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Effects of Halothane and Fentanyl on the Rate of CSF Production in Dogs

Using the open ventriculocisternal perfusion method, the rate of cerebrospinal fluid (CSF) production was examined in dogs anesthetized with either halothane (0.8%) or fentanyl (3.0 μg/kg/min for 20 min, then 0.2 μg/kg/min, intravenously), and nitrous oxide (60–70%) in oxygen. Halothane decreased the mean rate of CSF production from 0.047 ± 0.006 ml/min (mean ± SEM) in controls to 0.033 ± 0.005 ml/min. This effect persisted throughout 3.0–3.5 h of anesthesia. When the expired concentration of halothane was decreased from 0.8% to less than 0.1%, the mean rate of CSF production returned to control values within 45–50 min. Fentanyl produced no change in the mean rate of CSF production compared to controls. These data suggest that increased CSF volume does not contribute to increased intracranial pressure during prolonged halothane anesthesia. In patients at risk for increased intracranial pressure due to increased CSF volume, either halothane or fentanyl may be preferable to anesthetics that may increase CSF production, e.g., enflurane.