Differential Associations Between Delirium and Mortality According to Delirium Subtype and Age: A Prospective Cohort Study.

Objective: This study investigated the differential associations between delirium and mortality in terminally ill patients according to delirium subtype and age.

Methods: This was a prospective cohort study of terminally ill patients. Delirium was diagnosed using the confusion assessment method. Delirium subtypes were defined based on Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition criteria and the Delirium Rating Scale-98-R. A multivariate Cox proportional hazards regression analysis was used to examine predictors of mortality.

Results: Of the 322 cases, 98 patients (30.4%) were diagnosed as having delirium. The median (interquartile range) number of survival days after admission was 17.0 (10.0-36.0) days for patients with delirium and 28.0 (16.0-57.0) days for patients without delirium (p = .002). A multivariate analysis revealed that patients with hypoactive and mixed subtypes of delirium survived for shorter periods compared with patients without delirium (hazard ratio [HR] = 1.65 [95% confidence interval {CI} = 1.05-2.59, p = .029] and HR = 2.30 [95% CI = 1.44-3.69, p = .001], respectively). The hypoactive and mixed delirium subtypes exhibited significant interactions with age: younger age was associated with shorter periods of survival in patients with hypoactive and mixed subtype delirium (HR = 0.95 [95% CI = 0.93-0.98, p < .001] and HR = 0.97 [95% CI = 0.93-1.00, p = .038], respectively).

Conclusions: The hypoactive and mixed subtypes of delirium were associated with shorter survival periods in terminally ill patients, and these associations interacted significantly with age. These findings support the clinical and academic value of the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition specifiers that differentiate the diagnoses of delirium subtypes.