Brain death

• Brain death, usually called death by neurologic criteria (BD/DNC), is the permanent loss of function of the brain as a whole, including the brainstem, in a patient with a known catastrophic brain injury. ^[1]
• It is a clinical diagnosis built on three findings that must all be present: coma, brainstem areflexia and apnoea in response to hypercarbia and acidosis. ^[2]
• Before testing, the mechanism must be known and reversible confounders (hypothermia, hypotension, intoxicants, neuromuscular blockade, severe metabolic or endocrine derangement) must be corrected or excluded. ^[1]
• The main process standards used here are the AAN consensus guideline of 2023 (Greer and colleagues, which unified the earlier AAN 2010 adult and 2011 paediatric guidelines), the UK Academy of Medical Royal Colleges Code of Practice 2025, and the World Brain Death Project 2020. ^[1][4][5]
• Once the criteria are met, the patient is dead; the time of death is recorded, support is withdrawn or briefly continued for family reasons, and organ donation, where appropriate, is managed by a separate team with no overlap with the clinicians who made the determination. ^[1]

By the end of this page you should be able to:

1. Define brain death (BD/DNC) and distinguish it from coma, vegetative state and catastrophic brain injury that has not progressed to BD/DNC.
2. State the preconditions that must be satisfied before BD/DNC testing begins, including age, observation time, temperature and blood pressure thresholds.
3. List the brainstem reflexes that must be absent and how to test each without being misled by spinal reflexes or trauma.
4. Describe the apnoea test in order, including pre-oxygenation, baseline blood gases, the oxygenation method, and the blood-gas criteria that make it consistent with BD/DNC.
5. Name the accepted and unacceptable ancillary tests and the circumstances in which one is needed.
6. Recognise the mimics and confounders, and outline how to support families and manage the interface with organ donation.

Brain death is the most severe end of a spectrum of brain injury, not simply "very deep coma". In coma the brainstem often still works: pupils react, coughing is possible and breathing continues. In BD/DNC none of that remains, and the loss must be permanent—function is gone, will not return by itself, and will not be restored by treatment. ^[1][4] International and UK writing prefers the word permanent over irreversible for this; it is a clinical, prospective judgement rather than a philosophical claim about every possible future intervention. ^[4]

The underlying concept common to every major guideline is “permanent coma and loss of all brainstem function, coupled with the inability to breathe in the setting of an adequate stimulus” (hypercarbia and acidosis). ^[1] Because the brainstem’s reticular activating system is the best predictor that a comatose state will be permanent, most of the clinical examination is directed at showing loss of all brainstem reflexes. ^[1] Hypothalamic function may survive: diabetes insipidus and other neuroendocrine signs can occur and, in current guidance, do not contradict the diagnosis. ^[1]

A few confusions worth clearing up at the start. A patient with a severe brain injury and a flat electroencephalogram is not necessarily brain dead if the brainstem still functions. A patient kept alive while pregnant, or after primary posterior fossa (infratentorial) injury, may need special handling discussed below. And a disease that mimics brain death must be thought of every time; there is no shortcut.

The determination that someone has met neurologic criteria for death is a medical responsibility that leads to a legal declaration of death, and the process must be accurate and consistent. Most authorities, including the 2023 AAN guideline and the UK Code, define BD/DNC as permanent cessation of brainstem function in the setting of a known, catastrophic brain injury, identified by a standardised process. ^[1][4] The process begins with the presumption that the patient does not meet criteria; that presumption must then be disproved by examination. ^[1]

Practice has historically varied, which is exactly why the medical-education framework used here (^[3]) and the international project used below (^[2]) exist: to reduce error. The 2023 AAN guideline notes that lack of meticulous, guideline-concordant evaluation can lead to inaccurate diagnosis. ^[1]

Three editions are named throughout, and they largely agree on thresholds.

