A non-rebreathing coaxial anaesthesia system: dependence of end-tidal gas concentrations on fresh gas flow and tidal volume.
A non-rebreathing adaptation of the Bain coaxial anaesthesia circuit was developed in Nepal as a simple and economical anaesthetic system for underdeveloped countries. It was made by inserting a coaxial (Bain) tubing between an Ambu-E valve and an Ambu self-inflating bag. The present study examined the dependence of end-tidal gas concentrations on fresh gas flow and tidal volume during halothane/oxygen/air inhalation anaesthesia. Four levels of fresh gas flow with normocapnia (0.2-3 l.min-1) and three levels of tidal volume at a constant respiratory rate of 15 breath.min-1 (to achieve end-tidal carbon dioxide values of 4 +/- 0.5%, 5 +/- 0.5% and 6 +/- 0.5%) were introduced in random order. Twelve ASA class 1 and 2 adult patients having intra-abdominal or pelvic surgery were studied. With increasing fresh gas flow rates, there were proportionate increases in the end-tidal concentrations of oxygen and halothane; with decreasing tidal volume and therefore less air dilution, there were proportionate increases in the end-tidal concentrations of carbon dioxide, oxygen and halothane. Both effects were statistically and clinically significant. Thus, when this system is used as described, the end-tidal concentrations of oxygen and halothane are highly dependent upon both the fresh gas flow and the tidal volume.
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Department of Anesthesiology, Arabian Gulf University, CMMS, Manama, Bahrain.
D000328:Adult; D000769:Anesthesia, Inhalation / Q000295:instrumentation*; D018685:Anesthetics, Inhalation / Q000493:pharmacokinetics*; D002245:Carbon Dioxide / Q000502:physiology; D003906:Developing Countries; D004334:Drug Administration Schedule; D004867:Equipment Design; D006221:Halothane / Q000493:pharmacokinetics*; D006801:Humans; D010100:Oxygen / Q000008:administration & dosage*; D011659:Pulmonary Gas Exchange; D013990:Tidal Volume
D018685:Anesthetics, Inhalation; D002245:Carbon Dioxide; D010100:Oxygen; D006221:Halothane