Long-term outcome of delirium during intensive care unit stay in survivors of critical illness: a prospective cohort study

Introduction: Delirium is associated with impaired outcome, but it is unclear whether this relationship is limited to in-hospital outcomes and whether this relationship is independent of the severity of underlying conditions. The aim of this study was to investigate the association between delirium in the intensive care unit (ICU) and long-term mortality, self-reported health-related quality of life (HRQoL), and self-reported problems with cognitive functioning in survivors of critical illness, taking severity of illness at baseline and throughout ICU stay into account. Methods: A prospective cohort study was conducted. We included patients who survived an ICU stay of at least a day; exclusions were neurocritical care patients and patients who sustained deep sedation during the entire ICU stay. Delirium was assessed twice daily with the Confusion Assessment Method for the ICU (CAM-ICU) and additionally, patients who received haloperidol were considered delirious. Twelve months after ICU admission, data on mortality were obtained and HRQoL and cognitive functioning were measured with the European Quality of Life - Six dimensions self-classifier (EQ-6D). Regression analyses were used to assess the associations between delirium and the outcome measures adjusted for gender, type of admission, the Acute Physiology And Chronic Health Evaluation IV (APACHE IV) score, and the cumulative Sequential Organ Failure Assessment (SOFA) score throughout ICU stay. Results: Of 1101 survivors of critical illness, 412 persons (37%) had been delirious during ICU stay, and 198 (18%) died within twelve months. When correcting for confounders, no significant association between delirium and long-term mortality was found (hazard ratio: 1.26; 95% confidence interval (CI) 0.93 to 1.71). In multivariable analysis, delirium was not associated with HRQoL either (regression coefficient: -0.04; 95% CI -0.10 to 0.01). Yet, delirium remained associated with mild and severe problems with cognitive functioning in multivariable analysis (odds ratios: 2.41; 95% CI 1.57 to 3.69 and 3.10; 95% CI 1.10 to 8.74, respectively). Conclusions: In this group of survivors of critical illness, delirium during ICU stay was not associated with long-term mortality or HRQoL after adjusting for confounding, including severity of illness throughout ICU stay. In contrast, delirium appears to be an independent risk factor for long-term self-reported problems with cognitive functioning.