Permanent Global Ischemia Brain Death

The difference between the mean systemic arterial blood pressure and the intracranial pressure (ICP) (pressure of the CSF) maintains the cerebral perfusions pressure (CPP). A drop in arterial blood pressure or an increase in ICP depresses blood perfusion. When the CPP suddenly drops below a critical value (about 40 mm Hg), cerebral circulation gradually ceases. If blood flow is not restored, the nonperfused brain suffers total and irreversible damage, eventually leading to irreversible cessation of all functions of the brain, in both the cerebral hemispheres and the brainstem. Brain death is defined clinically as irreversible coma, apnea, and loss of all brainstem reflexes. Cardiorespiratory functions can be temporarily maintained with mechanical support and vasopressor agents.

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