The renin-angiotensin system and ACE inhibitors in the peri-operative period

Anaesthetists will encounter more patients in the peri-operative period on angiotensin-converting enzyme (ACE) inhibitor therapy because of their efficacy in the treatment of hypertension and cardiac failure. Pre-operative therapy with ACE inhibitors has been associated with severe hypotension after the induction of and during anaesthesia. While ACE inhibitors have not been found especially useful in managing the haemodynamic consequences of laryngoscopy and intubation, they may have a role when induced hypotension is required to minimize blood loss. It is now apparent that the renin-angiotensin system (RAS) plays a critical role in the defence of blood loss, and thus ACE inhibitors may have a deterimental effect in the peri-operative period in this respect. High thoracic epidural anaesthesia may not only have its well-known sympatholytic effect, but may also inhibit activation of the RAS system. However, on the positive side, ACE inhibitors have been shown to diminish the activation of cardiovascular mediators in cardiac surgical patients, are probably renoprotective during aortic surgery and have been shown to reduce myocardial infarct size after coronary occlusion in dogs, suggesting a possible myocardial protective effect. Thus further studies will be required to determine the exact role of ACE inhibitors in the peri-operative period.