Medical History

The initial evaluation of the potentially brain dead patient should focus on the patient’s history (see Figure 68.1). There should be an identifiable and reasonable cause to explain the patient’s current condition. Next, the clinician must exclude reversible causes of coma, such as toxic or metabolic causes. Any such confounding condition must be corrected before continuing the evaluation. These include gross physiologic disturbances, such as hypothermia, hypoxemia, and hypotension or circulatory shock; metabolic derangements, such as acidosis, hypo- or hyperglycemia, and renal or hepatic encephalopathy; and serious electrolyte disorders, such as hypo- or hypernatremia and hypo- or hypercalcemia.

Drug overdose or toxic exposure should always be ruled out in patients presenting to the ICU in coma and who otherwise appear brain dead. In most cases, if a patient has received sedatives or analgesics before the evaluation for brain death, adequate time (usually four times the excretion half-life of the substance, taking into account hepatic or renal dysfunction when present) for elimination of the substance must occur.

Particular attention must be given to patients in whom neuromuscular blocking agents were used to ensure they have been adequately cleared from the circulation (see Chapter 5). A peripheral nerve stimulator should be used in all patients undergoing evaluation for brain death who received neuromuscular blocking agents.

Physical Examination in Brain Death Determination

Brain death is a clinical diagnosis whose cardinal features are (1) coma, (2) absence of brain stem reflexes, and (3) apnea. Because of the critical role of the examination, many hospitals mandate consultation with a neurologist when patients are not already on a neurologic or neurosurgical service.

Absence of Brain Stem Reflexes

Pupillary reflexes should be assessed in a dimly lit room with the patient’s eyes initially closed. The eyes are opened and a bright light is applied sequentially to each pupil. The pupils should be observed for 30 seconds. A normal response is brisk constriction of the pupil. In brain death, the pupils must be nonreactive (“fixed”) and midsized. Excessively large or excessively small pupils should raise suspicion for drug intoxication.

The corneal reflex can be assessed by lightly touching the cornea with a sterile cotton swab or gauze. A normal response is a blink to the stimulus. In brain death, there should be no response.

The oculocephalic reflex (“doll’s eye reflex”) assesses vestibular and proprioreceptor responses. In an intact reflex, as the patient’s head is rotated laterally from one side to the other, the patient’s eyes move in the opposite direction. In a brain dead patient, the eyes remain fixed with the lateral turn. This maneuver should not, however, be performed in patients with potentially unstable cervical fractures.

The oculovestibular reflex (cold caloric reflex) assesses vestibular and midbrain functions but generally provides a stronger stimulus than the oculocephalic reflex. The external auditory canals should first be inspected to ensure that the tympanic membranes are intact and unobstructed. The head should be midline and elevated at 30 degrees to allow for maximal stimulation of the horizontal semicircular canal. A soft catheter is inserted into the canal and the ear is slowly (20 seconds or more) irrigated with at least 50 mL of iced water. The eyes are observed for ~1 minute. If the reflex is intact, both eyes deviate toward the irrigated ear followed by nystagmus with the fast phase beating away from the irrigated ear. In a brain dead patient, the eyes do not move at all. Any other response is not consistent with brain death.

The cough and gag reflexes test the integrity of the medulla and the lower cranial nerves (IX, X). The cough reflex is elicited by stimulating the carina with a deep suction catheter that is passed through the endotracheal tube. Normally this produces a vigorous cough. In a brain dead patient there should be no response. The gag reflex may be tested by gently tugging on the endotracheal tube. In many normal people this will produce gagging; in the brain dead patient, there is no response.

The apnea test is used to confirm brain death clinically only when the aforementioned preconditions have been met and when all other brain stem reflexes are absent. Because it requires an intact phrenic nerve and functioning diaphragm, it should not be performed if patients have a high cervical fracture or neuromuscular disease impairing diaphragmatic function. Maintaining adequate oxygenation during the test and documenting a rise in Paco₂ to a level that would stimulate respiration in an intact patient is critical to performing a successful apnea test (Box 68.1).

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