Effect of graft reperfusion on haemodynamics and gas exchange during liver transplantation

We have documented the changes in gas exchange, haemodynamic state and associated physiological variables which occurred after graft reperfusion in 20 patients undergoing uncomplicated orthotopic liver transplantation. Gas exchange was measured during constant ventilation using a metabolic monitor. After reperfusion, there were increases in VO2 (mean increase 57 (SD 25) ml min-1) (P < 0.001), VCO2 (mean increase 38 (17) ml min-1) (P < 0.001) and PaCO2 (mean increase 0.88 (0.56) kPa) (P < 0.001). These were associated with increases in cardiac output (1.2 (1.0) litre min-1 m-2) (P < 0.001) and mean pulmonary artery pressure (9 (6) mm Hg) (P < 0.001). There was a decrease in standard bicarbonate concentration (0.96 (1.6) mmol litre-1) (P < 0.02) and increase in hydrogen ion concentration (8.15 (5.9) mmol litre-1) (P < 0.001) consistent with the release of an acid load from the graft and previously ischaemic tissues. The increases in PaCO2 and hydrogen ion concentration were significantly larger in patients in whom venovenous bypass was used during the anhepatic period compared with the "piggyback" surgical technique. We found correlations between the changes in PaCO2 and VCO2 (r2 = 0.25, P < 0.02), cardiac output and VCO2 (r2 = 0.34, P < 0.01), and cardiac output and VO2 (r2 = 0.34, P < 0.01). We conclude that major alterations in gas exchange occur after reperfusion which result from alterations in metabolic rate and haemodynamic changes. These may be clinically relevant, particularly in patients at risk of cerebral oedema.