Tests for irreversible loss of brain stem function
Brain death is a clinical diagnosis of irreversible cessation of all cerebral and brain stem function due to a major intracerebral catastrophe (trauma, anoxia, mass lesion, infection, hemorrhage, etc.).
Complete loss of brain stem function begins with apneic coma. On examination, all brain stem reflexes (corneal, pupillary, gag, ciliospinal) are absent. The pupils are midposition or large and fixed. Oculocephalic and oculovestibular reflexes are absent.
Muscle tone is flaccid, with no spontaneous facial movement and no motor response to noxious stimuli.
This condition should be present for 6 to 24 hours in adults.
Metabolic causes (hypothermia, hypotension) and drug effects (neuromuscular blockers, sedative drugs) need to be ruled out.
Many local institutions have developed their own, slightly modified criteria for brain death.