Concepts of Brain Death

Criteria for Assessment Brainstem Death

There are certain preconditions that must be fulfilled and potentially reversible causes excluded prior to formal brainstem testing.

Brainstem testing in the UK should be performed by two qualified doctors, both of whom are competent with the procedure, have full registration with the GMC or equivalent international professional body for > 5 years, and at least one must be a consultant.

The tests should be performed by both doctors together and successful completion is required on two separate occasions.

Preconditions and Exclusion Criteria

Any patient considered for potential brainstem testing should meet the following preconditions:

• Suffering a disease with aetiology that is sufficiently severe to cause permanent cessation of brainstem function (this must include brain imaging at a minimum)
• Have had an assessment period long enough to exclude potential recovery
• Excluded reversible factors that may contribute to coma or apnoea (see below)

Additional caution or ancillary investigation should be used in uncommon circumstances (e.g. following decompressive craniectomy, or pathology isolated to the posterior fossa). Importantly, any spinal reflexes present may occur independent of the brainstem and does not preclude the diagnosis of brainstem death.

It is essential to exclude or correct any reversible causes present that may account for the patient’s condition, prior to continuing with the testing:

• Hypothermia
  • Core temperature must be at least 36 °C at the time of testing
• Sedative drugs
  • Includes any unknown or illicit drug substances
• Endocrine abnormalities
  • Thyroid or adrenal assays may be required if uncertain
• Metabolic abnormalities
  • Includes potassium, sodium, magnesium, phosphate, calcium levels, and glucose levels
• Profound neuromuscular weakness
  • Includes neuromuscular blockade or neuromyopathies
• Cervical spinal cord pathology
  • As this may preclude spontaneous breathing at the spinal cord level
• Cardiorespiratory disturbance
  • Target age appropriate or baseline parameters; clinicians should be confident that cardiovascular and respiratory disturbance is not contributing to coma or apnoea

Brainstem Testing

These tests are performed after physicians have confirmed that the patient satisfies the preconditions and has no reversible causes of coma.

All tests should be performed twice and time of brainstem death recorded upon completion of the second set of tests or the completion of all subsequent ancillary investigations later. Both brainstem reflex tests and apnoea tests should be recorded.

Electroencephalogram (EEG) and CT imaging often help the clinician in the overall picture, however do not form any part of the criteria in diagnosis of brainstem death.

Brainstem Reflex Testing

Pupillary Light Reflex

The afferent nerve is CN II, the Edinger Westphal nucleus in the midbrain is the involved brainstem nuclei, and the efferent nerve is CN III.

The test is performed by a bright light being shone into each pupil, testing for both direct and consensual reflexes. The response in brainstem death is the absence of pupillary constriction.

By TeachMeSeries Ltd (2026)

Figure 1
A schematic representation of the pupillary reflex

Corneal Reflex

The afferent nerve is CN V₁, the trigeminal and facial nuclei in the pons are the involved brainstem nuclei, and the efferent nerve is CN VII.

The test is performed by sterile gauze being used to lightly brush both corneas, testing direct and consensual blinking reflexes. The response in brainstem death is the absence of eyelid movement.

Vestibulo-Ocular Reflex

The afferent nerve is CN VIII, the vestibular and abducens nuclei in the pons and oculomotor nuclei in the midbrain are the involved brainstem nuclei, and the efferent nerves are III and VI (to the medial and lateral rectus muscles).

Otoscopy is initially used to check external auditory canals are clear. The test is then performed by placing the patient with their head up to 30° and 50 mL of ice-cold saline instilled into the external auditory meatus over 1 minute (both sides should be tested separately). The response in brainstem death is the absence of any eye movement. This should be performed on both sides.

Motor Response

The afferent nerve is CN V, the trigeminal and facial nuclei in pons are the involved brainstem nuclei, and the efferent nerve is CN VII.

The test is performed by applying pressure to the supra-orbital ridge and the response in brainstem death is the absence of motor response. This should be performed bilaterally.

Gag Reflex

The afferent nerve is CN IX, the spinal nucleus of V and nucleus ambiguus in medulla oblongata are the involved brainstem nuclei, and the efferent nerve is CN X.

The test is performed by stimulating the posterior hypopharynx at base of the tongue or soft palate using a depressor, suction catheter or laryngoscope. The response in brainstem death is the absence of a gag reflex. This should be performed bilaterally.

Cough Reflex

The afferent nerve is CN X, multiple nuclei forming a ‘cough centre’ in medulla oblongata are the involved brainstem nuclei, and the efferent nerve is CN X.

The test is performed by a bronchial or suction catheter being passed to the carina. The response in brainstem death is the absence of a cough.

TeachMeSeries Ltd (2019)

Figure 2
Transverse section of the trachea at the level of the carina

Apnoea Test

The apnoea test should only be performed after demonstration of absent brainstem reflexes. The test aims to demonstrate brainstem death by producing an acidotic respiratory stimulus without inducing hypoxia or cardiovascular instability.

Prior to the test, the absence of spontaneous respiratory effort should be confirmed. Various methods for the apnoea test have been described, however one such method includes:

• Pre-oxygenation with 100% O2
• Confirm starting PaCO2 ≥3 kPa by reducing ventilation (ensuring that the CO2 stimulation to breathe is at least normal).
• Disconnect from mechanical ventilation
• Observing for 5 minutes for any respiratory activity
• Confirm the following end-targets are met: (1) Arterial PaCO2 ≥ 8.0kPa (2) Arterial PaCO2 risen by ≥ 2.7kPa from starting level (3) Arterial pH is <7.3

Once the test has been completed, the ventilator should be reconnected, the correct acid-base status restored, before the repeat test is then performed.