Chemical apparatus and process disinfecting – deodorizing – preser – Analyzer – structured indicator – or manipulative laboratory... – Calorimeter
Patent
1994-02-10
1995-11-21
Snay, Jeffrey R.
Chemical apparatus and process disinfecting, deodorizing, preser
Analyzer, structured indicator, or manipulative laboratory...
Calorimeter
422 85, 128719, A61B 5097
Patent
active
054684510
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a device for indicating the presence of carbon dioxide, CO.sub.2, in the air exhaled by a patient. More particularly, the invention relates to a device of the kind comprising an indicator element which undergoes a reversible change of colour in response to the exposure thereof to air containing CO.sub.2 in concentrations of the same order of magnitude as the CO.sub.2 concentration of air exhaled by a human being.
DESCRIPTION OF THE RELATED ART
Indicator elements of this kind are known per se, see, for example, U.S. Pat. No. 4,728,499, WO89/07957 and WO91/05252. A major use of such indicator elements is to indicate the proper intubation of a patient's trachea (windpipe). This use relies on the fact that air exhaled by a human being contains CO.sub.2 in much higher concentrations, 4 to 6 percent, than does the air in the oesophagus (gullet), the CO.sub.2 concentration of which is approximately equal to that of the atmospheric air and thus is only a few hundredths of one percent.
Thus, with proper intubation, the air exhaled through the intubation tube, such as a tracheal catheter, will have a relatively high concentration of CO.sub.2 and will, therefore, cause a colour change of an indicator element of the above-mentioned kind which is located in the exhalation path, e.g. at the distal end of the intubation tube. For obvious reasons, the indicator element should be located such that it is readily viewable from the outside, and if its response is sufficiently rapid, it will change colour immediately upon the first exhalation and, consequently, will immediately indicate that the intubation tube does in fact extend into the trachea as desired, and not into the oesophagus.
If the indicator element responds sufficiently rapidly, the colour change will reverse on each inhalation and occur again on each exhalation. Known in the art are indicator elements which respond sufficiently rapidly to be able to follow the changes of the CO.sub.2 concentration with inhalations and exhalations at the normal respiration rate, which is on the order of 10 breaths per minute.
It has been found, however, that the response time increases gradually with the number of exhalations so that the indicator element will be unable to follow the changes after a number of exhalations have taken place. This increase of the response time causes no problem in the above-described use in which it is sufficient to detect that the intubation was successful, because, in principle, a single colour change suffices for that purpose. However, in cases in which it is desired to monitor the breathing in respect of the presence of CO.sub.2 for a longer period, such as for an hour or a few hours, known indicator elements are not suitable. In such cases, therefore, it has been necessary to rely on other types of CO.sub.2 detecting devices, primarily electrical instruments.
The reason why the response time of the known indicator elements increases gradually may be that the balance of the amount of water bound to the indicator element against the desired response time is upset under the influence of the moisture contained in the exhaled air.
An object of the invention is to provide an indicating device of the kind mentioned above which is capable of indicating the presence of CO.sub.2 in a patient's exhaled air over an extended period of time, namely such that a colour change of the CO.sub.2 indicator element is brought about and reversed with each breath of the patient throughout the monitored period.
This object is achieved with the construction of the indicating device which is set forth below.
SUMMARY OF THE INVENTION
The construction of the indicating device according to the invention is based on the concept of providing for the CO.sub.2 to operate in an environment which is of a character such that the amount of water in the indicator element, which amount has been selected or determined in connection with the preparation of the indicator element during its manufacture, remains substantially unchange
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MINCO AB
Snay Jeffrey R.
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