Effects of PEEP on splanchnic hemodynamics and blood volume.

The effects of intermittent positive pressure ventilation with PEEP on splanchnic circulation and hepatic oxygen supply were studied in six beagles. PEEP of 0, 0.5 and 1.0 kPa (0, 5, 10 cmH2O, PEEP0, PEEP5 and PEEP10, respectively) of 30 min duration was applied in a random sequence. Hepatic arterial blood flow and portal venous blood flow were measured by electromagnetic flow meters. Blood volume changes in the splanchnic area were assessed from hepatic and splenic dimensions determined by sonomicrometry. PEEP5 and PEEP10 were associated with proportional decreases in both hepatic blood flow and cardiac output, while mean arterial pressure remained unchanged. Reflecting the decrease in hepatic blood flow, the hepatic oxygen supply decreased with the level of PEEP, and hepatic venous hemoglobin oxygen saturation was significantly less during PEEP10 (55.1 +/- 14.3%) than during PEEP5 (62.6 +/- 17.4%) and PEEP0 (62.3 +/- 11.9%). Hepatic venous and portal venous pressure increased with the level of PEEP. Hepatic dimensions increased by 7-8% and 16-19% during PEEP5 and PEEP10, respectively, but no significant changes in splenic dimension were observed. We conclude that PEEP5 and PEEP10 are accompanied by a decrease in hepatic blood flow and oxygen supply along with hepatic congestion.