The renin-angiotensin system in swine during hypovolaemic shock combined with low-flow ischaemia of the sigmoid colon

Colonic ischaemia is a serious complication after aortic surgery, and is mo st frequent after repair of ruptured aortic aneurysms. It was felt that the increased risk of colonic ischaemia during shock might be the result of a local effect of the renin-angiotensin system in the splanchnic circulation, which is exacerbated by poor perfusion. In order to evaluate the activity of the renin-angiotensin system in the colonic circulation, a subtotal occl usion of the distal aorta was induced in nine pigs. A colonic flow reductio n of 70% was created for 4 hours. In the experimental group (n = 6), induce hypovolaemic shock. 20 cm(3)/kg blood was sampled at 45 min before resusci tation was performed with 20 cm(3)/kg haemaccel, The sham group (n = 3) did not have hypovolaemic shock induced, Blood samples were taken for determin ations of angiotensin ii, haemoglobin and lactate. Blood gas was obtained f rom the pulmonary artery and the caudal mesenteric vein for blood gas analy sis and lactate determinations. ANOVA and the Wilcoxon sum rank test were u sed for statistical analysis. There was a significant increase in angiotens in II after induction of ischaemia in both groups. The increase in angioten sin II in the splanchnic circulation was more prominent than the increase i n the systemic circulation (P < 0.01). In the experimental group, there was a sustained increase in angiotensin II levels in the splanchnic circulatio n following shock and reperfusion (P < 0/01). The increase in lactate conce ntrations. which was significantly higher in the experimental group (P < 0. 05), was evidence of intestinal ischaemia. There was a significant decline in cardiac output and blood pressure during the period of shock (P < 0.05). The combination of colonic ischaemia and hypovolaemic shock followed by re perfusion leads to an increase in angiotensin II activity. The increase of the local activity of the renin-angiotensin system in the splanchnic circul ation is more prominent after ischaemia and reperfusion. This is probably c aused by a selective response of the splanchnic vasculature to shock, ischa emia and reperfusion. (C) 1999 The International Society For Cardiovascular Surgery. Published by Elsevier Science Ltd. All rights reserved.