Hemodynamic changes with initiation of veno-venous bypass in orthotopic liver transplant patients

Removal of the liver to start the anhepatic stage of liver transplantation requires cross-clamping of the portal vein, inferior vena cava, and hepatic artery. Adverse effects occur from engorged splanchnic beds and decreased venous return. A veno-venous bypass from the inferior vena cava and portal vein to the axillary vein is used in an attempt to ameliorate these changes. The purpose of this study was to evaluate the effect of institution of veno-venous bypass on hemodynamics. Eight randomly selected adult patients undergoing orthotopic liver transplantation had general anesthesia induced with thiamylal and maintained with nitrous oxide and isoflurane. Cardiopulmonary data and arterial and mixed venous blood gases were measured prospectively using radial artery and pulmonary artery catheters. Measurements were taken under four conditions: (1) 10 minutes before bypass; (2) after partial bypass (vena cava to the axillary vein); (3) after partial bypass with portal vein clamping; and (4) after full bypass (vena cava and portal vein to the axillary vein). Statistically significant changes seen were a 22% decrease in cardiac output and a 47% increase in systemic vascular resistance (SVR). Bypass flow was lower than predicted. Venovenous bypass ameliorates, but does not fully prevent, the reduction of cardiac output and rise in SVR seen with initiation of the anhepatic stage. However, bypass does prevent the hypotension experienced during cross-clamping and for these reasons should be used routinely.