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Although the mass of the brain is only 2% of the total body mass, its energy requirement is more than seven times higher than that of the other organs. The main source of neuronal energy is the generation of ATP by the aerobic metabolism of glucose. The brain requires a steady blood supply to provide both substrate and oxygen at a constant rate. Complete arrest of the cerebral circulation leads to cessation of neuronal electrical activity and loss of the energy state and ion homeostasis within a few minutes. Depletion of high-energy phosphates, membrane ion pump failure, efflux of cellular potassium, influx of sodium, chloride and water, and membrane depolarization occur swiftly. If the interruption in blood flow persists for longer than 510 min at normothermia, irreversible cell damage is likely. (Astrup et al. 1981). Depolarization leads to the failure of neurotransmitter transport, which initiates a catastrophic biochemical cascade.