Suppressive actions of volatile anaesthetics on the response capability in cats.

摘要

PURPOSE: Suppression of response to a given stimulus by anaesthetics might be considered as a summation of the suppression of basal (pre-stimulus) activity and response capability (increased by stimulus). Anaesthetic suppression of each component in brain and cardiovascular variables by halothane, isoflurane or sevoflurane was compared in cats. METHODS: Thirty cats were allocated to one of three groups (n = 10 in each) according to the anaesthetic given. The sciatic nerve was stimulated after maintaining the end-tidal concentration of the anaesthetic at 1.3 or 2.0 MAC for at least 30 min. Cortical electroencephalogram (EEG), multi-unit activity in the mid-brain reticular formation (R-MUA), mean arterial pressure (MAP) and heart rate (HR) were measured before and after electrical sciatic nerve stimulation. RESULTS: The EEG patterns and R-MUA indicated greater suppression of activity in the brain by isoflurane (31 +/- 4% of awake state at 1.3 MAC, mean +/- SEM) and sevoflurane (38 +/- 5%) than by halothane (61 +/- 5%, P < 0.05), before stimulation. The R-MUA following the stimulation was not different among agents. The MAP and HR were not different among groups before stimulation, but following stimulation were greater in the sevoflurane group (137 +/- 9 and 103 +/- 9 mmHg at 1.3 and 2.0 MAC) than in the halothane group (103 +/- 5 and 76 +/- 3 mmHg, P < 0.05). CONCLUSION: Isoflurane and sevoflurane have greater suppressive action on the basal CNS activity than halothane at the same MAC, and that these two anaesthetics have a weak suppressive action on the response capability to peripheral stimulation.