[The central nervous system arousing effects of ketamine are decreased by addition of midazolam. A post-anesthesia study of patients following maxillary surgery with spontaneous respiration].

Abstract

The present study was done in order to investigate the central nervous activity in patients (n = 15) after maxillo-facial surgery, 5 and 90 minutes post ketamine-midazolam-anesthesia. The combination of a benzodiazepine with ketamine was thought to be beneficial to reduce the usual excitatory effects after ketamine postoperatively. In order to demonstrate these benefits EEG-power spectra as well somatosensory-evoked potentials were derived (Neurotrac). Additionally, the central nervous effects were correlated with blood pressure changes. 5 minutes post ketamine-midazolam-anesthesia EEG-power spectra showed a marked depression in the alpha, theta and delta power band when compared to the control-awake situation. However, power in the beta domain (13-30 Hz) was significantly elevated. 90 minutes post anesthesia the high power values returned back to control. In no instance were there any signs of theta-paroxysms which can be taken as an index for central excitation. In the evoked potential a significant increase in amplitude of the early N20 and late N50 peak was evident. This correlated with an increase in systolic blood pressure. 90 minutes post anesthesia only the late N50 peak still remained elevated suggesting some residual excitatory effects in the thalamo-cortical projection area to be present. The latter may reflect an increase in activity in the associative cortical areas of the cerebral cortex. In general however, the additional administration of midazolam resulted in a marked reduction in excitatory central nervous effects when compared to the well known excitation after sole ketamine injection. Thus, the beneficial venture of the two separate classes of anesthetics is advocated for clinical practice.