Abstract

Cerebral blood flow (CBF) is tightly regulated to meet metabolic demands, and it increases during hemodilution as arterial oxygen content (CaO₂) falls. Oxygent® is a perfluorocarbon (PFC) emulsion that has a high capacity to dissolve oxygen and can thus increase CaO₂ in patients breathing supplemental oxygen. PFCs have shown excellent oxygen therapeutic value in both phase II and phase III clinical trials. However, the effects of Oxygent® on CBF in hemodilution are unknown. We performed this study to investigate how Oxygent® alters CBF in rats undergoing stepwise isovolumetric hemodilution under isoflurane anesthesia with 100% oxygen ventilation. In vivo Laser Doppler Flow (LDF) probes measured CBF as blood was gradually replaced with equal volumes of either 5%Albumin (controls) or (1:1) PFC and Albumin. Hematocrit and blood gases were measured and CaO₂ calculated after each dilution. Target values were to achieve a hematocrit value of 10% and fluorocrit between 7.5-10%. We compared CBF in the Oxygent® vs. control group at decreasing levels of hematocrit and CaO₂ with repeated t-tests. At hematocrits less than 15%, CBF rate approached baseline in the Oxygent® group, and was lower than the control group (p = 0.004). At maximal hemodilution, Oxygent® treated rats also showed higher PaO₂ (p < 0.001) and required lower phenylephrine infusion rates to maintain blood pressure (p = 0.002). These data support that administration of Oxygent® improves tissue oxygenation during hemodilution.