COMPARATIVE EFFECTS OF PROPOFOL, PENTOBARBITAL, AND ISOFLURANE ON CEREBRAL BLOOD-FLOW AND BLOOD-VOLUME

While intravenous and volatile anesthetics have widely differing effec ts on cerebral blood flow (CBF), clinical studies suggest that the rel ative differences in their effects on intracranial pressure (ICP) may be smaller. Because acute changes in ICP are determined primarily by c hanges in cerebral blood volume (CBV), we compared the impact of propo fol, pentobarbital, and isoflurane on CBF and CBV in rats. Equipotent doses of the three agents were determined by tail-clamp studies. Anima ls were then anesthetized with propofol (20 mg/kg load, 38 mg . kg(-1) . h(-1) infusion), pentobarbital (30 mg/kg load, 20 mg . kg(-1) . h(- 1) infusion), or isoflurane 1.6-1.8%. Two hours later, CBF and CBV wer e measured using H-3-nicotine as a CBF tracer, and C-14-dextran and Tc -99m-labeled red cells as markers for cerebral plasma and red blood ce ll volumes (CPV and CRBCV), respectively. Total CBV was the sum of CPV and CRBCV. CBF was 2.0-2.6 times greater with isoflurane than with pr opofol or pentobarbital (137 vs. 67 and 52 ml . 100 g(-1) . min(-1), r espectively). By contrast, while CBV was greater in the isoflurane gro up than in either the propofol or pentobarbital groups, the magnitude of the intergroup differences were much smaller(propofol = 2.49 +/- 0. 28 ml/100 g; pentobarbital = 2.27 +/- 0.15 ml/100 g; isoflurane = 2.77 +/- 0.24 ml/100 g, mean +/- SD). These results suggest that the simpl e measurement of CBF may not adequately describe the cerebrovascular e ffects of an anesthetic, at least with respect to predicting the magni tude of the agents likely effects on ICP.