable source of hydroxyl ions for use in a device according to the invention. This compound is soluble enough in water to p~ovide an appropriate concentration of hydroxyl ions in item (i) to calibrate the device for medical use, but its carbonate reaction product with carbon dioxide is insoluble and therefore unable to buffer the decrease in pH. This makes possible the use of an indicator with a lower pK, such as metacresol purple, rather than, for example, thymol blue or phenol phthalein. This in turn allows for a longer exposure time in air.
While barium hydroxide has a similar chemical profile to calcium hydroxide, because of its toxicity, it cannot be used in a medical device unless very strict precautions are taken to avoid any possible contact with the patient and user.
Since an object of the present invention is to provide a device which is not only simple to use but also relatively cheap to produce, a device utilizing a potentially toxic material is impracticable. Furthermore, disposal of such material is subject to strict government regulatory guidelines.
Examples of suitable colorless compounds which provide an alkaline solution and which may be used in the device according to the invention~ subject to the selection of accompanying indicator, are calcium hydroxide, sodium carbonate, 13229`1S
lithium hydroxide, sodium hydroxide, potassium hydroxide, magnesium hydroxide, potassium carbonate, sodium barbital, tribasic sodium phosphate, dibasic sodium phosphate, potassium acetate, monoethanolamine, diethanolamine and piperidine.
Calcium hydroxide and sodium carbonate are particulary preferred.
Examples of suitable pH-sensitive indicators for use in the device of the invention are metacresol purple, thymol blue, c~esol red, phenol red, xylenol blue, a 3:l mixture of cresol red and thymol blue, bromthymol blue, neutral red, phenolphthalein, rosolic acid,~-naphtholphthalein and orange I
Metacresol purple is particulary preferred and a particularly preferred combination of carrier, base and indicator is Whatman No. 1 filter paper, calcium hydroxide and metacresol purple.
By using a different carrier, for example Whatman No. 3, all the other parameters must be adjusted to maintain the same kinetic performance characteristics. Whatman No. 3 has a lower diffusivity constant for OH- than Whatman No. l. Therefore, the concentration of OH- must be higher in the final solution producing a higher pH in the indicating component. This in turn, requires the selection of a matchinq pH indicator havinq a correspondingly higher pK, for example thymol blue.
A 3:l mixture of thymol blue and cresol red has a pK
very similar to metacresol purple and also may be used in a device according to the invention. However, this mixture adds complexity and the orange tinted yellow color achieved upon transition is not aesthetically pleasing.
Cresol red along has a pK even lower than metacresol 132'~9~
purple, but the red to yellow transition is less visually dramatic than the purple to yellow of metacresol purple.
The other ingredient of the aqueous solution which forms the indicating element of the invention is a hygroscopic, high-boiling, transparent, colorless, water-miscible liquid.
The purpose of this ingredient is to entrap sufficient water in the indicating element, for example when it is absorbed in a bibulous materlal and then dried in a hot air stream, to enable the exposed surface of the element to act as a reaction zone with the surrounding gas.
An essential criterion of the device is that the indicating element be immobilized in or on the carrier. This requires active drying of the impregnated carrier to achieve minimal moisture reten~ion so as to prevent migration or flow i of material while in use. However, since carbon dioxide will not react with the base without water, the presence of a certain minimum amount of water is necessary for the device to work. The hygroscopic liquid ensures that the required minimum amount of water is present in the indicating element when exposed to humid air or exhaled breath.
Examples of suitable hygroscopic liquids for use in the device of the invention are glycerol, propylene glycol, monothylene glycol, diethylene glycol, polyethylene glycol and various aliphatic alcohols. Because they are non-toxic and have antiseptic properties which inhibit bacterial and fungal growth, glycerol and propylene glycol or mixtures thereof are particularly preferred.
The following Examples illustrate the preparation of the indicating element used in the device according to the inventîon.
1322~
A 0.003 M aqueous solution of calcium hydroxide was prepared by dissolving calcium hydroxide in 5 ml. of freshly boiled, distilled water. The pH of the resulting solution was 11.6 to 11.7.