• AAN consensus guideline, 2023 (Greer, Kirschen, Lewis and others, Neurology 2023;101:1112–32). This combined the 2010 AAN adult and the 2011 paediatric guidelines into one document and is the principal process source for the numbers on this page. ^[1]
• World Brain Death Project, 2020 (Greer, Shemie, Lewis and others, JAMA 2020;324:1078–97). An international consensus that proposed minimum clinical standards and emphasised exclusion of confounders and mimics, paediatric, ECMO and hypothermia considerations, and resource availability. ^[2]
• UK Code of Practice for the Diagnosis and Confirmation of Death, 2025 update (Academy of Medical Royal Colleges; reviewed by Scott and Thomas, 2026). The authoritative UK medical consensus for all contexts and ages, using a “unifying concept of death”. It was the first major update for 17 years and incorporates the World Brain Death Project, Australian/New Zealand and Canadian sources. ^[4][5]
• Additional references: a medical-education framework for adults (Cormier and colleagues, 2026). ^[3]

Where the frameworks differ, the difference is stated with both values rather than being averaged away.

BD/DNC testing is for patients who have sustained catastrophic, permanent brain injury from an identified mechanism known to lead to BD/DNC—such as traumatic brain injury, a cerebrovascular event (subarachnoid or intracerebral haemorrhage, ischaemic stroke), a space-occupying lesion, hypoxic-ischaemic brain injury, central nervous system infection, a toxin ingestion or a metabolic disorder causing malignant cerebral oedema. ^[1]

Testing should not start when the patient is comatose and apnoeic with absent brainstem reflexes but there is no identified mechanism: the clinical picture may be caused by a reversible process. In that situation the next step is further diagnostic evaluation, not BD/DNC testing. ^[1] Neuroimaging must be consistent with the mechanism and the severity of the injury. ^[1]

Age limits. BD/DNC cannot be determined in infants under 37 weeks corrected gestational age: the brainstem reflexes may not yet be fully developed. ^[1] Both the 2023 AAN and 2025 UK guidance share this limit. ^[1][4]

Who performs the evaluation. The examining clinicians must be credentialed members of hospital staff who are adequately trained and competent in BD/DNC evaluation in adults or children, in accordance with local laws and institutional standards; trainees work under direct supervision. ^[1] In the UK the 2025 Code clarifies who may perform clinical testing and the competency expected. ^[4] In children, two clinicians must each perform a separate, independent examination, with a minimum interval of 12 hours between them in the AAN framework; in the UK under-2 group both tests are 24 hours apart and ancillary tests cannot be used. ^[1][4]

1. Observation period. The catastrophic injury must be permanent, so clinicians must wait a sufficient time after injury before testing, based on the pathophysiology of the injury. ^[1]
   • After hypoxic-ischaemic brain injury: at least 24 hours in patients aged 24 months or older, and at least 48 hours in infants and children under 24 months (whose open fontanelles may delay the rise in intracranial pressure and in whom the brainstem is more resistant to hypoxic injury). ^[1]
   • After medical or surgical treatment of raised intracranial pressure, wait again to ensure no recovery of function. ^[1]
   • The interval between examinations in children is built into the observation requirement above.
2. Hypothermia. Hypothermia suppresses brain function and delays clearance of sedating drugs. Core temperature must be at least 36°C before testing. ^[1] If the core temperature has been 35.5°C or below, wait at least 24 hours after rewarming to 36°C or above. ^[1] Under the 2025 UK Code a minimum of 24 hours’ observation applies after correction if the temperature was below 36°C, except for transient and temporary reductions (generally accepted as under 6 hours in total over the preceding 24 hours). ^[4]
3. Hypotension. Hypotension mimics loss of brain function. The patient must not be hypotensive; in adults maintain systolic blood pressure at least 100 mmHg and mean arterial pressure at least 75 mmHg; in children maintain both at or above the fifth percentile for age. ^[1] Where a patient’s known chronic baseline differs markedly from age-based norms, aim for that individual’s chronic baseline. ^[1] Intravenous fluids, vasopressors or inotropes may be needed before and during testing. ^[1]
4. **Intoxicants and drugs.**Exclude or correct CNS-depressing drugs and alcohol: urine and blood toxicology screening should be negative if clinically indicated; alcohol level must be no more than 80 mg/dL if measured; and drug levels that are present must be in the therapeutic or subtherapeutic range and considered not to contribute to the clinical state. ^[1] If levels are unavailable, allow at least 5 half-lives of any CNS-depressing drug or intoxicant to pass, and longer if there is hepatic or renal dysfunction, obesity or recent hypothermia; account for age-dependent metabolism in infants and older patients. ^[1] After pentobarbital the level must be under 5 µg/mL or below the laboratory’s lower limit of detection before testing. ^[1] AAN 2023 still requires at least 5 half-lives even in overdose situations (longer with organ dysfunction, obesity or hypothermia); the 2025 ACMT position statement considers 5 half-lives insufficient in massive overdose and recommends toxicology consultation. If confounders cannot be fully excluded, do testing to the fullest extent possible and, if metabolic derangements cannot be corrected, perform ancillary cerebral blood-flow testing. ^[1]
5. Metabolic and endocrine derangement. Severe metabolic, acid-base or endocrine abnormalities must be excluded or corrected; a multitude of reversible derangements can depress consciousness and even suppress brainstem reflexes. ^[1]
6. Neuromuscular blockade. Exclude pharmacologic paralysis by train-of-four stimulation or by the presence of deep tendon reflexes. ^[1]
7. ECMO and temperature-management situations. Special modifications to apnoea testing and blood-pressure targets apply for venoarterial ECMO, and these patients can still be tested; both guidelines treat ECMO as a manageable variant rather than a contraindication. ^[1][2]
8. Examinability. Accurate assessment can be impeded by trauma (orbital or facial swelling, anophthalmia, skull-base or cervical injury, ruptured tympanic membrane) and by severe neuromuscular disorders or spinal cord injury. Where a component cannot safely be assessed, ancillary testing is required rather than assuming it would have been absent. ^[1]

