Relation of portal hemodynamics to cardiac output during mechanical ventilation with PEEP.

The relation of portal hemodynamics to cardiac output (CO) during mechanical ventilation with 15 cm H2O PEEP was studied in 12 dogs under pentobarbital anesthesia. Cardiac output was measured by thermal dilution. Portal vein flow (PF) and superior mesenteric artery flow (SMAF) were measured by electromagnetic flow probes. Intraesophageal, intraabdominal, portal vein (PVP) and intrathoracic caval (CVP) pressures, as well as the intraluminal venous pressure gradient across the liver (PVP-CVP) were measured. Intravascular volume was expanded with dextran prior to the addition of PEEP. In nine animals, dextran plus PEEP maintained CO and visceral flows within 3% of control. In three animals, CO and visceral flows fell to the same proportion. There was no increase in hepatic resistance. PF showed a linear correlation with SMAF, and SMAF had a linear correlation with CO. In these experiments, the effect of PEEP on portal hemodynamics system is primarily the consequence of reduced CO.