Observations on pulmonary circulation during light ether anaesthesia in man.

Abstract

INVESTIGATIONS carried out during recent years have shed increasing light on the peripheral cardiovascular and respiratory effects of anaesthetic agents and techniques. By comparison much less information is available on the role of the pulmo~lary circulation in human haemodynamics and the effect of anaesthesia upon it. .I Until Cournand proved the ease and cfficac3 of cardiac catheterization, no method was available for the study of the lesser circulation that could be readily and safely applied in man. Many workers have stressed the ,importance of the pulmonarTy circulation in human haemodynamics but their Iconclusions have been based o11 either animal exp~rim<nts or deductions from observations of the systemic circttlation, o Johnson's study ~ of the effect of various anaesthetic techniques on the total circulatory system and on respiration was a monumental piece t~f work. He demonstrated for the first time by direct methods the importance of the lessgr. circulation and the role of the lung as an important blood depot ein man. His studies were made on surgical patients of both sexes in whom age, height, and w{eight varied greatly, hpwever, and some of whom suffered from cardio'respiratory disability. Sancetta and L3 nn's ~/ork 2.3 on spinal anaesthesia was excellent in that the subjects were given no vasopressors and they ,did not undergo operation. This may explain some of the minor differences in results of their work from that of Johnson. Li and Etsten 4 investigated the haemodynamic effects of c_~ clopropane and found that pulmonary artery pressure rose during, anaesthesia. In the course of some previous studies of the cardiovascular effects of halothane and of the azeotropic mixture of halothane and ether, 5 6 it had been observed that, as anaesthesia progressed, there was an increase in pulmonary artery pressure and an even more pronounced rise in total pulmonary resistance. Because of a number of variables in this study, such as changing depth of anaesthesia and the use of a new anaesthetic agent of relatively poorly understood properties, it was decided to investigate this phenomenon further and attempt to elucidate what changes occurred in the pulmonary circulation under more controlled conditions of anaesthesia.