A non-rebreathing coaxial anaesthesia system: dependence of end-tidal gas concentrations on fresh gas flow and tidal volume

Anaesthesia. 1997 Mar;52(3):237-41. doi: 10.1111/j.1365-2044.1997.033-az0059.x.

Abstract

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.

Publication types

  • Clinical Trial
  • Randomized Controlled Trial

MeSH terms

  • Adult
  • Anesthesia, Inhalation / instrumentation*
  • Anesthetics, Inhalation / pharmacokinetics*
  • Carbon Dioxide / physiology
  • Developing Countries
  • Drug Administration Schedule
  • Equipment Design
  • Halothane / pharmacokinetics*
  • Humans
  • Oxygen / administration & dosage*
  • Pulmonary Gas Exchange
  • Tidal Volume

Substances

  • Anesthetics, Inhalation
  • Carbon Dioxide
  • Oxygen
  • Halothane