Criteria for diagnosing brain stem death

MD O'BRIEN

The traditional criteria of cardiac and respiratory arrest for the certification of death are appropriately used in the huge majority of cases, but the development and widespread use of cardiac resuscitation and artificial ventilation in the late 1960s created a need to redefine the criteria of death in the very small numbers of patients in apnoeic coma, who could be maintained on a ventilator for days or weeks, a need made more pressing by the demand for organs for transplantation.1

Twenty years ago, many such patients were ventilated until asystole supervened, by which time the brain had often liquefied. Over several years the concept that apnoeic coma, caused by irreversible destruction of the brain stem, was incompatible with life led to the establishment of criteria to diagnose brain stem death. Brain stem death equates with death of the brain as a whole but not, of course, with death of the whole brain. Wij dicks2 has reviewed the brain death criteria throughout the world, obtaining information from 80 countries. Practice guidelines for brain death in adults were present in 70 countries and these were associated with legal standards, relating to organ transplantation, in 55 countries. The criteria varied considerably, many countries including the United States, require death of the whole brain, while many others follow the United Kingdom criteria for brain stem death. There were major differences in the requirement for apnoea testing. Forty one countries required an apnoea test with specified Pco2 targets, 20 countries required disconnection from the ventilator only which may result in inadequate respiratory centre stimulation, and nine countries had no apnoea test requirement.

Brain stem death can be ascertained clinically at the bedside with absolute reliability and without the use of special techniques such as EEG, evoked responses, neuroimaging or blood flow measurements, provided that the appropriate protocol is rigorously followed. If these criteria are met, life support systems may be withdrawn with the confidence that recovery cannot occur. Organs may then be removed for transplantation and better use made of intensive care facilities. Relatives should be kept fully informed at each stage in this process.

If ventilation is maintained, cardiac asystole usually occurs within a few days and nearly always within a week or two. However, there are a number of well-documented patients who have filled the criteria for brain stem death, but who have maintained vital organ function on a ventilator for extended periods. Shewmon identified 175 patients from his own experience and in a search of the literature who survived more than one week.3 Of these, there was sufficient information for a detailed analysis in 56 patients, 17 survived for two months, seven for six months and four for over a year. There was a single patient whose vital organs except the brain were still functioning at the time of the report after 10 years. However, in this patient multimodal evoked potentials showed no intracranial response, magnetic resonance angiography showed no intracranial blood flow and neuroimaging showed that the entire cranial cavity was filled with disorganised membranes, proteinaceous fluids and ghost-like outlines of the former brain. It is clear that this patient had been dead for many years, but there is still widespread misunderstanding of the concept of brain stem death and confusion in the minds of relatives. Further confusion arises over the differentiation of brain stem death from the persistent vegetative state, which has been discussed by Cranford4 and Jennett.5 Patients in the persistent vegetative state have a functioning brain stem and breathe spontaneously. They may show apparent sleep-wake cycles. This state may persist for years, but these patients do not fulfil the criteria for brain stem death and cannot be certified as dead. In the United Kingdom, withdrawal of medical support or stopping feeding requires judicial approval.

The diagnosis of brain stem death requires preconditions that are of critical importance. Examples in the medical literature claiming survival after brain stem death have failed to fulfil the preconditions. Only when the cause of the brain damage has been established and is known to be irreversible should the tests of brain stem function be carried out. These are tests of reflex function of the brain stem. Although the oculocephalic reflex (doll's eye movement) was not part of the United Kingdom code,1 it is worth doing because it is simple and easy to elicit. If the oculocephalic reflex is present, there is no need to proceed further. The pupil light reflex should be elicited with a bright light; the light from an ophthalmoscope is not sufficient. Similarly, the corneal and gag reflexes should be sought with adequate stimuli, which need to be relatively coarse compared with those used in a conscious patient. In addition, motor responses should be sought by adequate stimulation in the trigeminal nerve territory and in the limbs. Ice cold water irrigation of the tympanic membrane should not elicit any eye movement. Tonic deviation of either eye during this test indicates some residual brain stem function. These are all straightforward bedside tests and should not create any difficulties. The tests for spontaneous ventilation with blood gas analysis and specific Pco2 targets is usually carried out by an anaesthetist, who should be available together with the appropriate equipment in all intensive care units where these problems are likely to arise.

The criteria have been set out in a form suitable for reproduction and inclusion in a patient's notes (Box 13.1).6 The background to the concept of brain stem death, the historical aspects, and its validation has been fully discussed by Pallis.78

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