Association between incident delirium and 28-and 90-day mortality in critically ill adults: a secondary analysis

Background While delirium prevalence and duration are each associated with increased 30-day, 6-month, and 1-year mortality, the association between incident ICU delirium and mortality remains unclear. We evaluated the association between both incident ICU delirium and days spent with delirium in the 28 days after ICU admission and mortality within 28 and 90 days. Methods Secondary cohort analysis of a randomized, double-blind, placebo-controlled trial conducted among 1495 delirium-free, critically ill adults in 14 Dutch ICUs with an expected ICU stay >= 2 days where all delirium assessments were completed. In the 28 days after ICU admission, patients were evaluated for delirium and coma 3x daily; each day was coded as a delirium day [>= 1 positive Confusion Assessment Method for the ICU (CAM-ICU)], a coma day [no delirium and >= 1 Richmond Agitation Sedation Scale (RASS) score <= - 4], or neither. Four Cox-regression models were constructed for 28-day mortality and 90-day mortality; each accounted for potential confounders (i.e., age, APACHE-II score, sepsis, use of mechanical ventilation, ICU length of stay, and haloperidol dose) and: 1) delirium occurrence, 2) days spent with delirium, 3) days spent in coma, and 4) days spent with delirium and/or coma. Results Among the 1495 patients, 28 day mortality was 17% and 90 day mortality was 21%. Neither incident delirium (28 day mortality hazard ratio [HR] = 1.02, 95%CI = 0.75-1.39; 90 day mortality HR = 1.05, 95%CI = 0.79-1.38) nor days spent with delirium (28 day mortality HR = 1.00, 95%CI = 0.95-1.05; 90 day mortality HR = 1.02, 95%CI = 0.98-1.07) were significantly associated with mortality. However, both days spent with coma (28 day mortality HR = 1.05, 95%CI = 1.02-1.08; 90 day mortality HR = 1.05, 95%CI = 1.02-1.08) and days spent with delirium or coma (28 day mortality HR = 1.03, 95%CI = 1.00-1.05; 90 day mortality HR = 1.03, 95%CI = 1.01-1.06) were significantly associated with mortality. Conclusions This analysis suggests neither incident delirium nor days spent with delirium are associated with short-term mortality after ICU admission.