Environmental risk factors for delirium in hospitalized older people.

Objectives: To evaluate the relationship of environmental risk factors in hospitals to changes over time in delirium symptom severity scores.

Design: Observational prospective clinical study with repeated measurements, several times during the first week of hospitalization and then weekly during hospitalization.

Setting: University-affiliated general community hospital.

Participants: Four hundred forty-four patients age 65 and older admitted to the medical wards: 326 with delirium and 118 without delirium. Patients with prior cognitive impairment were oversampled.

Measurements: The severity of delirium symptoms was measured with the Delirium Index, a scale developed and validated by our group, based on the Confusion Assessment Method. Potential environmental risk factors assessed included isolation, hospital unit, room changes, levels of sensory stimulation, aids to orientation, and presence of medical (e.g., intravenous) or physical restraints.

Results: Controlling for initial severity of delirium and patient characteristics, variables significantly related to an increase in delirium severity scores included hospital unit (intensive care or long-term care unit), number of room changes, absence of a clock or watch, absence of reading glasses, presence of a family member, and presence of medical or physical restraints.

Conclusion: The associations of intensive care and medical and physical restraints with severity of delirium symptoms may be due to uncontrolled confounding by indication. However, the other factors identified suggest potentially modifiable risk factors for symptoms of delirium in hospitalized older people.