Neurology · Topic 14 of 22
Brain Death Determination
Neurology · death by neurologic criteria
Brain Death Determination
A known catastrophic injury, no confounders, no brainstem function and a positive apnea test: the 2023 guideline's path to death by neurologic criteria.
Key numbers
Temperature ≥36 °C and MAP ≥75 mmHgT ≥ 36 °C · MAP ≥ 75
Apnea test: PaCO₂ ≥60, pH <7.30PaCO₂ ≥ 60, ≥ 20 rise
Wait 24 hours after anoxic injury or rewarming≥ 24 h
01 · Defined byTemperature ≥36 °C and MAP ≥75 mmHg
Before evaluation, keep core temperature at least 36 °C and, in adults, SBP at least 100 mmHg and MAP at least 75 mmHg (fluids or vasopressors as needed).
02 · DoNo brainstem reflexes on exam
The exam requires coma with no brain-mediated motor response to noxious stimuli (spinal reflexes allowed), no pupillary response to bright light, and absent corneal, oculocephalic, oculovestibular, gag and cough reflexes bilaterally.
03 · Defined byApnea test: PaCO₂ ≥60, pH <7.30
The apnea test supports brain death when there are no respirations while PaCO₂ reaches at least 60 mmHg and at least 20 mmHg above baseline, with pH below 7.30.
01
What it is
Core ideaPermanent loss of all brain function, including brainstem must knowBrain death/death by neurologic criteria is permanent cessation of all brain function, including the brainstem — coma, absent brainstem reflexes and apnea — from a known, catastrophic, irreversible injury; it is legal death.
02
Do right now
In this orderFirst moves
1
→Wait 24 hours after anoxic injury or rewarming≥ 24 h
2
→Temperature ≥36 °C and MAP ≥75 mmHgT ≥ 36 °C · MAP ≥ 75
3
→No brainstem reflexes on exam
4
→Preoxygenate 10 minutes; start from normal PaCO₂
5
Apnea test: PaCO₂ ≥60, pH <7.30PaCO₂ ≥ 60, ≥ 20 rise
Why each step
Wait 24 hours after anoxic injury or rewarmingWait at least 24 hours after hypoxic-ischemic injury (e.g., cardiac arrest) in patients aged 2 years or older, and 24 hours after rewarming to ≥ 36 °C if temperature fell to ≤ 35.5 °C.
Temperature ≥36 °C and MAP ≥75 mmHgBefore evaluation, keep core temperature at least 36 °C and, in adults, SBP at least 100 mmHg and MAP at least 75 mmHg (fluids or vasopressors as needed).
No brainstem reflexes on examThe exam requires coma with no brain-mediated motor response to noxious stimuli (spinal reflexes allowed), no pupillary response to bright light, and absent corneal, oculocephalic, oculovestibular, gag and cough reflexes bilaterally.
Preoxygenate 10 minutes; start from normal PaCO₂Before the apnea test, preoxygenate with 100% oxygen for at least 10 minutes and confirm PaCO₂ 35–45 mmHg and pH 7.35–7.45; during apnea give oxygen by tracheal catheter (4–6 L/min) or CPAP.
Apnea test: PaCO₂ ≥60, pH <7.30The apnea test supports brain death when there are no respirations while PaCO₂ reaches at least 60 mmHg and at least 20 mmHg above baseline, with pH below 7.30.
03
Red flags & don'ts
Avoid harmExclude sedatives, paralytics and metabolic confounders avoidExclude confounders: allow at least 5 half-lives for CNS depressants, alcohol level 80 mg/dL or less, confirm no paralysis by train-of-four or deep tendon reflexes, and correct severe metabolic derangements.
04
The rules
Know theseAbort apnea test for hypotension, desaturation, arrhythmiaAbort the apnea test for SBP < 100 or MAP < 75 mmHg despite treatment, SpO₂ below 85% or unstable arrhythmia; draw a blood gas, then repeat safely or order an ancillary test.
Adults need one complete examinationIn adults one complete examination with apnea test suffices (a second, independent exam is optional); children need 2 examinations by different clinicians at least 12 hours apart.
Ancillary tests only when the exam is incompleteOrder ancillary testing only when exam or apnea-test components cannot be done or interpreted (facial or cervical injury, unsafe apnea test) or metabolic derangements cannot be corrected — never instead of the exam.
Ancillary test must show absent intracranial blood flowAccepted ancillary tests show absent intracranial flow: 4-vessel catheter angiography, radionuclide perfusion scintigraphy, or transcranial Doppler (adults only); EEG, evoked potentials, CT angiography and MR angiography are not recommended.
Time of death: final apnea-test blood gasThe legal time of death is the time the final apnea test's arterial blood gas result is reported and shows PaCO₂ and pH meeting criteria.
Credentialed clinicians, including privileged APPs, may examineDetermination requires a trained, competent, credentialed clinician; advanced practice providers may perform it when credentialed to do so independently, otherwise a supervising attending must be present for the entire evaluation.
05
Teach & follow up
Patient educationWarn families about spinal reflex movementsInform the family before evaluation and offer to let them watch; explain that spinally mediated movements (including the Lazarus sign after ventilator withdrawal) can occur and do not negate brain death.
06
More detail
ReferenceShow 5 reference facts
With a primary posterior fossa injury, neuroimaging must show catastrophic supratentorial injury before evaluation, because isolated brainstem injury can leave cortical function.
On ECMO, raise PaCO₂ by lowering sweep gas to 0.2–1 L/min or adding CO₂; on venoarterial ECMO both the distal arterial line and post-oxygenator samples must meet criteria.
With chronic CO₂ retention, use the known baseline PaCO₂; if the baseline is unknown, the apnea test is done and ancillary testing is also required.
Children under 24 months need at least 48 hours after hypoxic-ischemic injury; pediatric blood pressure must be at or above the 5th percentile for age; brain death cannot be determined before 37 weeks' gestational age.
Oculovestibular testing: confirm intact tympanic membranes, raise the head 30° and irrigate each ear with 50 mL of ice water — no eye movement on either side is consistent with brain death.
Brain death is death — the clock time is when the final apnea-test blood gas meets criteria.
Sources · Greer DM et al. Pediatric and Adult Brain Death/Death by Neurologic Criteria Consensus Guideline (AAN/AAP/CNS/SCCM). Neurology 2023;101:1112–1132 · Merck Manual Professional — Brain Death (Jul 2026) · Merck Manual Professional — Overview of Coma and Impaired Consciousness (cold caloric technique) · Starter sheet built from the verified AGACNP fact map (facts reviewed 2026-10-15).