Metacresol purple sodium salt was added to the solution so that the concentration of the indicator was 0.12%. An equal volume of propylene glycol was added and the solution stirred to obtain a homogeneous mixture. A 10% additional volume of glycerol was added to the mixture. The glycerol improves penetrability and diffusion into the filter paper.
The resulting solution, having a pH of about 9.6, was applied to a double layer of Whatman No. 1 filter paper and the surface of the paper was then dried by passing a stream of heated air over it for several seconds.
The impregnated paper may be cut into strips and immediately used in a device according to the invention, as described hereinafter, or, if stored for future use, should be protected from prolonged exposure to ambient atmosphere by being stored in a sealed container under an atmosphere of nitrogen or over soda-lime ~ranules.
When the impregnated strip is incorporated in a device according to the invention, said device is packaged in a gas impermeable metallic foil. Said package is sealed after the atmosphere therein has been purged from carbon dioxide by nitrogen gas or by air which has been passed over soda-lime granules The impregnated strip made in accordance with this Example stays purple for more than two hours in an atmosphere containing 0.03% carbon dioxide. Upon exposure to an atmosphere 13229~
containing 5% carbon dioxide, the strip turns bright yellow within three to five seconds. In 2% carbon dioxide the yellow color is achieved in 7 to 10 seconds.
(a) A 0.0065 M aqueous solution of sodium carbonate was prepared by dissolving sodium carbonate in 5 ml. of carbon dioxide-free, distilled water. The pH of the resulting solution was approximately 11Ø 0.005% w/v of thymol blue was added to the solution. An egual volume of glycerol was added and the solution stirred to provide a homogeneous mixture having a pH
of about 9.4.
The resultant mixture was absorbed on a strip of Whatman No. 1 filter paper and the impregnated paper was dried in a stream of hot air.
lS When exposed to varying concentrations of carbon dioxide, the impregnated strip responded as follows:-C2 Concentration Contact Time Color of Strip oO blue 0.03% (ambient air) 10 minutes blue-green 0.03% 15 minutes green 2.0% 5 seconds yellow 5.0% 1 second yellow This chemical system is slightly too sensitive, since some color change occurs in ambient air within 15 minutes.
~ b) Example 2(a) above was repeated except that propylene glyc~l was substituted for the glycerol. The performance characteristics of the impregnated strip were 13 2 2 9 ~ ~
substantially similar to those of the strip of (a~ above.
A solution of sodium carbonate, water and glycerol was made as in Example 2(a) but instead of thymol blue, the indicator was metacresol purple (sodium salt). Metacresol purple has a lower pK than thymol blue. The substitution of metacresol purple solves the sensitivity problem in ambient air but produces a very slight greenish tint to the yellow color after 5 seconds exposure to 5% carbon dioxide. This slightly incomplete transition is the result of buffering by the bicarbonate reaction product.
An interesting property of this system is its extremely rapid return to the original purple color when returned to ambient air. Accordingly, this pH 9.4, sodium carbonate, 15 , glycerol, metacresol purple indicator system is a useful alternative to the preferred calcium hydroxide system illustrated in Example 1.
The response characteristics of a strip of Whatman No. 1 filter paper impre~nated with the solution of this Example are as follows:-C2 Concentration Contact Time Color of Strip O oo bright purple 0.3%2 hours bright purple 2.0%10 seconds greenish yellow 5.0%5 seconds greenish yellow ComParati~e ~xamPle 4 This Example is included to illustrate the importance 132294~
of balancing the parameters of the scheme used in theinvention.
By using a similar system to that illustrated in Example 2 but increasing the concentration of sodium carbonate to produce a O.lM aqueous solution having a pH of 11.6 before addition of the hygroscopic liquid, the system behaves as follows:- -C2 ConcentrationContact Time Color of Strip lo 0.03%3 hours blue 0.3%10 minutes blue 5.0~20 seconds blue 100%1 second yellow Since the strip did not change color in less than 20 l~ seconds in the presence of S.0% carbon dioxide, it lacks the rapid response required and therefore is not suitable for a device according to the invention.
In contrast, a thymol blue system using a 0.00016 aqueous solution of sodium carbonate having a pH of approximately 10.0 ~efore addition of the hygroscopic liquid also is not suitable for a device according to the invention because, in this case, the contact time for a color change in thc presence of 0 03% or 0.3% carbon dioxide is too shor~, accentuating the problem discussed in Example 2.
