THE purpose of this paper is to record and discuss some important circulatory changes which occur in patients subjected to major surgery under general anaesthesia. It is recognized that haemorrhage (Glasser and Page, 1948)~ local fluid loss into traumatized tissue (Phemister, 1928 ; Blalock, 1930), anaesthesia (Zweifach, Hershey, Rovenstine, Lee, and Chambers, 1945)~ and perhaps noxious nervous stimulation (Crile, 1901 ; Slome and O'Shaughnessy, 1938) may each, in part, be responsible for the development of these changes, but our main object is to present an overall picture of the circulatory adjustments which take place during the course of major abdominal operations performed under general anaesthesia.
METHODS OF STUDY
Thirty-two adult patients, 18 male and 14 female, undergoing major abdominal operations have been studied. The average age of the patients was 56 years, the range 31 to 80 years.
The patients were sedated, under direction of our anaesthetists, with combinations of morphine, atropine, and scopolamine. The anaesthetics used were combinations of pentothal, curare, cyclopropane, nitrous oxide, and oxygen.
The cardiac index, peripheral blood-flow, bloodpressure, and overall resistance were determined.
Cardiac Index.-This was determined first in the pre-anaesthetic sedated period, and then subsequently during the period of anaesthesia and operation.
A cardiac catheter was introduced into an antecubital vein under local anaesthesia and guided into the right auricle of the heart (McMichael and Sharpey-Schafer, 1944). The catheter was left in position throughout the operation and its patency was maintained by a slow drip of heparinized saline containing I ml. of heparin (500 international units) per litre. The maximum amount of saline used never exceeded 600 ml.
Mixed venous blood was withdrawn from the catheter into an oiled syringe, transferred into a bottle containing oil, and stored on ice until analysed for its oxygen content. Arterial blood samples were obtained by direct femoral or brachial artery puncture and were similarly collected and stored. The arterial samples during operation were obtained from either a radial or a brachial artery, but if access proved to be impossible, the arterial oxygen content was deduced from the oxygen capacity of fully saturated venous blood. An arterial saturation of 96 per cent was assumed (Douglas and Edholm,