This study evaluated both the isolated and combined effects of intravenous vasopressin and volume replacement on cardiac output and portal pressure in hypovolemic dogs. Following acute hemorrhage and sustained hypotension (60 mm Hg for 45 min), 20 anesthetized dogs received either: no treatment; intravenous vasopressin (20 units/30 min); Ringer's lactate (volume equal to shed blood/30 min); or intravenous vasopressin and Ringer's lactate. At 30 minutes after hypotension, cardiac output decreased 52% and portal pressure decreased 61% in control animals. Hypovolemia plus intravenous vasopressin resulted in significant reductions in cardiac output (41%) and portal pressure (62%) compared to baseline recordings, but not compared to control animals. Following hypovolemia and Ringer's lactate, cardiac output and portal pressure increased to prehemorrhage levels. With vasopressin and Ringer's lactate, portal pressure remained decreased (39%), while cardiac output returned to prehemorrhage levels. This study demonstrates that administration of intravenous vasopressin during hypovolemia does not cause an added reduction in cardiac output and does not prevent restoration of the normal cardiac output by volume replacement. Moreover, administration of vasopressin during volume replacement prevented a return of portal venous pressure to prehemorrhage levels.
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