Altered States of Consciousness
The principal states of altered consciousness are as follows:
1.
Anxiety
and
lethargy
are conditions where arousal and awareness are
intact, but there is a change in
attentiveness
(i.e., the degree of aware-
ness).
2. A
locked-in state
is a condition where arousal and awareness are
intact, but there is almost total absence of motor responsiveness.
This condition is caused by bilateral injury to the motor pathways in
the ventral pons, which disrupts all voluntary movements except
up-down ocular movements and eyelid blinking (1).
3.
Delirium
and
dementia
are conditions where arousal is intact, but
awareness is altered. The change in awareness can be fluctuating (as
in delirium) or permanent (as in dementia).
4. A
vegetative state
is a condition where there is some degree of arous-
al (eyes can open), but there is no awareness. Spontaneous move-
ments and motor responses to deep pain can occur, but the move-
ments are purposeless. After one month, this condition is called a
persistent vegetative state
(2).
5.
Coma
is characterized by the total absence of arousal and awareness
(i.e., unarousable unawareness). Spontaneous movements and
motor responses to deep pain can occur, but the movements are pur-
poseless.
6.
Brain death
is similar to coma in that there is a total absence of arous-
al and awareness. However, brain death differs from coma in two
ways: (a) it involves loss of all brainstem function, including cranial
nerve activity and spontaneous respirations, and (b) it is always irre-
versible.
Sources of Altered Consciousness
The nontraumatic causes of altered consciousness are indicated in Figure
44.1. In a prospective survey of neurologic complications in a medical
ICU (3), ischemic stroke was the most frequent cause of altered con-
sciousness on admission to the ICU, and septic encephalopathy was the
most common cause of altered consciousness that developed after admis-
sion to the ICU. Nonconvulsive status epilepticus should always be con-
sidered when the source of altered consciousness is not clear (see Chapter
45).
Septic Encephalopathy
Septic encephalopathy is a global brain disorder associated with infec-
tions that originate outside the central nervous system. This condition is
reported in 50 – 70% of ICU patients with sepsis, and can be an early sign
of infection, especially in elderly patients (3,4). Septic encephalopathy is
similar to hepatic encephalopathy (described in Chapter 39) in that both
conditions are characterized by cerebral edema, and involve the accumu-
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Nervous System Disorders
