Tissue oxygenation during liver transplantation.

OBJECTIVES

a) To assess perioperative changes in tissue oxygenation parameters during liver transplantation; b) to evaluate the need for venovenous bypass as hemodynamic support; and c) to assess the efficacy of mixed venous oxygen saturation monitoring and the importance of lactate determinations in the management of patients following liver transplantation.

DESIGN

Prospective case series.

SETTING

Liver transplant unit in a university hospital.

PATIENTS

A total of 68 consecutive patients undergoing liver transplantation. The entire population was analyzed before and after transplantation, dividing the patients into two groups, based on whether their initial cardiac index was higher (n = 37) or lower (n = 31) than 4.5 L/min/m2.

MEASUREMENTS

Hemodynamic measurements and blood gas analyses were made before incision, before vascular clamping (including hepatic artery, portal vein and inferior vena cava), during the anhepatic phase, and at 5, 30, 60, and 120 mins following unclamping. Oxygen transport and oxygen consumption values were calculated. Serum lactate concentrations were measured by enzymatic technique.

MAIN RESULTS

Mixed venous oxygen saturation was correlated with oxygen transport (Do2) in the whole population in which an abnormal oxygen consumption (Vo2)-Do2-dependent relationship occurred from the beginning of operation until 30 mins following unclamping. The comparison between hyperdynamic patients (initial cardiac index greater than 4.5 L/min/m2) with impaired tissue oxygenation and normodynamic patients showed that mixed venous oxygen saturation failed to correlate with Do2 when the cardiac index was greater than 4.5 L/min/m2 and that the Vo2-Do2 dependency was only noted in these patients. The serum lactate concentrations were similar in both groups.

CONCLUSIONS

The Vo2-Do2-dependent relationship and mixed venous oxygen saturation-Do2 correlation noted in the 68 studied patients suggest the need for venovenous bypass and the reliability of mixed venous oxygen saturation monitoring in all patients scheduled for liver transplantation. However, a sharper comparison between hyperdynamic and normodynamic patients demonstrated the lack of efficacy of mixed venous oxygen saturation monitoring in predicting adequate tissue oxygenation in the first group and the mandatory need for venous shunting to limit tissue hypoxia which occurred despite its use only in these patients. Lactic acidosis appeared similarly in both groups and could not be linked to tissue hypoxia.