Experimental study of liver dysfunction evaluated by direct indocyanine green clearance using near infrared spectroscopy.

BACKGROUND Blood clearance of indocyanine green (ICG) is an objective test of liver function. Hepatic ICG clearance can now be measured directly using near infrared spectroscopy (NIRS). The aim of this study was to evaluate measurement of hepatic ICG clearance by NIRS in an animal model of acute hepatic dysfunction. METHODS New Zealand white rabbits (n = 36) underwent laparotomy for liver exposure. Hepatic blood flow and microcirculation were measured along with hepatic ICG concentration by NIRS. Hepatic ICG clearance was measured in groups of six animals after reduction of the hepatic blood flow by hepatic artery occlusion and portal vein partial occlusion, lobar ischaemia and reperfusion (I/R), colchicine administration and bile duct ligation. Hepatic ICG uptake and excretion rates were calculated by a non-linear least square curve fitting method from the ICG concentration-time curve. RESULTS There was a significant positive correlation between hepatic ICG rate of uptake and both hepatic blood flow and microcirculation (r = 0.79, P = 0.0001; r = 0.59, P = 0.005 respectively). I/R resulted in a significant reduction of both the rates of ICG uptake (mean(s.d.) 0. 85(0.59) min-1; P = 0.0002 versus control) and ICG excretion (0. 020(0.006) min-1; P = 0.02 versus control). Colchicine decreased the rate of hepatic ICG excretion (0.030(0.010) min-1; P = 0.02 versus control) as did bile duct ligation (0.002(0.001) min-1; P = 0.01 versus control). CONCLUSION Measurement of hepatic ICG clearance by NIRS is a promising technique for assessing hepatic parenchymal dysfunction and may have application in liver surgery and transplantation.