2s EXAMPLE S
A 0.1 ~ aqueous solution of sodium hydroxide was prepared by dissolving sodium hydroxide in 5 ml. of carbon dioxide-free distilled water. 0.OOS~ w/v thymol blue was added followed by an equal volume of propylene glycol. The 1h 1322~
resultant solution was absorbed on Whatman No. 1 filter paper.
The impregnated paper strip was exposed to varying concentrations of carbon dioxide and performed as follows:
C2 Concentration Contact Time Color of Strip 0.03% 45 minutes blue 0.3% 50 seconds blue ~ S.0% 1 second green Lithium hydroxide was substituted for sodium hydroxide with similar results.
An a~ueous solution containing 0.67~ monoethanolamine was prepared by dissolving the monoethanolamine in 5 ml. of 15' carbon dioxide-free, distilled water. 0.005% w/v metacresol purple was added to the solution followed by an equal volume of propylene glycol.
The resultant mixture was absorbed on filter paper in a similar manner to that illustrated in previous Examples.
Exposure to various concentrations of carbon dioxide gave the following results:-C2 Concentration Contact Time Color of Strip 0% oo deep purple 0.03% 0.5 second light purple 0.03% 1 hour light purple 0.3% 3 minutes light purple 2.0% 8 seconds greenish yellow ~7 1322~
5.0% rJ 1 second yellow Exàmple 6 was r~peated using a 2.5% solution ofmonoethanolamine and thym~l blue as indicator. The following results were obtained:-C2 Concentration Contact Time Color of Strip _ % CO blue 0.03% 1 second blue-green 0.03% 3 hours blue-green 2.0% 8 seconds green 5.0% 2 seconds yellow-green Within one second of exposure to ambient air the surface pH drops from 12.4 to approximately 9.2 ~blue-qreen lS color) ~ut does not change thereafter to any measureable degree from this steady state value. However, exposure to 5%
carbon dioxide rapidly causes a kinetic transition (yellow color) to occur, i.e. within one to two seconds.
The preferred embodiment of the invention is a device for determining the placPment of an endotracheal catheter in a patient and, conse~uently, the configuration of th~ devic~, particularly the enclosure, is such that it is adapted to be connected to a standard endotracheal catheter. The invention will now be particularly described with reference to such pref~xred embodiment as illustrated in the accompanying drawings in which:-Fisure 1 ls an exploded view of thc device showing therelative position of the component parts;
1322~
Figure 2 is a side cross-section of the device fully assembled;
Figure 3 is an end elevation of the inlet end of the device;
Figure 4 is a plan of one of the spool supports;
Figure 4a and 4b illustrate alternative configurations for the spool supports; and Figure 5 is a side elevation of the support of Figure 4.
The preferred embodiment illustrated in Figures l and 2 of the drawings comprises a cylindrical housing l having at its proximal end a cone-shaped coupling 2 terminating in a cylindrical connector 3 and at its distal end a cone-shaped coupling 4 terminating in a cylindrical connector 5.
In this embodiment the proximal cone-shaped coupling 2 is integral with the cylindrical connector 3 and is made from a transulucent white plastic, for example, polyethylene or polypropylene. The integral coupling/connector unit is separate fxom the housing l (Figure 2) but is secured thereto by a screw thread 6.
Likewise, the distal cone-shaped coupling 4 is - integral w~th the cylindrical connector 5, is made from a similar translucent plastic and is secured to the housing by a screw thread ?
The cylindrical housing l is made from a clear, colorless, transparent plastic, for example, an acrylic polymcr, such as that available under the Trademark PLEXIGLAS, poly~ethyl acrylate, polymethyl methacryla~e, polycarbonate, polystyrene or styrene-acrylonitrile I ~
1322~
copolymer.
When the housing and coupling/connector units are connected to each other they effectively form an enclosure having an inlet formed by proximal connector 3 and an outlet formed by distal connector 5.
