Comparison of the effects of propofol and isoflurane anaesthesia on right ventricular function and shunt fraction during thoracic surgery.

I.v. anaesthetic agents, including propofol, have not been shown to inhibit hypoxic pulmonary vasoconstriction (HPV). This may encourage the use of propofol in thoracic surgery where one lung ventilation (OLV) is required. We have compared the effects of maintaining anaesthesia with either isoflurane or propofol infusion on right ventricular function and shunt fraction. We studied 10 patients who received isoflurane and 12 who received propofol. When OLV commenced there was a greater reduction in both mean cardiac index (3.2 (SEM 0.2) to 2.4 (0.1) litre min-1 m-2 for propofol, and 3.4 (0.2) to 3.3 (0.4) litre min-1 m-2 for isoflurane) and right ventricular ejection fraction (0.45 (0.03) to 0.37 (0.02) for propofol, and 0.48 (0.02) to 0.42 (0.02) for isoflurane) in patients who received propofol. Furthermore, these reductions were sustained for longer in the propofol group. However, propofol was not associated with a significant increase in shunt fraction during OLV, which increased threefold in patients who received isoflurane.

The renin-angiotensin system and angiotensin converting enzyme (ACE) inhibitors.

Anaesthetists will encounter increasing numbers of patients who are receiving long-term treatment with ACE inhibitors for hypertension, congestive heart failure and prophylactically following myocardial infarction. Our understanding of the physiology and pharmacology of the renin-angiotensin system has dramatically increased in the last decade, and has led to the discovery of endogenous renin-angiotensin systems which may be physiologically more important than the better understood circulating system. There are several reports of adverse interactions between anaesthesia and ACE inhibitors, manifested as hypotension and bradycardia, which may be delayed until the postoperative period. The mechanism behind them is not understood and, as yet, no published studies have attempted to address this issue. It is possible, however, that dehydration associated with the pre-operative fast may play an important role. ACE inhibitors may, in the future, prove to be useful in the subspecialties of cardiac and vascular anaesthesia, where they might be used in an attempt to preserve cardiac function following periods of ischaemia and cardiopulmonary bypass, and to avoid renal damage following aortic cross-clamping. Meanwhile, it would seem prudent to exercise caution when anaesthetising patients taking ACE inhibitors and to be fully prepared to treat the hypotension and bradycardia which may occur.