Anesthetic Influences on the Pulmonary Circulation

Abstract

Most current textbooks (1,2) conclude that general anesthetic agents, whether injectable or inhalational, have relatively little apparent effect on the pulmonary circulation. This conclusion is primarily based on measurements of pulmonary artery pressure or calculations of the overall pulmonary vascular conductance (or resistance), both of which are functions of so many variables that only gross changes are detectable. The available data concerning anesthesia has rapidly expanded in both quantity and sophistication and the work has established that general anesthetic agents alter lung mechanics, blood volume distribution, cardiac output, myocardial contractility, vascular tone, blood pH and carbon dioxide tension, pulmonary blood flow distribution and the effectiveness of the major active regulator of pulmonary blood flow, hypoxic pulmonary vasoconstriction (HPV). All of these factors influence the pulmonary circulation and, therefore, anesthesia could be expected to be accompanied by more or less profound changes. In the previous lecture concerning the regulation of the pulmonary circulation, some of these factors were discussed and a model was introduced that provides quantitative insight as to the outcome and mechanisms of multiple influences on the pulmonary circulation and gas exchange (3,4). With such an approach, it is possible to suggest which of the many changes introduced during general anesthesia have predominant effects.