INHALATIONAL ANESTHETICS INHIBIT SPREADING DEPRESSION - RELEVANCE TO MIGRAINE

Cortical spreading depression (SD) has not been shown in the human neo cortex by direct cortical recordings. However, animal studies suggest that cortical injury, such as that occurring during neurosurgical proc edures, should result in the initiation of SD. It is possible that inh ibition of SD by volatile anesthetic agents may partially explain the failure to observe SD in the human neocortex during surgery. This stud y examines the effect of the anesthetic agents alpha-chloralose, halot hane, nitrous oxide and isoflurane on the initiation of cortical SD in the cat neocortex. SD was seen in 100% of cats anesthetized with alph a-chloralose (n=15), in 3 of 7 (42%) animals anesthetized with isoflur ane (p<0.05, chi(2) with Yates correction) and none of the animals (n= 4, 6 hemispheric preparations) anesthetized with halothane (p<0.005, c hi(2) with Yates correction, halothane vs ct-chloralose group). In all cases this inhibitory effect was reversible. In four animals the admi nistration of nitrous oxide (66%) reduced the inspired concentration o f isoflurane required to inhibit SD by 0.75%. This study suggests that halothane, and to a lesser extent isoflurane and nitrous oxide, prote ct against the initiation of cortical SD. This observation may partial ly explain why SD has not been demonstrated in human neocortex during surgery. Further studies are needed to determine if SD may occur under pathological conditions, such as during migraine with aura, where the cortex may be predisposed to SD.