RATE OF CEREBROSPINAL-FLUID FORMATION, RESISTANCE TO REABSORPTION OF CEREBROSPINAL-FLUID, BRAIN-TISSUE WATER-CONTENT, AND ELECTROENCEPHALOGRAM DURING DESFLURANE ANESTHESIA IN DOGS

Intracranial pressure (ICP) has been shown to increase dramatically during desflurane anesthesia, possibly as a result in part of an increase in the rate of cerebrospinal fluid (CSF) formation (V(f)) or a decrease in the rate of CSF reabsorption. To examine this phenomenon, I designed a study to measure V(f), resistance to reabsorption of CSF (R(a)), brain tissue water content, and the electroencephalographic activity (EEG) during desflurane anesthesia in dogs. V(f). and R(a) were determined using ventriculocisternal perfusion of mock CSF labeled with blue dextran. EEG activity was determined using aperiodic analysis. At the end of the study, brain tissue water contents of gray and white matter were determined by dry/wet weight ratios. Eighteen dogs were allocated into three groups. Group 1 (n = 6) was examined at five experimental conditions during normocapnia; group 2 (n = 6) was examined at five experimental conditions during hypocapnia. The experimental conditions for groups 1 and 2 were (a) baseline (halothane 0.5-1.0% inspired plus thiopental 12 mg . kg-1 IV given over 15 min followed by IV infusion at 12 mg . kg-1 . h-1), (b) 0.5 MAC (3.5 +/- 0.1% expired) and (c) 1.0 MAC (7.0 +/- 0.1 % expired) desflurane at normal CSF pressure, and (d) and (e) 0.5 and 1.0 MAC desflurane at increased CSF pressure (> 30 cm H2O). Group 3 (n = 6), the control group, was examined over the same time period as groups 1 and 2. In the control group, desflurane was not administered; instead, the baseline condition (i.e., halothane plus thiopental) was maintained throughout the study. In group 2, desflurane 0.5 and 1.0 MAC increased V(f) from a baseline value of 0.047 +/- 0.017 (mean +/- SD) to 0.077 +/- 0.029 and 0.083 +/- 0.032 ml . min-1 (p < 0.05) at the condition of hypocapnia combined with increased CSF pressure but not at the other experimental conditions for that group or for group 1. Desflurane caused no significant change of R(a) or gray or white matter brain tissue water content in either group 1 or 2. EEG activity edge and number of beta waveforms decreased while the power and number of delta waveforms increased when the desflurane concentration rose from 0.5 to 1.0 MAC. I conclude that during hypocapnia and increased CSF pressure, V(f) increases during 0.5 and 1.0 MAC desflurane. Desflurane-induced increase of V(f) may have contributed to the high ICP previously reported with desflurane under conditions of hypocapnia and increased CSF pressure but not during normocapnia.