INDOCYANINE GREEN: OBSERVATIONS ON ITS PHYSICAL PROPERTIES, PLASMA DECAY, AND HEPATIC EXTRACTION*

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Abstract
The physical properties of indocyanine green (ICG) and its removal from the circulation of human subjects was studied. Optical absorption peak was at 815 m[mu] in albumin solution and at 790 m[mu] in water. On plasma electrophoresis 95% of the dye migrated with albumin and small amounts with other plasma proteins. In normal human subjects after intravenous administration the dye was not found in the urine, nor was removal in the periphery demonstrated by arteriovenous differences across the limbs. On the other hand dye appeared in the bile within 15 minutes in 2 subjects. In 9 subjects without liver disease mean initial plasma decay rate was 18.5 [plus or minus] 3.1%/minute, compared with 13.8 [plus or minus] 2.1% for sulfobromophthalein (BSP). Patients with cirrhosis demonstrated diminished initial decay rates, averaging 7.8%/minute for ICG and 4.3%/minute for BSP. Correlation "r" between these decay rates was 0.92. While patients with mild liver disease removed ICG more rapidly than BSP, 2 patients with marked hepatic dysfunction removed BSP more rapidly. Satisfactory and stable extraction rates of ICG during constant intravenous infusion and essentially exclusive removal by the liver suggested that the dye had value in estimating hepatic blood flow by use of the Fick principle.