Kinetics of indocyanine green removal from the blood

TLDR: Clinically, it is not possible to use a sufficiently large dose of dye to measure capacity of hepatocytes to remove ICG independent of blood flow, but it should be possible to calculate maximal removal capacity from several submaximal values if hepatic uptake of dyes obeys Michaelis-Menten kinetics.

Abstract: Studies of kinetics of dye removal from the blood have greatly advanced our understanding of hepatic physiology. The dyes used mainly to investigate hepatic circulation and function are sulfobromophthalein, rose bengal and indocyanine green (ICG). This paper will be concerned with kinetics of hepatic removal of ICG. This dye appears to be bound primarily to alpha 1-lipoproteins in serum.' It does not exhibit extrahepatic removal or enterohepatic c i r c u l a t i ~ n , ~ ~ ~ is not chemically altered during its transit through the liver 2 9 4 and is nontoxic in the doses e m p l ~ y e d . ~ Accurate and continous recording of ICG blood levels is possible using dichromatic ear den~itometry.~ Different doses of ICG have been used to test liver function in man, ranging from 0.25-5 mg/kg body weight. Studies of clearance of 0.25-0.5 mg of ICG are relatively insensitive in detecting mild liver disease, whereas removal of 5.0 mg/kg of this dye furnishes a highly sensitive index to hepatic function in these instance^.^ Liver blood flow is rate limiting with low dye concentrations, and the amount of ICG removed from the circulation per unit of time is primarily a measure of liver blood flow. The ability of hepatocytes to take up dye becomes rate limiting at very high dye concentrations, and ICG clearance under these circumstances represents a sensitive measure of liver cell function. Clinically, it is not possible to use a sufficiently large dose of dye to measure capacity of hepatocytes to remove ICG independent of blood flow. Nevertheless, it should be possible to calculate maximal removal capacity from several submaximal values if hepatic uptake of dyes obeys Michaelis-Menten kinetics.