Possible overestimation of indocyanine green-derived plasma volume early after induction of anesthesia with propofol/fentanyl

Apparently large plasma volumes derived by indocyanine green (PV-ICG) have been determined in the initial period after induction of anesthesia. We tested the hypothesis that possible overestimation of PV-ICG occurs shortly after anesthetic induction. Anesthesia was induced in 13 patients with fentanyl bolus 2 mug/kg and propofol infusion 0.5 mg(.)kg(-1.)min(-1) IV until patients lost consciousness and was then maintained with a propofol infusion. PV-ICG and the initial distribution volume of glucose (IDVG) were assessed at 15 min before and at 15 min after anesthetic induction. Plasma ICG and glucose concentrations were measured from serial blood samples taken before and through 7 min after injection of ICG 25 mg and glucose 5 g. PV-ICG and IDVG were calculated using a one-compartment model. PV-ICG was significantly increased by an average of 15.3% after induction, from 2.29 +/- 0.38 (SD) L to 2.64 +/- 0.31 L (P < 0.001). The mean hematocrit (Hct), concentrations of hemoglobin (Hb), and total plasma proteins at postinduction decreased compared with those at preinduction by 2.9%, 2.2%, and 2.3%, respectively (P < 0.05). Percentile increase in plasma volume calculated from Hb and Hct before and after induction was 4%. Consequently, an 11% overestimation in PV-ICG was observed. IDVG remained unchanged. Therefore, the ratio of PV-ICG/IDVG increased from 0.40 +/- 0.05 before induction to 0.48 +/- 0.06 after induction (P < 0.01). These results validate the hypothesis that possible overestimation of PV-ICG occurs during a definable period of time after propofol anesthetic induction. The present results also support the PV-ICG/IDVG ratio as a measure of possible overestimation of PV-ICG or fluid redistribution from the central to the peripheral tissues.