Brain death - Disorders of consciousness and memory

Brain death

Definition

This is defined as ‘irreversible loss of the capacity for consciousness combined with the irreversible loss of the capacity to breathe’.

Aetiology

The brainstem is the seat of consciousness and of respiratory drive. Any intracranial cause or a systemic cause such as severe, prolonged hypoxia or hypotension can lead to brainstem death.

In view of the fact that many patients may be established on a ventilator prior to brain death being diagnosed, ways of assessing brain death have been developed, to allow the withdrawal of ventilation. Although patients who fulfil these criteria can be kept alive by ventilation, eventually they will die from other causes.

Clinical features

In order to diagnose brainstem death several criteria must be met.

Prior to brainstem testing, the following preconditions must be fulfilled:

·        There must be a diagnosis for the cause of the irreversible brain damage, e.g. head injury, subarachnoid haemorrhage or anoxic, ischaemic damage.

·        The patient must be unresponsive (GCS = 3), and have no spontaneous respiratory efforts on the ventilator.

·        There must be no possibility of drug intoxication, including any recent use of anaesthetic agents or paralysing agents.

·        Hypothermia should be excluded and body temperature must be >35◦ C.

·        There must be no significant metabolic, endocrine or electrolyte disturbance causing or contributing to the coma.

Brainstem testing

This should be carried out by two experienced clinicians (one a consultant, another an experienced registrar or consultant) on two separate occasions 12 hours apart. These tests are designed to show that all brainstem reflexes have been lost completely.

Pupils fixed and unresponsive to light. Absent corneal reflexes.

Absent vestibuloocular reflexes on ice-cold water being instilled into each ear.

Absent cough and gag reflexes on pharyngeal, laryngeal or tracheal stimulation.

No motor response within the cranial nerve distribution (eye, face, head) elicited by stimulation of any somatic area such as nail bed pressure, supraorbital pressure and Achilles tendon pressure.

Apnoea testing

The patient is pre-ventilated with 100% oxygen and continuous oxygen administered via a tracheal catheter (to prevent hypoxia during the test) and then the ventilator is disconnected and the pCO2 is allowed to climb to 6.65 kPa. No respiratory effort should occur.

If all the above criteria are fulfilled, the patient is diagnosed as brainstem dead, and ventilation may be with-drawn. They may be suitable for organ donation, if the family consent.

Patients with some evidence of brainstem activity may still have a very poor prognosis. Death may occur due to cardiovascular collapse, e.g. sepsis, cardiac arrhythmia. However, if the patient remains stable, but with very little brain function, it may be appropriate to withdraw life prolonging treatment, but this may require application to the courts.