Movement associated with high cerebral concentrations of isoflurane: no evidence of seizure activity

This study examined the effect of high cerebral concentrations of isoflurane on the electroencephalogram (EEG) and motor activity while using an experimental preparation in which isoflurane can be selectively delivered to the in situ goat brain. In a previous study we found that isoflurane (> 6%), when selectively delivered to the brain, was associated with spontaneous movement.

In each of six goats, the cerebral circulation was isolated and cannulae inserted into a carotid artery and the jugular veins to permit selective delivery of isoflurane using a bubble oxygenator-roller pump system. The EEG was measured while isoflurane (1.3%, 3% and 10-12%) was delivered to the brain; isoflurane concentration in the torso during these periods was 1.3%, 0.3% and 0.3% respectively.

The EEG was active at isoflurane 1.3% but was isoelectric with spike activity at 3% and 10-12%; EEG power decreased from 32,249 +/- 15,241 microV2 (mean +/- sd) during the control period (isoflurane = 1.3%) to 1761 +/- 2435 microV2 when cranial isoflurane = 3%, and 3346 +/- 4780 microV2 when cranial isoflurane = 10-12% (P < 0.05). When cranial isoflurane concentration was 10-12%, with the torso isoflurane concentration at 0.3%, spontaneous motor activity occurred, including stiffening, extremity and jaw movement and blinking. The EEG returned to normal when isoflurane concentration was decreased to 1.3%.

The presence of spontaneous movement with concomitant high cranial concentrations of isoflurane and isoelectric EEG is unexplained, but is consistent with a facilitatory effect of isoflurane on motor activity, presumably at a subcortical level.