Residency · Residency · Neurosurgery
Brain Death Determination
Introduction
Brain death is the irreversible cessation of all functions of the entire brain, including the brainstem. It is a legal and medical definition of death accepted worldwide, though specific diagnostic criteria vary by jurisdiction. Neurosurgeons are frequently involved in brain death determination given their role in managing patients with catastrophic neurological injuries. Rigorous adherence to established protocols protects patients, families, and the integrity of organ donation processes.
Prerequisites Before Testing
Establish the Cause
A known, irreversible cause of coma must be identified before brain death testing can proceed. Examples include massive intracranial hemorrhage, severe traumatic brain injury, large hemispheric stroke, and anoxic brain injury. Neuroimaging must demonstrate a devastating brain injury consistent with the clinical picture. If the cause of coma is uncertain, brain death cannot be declared.
Exclude Confounders
Several reversible conditions can mimic brain death and must be systematically excluded. The patient's core temperature must be at least 36 degrees Celsius (some protocols accept 35 degrees Celsius or above) before testing, as hypothermia can suppress brainstem function. Hemodynamic stability should be ensured, with systolic blood pressure maintained at or above 100 mmHg, using vasopressors if necessary. CNS depressants such as barbiturates, benzodiazepines, and opioids must be excluded through drug levels or by waiting at least five half-lives for metabolism. Severe metabolic derangements including electrolyte abnormalities, hepatic encephalopathy, uremia, and hypoglycemia require correction. Neuromuscular blockade must also be excluded, typically by using a peripheral nerve stimulator with train-of-four testing if paralytic agents were administered.
Clinical Examination
Coma
The patient must show no evidence of arousal or awareness in response to maximal stimulation, including centrally applied painful stimuli. The Glasgow Coma Scale score is 3 (Eye 1, Verbal 1, Motor 1), and there should be no spontaneous movements, seizures, or posturing. Importantly, spinal reflexes such as deep tendon reflexes, plantar responses, and the Lazarus sign may persist after brain death because they are mediated by the spinal cord and do not preclude the diagnosis.
Absence of Brainstem Reflexes
Each brainstem reflex must be individually tested and documented as absent. The pupillary light reflex is tested by shining a bright light into each eye; pupils should be fixed and non-reactive, typically mid-position or dilated at 4 to 9 mm. The corneal reflex is assessed by touching the cornea with a cotton wisp or saline drop, with no blink response expected. The oculocephalic reflex (doll's eyes) is tested by briskly turning the head from side to side, provided the cervical spine is cleared, and there should be no eye movement. The vestibulo-ocular reflex is tested by irrigating each ear canal with 50 mL of ice water, waiting five minutes between sides, with no eye deviation expected. The gag reflex is assessed by stimulating the posterior pharynx, and the cough reflex by performing deep tracheal suctioning, with neither producing a response. Finally, the facial motor response is tested by applying nailbed or supraorbital pressure, with no grimace expected.
| Reflex | Cranial Nerves Tested | Stimulus | Absent Response (Brain Death) |
|---|---|---|---|
| Pupillary light | CN II, III | Bright light to each eye | Fixed, non-reactive pupils (4-9 mm) |
| Corneal | CN V, VII | Cotton wisp or saline to cornea | No blink |
| Oculocephalic (doll's eyes) | CN III, VI, VIII | Brisk head turning | No eye movement |
| Vestibulo-ocular (cold calorics) | CN III, VI, VIII | 50 mL ice water each ear | No eye deviation |
| Gag | CN IX, X | Posterior pharynx stimulation | No gag |
| Cough | CN X | Deep tracheal suctioning | No cough |
| Facial motor | CN V, VII | Nailbed/supraorbital pressure | No grimace |
Apnea Test
The apnea test confirms the absence of respiratory drive from the brainstem and is a critical component of brain death determination. The protocol begins with preoxygenation using 100% FiO2 for at least 10 minutes, targeting a PaO2 above 200 mmHg. A baseline arterial blood gas is obtained, and PaCO2 should be normalized to 35 to 45 mmHg before starting. The ventilator is then disconnected, and oxygen is delivered via a tracheal cannula at 6 to 10 liters per minute for passive oxygenation. The patient is observed for 8 to 10 minutes for any respiratory effort. A repeat ABG is drawn, and the test is considered positive (supporting brain death) if there is no respiratory effort and the PaCO2 reaches at least 60 mmHg with a rise of at least 20 mmHg above baseline. The test must be aborted if hypotension (systolic BP below 90), oxygen desaturation (SpO2 below 85%), or cardiac arrhythmia occurs. If the apnea test cannot be completed, an ancillary test is required.
