There are cases on record in which a patient with an isoelectric EEG has had preserved brainstem reflexes so that cerebral unresponsiveness and a flat EEG do not alone signify brain death; isoelectric EEG may also be reversible in states of profound hypothermia or intoxication with sedative-hypnotic drugs and immediately following cardiac arrest. Therefore, it has been recommended that the diagnosis of brain death not be entertained until several hours have passed from the time of initial observation. If the examination is performed at least approximately 6 h after the precipitating event, and there is prima facie evidence of overwhelming brain injury from trauma, or massive cerebral hemorrhage (the most common conditions causing brain death), there is probably no need for serial testing. If cardiac arrest was the antecedent event, or the cause of neurologic damage is unclear, or drug or alcohol intoxication could reasonably have played a role in suppressing the brainstem reflexes, it is advisable to wait about 24 h before repeating the testing and pronouncing the patient dead. Toxicologic screening of the serum or urine is requisite in these circumstances.
The impact of any requirement to perform a second brain death examination at some interval such as 6 h has been studied by Lustbader and coworkers. Their extensive survey in New York State, where a second examination had been recommended by a panel, was instructive; of 1,311 adult and pediatric cases, none who were found to be brain dead regained brainstem function on a second test that was performed about 18 h later. However, 12 percent had cardiac arrest and in others, consent for organ donation was withheld during the time between examinations. Several authoritative authors have argued on this basis against a second brain death test.
Because evoked potentials show variable abnormalities in brain-dead patients, they are probably not of primary value in the diagnosis but if performed, all cerebral activity should be absent. Some centers use nuclide brain scanning or cerebral angiography to demonstrate an absence of blood flow to the brain, equating this with brain death. This approach is acceptable and may be necessary if facial trauma, burns or other injury prevent evaluation of pupillary and ocular reflexes but there are technical pitfalls in the use of these methods. The specificity of radionuclide scanning is close to 100 percent but there is a self-referential aspect to this statement as the clinical diagnosis has been used as a gold standard. An additional problem arises in the observation that the sensitivity may be only about 75 percent (Joffe et al). False-negative tests are possible if a small amount of filling of the intracranial vertebral arteries with angiography or nuclide uptake in the inferior cerebellum is demonstrated. The same can be said for a degree of imprecision in transcranial Doppler sonography, which in brain death shows a to-and-fro, pendelfluss blood-flow pattern in the basal vessels.
The main difficulties that arise in relation to brain death are not the technical ones discussed above, but those involving the sensitive conversations with the family of the patient and, to some extent, with other medical professionals. These tasks often fall to the neurologist. It is best not to embark on clinical or EEG testing for brain death unless there is a clear intention on the part of the physician to remove the ventilator or follow through with organ donation at the end of the process. The nature of testing for brain death and its potential outcome should be explained to the family in plain language. The family’s desires regarding organ transplantation should be sought after adequate time has passed for them to absorb the shock of the circumstances. Neurologists must, of course, resist pressures from diverse sources that might lead them to the premature designation of a declaration of brain death. To avoid the appearance of conflict of motivations, most centers have a separate team, often from an organ bank, to address the issues of organ transplantation after brain death has been established. The complex matter of a family’s desire to maintain ventilation and other medical support in a brain-dead relative is best addressed with consideration and counseling by the physician and clergy, ethics (“optimal care”) committees, and hospital staff, so as to avoid confrontation. Time often allows such situations to be defused.