Appendix 13 - Brain death criteria

Summary

There are several hospital policies on the criteria for brain death, for example that published in 1968 by the Ad Hoc Committee of the Harvard Medical School to Examine the Definition of Brain Death.

Nature of coma must be known

• Known structural disease or irreversible systemic metabolic cause that can explain the clinical picture.

Some causes must be ruled out

• Body temperature must be above 32.2 °C to rule out hypothermia.

• No chance of drug intoxication or neuromuscular blockade.

• Patient is not in shock.

Absence of cerebral and brain stem function

• Unresponsive to stimuli (i.e., no flexor or extensor posturing).

• Absent pupillary reflex.

• Absent caloric vestibular–ocular reflex.

• Absent corneal reflex.

• Absent gag reflex.

• Absent cough reflex.

• Areflexic: the limbs are flaccid, and there is no movement, although primitive withdrawal movements in response to local painful stimuli, mediated at a spinal cord level, can occur (i.e. not decorticate or decerebrate).

• Absent respiratory drive by apnea test.

• Some protocols require independent exams 6 hours apart by neurologist or neurosurgeon.

• Some protocols recommend 12-hour observation.

Apnea test

• Preoxygenate with 100% O₂. Get baseline arterial blood gas (pH and pCO₂ should be normal).

• Disconnect ventilator and give 100% O₂ by blow-by. Observe for spontaneous respirations. (If hypotension or arrhythmia occurs, immediately reconnect the ventilator.)

• After 10 minutes, or at earlier calculated interval, draw arterial blood gases, then reconnect the ventilator.

• Patient is apneic if pCO₂ > 60 mm Hg and there is no respiratory effort.

Confirmatory tests

These are not necessary to diagnose brain death. However, some protocols allow the diagnosis of brain death based on these studies.