Carbon dioxide measurement from expired gases in a partial rebreathing anesthesia circuit

摘要

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.