Does indocyanine green accurately measure plasma volume independently of its disappearance rate from plasma in critically ill patients?

Objective: To determine whether plasma volume determined by the indocyanine green (ICG) dilution method (PV-ICG) is equally accurate independently of its disappearance rate from plasma in the critically ill. Design: Retrospective clinical investigation. Setting: Intensive care unit of a university teaching hospital. Patients and methods: 192 adult patients were initially enrolled. The PV-ICG and the initial distribution volume of glucose (IDVG) were calculated utilizing a one-compartment model by simultaneous administration of ICG 25 mg and glucose 5 g on the first day of measurement in each patient. Twenty-one patients were excluded from the study because of a higher PV-ICG/IDVG ratio (10.45) indicating apparent overestimation of the PV-ICG associated with the generalized protein capillary leakage. The remaining 171 patients were divided into four groups according to the magnitude of their disappearance rate of ICG from plasma (Ke-ICG). Results: Convergence was assumed consistently in each ICG or glucose decay curve, even in the lower Ke-ICG less than 0.10/min. The relationship between the two volumes was not statistically different among groups. Conclusions: The results suggest that the measurement of the PV-ICG can be equally accurate independently of its disappearance rate from plasma unless there is generalized protein capillary leakage.