Page 1118 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

CHAPTER 82: Delirium in the Intensive Care Unit 757

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than 20,000 observations. Among patients who developed delirium, pure factors. Patients who are highly vulnerable to developing delirium
hyperactive delirium was rare (<5%), whereas hypoactive was present (ie, who have multiple predisposing risk factors) may become delirious
in 45% and the mixed subtype—with alternating periods of hypoactive with only minor insults, whereas those with low baseline vulnerability
and hyperactive delirium—was the predominant manifestation (54%). may require a greater insult to become delirious. Predisposing risk
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Interestingly, hypoactive delirium was significantly more common in factors, those related to patient characteristics or underlying chronic
patients over the age of 65. Similarly, in a cohort of 100 surgical and pathology, are difficult to alter, whereas precipitating factors, such as
trauma ICU patients, the prevalence of hypoactive delirium was greater those related to the acute illness or the ICU environment, represent areas
than 60%. The risk factors for, and clinical implications of, these of risk that are modifiable or preventable (Table 82-2).
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subtypes are the subject of ongoing investigations. 23 Baseline risk factors that have been identified in both ICU and non-ICU
Because sedation is commonly used in the ICU, the period sur- populations include older age, depression, vision impairment, hearing
rounding cessation of sedation represents a scenario in the ICU during impairment, hypertension, history of smoking, history of alcohol use,
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which delirium could be easily recognized but is often missed. Delirious living single at home, underlying cognitive impairment or dementia, and
patients emerging from the effects of sedation may do so peacefully or APOE4 polymorphism. 9,10,13,34-37 Numerous features of the acute critical
in a combative manner. The “peaceful” patients are often erroneously illness have been identified as delirium risk factors in studies specifically
assumed to be thinking clearly. Delirium in this context is referred to examining ICU patients; these include admission to an ICU for a medical
as hypoactive delirium and is characterized by lethargy, drowsiness, and illness, high severity of illness (indicated by high APACHE II and SAPS II
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infrequent spontaneous movement, which contributes to delirium scores), need for mechanical ventilation, receipt of sedative and/or anal-
being overlooked unless the patient is specifically screened for its gesic medications (particularly when used to induce coma), respiratory
presence. 24-28 Even in the absence of agitation, such delirium can lead disease, anemia, hypotension, hypocalcemia, hyponatremia, azotemia,
to adverse outcomes such as reintubation, which itself has been shown to transaminitis, hyperamylasemia, hyperbilirubinemia, acidosis, fever, infec-
increase the risk of prolonging the ICU stay, transfer to a long-term care tion, sepsis, gastric tubes, bladder catheters, arterial lines, and more than
or rehabilitation facility, and death. In addition, hypoactive delirium is three infusing medications. 9,13,17,35-39 Risk factors related to the ICU envi-
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associated with immobility in the ICU, which itself places patients at ronment include lack of daylight in the ICU, isolation, lack of visitors, and
risk for adverse outcomes, including aspiration, pulmonary embolism, sleep disturbances. 37,40
and decubitus ulcers. Though difficult to accurately measure in ICU patients, sleep depriva-
In contrast to patients with hypoactive delirium are agitated or combat- tion is believed to be nearly universal in the ICU and has long been pro-
ive patients with hyperactive delirium; these patients are at risk not only posed as a risk factor for delirium. The relationship, however, between
for self-extubation and subsequent reintubation but also for pulling out sleep disturbance and delirium in the ICU remains controversial, and
central venous catheters and even falling out of bed. These hyperactive there is significant overlap in the symptoms of both syndromes such
patients are often given large doses of sedatives that lead to heavy seda- that either may present with inattention, fluctuating mental status and
tion and prevent timely liberation from mechanical ventilation, placing cognitive dysfunction, making it difficult to ascertain whether sleep
patients at risk for remaining delirious or even comatose and on invasive deprivation causes delirium or vice versa. 40,41 On average, ICU patients
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mechanical ventilation unnecessarily. To avoid this difficult and danger- sleep between 2 and 8 hours in a 24-hour period, often with severe and
ous cycle, health care professionals should minimize use of psychoactive frequent disruptions and only a small fraction of “restorative,” rapid eye
medications and frequently assess patients for delirium, especially during movement (REM) sleep. In repeated studies, between one-third and
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the transition from drug-induced or metabolic coma to wakefulness. one-half of patients’ sleep in the ICU occurs during daytime hours. 42,43
Reasons for poor sleep in this setting are multifactorial. The ICU envi-
RISK FACTORS ronment, with its continuous cycle of alarms, lights, and care-related
interruptions interferes with a patient’s sleep cycle and may disrupt
Nearly every ICU patient is exposed to one or more risk factors for their circadian rhythm. 41,43 Acute illness, with symptoms such as nausea,
delirium; the average patient in one study, in fact, had 11 identifiable pain, and fever, may also disrupt sleep. Mechanically ventilated patients
risk factors for delirium. These risk factors may be divided into may additionally suffer sleep disruptions due to anxiety, ventilator
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predisposing (baseline) factors and precipitating (hospitalization-related) dyssynchrony, central apneas, and mode of mechanical ventilation.
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TABLE 82-2 Risk Factors for Delirium
Host Factors Factors Relating to Critical Illness Environmental and Iatrogenic
Not modifiable or preventable Age High severity of illness Lack of daylight
Hypertension Respiratory disease Isolation
APOE-4 Medical illness
Preexisting cognitive impairment Need for mechanical ventilation
Alcohol use Number of infusing medications
Tobacco use
Depression
Potentially modifiable/preventable Hearing or vision impairment Anemia Lack of visitors
Acidosis Sedatives/analgesics (eg, benzodiazepines
Hypotension and opiates)
Infection/sepsis Immobility
Metabolic disturbances (eg, hypocalcemia, hyponatremia, Bladder catheters
azotemia, transaminitis, hyperamylasemia, Vascular catheters
hyperbilirubinemia) Gastric tubes
Fever Sleep deprivation
APOE-4, apolipoprotein E polymorphism.
Note: Risk factors for delirium can relate to the host, those relating to critical illness and those relating to the intensive care unit environment or treatment of critical illness. Within each of these divisions, there are
risk factors that are preventable or potentially modifiable and those that are not preventable or modifiable.

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