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Delirium, defined as an acute disorder of attention and global cognitive function, is a common, serious, and potentially preventable source of morbidity and mortality for hospitalized older persons. It occurs in 14% to 56% of such persons and represents the most frequent complication of hospitalization for this group. With the aging of the U.S. population, delirium has assumed heightened importance because persons aged 65 years and older presently account for more than 49% of all days of hospital care. Delirium complicates hospital stays for at least 20% of the 12.5 million patients 65 years of age or older who are hospitalized each year and increases hospital costs by $2500 per patient, so that $6.9 billion (in 2004 U.S. dollars) of Medicare hospital expenditures are attributable to delirium. Importantly, substantial additional costs linked to delirium accrue after hospital discharge because of the increased need for institutionalization, rehabilitation services, closer medical follow-up, and home health care. Delirium often initiates a cascade of events in older persons, leading to a downward spiral of functional decline, loss of independence, institutionalization, and ultimately, death. These statistics highlight the importance of delirium from both clinical and health policy perspectives. In fact, a recent consensus panel identified delirium as among the top three target conditions for quality-of-care improvement for vulnerable older adults. With its common occurrence, its frequently iatrogenic nature, and its close linkage to the processes of care, incident delirium can serve as a marker for the quality of hospital care and provides an opportunity for quality improvement.

The definition of and diagnostic criteria for delirium continue to evolve (Table 53-1). The standardized criteria for delirium that appear in the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision (DSM-IV-TR) remain the current diagnostic standard. Expert consensus was used to develop these criteria, however, and performance characteristics such as diagnostic sensitivity and specificity have not been reported for DSM-IV criteria. A standardized tool, the Confusion Assessment Method (CAM), provides a brief, validated diagnostic algorithm that is currently in widespread use for identification of delirium. The CAM algorithm relies on the presence of acute onset and fluctuating course, inattention, and either disorganized thinking or altered level of consciousness. The algorithm has a sensitivity of 94% to 100%, specificity of 90% to 95%, and high interrater reliability. Given the uncertainty of diagnostic criteria for delirium, a critical area for future investigation is to establish more definitive criteria, including epidemiologic and phenomenologic evaluations assisted by advances in functional neuroimaging and other potential diagnostic marker tests.

Table 53-1 Diagnostic Criteria for Delirium

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