Nitroprusside prevents adverse hemodynamic effects of vasopressin

The influence of vasopressin and sodium nitroprusside on liver circulation was investigated in 18 dogs. Cardiac output was determined by the thermal dilution technique using a Swan-Ganz catheter. Hepatic artery and portal vein flows were measured with electromagnetic flowmeters. The infusion of vasopressin (0.01 unit/kg/min) caused a 13% increase in mean arterial pressure, a 38% decrease in cardiac output, a 57% decrease in portal blood flow, and a 35% decrease in portal pressure. Hepatic artery blood flow initially decreased, then increased, and eventually exceeded the baseline value by 25%. The addition of sodium nitroprusside infusion (10 microgram/kg/min) returned the mean arterial pressure to baseline value and increased cardiac output to 83% of baseline value. Portal blood flow remained unchanged, even though an additional decrease in portal pressure of 11% and a further increase in hepatic artery blood flow of 45% were observed. Nitroprusside minimizes the undesirable effects of vasopressin and augments the desirable ones in normal dogs. The combination of these drugs may be more beneficial to patients with esophageal and gastrointestinal bleeding than vasopressin alone.