Clinical Pearls & Morning Reports
Published December 29, 2021
The process for determining brain death includes five components: ensuring that certain prerequisites are met, neurologic examination, apnea testing, ancillary testing (if necessary), and documentation. Read the NEJM Clinical Practice Article here.
Q: What are some of the factors that may confound a determination of brain death?
A: Numerous criteria must be met before a determination of brain death. In addition to determining the underlying cause of death and ensuring irreversibility, clinicians must be aware of factors that may confound the determination. These include dysregulation of temperature, blood pressure, electrolyte levels, and acid–base status, and intoxication, including from self-administered toxins (e.g., opioid overdose) or medications received during the course of treatment (e.g., benzodiazepines or barbiturates) to prevent seizures or to treat elevated intracranial pressure. Failure to account for persistent effects of central nervous system depressants is one of the most common causes of false determination of brain death.
Q: Does a clinical examination need to be performed more than once to determine brain death in adults in the United States?
A: Adult guidelines require one or two examinations, and evidence suggests that one may be sufficient. Among more than 1400 cases (largely in adults) in which brain death was determined with the use of two examinations, there were no instances in which the second examination was inconsistent with the first. Nonetheless, many states and institutions require two examinations — a more conservative approach.
A: Apnea testing assesses function of the medulla by allowing carbon dioxide levels to rise and the pH to fall sufficiently to maximally stimulate medullary respiratory centers; the absence of respiratory effort in response to hypercarbia and acidosis is consistent with brain death. Decisions regarding apnea testing must take into consideration the patient’s pulmonary and hemodynamic stability. The main risk is cardiovascular collapse, which can be mitigated by ensuring adequate oxygenation before testing. Apnea testing should only take place in an intensive care setting with continuous blood pressure and oxygenation monitoring and after all other clinical testing is consistent with brain death.
A: Ancillary testing should be conducted only when the clinical examination cannot be performed fully (e.g., in cases of severe facial trauma or swelling) or safely (e.g., apnea testing in a patient with hemodynamic or pulmonary instability). Testing of cerebral perfusion is the preferred method of ancillary testing; evidence of cerebral blood flow precludes a diagnosis of brain death. Digital subtraction angiography (DSA) has long been used in the determination of brain death, but it is labor intensive and associated with a risk of nephrotoxicity. Transcranial Doppler ultrasonography has also been accepted as a means of determining brain death and can be performed at the bedside, but its effectiveness depends on the ability of the operator, and in certain circumstances it is considered to be invalid. Alternatively, perfusion can be measured with the use of radionuclide angiography or perfusion scintigraphy, which have a specificity similar to that of DSA. Although numerous studies have supported the use of CT angiography, magnetic resonance imaging, and magnetic resonance angiography, these types of imaging have not been assessed in comparison with DSA and have been criticized for having unacceptably high false positive rates. Consequently, they are not currently recommended.