The clear transparen~ plastic used for the cylindrical hcusing provides an effective window 8 for viewing the indicator component 9, which comprises a strip of filter ' paper impregnated with an indicator element such as that illustrated in Example 1 herein. Fogging of said window by the humidity in exhaled breath is prevented by coating thc inner surface of the window with a suitable anti-fogging surfactant, such as dioctyl sodium sulfosuccinate.
The indicator strip 9 is securely wrapped around the center of a cylindrical spool which is made from a rigid plastic, such as polyethylene. The spool 10 is mounted at each end on an inwardly facing flange 11 of a support 12.
The supports 12 are substantially circular in shape and have a plurality of apertures 13 which allow su~stantially unrestricted flow of gas through the d~vice when in use.
Said apertures may be a series of circular holes, as illustrated in Figure 4, or may be a different arrangement of holes as illustrated in Figures 4a and 4b.
Th~ spool supports 12 are preferably made from a clear 2s plastic, similar to that used for the cylindrical housing.
Each of the spool supports is mounted in a groovc between each cone-shaped coupling and each end of the cylindrical housing, and is secured in place when each coupling is screwed to the housing, as illustrated in Figure 13229~
2.
The device containing the indicating component mounted on the spool within the transparent cylindrical housing should be assembled under a carbon dioxide-free atmosphere S and then sealed within a gas-impermeable metallic foil 14 until re~ui.red for use.
A device such as that described above having an indicator component as illustrated in Example 1 provides a . rapid response and reliable means for visually detecting the 1~ presence of more than 2~ carbon dioxide in exhaled breath passing through a catheter placed in the trachea of an apneic patient, in accordance with the method described herein.
~1 ~ .
Claims (15)
1. An apparatus for determining whether respiratory gas is present in a gaseous sample, said apparatus comprising an enclosure for collecting the sample and a detector within the enclosure which is adapted to be viewed, said detector comprising a carrier having fixedly attached thereto an indicating element formed from (i) an aqueous solution and (ii) a chromogenic pH sensitive indicator, wherein the nature and concentration of the colourless compound in (i) is correlated to the nature and concentration of indicator (ii) so that no colour change occurs for at least 15 minutes when the indicating element is exposed to an atmosphere having a concentration of 0.03% carbon dioxide, but a colour change is produced within 20 seconds when said indicating element is exposed to an atmosphere containing at least 2% carbon dioxide.
2. Apparatus according to claim 1 wherein said carrier comprises an inert bibulous material.
3. Apparatus according to claim 2 wherein said carrier comprises an inert fibrous material.
4. Apparatus according to claim 3 wherein the carrier is filter paper.
5. Apparatus according to claim 1 wherein said chromogenic substance has a pK which is lower by about 1.0-1.5 pH units than the pH of said aqueous solution (i).
6. Apparatus according to claim 1 wherein said colourless compound in (i) is calcium hydroxide, sodium carbonate, lithium hydroxide, sodium hydroxide, potassium hydroxide, magnesium hydroxide, potassium carbonate, sodium barbital, tribasic sodium phosphate, dibasic sodium phosphate, potassium acetate, monoethanolamine, diethanolamine or piperidine.
7. Apparatus according to claim 1 wherein said pH-sensitive indicator is metacresol purple, thymol blue, cresol red, phenol red, xylenol blue, a 3:1 mixture of cresol red and thymol blue, bromthymol blue, neutral red, phenolphthalein, rosolic acid, -naphtholphthalein or orange I.
8. Apparatus according to claim 1 wherein the indicating element includes a hygroscopic liquid.
9. A device according to claim 8, in which said hygroscopic liquid is water-miscible and is glycerol, propylene glycerol or a mixture thereof.
10. Apparatus according to claim 1 which is sealed by enveloping the enclosure in a gas-impermeable metallic foil.
11. Apparatus according to claim 1 wherein said detector comprises a sheet of filter paper impregnated with an indicating element formed from (i) an aqueous solution of sodium carbonate or calcium hydroxide, (ii) glycerol or a mixture of glycerol and propylene glycol; and (iii) metacresol purple sodium salt.
12. Apparatus according to claim 1 wherein said enclosure is a cylindrical body 1 of transparent plastic, the inlet 3 and outlet 5 thereof having narrower diameters than the cylindrical body of the enclosure and the shape of the inlet 3 is such that of a cylindrical connector which will fit on the end of a standard endotracheal catheter.
