Glucose dilution can detect fluid redistribution following phentolamine infusion in dogs

Objective: We have recently reported that the initial distribution volume o f glucose (IDVG) reliably measures the central extracellular fluid (ECF) vo lume in the presence of fluid gain or loss. However, it is not clear if IDV G consistently reflects central-ECF volume when redistribution of fluid occ urs in the absence of fluid gain or loss. This study was designed to invest igate changes in fluid volumes during phentolamine infusion in dogs. Design: Prospective animal study. Setting: Institutional animal research laboratory. Subjects: Fourteen anesthetized and ventilated mongrel dogs. Interventions: Anesthetized animals were mechanically ventilated and receiv ed infusions of normal saline (n = 7) or phentolamine (10 mu g kg min) (n = 7). Plasma volume was estimated using the indocyanine green (ICG) dilution method (PV-ICG) and IDVG was calculated using a one-compartment model by s imultaneous administration of ICG 0.5 mg/kg and glucose 100 mg/kg before, d uring, and after infusion of either drug. Measurements and results: PV-ICG during infusion was not different between groups. However, IDVG significantly decreased (P < 0.05) following phentola mine infusion when compared with normal saline infusion. Conclusion: Our results suggest that IDVG rather than PV-ICG consistently m easures central extracellular fluid volume, even when redistribution of flu id occurs.