Humidity in anaesthesiology III. Heat and moisture patterns in the respiratory tract during anaesthesia with the semi-closed system

Abstract

Experimental data have been presented which suggest that bypassing the nose with artificial airways is well compensated by the ability of these airways to imitate the heat and moisture exchange normally occurring in the nose. The lower airway can also carry on during anaesthesia the same heating, moistening, and recondensing functions that it apparently performs during normal life. Our results, obtained during clinical anaesthesia with the semi-closed circle absorption, indicate that the heat and moisture patterns disclosed along the airway are similar, in practice, to those found in the conscious subject breathing through his nose. This is so mainly for the following reasons: (1) inspired gas mixtures enter the airway with a water vapour tension higher than that usually found in ambient air; ( 2 ) moisture from expired air is conserved by condensation all along the airway and is recaptured during the next inspiratory phase. The high concentrations of water made available through these processes reduce the burden laid upon the respiratory mucosa to transudate further amounts of water. Wide temperature oscillations between inspiration and expiration occur in the respiratory tract until the lower airway is reached. These variations are important features in the physiological mechanisms of water condensation in expiration and water recapture in inspiration. Through these temperature changes, the respiratory tract mucosa, the endotracheal tube, and the swivel valve adjust the amount of water conserved during expiration and contribute significantly to water economy and balance during the anaesthesia with the semi-closed circle. © 1967 Canadian Anesthesiologists.