Chemical apparatus and process disinfecting – deodorizing – preser – Analyzer – structured indicator – or manipulative laboratory... – Calorimeter
Patent
1992-05-29
1995-12-05
Redding, David A.
Chemical apparatus and process disinfecting, deodorizing, preser
Analyzer, structured indicator, or manipulative laboratory...
Calorimeter
422 57, 422 58, 422 85, 436133, 436169, 436900, 128719, A61M 1600, H62B 906, G01N 1700, G01N 3122
Patent
active
054726689
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention is concerned with devices which provide a detectable indication that a volume of gas has an increased proportion of carbon dioxide compared to that present in normal ambient air. Such devices have a number of uses, one major use being to provide an indication of whether a tube has been correctly located in the airway (trachea) of a patient. There are many clinical situations where it is necessary to place a tube in the trachea of a patient. This is done in order to supply air or a mixture of oxygen and other gases to the lungs of the patient. The correct placement of the tube in the trachea is very important. Accidents have been reported where the tube has been inadvertently placed in the oesophagus. It has been observed that the air in the trachea contains about 6%carbon dioxide, whereas the oesophagus contains air in which the concentration of carbon dioxide is normal (about 0.03%).
2. Description of the Prior Art
Indicator devices which can detect the presence of an elevated proportion of carbon dioxide compared to that in air, and which can be used to determine whether a patient has been correctly intubated are described in U.S. Pat. No. 4728499, W089/07957 and W090/01695.
In all of these indicator devices, an indicator material is dispersed throughout a body of porous material: because the gas to be tested has to be passed through the body, the rate of flow is slow and therefore the response time is unacceptably long.
We have now devised an indicator device which has a rapid response, because of the manner in which the indicator material is provided.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a carbon dioxide monitor which comprises a substrate having thereon an indicating film comprising an intimate mixture of a transparent film-forming polymer vehicle, a plasticiser therefor, an indicator material which undergoes a colour change on exposure to carbon dioxide, said indicator material being a salt of an indicator anion and a lipophilic organic quaternary cation.
The monitor according to the invention may, in some embodiments, be supplied in a sealed, gastight package, such as a pouch or sachet. Such a sachet may be formed from metallised polymer film, which is opaque in addition to being gas-impermeable.
When the monitor according to the invention is to be used to determine whether a patient has been correctly intubated, it is preferably provided in sterilised form in such a sealed package. In this embodiment of the invention, the monitor preferably consists of gamma-pay sterilisable materials.
During gamma ray sterilisation acidic moities tend to be generated within the sensor films which may result in the film pH becoming too low to permit the effective indication of carbon dioxide (the indicator dye is permanently present in the acid form). This difficulty may be overcome simply by the incorporation of extra quantities of quaternary cation buffer salt. The latter neutralizes acid as it is generated within the film and keeps the film pH within acceptable limit.
The indicating film is preferably formulated such that no detectable colour change takes place on exposure to room air (ambient carbon dioxide 0.03%) for a prolonged period, while the response to carbon dioxide levels of 2 to %% is rapid (generally about 1 to 2 seconds). The range 2 to %% is of importance medically, because this corresponds to the concentration present in exhaled breath.
The colour change may be observed visually (in which case a qualitative indication of carbon dioxide concentration is obtained) or spectrophotometrically (when a quantitative indication of the carbon dioxide concentration may be obtained).
The transparent film-forming polymer vehicle should be compatible with the indicator material, such that the latter does not exude or otherwise undergo phase separation over a prolonged period; it should in addition be hydrolytically stable (as should the plasticiser) in order to avoid unwanted chang
REFERENCES:
patent: 4418037 (1983-11-01), Katsuyama
patent: 4495291 (1985-01-01), Lawton
patent: 5124129 (1992-06-01), Riccitelli et al.
McMurray Neil
Mills Andrew
Abbey Biosystems Limited
Redding David A.
Schindler Edwin D.
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