1 What is delirium?

Delirium is defined by the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) as:

2 Why is it important to diagnose delirium?

The true prevalence and magnitude of delirium have been poorly documented because a myriad of terms, such as acute confusional state, intensive care unit (ICU) psychosis, acute brain dysfunction, and encephalopathy have been used historically to describe this condition. Although the overall prevalence of delirium in the community is only 1% to 2%, the prevalence increases with age, rising to 14% among those more than 85 years old. It may range from 14% to 24% with incidence rates up to 60% among general hospital populations, especially in older patients and those in nursing homes or post–acute care settings. In critically ill patients in the ICU (medical, surgical, trauma, and burn units) the reported prevalence of delirium is 20% to 80%, depending on the severity of illness, and may be closer to 80% in those who are receiving mechanical ventilation. In spite of this, the condition is often unrecognized by clinicians or the symptoms are incorrectly attributed to dementia or depression or considered an expected, inconsequential complication of critical illness. Numerous national and international surveys have shown a disconnect between the perceived importance of delirium, the accuracy of diagnosis, and the implementation of management and treatment techniques. Given that delirium is the most common organ dysfunction seen in critically ill patients and is associated with worse acute and long-term outcomes, it is important to diagnose and manage the disease by implementation of validated screening protocols.

3 What morbidity and mortality are associated with delirium?

Delirium is a strong predictor of a longer hospital stay, longer times receiving mechanical ventilation, higher costs, and increased risk for death. Additionally, each additional day with delirium increases the risk for dying by 10%. Patients with longer periods of delirium are also associated with more cognitive decline, when evaluated after 1 year, attesting to the importance of detecting and managing delirium early in the course of illness.

4 Describe the clinical features of delirium

The most important feature of delirium is a disturbance of consciousness accompanied by inattention and a change in cognition that cannot be explained by preexisting or evolving dementia. The condition develops over a short period of time, usually hours to days, and tends to fluctuate during the course of the day.

Delirium may be manifested by a reduced clarity of awareness of the environment and ability to focus, sustain, or shift attention. This may be accompanied by memory impairment, disorientation, or language disturbance. Speech or language disturbances may be evident as dysarthria, dysnomia, dysgraphia, or even aphasia. In some cases, speech is rambling and irrelevant, in others pressured and incoherent, with unpredictable switching from subject to subject. Perceptual disturbances may include misinterpretations, illusions, or hallucinations. Delusion is often associated with a disturbance in the sleep-wake cycle. Patients may also exhibit anxiety, fear, depression, irritability, anger, euphoria, and apathy.

5 What are the subtypes of delirium?

Delirium can be classified by psychomotor behavior into the following:

Patients with both features have mixed delirium.

6 Describe risk factors for delirium

Many risk factors for delirium exist, and these can be divided by host, acute illness, and iatrogenic and environmental factors (Table 73-1). Many of these factors are modifiable. Fortunately, several mnemonics can aid clinicians in recalling the list; two common ones are IWATCHDEATH and DELIRIUM (Table 73-2).

^{Table 73-1} Risk Factors for Delirium

^* Modifiable risk factors.

^{Table 73-2} Mnemonics for Risk Factors for Delirium

7 How is delirium diagnosed?

The diagnosis of delirium is primarily clinical and is based on careful bedside observation of key features. It is a two-step process. Level of arousal is first measured, and, if the patient is arousable, delirium evaluation can be performed by instruments such as the Confusion Assessment Method or the Delirium Rating Scale–Revised 98 (DRS-R 98) in hospitalized patients. The DRS-R 98 provides a measure of severity of delirium in addition to the ability to diagnose delirium. In the ICU, delirium can be diagnosed by using a sedation scale to assess arousal followed by either the Confusion Assessment Method for the ICU (CAM-ICU) or the Intensive Care Delirium Screening Checklist (ICDSC); both these instruments are reliable and have been validated in critically ill patients.

8 How can detection of delirium be improved?

The Society of Critical Care Medicine (SCCM) has published guidelines for the use of sedatives and analgesics in the ICU. They recommend routine monitoring of pain, anxiety, and delirium with use of validated tools and documentation of responses to therapy for these conditions. A number of tools have been developed recently and validated for use, in both patients with endotracheal tubes in place and those without endotracheal tubes, and measured against a gold standard, the DSM criteria. These are the following: