Table 5.2. Criteria for brain death Prerequisite
All appropriate diagnostic and therapeutic procedures have been performed and the patient's condition is irreversible. Criteria (to be present for 30 minutes at least 6 hours after the onset of coma and apnea)
2. Apnea (no spontaneous respirations)
3. Absent cephalic reflexes (pupillary, corneal, oculoauditory, oculovestibular, oculocephalic, cough, pharyngeal, and swallowing)
Absence of cerebral blood flow by radionuclide brain scan hypothermia and drug intoxication must first be excluded. Trauma patients are often intoxicated with alcohol. Thus, 8 hours should be allowed to pass if alcohol use is suspected before a diagnosis of clinical brain death can be made. Patients in intensive care units may also be under the influence of sedative or paralytic agents.
Clinical testing is relatively straightforward and examines the presence of brain stem reflexes and the presence of total apnea. Five brain stem reflexes should all be absent in order to diagnose brain stem death: pupillary response to light, corneal reflex to touch, vestibulo-ocular reflex using the cold caloric test, the gag reflex, and the apnea test. The apnea test demonstrates the absence of respiratory drive to PaCO2 greater than 50 mmHg. During apnea, the PaCO2 rises by about 2 mmHg/ min; thus, if the starting PaCO2 is over 30, the PaCO2 will rise to over 50 mmHg in about 10 minutes. To prevent hypoxia during these 10 minutes, the patient should be preoxygenated prior to the test. Confirmatory studies, although not necessary, include serial electroencephalography and radionuclide scan to assess cerebral perfusion.
Death may also be declared by cardiopulmonary criteria, and in certain instances, particularly when patients are being withdrawn from support, organ donation is possible. This type of donation is referred to as donation after cardiac death (DCD) or non-heart-beating donation. Prior to the Harvard criteria defining brain death in 1968, all organ donors were DCD donors. Although some warm ischemia occurs in these donors, several centers have shown that renal and extrarenal donation is possible. Recently the Institute of Medicine (IOM) reviewed non-heart-beating organ donation, published guidelines, and concluded that NHBDs are a medically and ethically acceptable source of donor organs. Currently, NHBDs comprise 2% of organ donors and this percentage will likely increase since the results of transplantation have been shown to be acceptable.
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