Hepatic blood flow: accuracy of estimation from infusions of indocyanine green in anaesthetized cats.

Experiments were performed to determine the accuracy of the estimation of hepatic blood flow from infusions of indocyanine green (ICG) in anaesthetized cats. The estimated flows were compared to hepatic blood flows measured directly in a hepatic venous long-circuit preparation. This preparation allowed direct measurement and alteration of hepatic blood flows, and collection of arterial and mixed hepatic venous blood samples without depletion of blood volume in the animal. Mean hepatic plasma flows estimated during infusions of 3.22 and 6.44 nmol kg-1 min-1 were reliable indicators of true hepatic flow at three different flow levels, provided that a sufficiently long time (greater than 30 min) was allowed for distribution equilibrium and that data from several animals were pooled to reduce random variability. Variability arose through subtraction of plasma arterial and hepatic venous levels to obtain the arteriovenous difference. Estimations of hepatic plasma flow by intravenous infusions of ICG were more accurate and reliable than estimations from bolus injections of ICG, or intravenous infusions of galactose studied previously. The kinetics of hepatic uptake of ICG are complex. Extraction and clearance of ICG fell steadily with time during the infusions and constant plasma ICG levels were not attained during 150 min infusions. This is attributed to the effects of accumulation of ICG within the liver cells since hepatic uptake substantially exceeded biliary excretion rate. Total ICG concentrations in sinusoid and liver cells increased in parallel. The concentration in the liver cell was 88 (60-115) times the concentration in the sinusoid but we have no data on whether or not the free concentrations in plasma and cell were in equilibrium.