What are the criteria and tests for diagnosing brain death?

Brain Death Diagnosis Criteria and Testing

Brain death determination requires a comprehensive clinical examination showing complete unresponsiveness to all stimuli, absence of all brainstem reflexes, and absence of respiratory effort during apnea testing, with two separate examinations performed by different qualified physicians separated by age-specific observation periods. 1

Prerequisites for Brain Death Evaluation

Before proceeding with brain death testing, ensure:

• Known irreversible cause of coma is established 2, 1
• Reversible conditions are corrected:
  • Core temperature >35°C
  • Normal blood pressure
  • Corrected metabolic disturbances
  • Discontinued sedatives, analgesics, and neuromuscular blockers with adequate clearance time 1
  • Train of Four (TOF) of 4/4 if neuromuscular blocking agents were used 1

Clinical Examination Components

1. Coma Assessment

• Complete unresponsiveness to all stimuli, including painful stimuli 1
• No purposeful movement (spinal reflexes may persist and should not be confused with brain function)

2. Brainstem Reflex Testing

All of the following must be absent:

• Pupillary light reflex (fixed, dilated pupils)
• Corneal reflex
• Oculocephalic reflex (doll's eyes)
• Oculovestibular reflex (cold caloric)
• Gag and cough reflexes 1

3. Apnea Testing

This is a critical component that confirms absence of respiratory drive:

• Preoxygenate with 100% oxygen
• Disconnect from ventilator while providing oxygen
• Monitor for respiratory movements
• PaCO₂ must reach ≥60 mmHg AND ≥20 mmHg above baseline
• No respiratory effort should be observed during testing 2, 1

Observation Periods and Timing

Required observation periods between examinations vary by age:

• Term newborns (37 weeks to 30 days): 24 hours
• Infants and children (30 days to 18 years): 12 hours 2, 1

Important: Assessment should be deferred for 24-48 hours after cardiopulmonary resuscitation or severe acute brain injuries 1

Ancillary Testing

Ancillary tests are not required but may be used when:

• Components of examination or apnea testing cannot be completed safely
• Uncertainty exists about neurologic examination results
• Medication effects may be present
• To reduce the inter-examination observation period 2

Common ancillary tests include:

• Electroencephalography (EEG) - shows electrocerebral silence
• Cerebral blood flow studies - show absence of cerebral circulation
  • Four-vessel cerebral angiography (gold standard)
  • Radionuclide cerebral blood flow studies 1

Common Pitfalls to Avoid

• Misinterpreting spinal reflexes as brain function
• Inadequate observation time
• False detection of respiratory effort
• Performing testing too early after injury
• Failing to correct reversible conditions 1
• Testing in patients with hypothermia, drug intoxication, or metabolic disorders 3

Documentation Requirements

Documentation should include:

• Clinical examination criteria
• Results of apnea testing
• Results of any ancillary testing
• Determination of irreversibility
• Confirmation by a second physician 1

Special Considerations

For pediatric patients, particularly preterm infants less than 37 weeks gestational age, guidelines are insufficient and special caution should be exercised 2.

When apnea testing cannot be safely performed, ancillary studies become necessary to support the diagnosis of brain death 2, 4.

Brain death determination is a legal definition of death and allows for declaration of death even with continued cardiorespiratory function supported by mechanical ventilation 5.