Marino The ICU Book 4e, IE

812 Nervous System Disorders

death determination, but the consensus goal is to establish: (a) irreversible coma, (b) the absence of brainstem reflexes, and (c) the absence of sponta- neous respirations. Prior to performing a brain death examination, other confounding conditions (e.g., hypothermia) should be corrected. If the eti- ology of the coma is unclear, an electroencephalogram should be performed to search for nonconvulsive status epilepticus. If the clinical evaluation for brain death is equivocal, then confirmatory testing may be required. (See the bottom of Table 44.5 for a list of the accepted confirmatory tests). The Apnea Test The most convincing evidence of brain death is the absence of sponta- neous respiratory efforts in the face of an acute increase in arterial PCO 2 (which is normally a potent respiratory stimulus). This is evaluated with the apnea test, which involves removing the patient from ventilatory support and observing for spontaneous breathing efforts as the arterial PCO 2 rises. Because the apnea test can cause hypotension, hypoxemia and cardiac arrhythmias, it is typically the last test performed in the brain death determination. The following steps are involved in the apnea test: 1. Prior to the test, the patient is preoxygenated with 100% O 2 , and an arterial blood gas is obtained to establish the baseline arterial PCO 2 (PaCO 2 ). 2. The patient is then separated from the ventilator and oxygen is insufflated into the endotracheal tube (apneic oxygenation) to help prevent O 2 desaturation during the apneic period. (A pulse oxime- ter should be used to monitor the arterial O 2 saturation.) 3. The goal of the apnea test is to allow the PaCO 2 to rise 20 mm Hg above baseline. The PaCO 2 rises about 3 mm Hg per minute during apnea at normal body temperatures (33), so an apnea period of 6 – 7 minutes should be sufficient for achieving the target PaCO 2 . A repeat arterial blood gas is obtained at the end of the apnea period, and the patient is placed back on the ventilator. 4. If apnea persists despite a rise in PaCO 2 ≥ 20 mm Hg, the test con- firms the diagnosis of brain death. 5. The apnea test is risky, and often cannot be completed because of severe O 2 desaturation, hypotension, or serious cardiac arrhyth- mias (34). If the apnea test cannot be completed, confirmatory test- ing may be required to establish the diagnosis of brain death. Lazarus’ Sign Brain-dead patients can exhibit brief, spontaneous movements of the head, torso, or upper extremities ( Lazarus’ Sign ), especially after they are removed from the ventilator (35). These movements are the result of neu- ronal discharges in the cervical spinal cord, possibly in response to hypoxemia, and they can be a source of angst when they appear after the patient has been pronounced brain dead and is removed from the venti- lator.