THE DIAGNOSIS OF DEATH

The Brain Death

Despite advances in medical technology, the medical science can never achieve immortality. Death indeed is the ultimate truth of life and we as pediatricians are quite used to facing children with acute catastrophic life- threatening diseases and terminal illnesses. Many critically sick children are supported by artificial life-sustaining measures like vasopressors and mechanical ventilation in whom criteria of brain death are used to declare them as dead. The prolonged and unnecessary maintenance of a “dead”’ child on a life support system is an extremely stressful experience for the parents and expensive for the state. Accurate timing of brain death is also important to harness the organs of children, whose parents are willing, for cadaveric transplant of heart, lungs, liver and kidneys. Following the enaction of Human Organ Transplant Act by many countries, it is legally justified to remove organs from brain dead patients who are still having heart beats.

Death is diagnosed when chi Id has sustained either (1) irreversible cessation of circulatory and respiratory functions or (2) there is irreversible cessation of all functions of the entire brain including the brainstem. Coma and apnea must cocxist, for the diagnosis of brain death. After the brain is dead and spontaneous respirations have ccased, the heart may continue to beat if mechanical ventilation maintains adequate oxygenation of blood.

History

The probable cause of coma should be ascertained to ensure that there is no remediable or reversible condition. Identify and exclude any potentially reversible toxic and metabolic disorders, use of sedative-hypnotic drugs or paralytic agents, hypothermia, drowning, hypotension and surgically correctable condition.

Cessation of Circulation and Breathing efforts

Vigorous cardiopulmonary resuscitation (CPR) should be continued for atleast 30 minutes while continuously monitoring vital signs. Absence of heart beats and spontaneous respiratory efforts during an appropriate period of observation (at least 30 min) is a satisfactory criteria of clinical death. When a patient is attached to an ECG monitor, flat tracings are indicative of cellular death.

The diagnosis of cessation of breathing poses practical difficulties in babies on a ventilator. The ventilator can be periodically switched off and spontaneous respiratory movements are watched. It is essential to maintain paCo2 of the patient between 40-50 mm Hg (so that there is enough drive for the respiratory Renter) before the ventilator is switched off.

The Brain Death

The Brain DeathThe current legal definition of death requires clinical evidences of irreversible brainstem death. In deeply comatosed patients (absence of facia! grimace on firm pressure over the supraorbital region) on assisted ventilation and advanced life support systems, it is futile to continue with life support measures if neurologic functions have irreversibly ceased. The cessation of neurologic functions is assessed by evaluation of following brainstem reflexes:

(a) Pupillary response to light. The pupils should be dilated and fixed on both sides without any response to bright light. It is mediated by components of the optic and oculomotor nerves located in mesencephalon.

(b) Corneal reflex. The corneal reflex should be absent. The corneal reflex is elicited by touching the cornea with a wisp of cotton and observing the reflex closure of the eyelids. It is mediated by sensory (5th nerve) and motor (7th nerve) components having neuroanatomic centers within pons.

(c) Oculocephalic reflex or ‘Dolls’ head eye movements are elicited by rotation of the patient’s head from one side to the other or up and down with eyelids held open. In a comatosed child with intact brain stem, when head is turned to one side and maintained in that position for a few seconds, there are conjugate movements of both the eyes to the opposite side. When oculocephalic reflex is affected, there is either no conjugate movements of the eye balls or there are dysconjugate movements.

(d) Vestibulo-ocular reflex. The tympanic membranes must be intact and there should be no local trauma before this reflex is elicited. About 20 ml ice- cold water is slowly injected into each auditory canal and directed towards the tympanic membrane. When caloric response is intact there is tonic deviation or nystagmoid movements of both eyes towards the side being stimulated. The absence of any response is indicative of brain stem dysfunction. Both oculocephalic and oculo-vestibular reflexes are mediated by fibers from the vestibular portion of the 8th nerve with nuclei in the pons. From these pontine centers impulses are conveyed to the 6th nerve nucleus through internuclear synapses, causing lateral movements of the eyes towards side of stimulus. Synapses exist between 6th nerve nucleus and 3rd nerve nucleus through medial longitudinal fasiculus coursing through pons and mesencephalon, resulting in medial deviation of the eye on the contralateral side.

(e) Oropharyngeal reflex. The gag reflex and cough reflex response to suction of oropharynx and trachea should be absent.

It must be remembered that spinal segmental responses and deep tendon jerks may persist even in the presence of brain death.

Observation Period According to Age

The brainstem reflexes should be elicited in all comatosed children before disconnecting the ventilator. The criteria for brain death are not well defined in preterm babies and term neonates less than 7 days old. In newborn babies two EEG’s taken 48 hr apart should show electro-cerebral silence or dynamic scan (133 xenon CT or PET) should demonstrate absence of cerebral blood flow for more than one hour. The cessation of all brain functions must persist for atleast 48 hours, 24 hours and 12 hours for infants upto 2 months, 2 months to 1 year and older than one year respectively. The observation period may be reduced if the EEG demonstrates electrocerebral silence or the cerebral radio-nuclide study does not visualize cerebral arteries.

The children with potentially reversible conditions such as narcotic poisoning, exposure to severe cold, neuromuscular blockade, drowning and trauma should be watchcd for a longer period of time. EEG is not mandatory for the diagnosis of irreversible brain damage but if it remains isoelectric for 30 min it suggests brain death. Brain stem evoked responses, radioisotope bolus cerebral angiography, xenon CT, digital subtraction angiography, visualisation of cerebral arterial pulsations by real-time cranial ultrasound and gamma-scintigraphy are also reliable criteria of brain death though of limited practical utility. Four-vessels intracranial angiography is diagnositc of cessation of circulation to the brain but is cumbersome. Doppler determination of cerebral blood flow velocity and evoked potentials are being investigated for the diagnosis of ‘brain death’. The treating physician must, however, satisfy himself with reasonable certainty that the patient’s vital functions pertaining to heart, lungs and even brain have irreversibly ceased before the tragic news of death is communicated to the parents.