Absence of Cardiovascular Collapse

When intracranial pressure increases, systemic hypertension occurs as a result of the Cushing phenomenon. This is followed by a sudden decrease in blood pressure because of sudden interruption of vasomotor output from the brainstem and hypothalamus to the spinal cord. Hypotension usually resolves spontaneously within several days because of restoration of spontaneous activity of the spinal cord's vasomotor neurons. Because hypotension suppresses cerebral blood flow and perhaps electroencephalographic activity and can promote a spurious diagnosis, administration of vasopressor is required. Vasopressor occasionally restores electroencephalographic activity for the determination of brain death.