Brain Death (also see Chapter 79 )

The longest-standing criterion for death is irreversible cessation of cardiorespiratory function. Death has become less well defined because the modern technology of organ system support allows clinicians to maintain cardiopulmonary function indefinitely, even after brain function has permanently ceased. These medical advances have necessitated a reassessment of the definition of death; brain death is a clinical and legal definition of death that describes permanent cessation of brain function.

Clinical criteria for brain death include irreversibly absent cerebral and brainstem functions. Absent cerebral function is recognized when there is no cortically mediated receptivity or response to external stimuli.^[216] Absent brainstem function is recognized when brainstem reflexes cannot be elicited: absent pupillary response to light and absent corneal, oculocephalic, oculovestibular, oropharyngeal, and respiratory reflexes.

Irreversibility is determined when the cause of coma is sufficient to account for the loss of brain function and when the possibility of recovery is excluded by clinical observation or laboratory studies, or both. Laboratory studies that should be considered include analysis of blood and urine for toxic substances, EEG, radionuclide brain scans, cerebral angiography, and brainstem evoked potentials. These laboratory functions should be considered confirmatory in nature and supplementary to the clinical history and physical examination. It is important to identify any factors that can simulate the clinical or laboratory criteria for absent brain function; severe hypothermia (core temperature <30°C) and elevated barbiturate levels present the most common situation. Both hypothermia and the presence of barbiturates can significantly depress electrical activity in the brain and may render an EEG meaningless. In such cases, the technetium 99m (^99m Tc) radionuclide angiogram is useful. Patients with brain death have no arterial blood flow to the anterior and middle cerebral arteries and no venous flow in the sagittal sinus; blood flow to the extracranial tissues is preserved. This study is independent of the patient's core temperature or barbiturate level. It is usually helpful to have at least two physicians concur on the clinical or laboratory diagnosis of brain death, or on both. All evidence must be clearly documented in the patient's record.

Whenever a patient is declared brain dead, the family should be approached for the possibility of solid organ donation. Tissue donation (e.g., eyes and heart valves) can also be offered to families after the child has suffered cardiovascular death. Regional procurement agencies can provide protocols and support to the ICU staff, as well as to families.