Brain death means ‘the irreversible loss of the capacity for consciousness combined with the irreversible loss of the capacity to breathe’. Both these are essentially functions of the brain stem. Death, if thought of in this way, can arise either from causes outside the brain (i.e. respiratory and cardiac arrest) or from causes within the head. With the advent of artificial ventilation it became possible to support such a dead patient temporarily, although in all cases cardiovascular failure eventually supervenes and progresses to asystole.
Before considering a diagnosis of brain death it is essential that certain preconditions and exclusions are fulfilled.
• The patient must be in apnoeic coma (i.e. unresponsive and on a ventilator, with no spontaneous respiratory efforts).
• Irremediable structural brain damage due to a disorder that can cause brain stem death must have been diagnosed with certainty (e.g. head injury, intracranial haemorrhage).
• The possibility that unresponsive apnoea is the result of poisons, sedative drugs or neuromuscular blocking agents must be excluded.
• Hypothermia must be excluded as a cause of coma. The central body temperature should be more than 35°C.
• There must be no significant metabolic or endocrine disturbance that could produce or contribute to coma. There should be no profound abnormality of the plasma electrolytes, acid-base balance, or blood glucose levels.
DIAGNOSTIC TESTS FOR THE CONFIRMATION OF BRAIN DEATH
All brain stem reflexes are absent in brain death. The following tests should not be performed in the presence of seizures or abnormal postures.
• The pupils should be fixed and unresponsive to bright light. Both direct and consensual light reflexes should be absent. The size of the pupils is irrelevant, although most often they will be dilated.
• Corneal reflexes should be absent.
• Oculocephalic reflexes should be absent, i.e. when the head is rotated from side to side, the eyes move with the head and therefore remain stationary relative to the orbit. In a comatose patient whose brain stem is intact, the eyes will rotate relative to the orbit (i.e. doll’s eye movements will be present).
• There are no vestibulo-ocular reflexes on caloric testing.
• There should be no motor responses within the cranial nerve territory to painful stimuli applied centrally or peripherally. Spinal reflexes may be present.
• There must be no gag or cough reflex in response to pharyngeal, laryngeal or tracheal stimulation.
• Spontaneous respiration should be absent. The patient should be ventilated with 5% CO2 in 95% O2 for 10 min and then disconnected from the ventilator for a further 10 min. Oxygenation is maintained by insufflation with 100% oxygen at high flow rates via a catheter placed in the endotracheal tube. The patient is observed for any signs of spontaneous respiratory eforts. A blood gas sample should be obtained during this period to ensure that the PaC02 is sufficiently high to stimulate spontaneous respiration (>6.7 kPa [50 mmHg]).
The examination should be performed (and repeated after a few hours) by two doctors of senior status a minimum of 6 hours after the onset of coma or, if due to cardiac arrest, at least 24 hours after restoration of an adequate circulation.
It is not necessary to perform confirmatory tests such as EEG and carotid angiography, as these may be misleading.
In suitable cases, and provided the patient was carrying a donor card and/or the consent of relatives has been obtained, the organs of those in whom brain stem death has been established may be used for transplantation. In all cases in the UK the coroner’s consent must be obtained.