[abstract] THE EFFECT OF HIGH PRESSURE ON THE EEG BURST SUPPRESSION DOSE OF THIOPENTAL IN RATS

Abstract

The effect of high pressure on the induction dose of thiopental in rats was studied during continuousintravenous infusion. All animals were adapted to the restrained conditions in a pressure chamber for two weeks before the experiments, and had stainless steel screws and miniature connectors im-planted in the cranium. No sensory stimulation was applied during the experiments, and one second of electrical silence in the EEG-recording was chosen as the biological end point. Groups of animals were studied during continuousinfusion of thiopental 7.5 mg/kg/min into a previously implanted venous catheter at 1 ATA air, at 1 ATA He0, at 4 ATA air, and at 4 ATA air and 67 ATA He. The compression rate was 0.3 ATA/min, and one hour was spent at pressure before the experiment started. The mean induction doses were: 53.1 mg/kg at 1 ATA air, 46.4 mg/kg at 1 ATA He0, 45.3 mg/kg at 4 ATA air, and 73.9 mg/kg at 4 ATA air + 67 ATA He. We have thus confirmed the antagonistic effect of pressure on the thiopental sleep-dose at 71 ATA in rats. Adaptation, paracenthesis ,slow compression, and an additional hour of adaptation at pressure together with avoidance of sensory activation did not influence the degree of pressure induced barbiturate antagonism to any great extent, compared with the results of other investigators.