A Randomized Porcine Study in Low Cardiac Output of Vasoactive and Inotropic Drug Effects on the Gastrointestinal Tract.

BACKGROUND: Splanchnic vasodilation by inodilators is an argument for their use in critical cardiac dysfunction. To isolate peripheral vasoactivity from inotropy, such drugs were investigated, and contrasted to vasopressors, in a fixed low cardiac output (CO) model resembling acute cardiac dysfunction effects on the gastrointestinal tract. We hypothesized that inodilators would vasodilate and preserve the aerobic metabolism in the splanchnic circulation in low CO. METHODS: In anesthetized pigs, CO was lowered to 60% of baseline by partial inferior caval vein balloon inflation. The animals were randomized to placebo (n = 8), levosimendan (24 µg kg-1 bolus, 0.2 µg kg-1 min-1, n = 7), milrinone (50 µg kg-1 bolus, 0.5 µg kg-1 min-1, n = 7), vasopressin (0.001, 0.002 and 0.006 U kg-1 min-1, 1 h each, n = 7) or norepinephrine (0.04, 0.12, and 0.36 µg kg-1 min-1, 1 h each, n = 7). Hemodynamic variables including mesenteric blood flow were collected. Systemic, mixed-venous, mesenteric-venous, and intraperitoneal metabolites were analyzed. RESULTS: Cardiac output was stable at 60% in all groups, which resulted in systemic hypotension, low superior mesenteric artery blood flow, lactic acidosis, and increased intraperitoneal concentrations of lactate. Levosimendan and milrinone did not change any circulatory variables, but levosimendan increased blood lactate concentrations. Vasopressin and norepinephrine increased systemic and mesenteric vascular resistances at the highest dose. Vasopressin increased mesenteric resistance more than systemic, and the intraperitoneal lactate concentration and lactate/pyruvate ratio. CONCLUSION: Splanchnic vasodilation by levosimendan and milrinone may be negligible in low CO, thus rejecting the hypothesis. High-dose vasopressors may have side effects in the splanchnic circulation.