13. Apparatus according to Claim 12 wherein the inner surface of said cylindrical body is coated in an antifogging surfactant.
14. Apparatus according to claim 1 in which the colour change is produced within 5 seconds when said indicating element is exposed to an atmosphere containing at least 2% carbon dioxide.
15. Apparatus according to claim 2, in which said bibulous material is filter paper or fibrous synthetic material.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US896,360 | 1986-08-13 | ||
| US06/896,360 US4728499A (en) | 1986-08-13 | 1986-08-13 | Carbon dioxide indicator device |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1322945C true CA1322945C (en) | 1993-10-12 |
Family
ID=25406072
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000544371A Expired - Fee Related CA1322945C (en) | 1986-08-13 | 1987-08-12 | Indicator device |
Country Status (22)
| Country | Link |
|---|---|
| US (1) | US4728499A (en) |
| EP (1) | EP0257916B1 (en) |
| JP (1) | JPS6375541A (en) |
| KR (1) | KR880003188A (en) |
| CN (1) | CN1015665B (en) |
| AT (1) | ATE117086T1 (en) |
| AU (2) | AU7681487A (en) |
| BR (1) | BR8704190A (en) |
| CA (1) | CA1322945C (en) |
| CS (1) | CS593187A2 (en) |
| DD (1) | DD261652A5 (en) |
| DE (1) | DE3750974T2 (en) |
| DK (1) | DK421087A (en) |
| ES (1) | ES2066761T3 (en) |
| FI (1) | FI873469A (en) |
| IE (1) | IE66319B1 (en) |
| IL (1) | IL83502A (en) |
| NO (1) | NO873390L (en) |
| NZ (1) | NZ221430A (en) |
| WO (1) | WO1988001384A1 (en) |
| YU (1) | YU151087A (en) |
| ZA (1) | ZA875948B (en) |
Families Citing this family (144)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0647010B2 (en) * | 1986-03-26 | 1994-06-22 | ボ−ド・オブ・リ−ジエンツ、ザ・ユニバ−シテイ−・オブ・テキサス・システム | Endotracheal device |
| US4994117A (en) * | 1986-08-13 | 1991-02-19 | Fehder Carl G | Quantitative carbon dioxide detector |
| US4790327A (en) * | 1987-07-27 | 1988-12-13 | George Despotis | Endotracheal intubation device |
| WO1989007957A1 (en) * | 1988-02-26 | 1989-09-08 | Brigham And Women's Hospital | Co2 indicator for placement of tracheal tubes |
| AU3347189A (en) * | 1988-02-26 | 1989-09-22 | Meridian Medical Corporation | Carbon dioxide detection |
| US5197464A (en) * | 1988-02-26 | 1993-03-30 | Babb Albert L | Carbon dioxide detection |
| US5005572A (en) * | 1988-02-26 | 1991-04-09 | Brigham & Women's Hospital | CO2 indicator and the use thereof to evaluate placement of tracheal tubes |
| US4945918A (en) * | 1988-05-04 | 1990-08-07 | Abernathy Charles M | Method and apparatus for monitoring a patient's circulatory status |
| US5124129A (en) * | 1988-07-29 | 1992-06-23 | Mallinckrodt Medical, Inc. | Carbon dioxide indicator |
| WO1990001695A1 (en) * | 1988-07-29 | 1990-02-22 | Mallinckrodt, Inc. | Carbon dioxide indicator |
| US4928687A (en) * | 1988-10-11 | 1990-05-29 | The University Of Florida | CO2 diagnostic monitor |
| US5156159A (en) * | 1988-10-11 | 1992-10-20 | University Of Florida | CO2 diagnostic monitor with rupturable container |
| GB8922049D0 (en) * | 1989-09-29 | 1989-11-15 | Medical Instrumentation Consul | Carbon dioxide monitor |
| US5193544A (en) * | 1991-01-31 | 1993-03-16 | Board Of Trustees Of The Leland Stanford Junior University | System for conveying gases from and to a subject's trachea and for measuring physiological parameters in vivo |
