Carbon dioxide measurement from expired gases in a partial rebreathing anesthesia circuit
First Claim
1. A method of determining arterial carbon dioxide tension from mixed expired gases of a patient utilizing a partial rebreathing anesthesia circuit consisting of the following steps:
- measuring continuously carbon dioxide tension of said mixed expired gases with an electrode inserted therein, an output of said electrode having a high impedance;
converting said high impedance of said elecrode output in an impedance converter to a lower impedance level;
shielding and isolating said electrode output until conversion to said lower impedance;
generating an antilog function from said lower impedance level of said electrode output;
scaling said anilog function to account for variations between carbon dioxide tension of said mixed expired gases and said arterial carbon dioxide tension, to give a scaled output signal directly related to said arterial carbon dioxide tension, said variations including an arthmetic addition to said antilog function to give said scaled output signal thereby accounting for diffusion, mixing and temperature variations.
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Abstract
A method of determining arterial carbon dioxide tension from mixed expired gases of a patient utilizing a partial rebreathing anesthesia circuit. An electrode is inserted into expired gases of a patient to measure expired carbon dioxide tension. An output signal from the electrode, which indicates expired carbon dioxide tension, has a very high impedance. By reducing the impedance of the output signal, a more usable signal is obtained. Also, the signal must be converted to a relatively linear function, which is then scaled to give a visual indication proportionate to the arterial carbon dioxide tension. The electrode is pre-calibrated by gases having known percentages of carbon dioxide. The scaling factor is included to compensate for differences between the expired carbon dioxide tension and arterial carbon dioxide tension.
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Citations
7 Claims
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1. A method of determining arterial carbon dioxide tension from mixed expired gases of a patient utilizing a partial rebreathing anesthesia circuit consisting of the following steps:
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measuring continuously carbon dioxide tension of said mixed expired gases with an electrode inserted therein, an output of said electrode having a high impedance; converting said high impedance of said elecrode output in an impedance converter to a lower impedance level; shielding and isolating said electrode output until conversion to said lower impedance; generating an antilog function from said lower impedance level of said electrode output; scaling said anilog function to account for variations between carbon dioxide tension of said mixed expired gases and said arterial carbon dioxide tension, to give a scaled output signal directly related to said arterial carbon dioxide tension, said variations including an arthmetic addition to said antilog function to give said scaled output signal thereby accounting for diffusion, mixing and temperature variations. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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Specification