Haemodynamic effects of an angiotensin-converting enzyme inhibitor and angiotensin receptor antagonist during hypovolaemia in the anaesthetized pig

Abstract

Renin-angiotensin system antagonists, either angiotensin-converting enzyme (ACE) inhibitors or angiotensin II receptor (AT(1)) antagonists, may interfere with regulation of arterial pressure during anaesthesia. This study aimed to compare the haemodynamic profile of anaesthetized pigs, which were subjected to haemorrhage in the presence of the ACE inhibitor enalaprilat or the AT(1) antagonist valsartan. Thirty-six pigs were assigned randomly to placebo, enalaprilat or valsartan groups. After a 30-min period of stabilization following anaesthesia and injection of the study drug, the animals were bled in two equal steps of 20% of their estimated blood volume (20% BV and 40% BV). After bleeding of 20% BV, the mean arterial pressure (MAP) decreased significantly but similarly in each group (20-25%) but the placebo and the enalaprilat groups had a significant decrease in cardiac index (CI, 22% and 16%, respectively) without significant change in systemic vascular resistance (SVR). Conversely, in the valsartan group, SVR decreased significantly (23%, P<0.02 vs other groups) without significant change in CI (-4%). After bleeding of 40% BV, the CI decreased significantly compared with 20% BV in the three groups (19% in the placebo and enalaprilat groups, 14% in the valsartan group) but the MAP decreased significantly in the enalaprilat group only (23%). The SVR increased significantly in the placebo group (P<0.01 vs each of the other groups), but there were no differences in the change in SVR between the other groups. Blockade of the renin-angiotensin system by either enalaprilat or valsartan leads to a similar decrease in arterial pressure during anaesthesia and haemorrhage but the haemodynamic profiles are quite different.