脳死とNeurosonology: 脳死の病態と判定基準

抄録

Neurosonological evaluations of both adult and child cases of brain death were reviewed. Also, the current status of Doppler examinations in confirmatory tests of brain death was compared among the European, North American, and Japanese criteria.
There are three unsolved problems related to cerebral circulation and metabolism in the pathophysiology of brain death. First, does persisting intracranial circulation demonstrated by neuroradiological (angiography, contrast CT, MRI, etc.) and color duplex examination indicate complete cerebral circulatory arrest? Second, does intracranial circulatory arrest continue after confirmation of brain death? (Does intracranial reperfusion occur after cessation of intracranial circulation?) Third, there are discrepancies between neuronal function data and cerebral circulation and metabolism (e.g., persisting cerebral circulation and glucose metabolism were identified in an infant case of clinical brain death and electrocerebral silence) .
Also, equivocal Doppler findings of cerebral circulatory arrest have been reported by Hassler et al. (1989) . Intracranial arteries are visualized clearly by color flow imaging despite evidence of cerebral circulatory arrest, such as oscillating flow or systolic spikes, by Doppler sonography. Continuous Doppler sonograms, with or without early systolic reverse flow, can be obtained for the cervical common carotid and internal carotid arteries, even if there is Doppler cerebral circulatory arrest in the intracranial arteries. Doppler findings in infants with open fontanelle probably differ from those of adults in the extra- and intracranial arteries, with regard to features such as diastolic tailing and late diastolic reversal.
Doppler examination as a confirmatory test of brain death is accepted in only two European countries and Canada. This is probably because of the above-mentioned reliability problems of Doppler tests, difficulty of insonation via temporal windows, the technical skill required by attending physicians or technologists, and the availability of neurosonological equipment in intensive care units.
Neurophysiological tests demonstrating cessation of cerebral circulation and metabolism, including Doppler examination, basically are subsided by clinical determination of brain death. Pathophysiological evaluations in cases of impending brain death are, however, extremely important and a promising research field in neurosonology.