It is appropriate to consider dose-regulated or quantitative closed-circuit anesthesia in terms of uptake of inhalation anesthetics from a reservoir bag which is never allowed to fill completely. The method which the authors have used routinely for 8 years requires reduction of the dose as a function of the inverse square root of elapsed anaesthesia time. Nitrogen does not accumulate because there is an inevitable loss of 20 to 100 ml/min between cuff and trachea. A simpler method, which has been well received, is that of "minimal flow" anesthesia (Virtue) with a constant fresh gas flow of 300 ml/min O2 and 200 ml/min N2O. "Low-flow" techniques typically entail use of 500 ml each of O2 and N2O per min.

Anesthesia, Inhalation↗

PubMed1977

Inspired O2 and N2O concentrations in essentially closed circuits.

By simulation of the FRC (functional residual capacity), washin of N2O was conceptually separated from uptake at the alveolar-capillary membrane. Data collected by mass spectrometry and pneumotachography during a period of 2 years showed a near-constant body uptake of N2O which makes clinical application of closed circuit N2O--O2 anesthesia simple and safe. The data failed to confirm accelerated washin by higher concentrations of N2O ("the concentration effect"), although there was a concentrating effect according to the law of mass action.

Air↗

PubMed1975

States of awareness during general anesthesia.

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Anesthesia, General↗