What ‘Brain-Dead’ Means

Brain death is defined as complete and irreversible cessation of brain activity. Absence of apparent brain function is not enough. Evidence of irreversibility is also required. Brain death is often confused with the state of vegetation.

Traditionally, death is cessation of all body function, including respiration and heartbeat. Since it is possible to revive some people after a period without respiration, heartbeat, or other visible signs of life, as well as to maintain respiration and blood flow artificially using life support treatments, an alternative definition of death is needed.

In recent decades, the concept of brain death has emerged. By brain death criteria, a person can be pronounced legally dead even if the heart continues to beat due to the life support measures. The first nation in the world to adopt the brain death as a definition of legal death was Finland in 1971.

Brain-Dead individual has no brain electrical activity, no clinical evidence of brain function. On physical examination, there is no response to pain. Cranial nerve reflexes, for example, pupillary response, oculocephalic reflex, corneal reflex and spontaneous respiration are absent.

It is very important to distinguish between brain death and states that mimic brain death like the state of brain due to barbiturate intoxication, sedative overdose, hypothermia, hypoglycemia, coma or chronic vegetative states. The concept that death can be defined as the irreversible cessation of brain function is universally recognized through judicial decisions or regulations. A physician who makes a determination of death in accordance with these criteria and accepted medical standards is not liable for damages in any civil action or subject to prosecution in any criminal proceedings for his acts or the acts of others based on that determination.

Studies indicate that a patient will not survive with irreversible coma, apnea, absence of brain stem reflexes, and an isoelectric electroencephalogram that persists for more that 6 hours after the onset of coma and apnea. The patient in coma with some remaining brain-related bodily function is not dead. Presence of any behavioral responses or brainstem reflexes indicates that brain death has not occurred and therefore is not dead. A patient in chronic vegetative state may remain in a prolonged coma indefinitely, yet the patient will not meet criteria for brain death and therefore cannot be pronounced dead. Two physicians, namely, a neurologist or a neurosurgeon and an intensive care specialist should together pronounce the clinical assessment of brain death. The international clinical guidelines for this assessment are absence of cerebral functions and absence of brain stem functions.

Absence of cerebral functions for the purpose of diagnosis of brain death is the cause of coma is known. The patient must be in deep coma without any response to verbal or painful stimuli. All reversible causes of coma must be ruled out including hypothermia, that is, core body temperature less than 33 degree Centigrade, drug intoxication, hypotension, neuromuscular blockade, and sedating medicines. Confirmatory tests that have to be performed for concluding absence of cerebral functions are: Electroencephalogram, cerebral angiography, isotope angiography. Electroencephalogram alone could not be used because electroencephalogram is influenced by hypothermia and drugs, so an isoelectric electroencephalogram is very mandatory for diagnosis of brain death.

Clinical examination must confirm absence of brain stem reflexes including pupillary size and reactivity, corneal reflex, oculovestibular reflex, gag reflex, and cough reflex. Apnea test must demonstrate absence of all spontaneous respiratory drive. These examinations must preferably be conducted by physicians who are familiar with performance of these tests. The test of absent breathing should be performed following hyperoxygenation on 100% oxygen on mechanical ventilation and adequate circulation should be maintained during the entire apnea test.

The pupillary signs include round, oval, or irregularly shaped pupils are compatible with brain death, and most pupils are midsize about 4-6 mm. The pupillary light reflex must be absent to pronounce brain death. Although, many drugs influence pupillary size, pupillary light reflex remains intact only in the absence of brain death. Atropine administered intravenously does not markedly affect pupillary response; similarly, neuromuscular blocking agents do not markedly influence pupillary size; however, topical administration of drugs and ocular trauma influence pupillary size and reactivity. Any preexisting ocular anatomic abnormalities may also confound pupillary assessment in brain death.

Ocular movements tests include both oculocephalic “doll’s eye;” and vestibulo-ocular “caloric test” reflexes are absent in brain death. Contraindications to testing for oculocephalic reflexes include suspected fracture or instability of the cervical spine. Likewise, contraindications to testing of vestibulo-ocular reflexes include impaired integrity of tympanic membranes. Oculocephalic reflex is elicited by rapidly and vigorously turning the head to 90 degrees laterally on both sides. The normal response is deviation of the eye to the opposite side of the head turning. In brain death, oculocephalic reflexes are absent, and no eye movements occur in response to head movements. The vestibulo-ocular reflex is elicited by elevating the head 30 degrees and irrigating both tympanic membranes with 50 milliliters of iced saline or water. In brain death, vestibulo-ocular reflexes are absent, and no deviation of the eyes occurs in response to ear irrigations.

Can a person who has been declared brain-dead be revived? No. Brain death is death, plain and simple.

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Posted January 22, 2017 by dranilj1 in Neuroscience

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