Effect of liver blood flow and function on hepatic indocyanine green clearance measured directly in a cirrhotic animal model

Background: Peripheral blood clearance of indocyanine green (ICG) has been used as a test of liver function but gives little information on biliary ex cretion. Hepatic ICG uptake and clearance can be measured directly by near- infrared spectroscopy (NIRS). Direct ICG measurement has not previously bee n correlated with liver blood flow and function in cirrhosis. Methods: Two groups of New Zealand white rabbits (n =12) underwent laparoto my for liver exposure. Cirrhosis was induced by feeding animals (n = 6) wit h a high-cholesterol (2 per cent) diet for 16 weeks. Hepatic blood flow and microcirculation were measured, Hepatic ICG concentration was measured dir ectly using NIRS probes on the liver surface. From the ICG concentration-ti me curve, hepatic ICG uptake and excretion rates were calculated by a non-l inear least square curve fitting method. Results: There was a significant reduction in ICG uptake rate (mean(s.d.) 0 .300(0.130) versus 2.040(0.420) min(-1); P= 0.0001) and ICG excretion rate (0.007(0.009) versus 0.227(0.096) min(-1); P = 0.002) in cirrhotic animals. The hepatic ICG uptake rate correlated with hepatic blood flow and flow in the microcirculation (r = 0.81, P = 0.002; r = 0.92, P < 0.001, respective ly). The hepatic ICG excretion rate was significantly associated with indic ators of impaired liver function including bilirubin (r = -0.86, P = 0.0004 ), aspartate aminotransferase (r = -0.81, P = 0.001) and lactate dehydrogen ase (r = -0.83, P=0.0008). Conclusion: ICG uptake measured directly by NIPS reflects the reduced liver blood how and perfusion in cirrhosis and its excretion correlates with the degree of liver parenchymal dysfunction, This technique may allow a more a ccurate method of liver function assessment than peripheral blood ICG clear ance.