Intoxicants should never be assumed harmless: the clinical findings of brain death can be reproduced by certain poisons and toxins, which is why a known mechanism and cleared or corrected confounders stand in front of every test. ^[1][2]

1. Recognise a known catastrophic brain injury and, when indicated, arrange the appropriate neuroimaging.
2. Stabilise the patient (airway, ventilation, circulation) and begin metabolic and pharmacological correction.
3. Observe for long enough to establish permanence.
4. Exclude all confounders; correct those that can be corrected.
5. Review the record and the imaging; confirm the mechanism.
6. Inform the family that evaluation for BD/DNC is being considered and, where policy allows, offer to let them witness the clinical evaluation.
7. Test brainstem reflexes and motor responses fully.
8. If everything is consistent, perform the apnoea test.
9. If a component cannot be tested safely or is uninterpretable, perform an accepted ancillary blood-flow test instead of the missing step.
10. If all criteria (or the equivalent ancillary proof) are met, record the time of death and manage family support, withdrawal of support and any donation pathway as described below.
11. If any test is inconsistent with BD/DNC, the diagnosis is not made; manage the patient, trend the examination and reassess at an appropriate interval.

Every number quoted comes from the opened guideline texts; where the frameworks differ (for example the observation period for children, or the 5-minute minimum apnoea period in the UK), both versions are shown. ^[1][4]

The three clinical elements are coma, brainstem areflexia and (finally) apnoea. ^[1][2] Examine the patient only after confirming the prerequisites above. Review the record first to confirm the mechanism of injury and the exclusion of confounders. ^[1]

Coma and motor response. The patient must be comatose and unresponsive to visual, auditory and tactile stimulation. ^[1] Apply noxious stimuli to the head and face, trunk and limbs; there must be no motor response mediated by the brain or brainstem, other than spinally mediated reflexes. ^[1] Movements arising in the spinal cord can occur in BD/DNC and do not invalidate the diagnosis. ^[1] If it is unclear whether a limb movement is spinally mediated, use an ancillary blood-flow test rather than arguing at the bedside. ^[1]

Pupillary light reflex. There must be no pupillary response to bright light bilaterally. ^[1] The World Brain Death Project describes the typical finding as pupils fixed in a midsize or dilated position and nonreactive to light. ^[2] Direct ophthalmic factors (trauma, oedema, anophthalmia, mydriatic drugs) may make the pupils unassessable, which is a valid reason to use angiography or radionuclide perfusion rather than to skip the step. ^[1]

