The diagnosis of brainstem death (Table2) must only be considered when the patient is in apneic coma as a result of irremediable structural brain damage caused by a disorder which is known to be capable of producing brain death.
The possibility that the patient's condition can be attributed to the effects of drugs, hypothermia, or metabolic or endocrine disorders must have been excluded before proceeding to the assessment of brainstem function. It is recognized that some metabolic and endocrine disturbances are a likely accompaniment of brainstem death (e.g. hypernatremia, diabetes insipidus), but these are the effect rather than the cause of the patient's condition and do not necessarily preclude the diagnosis of brainstem death.
Seizure activity and posturing, whether decorticate or decerebrate, are incompatible with a diagnosis of brain death. However, it is important to recognize that reflex movements of the limbs and trunk may occur after brainstem death. The physician must be able to explain the significance of such movements to the patient's relatives and friends, including the fact that they are reflex rather than voluntary.
A variety of acquired neuropathies and myopathies may complicate critical illness. Extreme neuromuscular weakness should not be confused with true apnea. It does not affect pupillary, corneal, oculocephalic or vestibulo-ocular reflexes, and therefore is usually easily distinguished from brainstem death. However, in all such cases brainstem death criteria are not satisfied because the diagnosis of a disorder that can lead to brain death has not been established, and there is no evidence of irremediable structural brain damage.
In the United Kingdom it is recommended that the examination of brainstem function should be performed by two physicians, either the consultant in charge of the case and one other (who should be clinically independent of the first and registered for more than 5 years) or the consultant's deputy (provided that he or she has been registered at least 5 years and has adequate appropriate experience) and one other. Neither should be a member of the transplant team. The tests should be performed on two separate occasions, with the interval between the two being agreed by all the staff involved. The first examination should normally be performed a minimum of 6 h after the onset of coma. However, when a patient has suffered from cardiac arrest, hypoxia, or severe circulatory insufficiency with an indefinite period of cerebral hypoxia, or is suspected of having cerebral air or fat embolism, it may take longer to establish the diagnosis. In such cases it is recommended that the first examination should be delayed for at least 24 h after restoration of an adequate circulation. In some patients the primary pathology may be unclear, and a confident diagnosis may only be reached by continued clinical observation and further investigations. A neurologist should be consulted if the diagnosis is in doubt.
In the United States various authoritative groups and institutions have issued guidelines for the diagnosis of brain death. These guidelines have legal implications and some of the recommendations vary between states, for example in the suggested time period over which the diagnosis is established and in recommendations for the use of confirmatory tests. In general the preconditions and exclusions are similar to those recommended in the United Kingdom. The cause of coma must be known and that cause must be adequate to explain the coma. The physical examination is also similar (I.a.bJ.e.3), although the intention is to demonstrate absent cerebral function as well as loss of all brainstem reflexes and the recommendations for apnea testing differ in detail from those in the United Kingdom. Most authors in the United States recommend that the findings should be confirmed on at least two occasions separated by about 12 h, although some suggest 24 h or more.
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Table 3 United States recommendations for clinical testing for brain death
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