Furosemide decreases cerebrospinal fluid formation during desflurane anesthesia in rabbits

Previous studies suggest that desflurane may increase cerebrospinal fluid (CSF) formation rate (Vf) and volume, particularly during conditions of hypocapnia combined with elevated CSF pressure. The present study was designed to determine whether treatments routinely used in patients during anesthesia for neurological surgery would decrease Vf during desflurane anesthesia in rabbits. Three groups of six rabbits each were examined at four experimental conditions. Condition 1 was the combination of isoflurane, normocapnia, and normal CSF pressure (baseline, all groups). Condition 2 was the combination of isoflurane (group 1) or desflurane (groups 2 and 3), hypocapnia, and elevated CSF pressure (27 and 33 cm H2O). Conditions 3 and 4 were the same as condition 2 with the addition of furosemide, dexamethasone, mannitol, or fentanyl in groups 2 and 3. Vf, resistance to reabsorption of CSF (Ra), and systemic values were determined at each experimental condition, and brain water content was determined at the end of the study. Mean baseline Vf was 9.8 +/- 2.6 microliters.min-1. During the combination of desflurane, hypocapnia, and elevated CSF pressure, furosemide decreased Vf to 3.2 +/- 1.7 microliters.min-1, mannitol increased plasma osmolality and decreased plasma sodium concentration, and fentanyl decreased heart rate and increased plasma potassium concentration. Values for Ra and brain water content did not differ between groups. Of the four treatments examined, only furosemide decreased Vf during the combination of desflurane, hypocapnia, and elevated CSF pressure.