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.
812
Nervous System Disorders
