What are the criteria for determining brain death (Brain Death)?

From the Guidelines

Brain death is diagnosed when a person has irreversibly lost all brain function, including the brainstem, and is determined by a clinical diagnosis based on the absence of neurologic function with a known irreversible cause of coma, as stated in the guidelines for the determination of brain death in infants and children 1. The criteria for determining brain death typically include three key components:

• An established cause of brain injury sufficient to cause death
• Complete unresponsiveness (coma) with absence of all brainstem reflexes, including pupillary light reflex, corneal reflex, oculocephalic reflex (doll's eyes), oculovestibular reflex (cold caloric testing), gag reflex, and cough reflex
• No respiratory effort during an apnea test, where the ventilator is temporarily disconnected while maintaining oxygenation, with documentation of an arterial PaCO2 20 mm Hg above the baseline PaCO2 and ≥ 60 mm Hg 1 Before testing, confounding factors must be ruled out, including severe hypothermia (temperature <32°C), significant hypotension, metabolic or endocrine disturbances, and the presence of central nervous system depressants or neuromuscular blocking agents, and these conditions should be corrected prior to examination for brain death 1. In some cases, ancillary tests may be used to assist the clinician in making the diagnosis of brain death, such as electroencephalography (EEG), cerebral angiography, transcranial Doppler ultrasonography, or nuclear medicine perfusion studies, particularly when standard clinical testing cannot be fully performed 1. The diagnosis of brain death should be made by physicians who have evaluated the history and completed the neurologic examinations, and requires at least two examinations, including apnea testing, with each examination separated by an observation period, which is 24 hours for neonates (37 weeks gestation to term infants 30 days of age) and 12 hours for infants and children (30 days to 18 years) 1. The clinical examination should be carried out by experienced clinicians who are familiar with infants and children, and have specific training in neurocritical care, and death is declared after confirmation and completion of the second clinical examination and apnea test 1.

From the Research

Brain Death Criteria

The diagnosis of brain death is made on clinical grounds and neurologic examination, with specific criteria set by major professional neurologic organizations such as the American Academy of Neurology (AAN) 2, 3. The clinical criteria for brain death include:

• Coma
• Absence of brainstem reflexes
• Apnea

Ancillary Tests

Ancillary tests are needed when neurologic examination or apnea test cannot be performed, and may include:

• Electroencephalogram (EEG) to confirm electrical activity loss
• Catheter cerebral angiogram to confirm loss of cerebral blood flow
• Transcranial Doppler
• Nuclear scintigraphy, such as 99m Techentium hexa methyl propylene amine oxime or 99mTechnetium-ethylene cysteine diethyl ester (99mTc-ethylene cysteine diethyl ester)
• Digital subtraction angiography, which remains the gold standard for confirmation of lack of cerebral blood flow 2

Imaging Markers

Imaging markers for brain death on various imaging modalities include:

• Nonopacification of the cortical middle cerebral arteries and internal cerebral veins on computed tomography angiogram (CTA)
• Lack of cerebral blood flow and blood volume in brainstem on CT perfusion
• Massive brain edema with herniations, poor gray or white matter differentiation, diffuse diffusion restriction, and nonvisualization of intracranial vessels on magnetic resonance imaging (MRI) 2
• Cerebral circulatory arrest indicated by flow patterns without forward flow progress on transcranial Doppler 2

Clinical Evaluation

The clinical evaluation of brain death involves a comprehensive clinical examination, including assessment of coma, cranial nerves, motor testing, and apnea testing 3, 4. The Full Outline of Unresponsiveness (FOUR) score and the Glasgow Coma Scale (GCS) can be used to evaluate the patient's level of consciousness and predict brain death 5. A physiological coma scale, such as the trigeminal-auditory Glasgow (Coma Scale) score (TAG score), can also be used to evaluate deep comatose patients and assist in management 6