Oculocephalic (doll's eyes) and oculovestibular (cold caloric) reflexes. These test the same cranial nerve pathways; the oculovestibular test provides the stronger stimulus. ^[1] Do not perform the oculocephalic test if there is concern about the cervical spine or skull base; use the oculovestibular test instead, applied bilaterally. ^[1] Where the oculocephalic test cannot be performed for cervical or skull-base reasons, BD/DNC can be diagnosed without an ancillary test provided the oculovestibular reflex is absent bilaterally and every other criterion is satisfied. ^[1]

Corneal reflex. Absent bilaterally. ^[1] Severe orbital or facial injuries may prevent safe testing. ^[1]

Facial movement to noxious stimulation. Absent. ^[2]

Sucking and rooting reflexes. In infants under 6 months, absent. ^[1]

Gag and cough reflexes. Both absent; the gag is tested by pharyngeal stimulation and the cough by deep tracheal suctioning. ^[1][2]

No cerebral (heart-rate, blood-pressure) response to stimulation should survive; but autonomic storm at the time of injury is not the same as a reflex tested now, and invasive tests are not part of the core examination.

Safety standard for the examination. All elements that can be assessed must be assessed and must be consistent with BD/DNC; if any component is inconsistent, the patient does not meet criteria. ^[1]

All adults need at least one apnoea test after the final neurologic examination; children need two, one after each neurologic examination. ^[1] Only attempt it once the other criteria are met and the patient's cardiopulmonary risk is judged acceptable; check that the patient is not hypoxaemic, hypotensive or hypovolaemic first. ^[1]

Before disconnection. Pre-oxygenate with 100% oxygen for at least 10 minutes to achieve a PaO2 above 200 mmHg. ^[1] Baseline arterial blood gas should show normal PaCO2 (35-45 mmHg) and pH (7.35-7.45) unless the patient has chronic hypercapnia, in which case the baseline PaCO2 should be the patient's chronic baseline level. ^[1] An invasive arterial line for repeated blood gas measurement is advisable. ^[1]

During the test (adults). Stop ventilation and deliver 100% oxygen at 4-6 L/min through a catheter placed just above the carina (resting inside the endotracheal tube or tracheostomy but less than 70% of its diameter, to avoid barotrauma), or use CPAP via the ventilator or a flow-inflating bag with a functioning PEEP valve. ^[1] In children, CPAP or a flow-inflating bag is preferred; tracheal insufflation is not recommended because of barotrauma and washout. ^[1]

Reading the result. Obtain an arterial blood gas after 8-10 minutes (earlier or more often with point-of-care testing if the patient is unstable). The test is consistent with BD/DNC only if there are no respirations, pH under 7.30 and PaCO2 at least 60 mmHg and at least 20 mmHg above the pre-test baseline (or above the known chronic elevated baseline). ^[1]

Abort immediately if a breath occurs (the criteria are not met), the systolic blood pressure is under 100 mmHg or mean arterial pressure under 75 mmHg in adults (or under the fifth percentile for age in children) despite treatment, oxygen saturation falls progressively under 85%, or there is a haemodynamically significant arrhythmia. ^[1] Obtain a blood gas before reconnecting if instability is imminent. ^[1]

If the targets are not reached and the patient was stable, continue or repeat the test; if hypoxaemia or hypotension caused failure, change the oxygenation method, repeat when safe or use an accepted ancillary test. ^[1] CO2 rises at about 2-3 mmHg per minute in normothermic patients. ^[1]

ECMO variant. On ECMO, pre-oxygenate through both the ventilator and the membrane lung; increase PaCO2 by adding exogenous CO2 or reducing sweep-gas flow to 0.2-1 L/min; and sample arterial blood gases from both the distal arterial line and the post-oxygenator circuit on venoarterial ECMO. Both sets of PaCO2 and pH values must meet the criteria. Avoid hypotension by increasing ECMO flows, fluids or vasopressors. ^[1]

One point that confuses teams: occasional premature stopping of an apnoea test because of a small drop in saturation. The guideline asks whether the patient can be kept off the ventilator safely while being oxygenated; if not, the abort thresholds above are the cut-off, not any arbitrary fall.

