Vasopressors and intestinal mucosal perfusion. Studies in cardiac surgical and critically ill patients

Abstract: During trauma, surgery and critically illness, splanchnic ischemia and reperfusion damage maythreaten the barrier function of the intestinal mucosa, leading to bacterial translocation, immuneactivation and subsequent development of systemic inflammatory response syndrome. Detection,prevention and treatment of intestinal mucosal hypoperfusion are therefore important forprevention of complications in critically ill patients. In this thesis, the intestinal mucosalperfusion, measured by laser Doppler flowmetry, has been studied during and after cardiacsurgery and in critically ill patients with vasodilatory shock, with focus on the effects ofvasopressor treatment.The intestinal mucosal perfusion was evaluated postoperatively in eighteen cardiac surgerypatients. Elevation of the systemic perfusion pressure with norepinephrine induced no change inintestinal mucosal perfusion, whereas the combination of norepinephrine and dopamine causedincreased mucosal perfusion. Furthermore, the differential effects of phenylephrine, a pure ?1-adrenoceptor agonist, and norepinephrine, which has both ?1-constricting and ?1- dilatingproperties, were investigated postoperatively in ten patients. Intestinal mucosal perfusion was notaltered by the vasopressors, whereas both drugs increased the global splanchnic oxygen extraction.This increase was more pronounced with phenylephrine, indicating a more pronounced globalsplanchnic vasoconstriction, compared to norepinephrine,In ten critically ill patients with multi organ failure and norepinephrine-dependentvasodilatory shock, the effects of norepinephrine-induced variations in perfusion pressure onglobal splanchnic and intestinal mucosal perfusion were evaluated. The intestinal mucosalperfusion and the global splanchnic oxygenation were not altered despite a change in meanarterial pressure from 60 to 90 mmHg.The autoregulation of intestinal mucosal perfusion during cardiopulmonary bypass wastested in ten cardiac surgery patients. Variations in perfusion pressure induced by alterations incardiopulmonary bypass flow rate revealed an intact autoregulatory capacity of the intestinalmucosa. Vasodilation with prostacyclin increased jejunal mucosal perfusion and abolished theautoregulatory capacity of the mucosa. The amplitude and frequency of the cyclic oscillation ofthe mucosal perfusion (vasomotion) increased with increasing perfusion pressureIn conclusion: Intestinal mucosal perfusion is not affected by clinical relevant doses of thevasopressors norepinephrine and phenylephrine, in postoperative patients and critically illpatients with vasodilatory shock. Phenylephrine causes a more pronounced global splanchnicvasoconstriction compared to norepinephrine. Addition of dopamine increases intestinal mucosalperfusion during norepinephrine infusion. Autoregulation of intestinal mucosal perfusion isintact during cardiopulmonary bypass.