6 The patient under chronic medication

Most high-risk patients scheduled for surgery benefit from treatment designed to improve both their symptoms and their life expectancy. Cardiovascular treatments interfere with regulatory mechanisms of blood pressure and regional circulations, or they affect the cardiac electrophysiology and contractility. This explains why most peri-operative circulatory abnormalities are not due to the effect of anaesthetic agents on the circulation but to the interactions between cardiovascular and anaesthetic agents, both of which alter the functioning of several physiological systems. On the other hand, when given perioperatively, some treatments are effective in blunting the circulatory response to surgical stimulation and post-operative stress. In this chapter we describe the interactions between treatments chronically taken by high-risk patients and anaesthesia. This subject makes one look at-physiology and pharmacology and allows a better understanding of the compensatory mechanisms activated in response to the stress of surgery and anaesthesia.