This prospective cohort study examined the effect of delirium duration on long-term cognitive impairment in patients receiving mechanical ventilation in an ICU. The cohort was drawn from the Awakening and Breathing Controlled (ABC) randomized trial and included adults mechanically ventilated for more than 12 hours and later discharged.

A total of 77 patients (median age, 61) were included in the analysis. Patients were severely ill at hospital admission, and 9% showed signs of preexisting cognitive impairment. Eighty-four percent had delirium while hospitalized, for a median of two days, with half the patients delirious for at least two days, and one in four for at least five days.

Patients' cognitive outcomes were determined by a neuropsychologist three and 12 months after study enrollment. A total of 80% and 72% of patients were cognitively impaired at three and 12 months, respectively. Cognitive impairment was directly related to the duration of delirium, with longer delirium associated with more severe impairment at both three and 12 months. Five days of delirium was associated with a 5-point lower cognitive battery mean score than one day of delirium when assessed three months after enrollment. Similarly, at the 12-month assessment, an increase from one to five days of delirium resulted in a decrease of almost 7 points in the cognitive battery mean score. The authors noted that duration of mechanical ventilation wasn't related to cognitive impairment when evaluated at three or 12 months.

While the study has drawbacks, such as limited generalizability and possible confounding factors, the authors suggest that there's enough evidence to show that cognitive decline occurred in most patients during their illness. Thus, delirium may predict cognitive impairment.