Ancillary Tests
Ancillary tests are used when the clinical examination or apnea test cannot be completed, such as in cases of facial trauma, severe pulmonary disease, or hemodynamic instability. Cerebral angiography is the gold standard ancillary test, demonstrating the absence of intracranial blood flow. Radionuclide cerebral perfusion scanning with Tc-99m HMPAO shows no intracranial uptake, producing the characteristic "hollow skull" sign, and is widely available and non-invasive. Transcranial Doppler ultrasonography may reveal a reverberating flow pattern, systolic spikes, or absent diastolic flow, though it is operator-dependent and cannot serve as the sole ancillary test in some jurisdictions. CT angiography is emerging as an accepted ancillary test that demonstrates lack of intracranial filling, with institutional protocols varying. Electroencephalography can show electrocerebral silence, defined as no electrical activity above 2 microvolts for 30 minutes, but it is susceptible to artifact in the ICU environment and is not preferred by many protocols.
Number of Examinations and Observers
The AAN 2010 guidelines for adults state that a single clinical examination including the apnea test is sufficient, although many institutions require two examinations separated by an observation period. Pediatric guidelines from 2011 require two examinations with mandatory observation periods: 24 hours between examinations for infants from term to 30 days of age, and 12 hours for children from 30 days to 18 years. An ancillary test can shorten these observation periods. The examining physician must be experienced in brain death determination, typically an attending neurologist or neurosurgeon, and should not be part of the organ transplant team.
Documentation
Thorough documentation is essential. All prerequisites, including the exclusion of confounders, must be recorded. Each component of the brainstem examination should be documented with its specific findings. The apnea test protocol, duration, and ABG results require detailed recording. The time of death is recorded as the time the second examination or confirmatory test is completed, not when the ventilator is discontinued. Meticulous documentation protects against legal challenges.
Communication with Families
Communication with families requires clarity and sensitivity. Brain death should be explained directly: "Your loved one has died. The brain has permanently stopped functioning." Confusing language should be avoided; the term "life support" is inappropriate because the patient is dead, and "organ-sustaining treatment" should be used if discussing donation. Families should be given time for questions, grief, and cultural or religious considerations. The organ procurement organization should be notified separately from the brain death conversation, as decoupling these discussions is recommended. Some religious and cultural traditions do not accept brain death as death, and legal accommodations exist in certain jurisdictions, including New Jersey and New York.
Clinical Pearls
All confounders, including hypothermia, drug intoxication, metabolic derangements, and neuromuscular blockade, must be excluded before brain death testing begins. The apnea test requires a PaCO2 of at least 60 mmHg and a rise of at least 20 mmHg above baseline with no respiratory effort to be considered positive. Spinal reflexes may persist after brain death and do not invalidate the diagnosis, but families should be counseled about this possibility to avoid confusion. The time of death is the time the final brain death examination is completed, not the time mechanical ventilation is withdrawn. Ancillary tests are confirmatory and are required only when the clinical examination or apnea test cannot be completed.
References
- Wijdicks EFM, Varelas PN, Gronseth GS, Greer DM. Evidence-based guideline update: Determining brain death in adults (AAN). Neurology. 2010;74(23):1911-1918.
- Nakagawa TA, Ashwal S, Mathur M, et al. Clinical report: Guidelines for the determination of brain death in infants and children. Pediatrics. 2011;128(3):e720-e740.
- Greer DM, Shemie SD, Lewis A, et al. Determination of brain death/death by neurologic criteria: The World Brain Death Project. JAMA. 2020;324(11):1078-1097.
- Russell JA, Epstein LG, Greer DM, et al. Brain death, the determination of brain death, and member guidance for brain death accommodation requests (AAN position statement). Neurology. 2019;92(5):228-232.