Disorders of Consciousness



Disorders of Consciousness





The ability to recognize and interact with the surroundings (i.e., consciousness) is the sina qua non of the life experience, and loss of this ability is one of the dominant signs of a life-threatening illness. This chapter describes the principal disorders of consciousness, with emphasis on delirium, coma, and brain death.


I. Altered Consciousness


A. Consciousness

Consciousness has two components: arousal and awareness.



  • Arousal is the ability to experience your surroundings.


  • Awareness is the ability to understand your relationship to your surroundings.


  • These two components are used to identify the altered states of consciousness described next.


B. Altered States of Consciousness



  • Anxiety and lethargy are conditions where arousal and awareness are intact, but there is a change in attentiveness (i.e., the degree of awareness).



  • 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).


  • Delirium and dementia are conditions where arousal is intact, but awareness is altered. The change in awareness can be fluctuating (as in delirium) or slowly progressive (as in dementia).


  • A vegetative state is a condition where there is some degree of arousal (eyes can open), but there is no awareness. Spontaneous movements and motor responses to deep pain can occur, but the movements are purposeless. After one month, this condition is called a persistent vegetative state (2).


  • Coma is characterized by the total absence of arousal and awareness. Spontaneous movements and motor re-sponses to deep pain can occur, but the movements are purposeless.


  • Brain death is similar to coma in that there is a total absence of arousal and awareness, but it 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 irreversible.


C. Sources of Altered Consciousness

The identifiable causes of altered consciousness are indicated in Figure 40.1. In a prospective survey of neurologic complications in a medical ICU (3), ischemic stroke was the most frequent cause of altered consciousness on admission to the ICU, and septic encephalopathy was the most common cause of altered consciousness acquired in the ICU.







FIGURE 40.1 Common causes of altered consciousness.


II. ICU-Related Delirium

Delirium is reported in 16–89% of ICU patients (4), and has an adverse effect on outcomes (5).


A. Clinical Features

The clinical features of delirium are summarized in Figure 40.2 (4,6).



  • Delirium is an acute confusional state with attention deficits, disordered thinking, and a fluctuating course (the fluctuations in behavior occur over a 24-hour period).


  • Over 40% of hospitalized patients with delirium have psychotic symptoms (e.g., visual hallucinations) (7); as a result, delirium is often inappropriately termed “ICU psychosis” (8).







    FIGURE 40.2 The clinical features of delirium.


3. Subtypes

The following subtypes of delirium are recognized:



  • Hyperactive delirium is characterized by restless agitation. This form of delirium is common in alcohol
    withdrawal, but it is uncommon in hospital-acquired delirium, accounting for 2% or fewer of cases (4).


  • Hypoactive delirium is characterized by lethargy and somnolence. This is the most common form of hospital-acquired delirium, and is responsible for 45–64% of cases (4). This type of delirium is often overlooked, and may explain why the diagnosis of delirium is often missed.


  • Mixed delirium involves episodes that alternate between hyperactive and hypoactive delirium. This type of delirium is reported in 6–55% of patients with hospital-acquired delirium (4).


4. Delirium vs. Dementia

Delirium and dementia are distinct mental disorders that are often confused because they have overlapping clinical features (i.e., attention deficits and disordered thinking). The principal features of delirium that distinguish it from dementia are the abrupt onset and fluctuating course.


B. Predisposing Conditions

Several conditions promote delirium in hospitalized patients, including: (a) advanced age, (b) sleep deprivation, (c) unrelieved pain, (d) prolonged bed rest, (e) major surgery, (f) encephalopathy, and (g) drugs (see next) (4,9,10).


1. Deleriogenic Drugs

Drugs that promote delirium include: (a) anticholinergic drugs, (b) dopaminergic drugs, (c) seritonergic drugs, and (d) benzodiazepines (10,11). The principal drugs that promote delirium in the ICU are the benzodiazepines (11).


C. Preventive Measures

Recommended measures for reducing the risk of delirium include: (a) adequate treatment of pain, (b) maintaining regular
sleep-wake cycles, (c) promoting out-of-bed time, (d) encouraging family visitation, and (e) limiting the use of deliriogenic drugs, if possible (4,11).


1. Dexmedetomidine

Sedation with dexmedetomidine is associated with fewer episodes of delirium than benzodiazepines (12,13). This drug provides an alternative to benzodiazepines for sedation in ICU patients who are at risk for delirium. For more information on dexmedetomidine, see Chapter 43, Section II-D.


D. Diagnosis

The current guidelines on the management of agitation and delirium (11) recommend periodic testing for delirium using validated screening tools like the Confusion Assessment Method for the ICU (CAM-ICU) (6), which is available at www.icudelirium.org.


E. Management

There is no universally-sanctioned drug therapy for hospital-acquired delirium.

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Nov 8, 2018 | Posted by in CRITICAL CARE | Comments Off on Disorders of Consciousness

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