Ancillary testing is not routinely needed; BD/DNC remains a clinical diagnosis. ^[1][2] It is used when a component of the neurologic examination or the apnoea test cannot safely be completed or interpreted, or when uncorrectable metabolic problems persist despite examination findings consistent with BD/DNC. ^[1] Unacceptable ancillary choices are explicitly excluded:

• EEG, auditory and somatosensory evoked potentials should not be used, because they do not assess the brainstem. ^[1]
• CT angiography and MRI/MR angiography should not be used, because of false-positive risk and inadequate validation. ^[1]
• Transcranial Doppler is acceptable in adults but not validated in children. ^[1]

Accepted when genuinely needed: 4-vessel catheter angiography and radionuclide perfusion scintigraphy (SPECT with a blood-brain-barrier-crossing agent, or planar perfusion angiography). ^[1] An open fontanelle, skull fracture, skull defect or cerebrospinal fluid shunt by itself does not justify ancillary testing. ^[1] An ancillary test must not be used to bypass elements that could be tested, or in the setting of hypothermia, uncorrected sedation or confounders. ^[1]

Neuroendocrine function and primary posterior fossa injury need specific handling. Neuroendocrine activity may persist and does not preclude diagnosis. ^[1] In primary posterior fossa (infratentorial) injury, the brainstem may be destroyed while some supratentorial function survives; imaging must show that the posterior fossa process has also produced catastrophic supratentorial injury before testing begins. ^[1]

The guideline explicitly lists reversible mimics of BD/DNC: Guillain-Barré syndrome, leptomeningeal carcinomatosis, snake bites, botulism and high cervical cord injuries. ^[1] More broadly, many medical conditions can produce a patient who looks comatose with absent brainstem reflexes and apnoea, including severe intoxication, drug overdose, profound hypothermia and profound hypotension. ^[1][2] Before any declaration, a conscious patient in locked-in syndrome, a patient with breath-taking movements driven by the spinal cord or peripheral nerves, and a patient who can still generate any brainstem-mediated activity must be excluded. ^[1]

Practical cautions:

• A spinal cord injury can abolish limb movement but leaves the brainstem entirely intact.
• Leptomeningeal or malignant disease may progress in a way that looks like catastrophic brainstem failure yet is reversible or focal.
• Envenomation and certain toxins can produce neuromuscular blockade without brain injury.
• Children under 24 months and recent hypothermic arrests require longer observation because their brains and brainstems recover differently.

Every one of these is handled by the preconditions already given (known mechanism, appropriate observation, corrected confounders), which is why the pathway refuses to be rushed.

Children. Use age-adjusted observation (48 hours under 24 months; 24 hours for hypoxic injury at 24 months or older), two independent examinations, two apnoea tests, and no ancillary testing under 2 years in the UK framework. ^[1][4] Under the AAN system two examinations are separated by at least 12 hours. ^[1] Hypoxic-ischaemic injury and persistent fontanelles are the reason for the long observation; the brainstem in infants is more resistant to hypoxic damage than other regions. ^[1]

Pregnancy. Pregnancy is not a contraindication to BD/DNC evaluation; pregnant patients with catastrophic brain injury are assessed and diagnosed in the same way. ^[1] If the fetus might still be viable, organ support may be continued after BD/DNC, with maternal-fetal medicine, neonatology and child neurology input; outcomes are uncertain and include some cases of successful delivery of a developmentally normal infant and some of intrauterine death. ^[1][4] Decisions require knowledgeable professional advice to surrogate decision-makers.

Older patients, organ dysfunction. Drug clearance delays make the 5-half-life rule conservative; adjust. ^[1]

Low-resource settings. Where CT perfusion, nuclear medicine or 4-vessel angiography are unavailable, the diagnosis remains clinical if all elements and the apnoea test can be completed safely and confounders excluded. ^[1][2] If they cannot, the wisest course is to treat and observe, and to seek specialist input rather than declare. Core standards (temperature, blood pressure, confounder control) cost relatively little and must not be skipped. ^[2]

This section is what the team actually does around the examination.