| US5279289A (en) * | 1991-10-15 | 1994-01-18 | Kirk Gilbert M | Resuscitator regulator with carbon dioxide detector |
| US6123075A (en) | 1991-10-15 | 2000-09-26 | Mallinckrodt, Inc. | Resuscitator regulator with carbon dioxide detector |
| GB9200431D0 (en) * | 1992-01-09 | 1992-02-26 | Abbey Biosystems Ltd | Carbon dioxide detector |
| DK13492D0 (en) * | 1992-02-04 | 1992-02-04 | Bo Holte | METHOD AND APPARATUS FOR INDICATING THE EXISTENCE OF CO2 |
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- 1987-08-11 CS CS875931A patent/CS593187A2/en unknown
- 1987-08-11 IL IL83502A patent/IL83502A/en not_active IP Right Cessation
- 1987-08-11 WO PCT/GB1987/000564 patent/WO1988001384A1/en unknown
- 1987-08-12 NZ NZ221430A patent/NZ221430A/en unknown
- 1987-08-12 ZA ZA875948A patent/ZA875948B/en unknown
- 1987-08-12 IE IE215587A patent/IE66319B1/en not_active IP Right Cessation
- 1987-08-12 BR BR8704190A patent/BR8704190A/en unknown
- 1987-08-12 EP EP87307121A patent/EP0257916B1/en not_active Expired - Lifetime
- 1987-08-12 NO NO873390A patent/NO873390L/en unknown
- 1987-08-12 DE DE3750974T patent/DE3750974T2/en not_active Expired - Fee Related
- 1987-08-12 CA CA000544371A patent/CA1322945C/en not_active Expired - Fee Related
- 1987-08-12 AT AT87307121T patent/ATE117086T1/en not_active IP Right Cessation
- 1987-08-12 DD DD87305973A patent/DD261652A5/en not_active IP Right Cessation
- 1987-08-12 JP JP62202609A patent/JPS6375541A/en active Pending
- 1987-08-12 AU AU76814/87A patent/AU7681487A/en not_active Abandoned
- 1987-08-12 ES ES87307121T patent/ES2066761T3/en not_active Expired - Lifetime
- 1987-08-12 DK DK421087A patent/DK421087A/en not_active Application Discontinuation
- 1987-08-12 CN CN87105619A patent/CN1015665B/en not_active Expired
- 1987-08-13 KR KR1019870008896A patent/KR880003188A/en not_active Application Discontinuation
- 1987-08-13 YU YU01510/87A patent/YU151087A/en unknown
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1989
- 1989-11-13 AU AU44621/89A patent/AU634986B2/en not_active Ceased
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| FI873469A0 (en) | 1987-08-10 |
| NO873390L (en) | 1988-02-15 |
| ZA875948B (en) | 1988-04-27 |
| IE66319B1 (en) | 1995-12-27 |
| EP0257916A1 (en) | 1988-03-02 |
| AU4462189A (en) | 1990-03-08 |
| DE3750974T2 (en) | 1995-05-18 |
| CN1015665B (en) | 1992-02-26 |
| CN87105619A (en) | 1988-02-24 |
| DK421087A (en) | 1988-02-14 |
| US4728499A (en) | 1988-03-01 |
| YU151087A (en) | 1989-12-31 |
| IE872155L (en) | 1988-02-13 |
| AU634986B2 (en) | 1993-03-11 |
| KR880003188A (en) | 1988-05-14 |
| DK421087D0 (en) | 1987-08-12 |
| BR8704190A (en) | 1988-04-12 |
| NZ221430A (en) | 1991-02-26 |
| NO873390D0 (en) | 1987-08-12 |
| IL83502A (en) | 1991-09-16 |
| FI873469A (en) | 1988-02-14 |
| DD261652A5 (en) | 1988-11-02 |
| WO1988001384A1 (en) | 1988-02-25 |
| DE3750974D1 (en) | 1995-02-23 |
| ES2066761T3 (en) | 1995-03-16 |
| IL83502A0 (en) | 1988-01-31 |
| CS593187A2 (en) | 1991-05-14 |
| AU7681487A (en) | 1988-02-18 |
| JPS6375541A (en) | 1988-04-05 |
| ATE117086T1 (en) | 1995-01-15 |
| EP0257916B1 (en) | 1995-01-11 |
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