Diagnosis of brain-stem death

The diagnosis is not technically difficult. In more and more countries, it is made on purely clinical grounds. The aim of the clinical tests is not to probe every neuron within the intracranial cavity to see if it is dead—an impossible task—but to establish irreversible loss of brain-stem function. This is the necessary and sufficient condition for irreversible unconsciousness and irreversible apnea, which together spell a dead patient. Experience has shown that instrumental procedures (such as electroencephalography and studies of cerebral blood flow) that seek to establish widespread loss of cortical function contribute nothing of relevance concerning the cardiac prognosis. Such tests yield answers of dubious reliability to what are widely felt to be the wrong questions. As the concept of brain-stem death is relatively new, most countries rightly insist that the relevant examinations be carried out by physicians of appropriate seniority. These doctors (usually neurologists, anesthetists, or specialists in intensive care) must be entirely separate from any who might be involved in using the patient’s organs for subsequent transplants.

The diagnosis of brain-stem death involves three stages. First, the cause of the coma must be ascertained, and it must be established that the patient (who will always have been in apneic coma and on a ventilator for several hours) is suffering from irremediable, structural brain damage. Damage is judged “irremediable” based on its context, the passage of time, and the failure of all attempts to remedy it. Second, all possible causes of reversible brain-stem dysfunction, such as hypothermia, drug intoxication, or severe metabolic upset, must be excluded. Finally, the absence of all brain-stem reflexes must be demonstrated, and the fact that the patient cannot breathe, however strong the stimulus, must be confirmed.

It may take up to 48 hours to establish that the preconditions and exclusions have been met; the testing of brain-stem function takes less than half an hour. When testing the brain-stem reflexes, doctors check for the following normal responses: (1) constriction of the pupils in response to light, (2) blinking in response to stimulation of the cornea, (3) grimacing in response to firm pressure applied just above the eye socket, (4) movements of the eyes in response to the ears being flushed with ice water, and (5) coughing or gagging in response to a suction catheter being passed down the airway. All responses have to be absent on at least two occasions. Apnea, which also must be confirmed twice, is assessed by disconnecting the patient from the ventilator. (Prior to this test, the patient is fully oxygenated by being made to breathe 100 percent oxygen for several minutes, and diffusion oxygenation into the trachea is maintained throughout the procedure. These precautions ensure that the patient will not suffer serious oxygen deprivation while disconnected from the ventilator.) The purpose of this test is to establish the total absence of any inspiratory effort as the carbon dioxide concentration in the blood (the normal stimulus to breathing) reaches levels more than sufficient to drive any respiratory centre cells that may still be alive.

The patient thus passes through a tight double filter of preconditions and exclusions before he is even tested for the presence of a dead brain stem. This emphasis on strict preconditions and exclusions has been a major contribution to the subject of brain-stem death, and it has obviated the need for ancillary investigations. Thousands of patients who have met criteria of this kind have had ventilation maintained: all have developed asystole within a few hours or a few days, and none has ever regained consciousness. There have been no exceptions. The relevant tests for brain-stem death are carried out systematically and without haste. There is no pressure from the transplant team.

The developments in the idea and diagnosis of brain-stem death came as a response to a conceptual challenge. Intensive-care technology had saved many lives, but it had also created many brain-dead patients. To grasp the implications of this situation, society in general—and the medical profession in particular—was forced to rethink accepted notions about death itself. The emphasis had to shift from the most common mechanism of death (i.e., irreversible cessation of the circulation) to the results that ensued when that mechanism came into operation: irreversible loss of the capacity for consciousness, combined with irreversible apnea. These results, which can also be produced by primary intracranial catastrophes, provide philosophically sound, ethically acceptable, and clinically applicable secular equivalents to the concepts of “departure of the soul” and “loss of the ‘breath of life,’ ” which were so important to some earlier cultures.