Medicine (RMH) - Theses
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ItemDevelopments in the evaluation of oxygen uptake with emphasis on cardiopulmonary exercise testing, and its application to the preoperative assessment of surgical patients( 2009)The introduction of the Swan-Ganz catheter into clinical practice in 1985 facilitated a paradigm change in the management of patients undergoing major surgery. This development made it possible to measure cardiac output and calculate oxygen delivery and uptake in real time at the bedside. These advances together with the development of the portable programmable computer, meant that the attending clinician had access to more data than had ever been possible before. The modern Intensive Care Unit (ICU) evolved alongside these developments, enabling the use of a constellation of high technology equipment which was becoming available. At the same time there was considerable controversy around what was the most appropriate use of the ICU. This controversy was not resolved by the introduction of APACHE II in 1985 which allowed intensivists to correlate severity of illness with survival more reliably than previously. Our group published a paper in 1988, which showed that it was possible to identify high-risk surgical patients pre-operatively with the use of the Swan-Ganz catheter and schedule them for ICU admission post-operatively. In the late 1980s the metabolic cart became available clinically. Using this machine it was possible to measure oxygen uptake and calculate cardiac output non-invasively during exercise. The physiological data that became available with the use of this technology made possible reliable risk assessment of patients scheduled for major surgery. In 1989 a unique opportunity became available to the author to compare data from exercising patients obtained with a metabolic cart with data obtained synchronously with a Swan-Ganz catheter. Comparing this data enabled the investigation of the physiology of exercise in patients with cardiac failure in a way that would not have been possible by use of either a Swan-Ganz catheter or a metabolic cart alone. In 1993 our group published a paper from our laboratory about risk evaluation in surgical patients using Cardiopulmonary Exercise Testing (CPET). The data in this paper was pivotal to the belief that post-operative mortality was a function of cardiac failure and not myocardial ischaemia. In 1999 we published a prospective study involving 548 patients scheduled for major surgery. The results in this paper showed that mortality was inexorably linked to ventricular function. The data suggested that myocardial ischaemia per se was not the cause of post-operatively mortality, unless it was associated with cardiac failure. Other methods of pre-operative evaluation are discussed and it is argued that some of the common methods in use are flawed e.g. the use of metabolic equivalents and the use of stair climbing. The American College of Cardiology and American Heart Association (ACC/AHA) guidelines on pre-operative evaluation of non-cardiac surgical patients, place considerable emphasis on both these methods. This thesis contains a critique of some of the key aspects of these guidelines. An increasing numbers of patients presenting for surgery are taking beta-adrenergic blocking drugs. The use of these drugs has received close examination both from the ACC/AHA guidelines and a contemporary major multicentre trial. It is argued that the use of CPET in evaluating the use of these drugs is very important as management protocols for these patients can be generated from CPET data.