The evolution of heat and moisture in the respiratory tract during anaesthesia with a non-rebreathing system.

Abstract

TttREE MAJOR DISADVANTACES are currently associated with non-rebreathing systems in anaesthesia. The first is the cost of discarding large amounts of expensive gases and vapours in the ambient atmosphere. The second, closely related to the first, is operating room pollution. 1,2 The third is concerned with the potentially harmful effects of flushing the respiratory tract with desiccated gas mixtures, z,4 We can imagine, in theory, the threatening sequence associated with the inhalation of a dehydrated gas mixture, particularly when the air-conditioning facilities of the nasal passages are being by-passed. It can be assumed that the dry gases will reach the trachea still completely dry, at a temperature very much the same as room temperature. Consequently, the inspired gas mixture will take up moisture and heat from the tracheobronehial tree, leading to local hypothermia, poor ciliary activity, decreased water content of mucus, impaired mucus rheology and accumulation of viscid secretions. This may not be a serious handicap to anyone who can cough forcibly, but for the operative patient, whose power to cough is impaired, it may be disastrous. The effects of dry anaesthetic gases on the tracheobronchial ciliated epithelium were recently described by Chalon, Loew and Malebranche. 5 Having sampled the ciliated epithelium of the tracheobronchial tree from bronchial lavage, they noticed deciliafion, loss of endplates and distortion and pyknosis of the nuclei. However, no measurements of the actual moisture in the tracheobronchial tree were done prior to sampling, so documentation on this aspect still remains very scant. The purpose of our work was to measure the heat and moisture pattern in the airways during clinical anaesthesia using a non-rebreathing system and to compare it with the semiclosed circle and normal patients at rest.