Concepts of brain oxygen sufficiency during seizures

To resolve conflicting evidence of oxygen sufficiency or insufficiency during seizures, signals of metabolic and circulatory function were monitored in rat cerebral cortex during recurrent seizures. Early seizures were accompanied by increased blood volume, increased tPO2, and oxidative shifts of cytochrome a,a3, indicative of oxygen sufficiency. Later seizures were accompanied by a smaller increment in blood volume, a fall in tPO2, and shifts toward reduction of cytochrome a,a3, suggesting that cerebral oxygen supply became insufficient to meet demand. Responses suggesting oxygen insufficiency occurred during short duration ictal bursts, interictal spikes or electrocortical stimulation at times when longer duration ictal episodes still were accompanied by responses signalling oxygen sufficiency. These data indicate that there is a progressive dissociation of the normally tight couple between neuronal activity, energy demand, and cerebral blood flow during status epilepticus. Systemic derrangements that often accompanied recurrent seizures also contributed to decreased cerebral oxygenation. These factors may cause the neuronal damage reported to follow prolonged status epilepticus.