Ancillary testing in brain death

Despite worldwide acceptance of the concept of brain death, there is marked variability in the use of ancillary testing. In most countries, ancillary tests are used primarily when confounding factors interfere with reliable completion of a clinical assessment, or physiologic instability precludes performance of an apnea test. Alternatively, in some countries, confirmatory ancillary tests are routinely required before brain death can be diagnosed. Ancillary tests assess brain function (e.g., electroencephalography) or blood flow (e.g., cerebral angiography). Evaluation of blood flow is affected less by confounding clinical factors and is now preferred in most jurisdictions. With angiographic techniques, a significant proportion of patients meeting clinical criteria for brain death have some opacification of proximal intracranial arteries. Consequently, the sensitivity of angiography is strongly influenced by the particular criteria that are used to define intracranial circulatory arrest. Lack of enhancement of the great cerebral and internal cerebral veins has the highest sensitivity. Worldwide experience with newer tests, such as computed tomography and magnetic resonance angiography, is growing. Radionuclide imaging has the advantage of not requiring use of potentially nephrotoxic contrast material. Transcranial Doppler ultrasonography can be brought to the bedside to demonstrate lack of brain blood flow. The specificity of imaging techniques in the detection of intracranial circulatory arrest has not been as well studied as their sensitivity.