EFFECT OF XENON ON CENTRAL-NERVOUS-SYSTEM ELECTRICAL-ACTIVITY DURING SEVOFLURANE ANESTHESIA IN CATS - COMPARISON WITH NITROUS-OXIDE

We have compared the effects of xenon and nitrous oxide on central ner vous system (CNS) electrical activity during sevoflurane anaesthesia i n cats by recording the electroencephalogram (EEG), multi-unit activit y of the midbrain reticular formation (R-MUA) and somatosensory evoked potentials (SEP). Basal anaesthesia with 2% and 5% sevoflurane was us ed. With 2% sevoflurane, 70% xenon initially produced rhythmic slow wa ves which were followed by bursts of high-amplitude sharp waves interr upted by low amplitude slow waves on the EEG. Xenon induced an initial increase, followed by a decrease in R-MUA. Nitrous oxide 70% decrease d the amplitude of the EEG activity which was associated with an incre ase in R-MUA. Xenon suppressed the amplitude of both the initial posit ive and negative deflections of the SEP to a greater extent than nitro us oxide. With 5% sevoflurane anaesthesia, both anaesthetics increased the frequency of spikes on the EEG and facilitated R-MUA. These findi ngs indicate that xenon has a stimulatory action on CNS background act ivity and a suppressive action on CNS reactive capability which is mor e potent than that of nitrous oxide.