Comparison of cns effects of propofol and thiopentone in cats

Abstract

Using cats with chronically implanted brain electrodes, we have compared the effects of propofol on CNS electrical activities with those of thiopentone. Ten cats were allocated to receive either propofol (n = 5) or thiopentone (n = 5). Cats were anaesthetized initially with 4% halothane in oxygen. The trachea was intubated and the lungs ventilated mechanically. A femoral artery and a vein in a forepaw were cannulated for arterial pressure monitoring and fluid infusion. After the inspired concentration of halothane was maintained at 0.5%, EEG in the cortex, the amygdala and the hippocampus, somatosensory evoked potential (SEP) and reticular multi-unit activity (R-MUA) were recorded. Incremental doses of propofol or thiopentone were administered i. v. at 5-min intervals during 0.5% halothane anaesthesia. The cumulative doses of propofol and thiopentone were 2, 5, 10 and 20mg kg-1, and 4, 10, 20 and 40 mg kg-1 respectively. Arterial pressure was maintained in excess of 100 mm Hg systolic by infusion of phenylephrine. All cats in the propofol group survived, but two in the thiopentone group died after the adminstration of thiopentone 40mg kg-1 Changes observed in CNS activity were dose-related in all cases. The EEG changed with the increments of doses of propofol or thiopentone, from fast, small amplitude to complexes of fast and slow, large amplitude activities, burst suppression and flat EEG. SEP latency was prolonged by both agents: the peak latency of N1 changed from 15 (SD 2) ms to 20 (5) ms with propofol 20mg kg-1, and from 14 (1) ms to 27(2) ms with thiopentone 40 mg kg-1. SEP amplitudes were depressed by both agents: the amplitude of N1 was depressed by 70 (29) % with propofol 20 mg kg-1 and by 60 (33) % with thiopentone 40mg kg-1. The R-MUA also was depressed by both agents: 85 (4) % with propofol 20 mg kg-1 and 85 (8) % with thiopentone 40mg kg-1. The R-MUA was depressed to 50% of control by propofol 3.2 (1.6) mg kg-1 or thiopentone 6.7 (5.0) mg kg-1. These depressive actions on the EEG, SEP and R-MUA induced by propofol were similar to those induced by twice the equivalent doses of thiopentone on an mg kg-1 basis. These results indicate that propofol has the same simple depressant effects as thiopentone on CNS electrical activity. © 1993 British Journal of Anaesthesia.