Atropine increases sevoflurane potency in cortical but not spinal networks during cholinergic overstimulation

In the event of mass destruction with nerve agents a number of victims can be expected to suffer from symptoms of cholinergic overstimulation due to intoxication as well as from physical trauma. Since previous studies have demonstrated that cholinesterase inhibitors may reverse general anaesthesia in humans this scenario raises the question of how these patients can be anaesthetised in order to enable surgical interventions. A likely reason for this reversal is a reduction of anaesthetic potency by acetylcholine as observed for volatile anaesthetics in vitro. In order to test whether a combination of cholinergic antagonists with general anaesthetics improves their potency, we investigated the effects of clinically relevant concentrations of atropine on sevoflurane potency in cortical and spinal slice cultures during cholinergic overstimulation. As the spinal cord and neocortex are important substrates for general anaesthetics cultured spinal and cortical tissue slices were obtained from embryonic and newborn mice, respectively. Drug effects were assessed by extracellular voltage recordings of spontaneous action potential activity. Application of acetylcholine elevated spontaneous activity in neocortical and spinal slices. Atropine (10 nM) reduced discharge rates and reversed the increase of spontaneous activity induced by acetylcholine. In the presence of acetylcholine and atropine sevoflurane caused a concentration-dependent decrease of neuronal activity in neocortical (EC(50)=0.35+/-0.33 MAC) and spinal slices (EC(50)=0.43+/-0.03 MAC). Comparing our results with previous studies which investigated the effects of acetylcholine on anaesthetic potency it is concluded that small concentrations of atropine increase sevoflurane potency in cortical networks during cholinergic overstimulation. Thus, in a clinical setting, we recommend that anaesthetic drugs should be co-applied with atropine for adequate performance of general anaesthesia.