Merck Manual

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Brain Death


Kenneth Maiese

, MD, Rutgers University

Reviewed/Revised May 2022
Topic Resources

Brain death is loss of function of the entire cerebrum and brain stem, resulting in coma, no spontaneous respiration, and loss of all brain stem reflexes. Spinal reflexes, including deep tendon, plantar flexion, and withdrawal reflexes, may remain. Recovery does not occur.

The concept of brain death developed because ventilators and drugs can perpetuate cardiopulmonary and other body functions despite complete cessation of all cerebral activity. The concept that brain death (ie, total cessation of integrated brain function, especially that of the brain stem) constitutes a person’s death has been accepted legally and culturally in most of the world.

Diagnosis of Brain Death

  • Serial determination of clinical criteria

  • Apnea testing

  • Sometimes electroencephalography (EEG), brain vascular imaging, or both

For a physician to declare brain death, a known structural or metabolic cause of brain damage must be present, and use of potentially anesthetizing or paralyzing drugs, especially self-administered, must be excluded.

If hypothermia is present, a core temperature < 35° C must be increased slowly to > 36° C, and if status epilepticus is suspected, EEG should be done. In adults, after all complicating medical conditions have been excluded and a comprehensive neurologic examination with the required testing has been done, brain death can be confirmed. Some states advise clinicians to do two separate examinations separated by at least 48 hours in children; this approach is not consistently recommended or required for adult patients (see table Guidelines for Determining Brain Death (in Patients > 1 Year) Guidelines for Determining Brain Death (in Patients > 1 Year*)† Guidelines for Determining Brain Death (in Patients <span class='symbol' >></span> 1 Year*)† ).

Examination includes

  • Assessment of pupil reactivity

  • Assessment of oculovestibular, oculocephalic, and corneal reflexes

  • Apnea testing

Sometimes EEG or tests of brain perfusion are used to confirm absence of brain activity or brain blood flow and thus provide additional evidence to family members, but these tests are not usually required. They are indicated when apnea testing is not hemodynamically tolerated and when only one neurologic examination is desirable (eg, to expedite organ procurement for transplantation).


Prognosis for Brain Death

The diagnosis of brain death is equivalent to the person’s death. No further treatment can prevent death.

After brain death is confirmed, all supporting cardiac and respiratory treatments are ended. Cessation of ventilatory support results in terminal arrhythmias. Spinal motor reflexes may occur during terminal apnea; they include arching of the back, neck turning, stiffening of the legs, and upper extremity flexion (the so-called Lazarus sign). Family members who wish to be present when the ventilator is shut off need to be warned of such reflex movements.

NOTE: This is the Professional Version. CONSUMERS: View Consumer Version
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