CIRCULATORY INFLUENCES OF ARTIFICIAL VENTILATION DURING NITROUS OXIDE ANAESTHESIA IN MAN I: INTRODUCTION AND METHODS

Abstract

Previous studies of the circulatory effects of artificial ventilation have failed to separate the effects of changes of intrathoracic pressure and of arterial Pco₂. This paper describes the methodology of a study designed to separate the independent and relative effects of these two ventilatory variables on the cardiovascular system. Particular attention has been paid to the factors which affect the accuracy of cardiac output determinations during anaesthesia. The mean difference between 125 paired cardiac output estimations was +40 ml, with a standard deviation of 220 ml. A method is described for the calculation of the ideal alveolar oxygen tension during the inhalation of gas mixtures containing exogenous carbon dioxide.