Brain Death

It is commonly accepted within the medical profession that a person is dead when his or her brain is dead, an understanding that has largely supplanted earlier cardiopulmonary criteria for death. This definition evolved in the context of common use of mechanical ventilation, which allowed the artificial maintenance of cardiac and pulmonary integrity even after the patient's brain no longer functioned. The fact that patients without consciousness, brain-stem reflexes, or measurable electrical activity in their brains can be sustained for long periods of time with mechanical ventilation led a committee at Harvard Medical School [Page 113]to address the issue of brain death in 1968. This committee defined brain death as a lack of responsiveness, movement, breathing, and brain-stem reflexes in the context of coma for which a cause has been identified, a state known as whole brain death (WBD). In the wake of the Karen Ann Quinlan controversy in 1976, many states worked to formally establish brain death as an acceptable criterion for death. Formal guidelines were published in 1981 by the President's Commission for the Study of Ethical Problems in Medicine and Biomedical and Behavioral Research. These recommendations included the use of confirmatory tests to reduce the length of required observation, ruling out shock before diagnosing brain death, and allowing a 24-hour observation period in cases of anoxic brain damage. After the guidelines were published, a number of individual states developed specific requirements, such as the need for two physicians to confirm brain death, permission for registered nurses to declare death with subsequent confirmation by a physician, and in some cases requirements that specific religious objections be honored.

In order to offer evidence-based practice parameters that might allow a more consistent approach to diagnosing brain death, the American Academy of Neurology published a report describing various clinical tools that might be used to establish brain death, including a description of apnea testing. Such guidelines are important because though the ideal might be for an experienced neurologist or neurosurgeon to evaluate patients, many smaller communities might not have access to such a medical professional. Several elements are required for the diagnosis. The absence of brain-stem reflexes must be documented. Brain-stem reflexes include response of pupils to light, the corneal reflex, the gag reflex, coughing with suctioning, sucking/rooting reflexes, and eye movement in the direction of the tympanic membrane stimulated with cold water after the head has been tilted 30 degrees (cold caloric stimulation). Likewise apnea must be documented.

Apnea is documented by disconnecting a patient from a ventilator and watching for breathing efforts as arterial carbon dioxide is monitored. It is defined as no respiratory effort at a partial pressure of carbon dioxide of 60 mm Hg or 20 mm Hg higher than the normal baseline. During apnea testing, the patient continues to be oxygenated. Coma is documented by absence of motor responses to painful stimuli, such as pressing on the nail bed of a finger or the supraorbital nerve above the eye socket. Computed tomographic scanning is important for determining the cause of brain death, though it does not replace careful examination. Similar guidelines were published in Canada in 2000 by the Canadian Neurocritical Care Group.

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