Harvard criteria

The 1968 Harvard criteria defined brain death (irreversible coma) as the permanent absence of all brain function, including the brainstem. The essential clinical signs required included complete unresponsivity to all stimuli, the absence of any spontaneous muscular movements or breathing, and the loss of all reflexes, notably fixed and dilated pupils and absent cranial nerve reflexes like the gag and cough reflexes. The criteria further stipulated that hypothermia and drug intoxication must be ruled out as confounding factors and required a flat electroencephalogram (EEG), repeated after 24 hours, to confirm the total lack of electrical brain activity.