Marino The ICU Book 4e, IE

800 Nervous System Disorders

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-