Peri-anhepatic phase oxygen kinetics in porcine liver transplantation

Background. We applied a liver transplantation animal model to examine the relationship between oxygen delivery and consumption. The presence of pathologic flow-dependent oxygen consumption was investigated during and after the anhepatic phase. The effect of venous-to-venous bypass on oxygen kinetics was evaluated. Methods. Twelve pigs were randomly divided into two groups. The non-bypass group consisted of six pigs that were subjected to clamping of the hepatic artery, portal vein, and the superior and inferior vena cava to produce an anhepatic phase. The bypass group consisted of six pigs that underwent vascular clamping and liver transplantation with venous bypass. Hemodynamics, oxygen delivery index (DO₂) and oxygen consumption index (VO₂) were recorded during the peri-anhepatic phase. Best-fit regression lines were calculated for DO₂ vs VO₂. Results. In the pigs without venous bypass, the blood pressure, cardiac index and VO₂ dropped significantly after vascular clamping and lactic acidosis developed. In pigs with venous bypass, vascular clamping induced a significant decline of cardiac output and DO₂ but VO₂ was maintained by a compensatory increase in oxygen extraction ratio. DO₂ and VO₂ after the release of vascular clamping increased significantly higher than that before vascular clamping. The O₂ supply-dependent regression line was drawn from the points below critical oxygen delivery with a slope of 0.232 (95% CI = 0.110-0.3541, r² = 0.50, p = 0.010). The pathologic supply-dependent line was drawn from the points with supranormal DO₂ and VO₂ with a slope of 0.185 (95% CI = 0.050-0.333, r² = 0.510, p = 0.029). The slope of the supply-independent line was 0.0089 (95% CI = -0.030-0.050, r² < 0.009, p = 0.12). Conclusions. Oxygen delivery dropped below the critical level and flow-dependent oxygen consumption developed during the anhepatic phase without venous bypass. Venous-to-venous bypass is necessary to maintain a critical DO₂ and stable hemodynamics during porcine liver transplantation. Pathologic flow-dependent oxygen consumption developed after the anhepatic phase.