Hepatic clearance of indocyanine in the dog

The clearance and extraction by the liver of the dye, indocyanine green, was studied in dogs anesthetized with sodium pentobarbital (30 mg/kg). A simultaneous comparison ‘ in vivo’ indicated that within experimental error indocyanine space equals Evans blue space. Additional in vitro experiments suggest that indocyanine space is a reasonably satisfactory measure of plasma volume. Adequate mixing of the injected dye occurs within 2–3 minutes after injection. From 2 to 20 minutes after injection, the peripheral arterial and hepatic venous decay slopes are logarithmic and easily analyzable. Right hepatic vein concentrations of indocyanine were consistently higher (3.3%) than those of the left. Most of the assumptions made in the clearance-extraction principle of measuring hepatic flow are valid. At least two factors, the obtaining of representative hepatic venous samples and determination of true extraction ratio (because of hepatic circulatory time) represent ill-defined sources of error. The soundness of the clearance-extraction principle and unique characteristics of indocyanine make the single injection method a potentially useful tool for study of hepatic blood flow.