Vasodilation due to impaired vascular tone is common in liver failure. Vasoconstrictor drugs are almost always required during the anhepatic phase of a liver transplant to maintain blood pressure unless venovenous bypass is employed. Argininevasopressin can be used as a vasoconstrictor instead of or in addition to norepinephrine for this purpose, but the effect of vasopressin on the portal vein pressure and flow in this setting is unknown. Portal vein pressure, portal vein blood flow, hemodynamic variables, and plasma vasopressin levels were measured in 16 patients during liver transplantation after ligation of the hepatic artery before and after a vasopressin infusion of 3.8 Ϯ 1.1 units/hour. Measurements were performed on the native liver prior to caval clamping. After vasopressin infusion, the portal vein pressure decreased significantly from 24.0 Ϯ 6.5 to 21.5 Ϯ 7.4 mm Hg [mean Ϯ standard deviation (SD), P ϭ 0.006]. The portal vein blood flow also decreased (from 1.01 Ϯ 0.53 to 0.76 Ϯ 0.53 L/minute, mean Ϯ SD, P Ͻ 0.0001), as did the portal vein blood flow to cardiac output ratio (from 0.14 Ϯ 0.06 to 0.10 Ϯ 0.07, mean Ϯ SD, P Ͻ 0.0001). In conclusion, vasopressin significantly decreased portal vein pressure and flow of the native liver without decreasing cardiac output or intestinal perfusion in patients undergoing liver transplantations. Liver Transpl 14: [1664][1665][1666][1667][1668][1669][1670] 2008 Patients in hepatic failure who require a liver transplant often exhibit profound vasodilatation and are able to maintain adequate perfusion pressure only by increasing cardiac output.1 Without the use of portocaval bypass or preservation of the recipient vena cava (the piggyback technique), cardiac preload decreases significantly upon clamping of the inferior vena cava, and decreased cardiac output and arterial blood pressure follow.Sympathomimetic drugs such as norepinephrine and epinephrine are used to maintain an adequate arterial blood pressure during the anhepatic phase. We have observed that a low-dose infusion of arginine-vasopressin (AVP), either alone or in combination with norepinephrine, is also potentially effective for this purpose, but we did not know if vasopressin had a beneficial effect on portal blood flow and pressure in patients undergoing liver transplantations. Vasopressin is a potent vasoconstrictor in vasodilatory septic shock, [2][3][4] and vasopressin analogues such as ornipressin and terlipressin have been used successfully to treat hepatorenal syndrome. 5,6 Vasopressin causes splanchnic Abbreviations: ABG, arterial blood gas; AVP, arginine-vasopressin; CO, cardiac output; CVP, central venous pressure; DBP, diastolic blood pressure; DPAP, diastolic pulmonary artery pressure; FFP, fresh frozen plasma used intraoperatively; g-a, gastric/arterial; LOS, length of stay; LRLT, living related liver transplantation; MAP, mean arterial pressure; MELD, Model for End-Stage Liver Disease; MPAP, mean pulmonary artery pressure; NAFLD, nonalcoholic fatty liver disease; OLT, orthotopic liver trans...