• Before testing: secure the airway and optimise ventilation and circulation; correct reversible causes; maintain temperature and blood pressure; manage sedation and neuromuscular blockade; discuss the plan with the family.
• During testing: one clinician clearly leads; a second records. Evidence of any brain-mediated activity or a breath stops the process and the criteria are not met. ^[1]
• Haemodynamics during apnoea testing: pre-oxygenate as specified, ensure euvolaemia, titrate vasopressors; stop for the abort thresholds already listed, not for any incidental dip. ^[1]
• Children: two clinicians, two examinations, two apnoea tests. ^[1]
• After a “not met” result: continue critical care, review the diagnosis and imaging, and trend the examination; do not repeat the whole process too soon if nothing has changed.
• After criteria are met: assign the time of death per the protocol (below) and then decide, per institutional policy and the family’s needs, whether to continue organ support briefly or withdraw promptly.

Escalate or refer early when:

• the mechanism of catastrophic brain injury is unclear, or the scan and the clinical state do not fit; seek neurology or neurosurgery and repeat imaging. ^[1]
• A confounder cannot be corrected (for example a drug overdose with renal failure, or uncorrectable metabolic derangement): involve pharmacy, clinical pharmacology and nephrology; ancillary testing may be required. ^[1]
• the apnoea test would be unsafe because of severe lung or cardiovascular disease, or because the patient is on ECMO: refer to neurocritical care before proceeding. ^[1]
• the eyes or ears cannot be examined: in UK practice this itself requires an ancillary test. ^[4]
• family disagreement or distress is significant, or the team is uncertain about withdrawing support: senior clinician, ethics committee or legal advice as local law requires. ^[4]
• organ donation is being considered: transplant coordination, and strict separation of the declaration team from the donation and surgical teams. ^[1]
• in children: paediatric neurology and paediatric intensive care expertise. ^[1]

What to record. Document the basis for the diagnosis in enough detail that another clinician can see why it was made: mechanism of injury, supporting neuroimaging, the observation period, the corrected or excluded confounders with their measured levels (temperature, blood pressure, drug and alcohol levels, train-of-four, metabolic panel), each element of the neurologic examination, apnoea test times and arterial blood gas and haemodynamic data, and whether an ancillary test was used with its result. Record consent discussions and family communication. ^[1] In the UK, nationally agreed diagnostic forms are available for recording the determination of death using neurological criteria. ^[4]

Time of death. For a patient who meets clinical criteria, assign the time of death as the moment during the final apnoea test when the arterial blood gas is reported and demonstrates PaCO2 and pH consistent with the criteria. ^[1] Where an ancillary test is required, assign the time the attending clinician records that the result is consistent with BD/DNC. ^[1] Time-of-death decisions are often emotionally charged; assigning them consistently is part of being accurate and is not a matter for negotiation. ^[4]

Family communication. The UK Code includes an entirely new section on communication with family and friends about the diagnosis and confirmation of death, with guidance on where, when and how these discussions should happen, and stresses that diagnosing death must be accompanied by clear, respectful communication. ^[4] Practical points that flow from this and from the AAN guideline:

• Use plain language: say that the person has died. Explain that the ventilator is moving air through the lungs after death, rather than being the one thing keeping a living patient going. ^[1][4]
• Make a reasonable attempt to inform the family before starting the evaluation and, where policy allows, offer them the option of witnessing the clinical evaluation, including apnoea testing, explaining that spinal, muscle or nerve activity may occur and does not invalidate the diagnosis. ^[1]
• Communication should be clear, concise and supportive, in simple terms, with appropriate emotional support. ^[1]
• Plan enough time, allow silence and repeated explanations, use an interpreter rather than family members if language differs, and involve chaplaincy or social work if religious, cultural or financial concerns arise. ^[2]
• Consensus guidance differs on formal consent: the 2023 AAN position is that consent is not required before evaluating for BD/DNC unless institutional policy or local law requires it, whereas the UK Code leaves the legal position on consent less settled and best practice is to discuss and agree testing with the family, escalating to senior or legal advice if there is intractable disagreement. ^[1][4]

Interaction with organ donation. A few principles matter:

• The clinician making the BD/DNC determination must consider only the interests of the patient and must have no direct involvement in donation decision-making; and no clinician involved in surgical organ recovery may participate in the determination itself. ^[1]
• Discussions about donation are better led by staff trained in donation, and only after the family has understood that death has occurred. ^[1][2]
• The determination itself must not be influenced by whether organs will be donated or by the retrieval team’s timeline.
• After declaration, the donor is supported (ventilation, circulation, normothermia) while organs and tissues are assessed, under national and local protocols.
• Withdrawal of support and the physical logistics of donation follow local practice; a reasonable but limited period of continued support can be arranged to allow family time with the deceased. ^[1]
• Law on deemed (presumed) versus explicit consent to donation varies by jurisdiction; this page cannot substitute for local legal guidance, only help the team recognise when to seek it. ^[2][4]

• Equating brain death with “no brainstem reflexes on one look”. The clinical examination and its preconditions must be fully satisfied; if a component cannot be assessed it must be replaced by an accepted ancillary test, not assumed absent. ^[1]
• Treating an absent pupil or corneal reflex as sufficient evidence of cerebral death; these are only two components.
• Being misled by spinally mediated limb posturing or movements; such movements do not invalidate BD/DNC, and if there is doubt the decision is made with cerebral blood-flow proof. ^[1]
• Accepting ancient habits: using EEG, CT angiography or MR angiography as “confirmatory” tests. ^[1]
• Applying adult observation and apnoea rules to infants, or testing at all under 37 weeks corrected age. ^[1][4]
• Omitting the pH criterion: the 2023 AAN and 2025 UK standard requires pH under 7.30 as well as PaCO2 at or above 60 mmHg, even though not every historical or international protocol used it. ^[1][4]
• Declaring in primary posterior fossa injury without imaging evidence of catastrophic supratentorial injury. ^[1]
• Leaving the family unprepared, then expecting them to understand a donation conversation. ^[1][4]
• Allowing donation logistics to rush the determination; the roles must be separated. ^[1]
• Continuing support indefinitely after legal death without a policy pathway; use the process for resolving disagreements. ^[1]

• Brain death (BD/DNC) is permanent loss of the whole brain including the brainstem, diagnosed clinically by coma, brainstem areflexia and apnoea.
• The mechanism must be known and severe; testing before then risks a false diagnosis.
• Temperature must be at least 36°C, blood pressure adequate (SBP at least 100 mmHg and MAP at least 75 mmHg in adults), and intoxicants, sedating drugs, neuromuscular blockade and severe metabolic derangements corrected or cleared.
• Hypoxic-ischaemic injury demands 24 hours' observation in adults and 48 hours in children under 24 months.
• Brainstem reflex testing must be exhaustive (pupils, corneal, oculocephalic/oculovestibular, facial, gag, cough; sucking and rooting under 6 months; motor response); spinal reflexes are allowed.
• Apnoea is consistent with BD/DNC only with no breaths, pH under 7.30 and PaCO2 at least 60 mmHg and at least 20 mmHg above baseline, after pre-oxygenation to PaO2 above 200 mmHg.
• EEG, evoked potentials, CT angiography and MR angiography should not be used; cerebral blood-flow tests (4-vessel angiography, radionuclide perfusion, adult transcranial Doppler) are the accepted ancillary options.
• Children need two examinations by two clinicians, separated by at least 12 hours, plus two apnoea tests.
• Reversible mimics (Guillain-Barré, leptomeningeal disease, snake bites, botulism, high cervical cord injury and others) must be excluded by the preconditions.
• Primary posterior fossa injury can spare supratentorial function; imaging must show catastrophic supratentorial involvement first.
• The time of death is the moment the final qualifying apnoea blood gas is reported (or, for ancillary diagnosis, when the attending documents the result).
• Communication should use plain language, allow repeated explanation and observation where policy allows; donation conversations are led separately by trained staff and the determination team must not overlap with recovery teams.
• The main references are the AAN 2023 consensus guideline, the World Brain Death Project 2020, and the UK Code of Practice 2025.

Read next: approach to the unconscious patient and coma, increased intracranial pressure, brain herniation syndromes, stroke and brainstem stroke, status epilepticus, hypoxic-ischaemic brain injury, spinal cord injury, traumatic brain injury, intracranial hypertension management, organ transplantation and donor management, intensive care management, end-of-life communication.