Importance: The relationship between critical illness and psychiatric illness is unclear.
Objective: To assess psychiatric diagnoses and medication prescriptions before and after critical illness.
Design, setting, and participants: Population-based cohort study in Denmark of critically ill patients in 2006-2008 with follow-up through 2009, and 2 matched comparison cohorts from hospitalized patients and from the general population.
Exposures: Critical illness defined as intensive care unit admission with mechanical ventilation.
Main outcomes and measures: Adjusted prevalence ratios (PRs) of psychiatrist-diagnosed psychiatric illnesses and prescriptions for psychoactive medications in the 5 years before critical illness. For patients with no psychiatric history, quarterly cumulative incidence (risk) and adjusted hazard ratios (HRs) for diagnoses and medications in the following year, using Cox regression.
Results: Among 24,179 critically ill patients, 6.2% had 1 or more psychiatric diagnoses in the prior 5 years vs 5.4% for hospitalized patients (adjusted PR, 1.31; 95% CI, 1.22-1.42; P<.001) and 2.4% for the general population (adjusted PR, 2.57; 95% CI, 2.41-2.73; P<.001). Five-year preadmission psychoactive prescription rates were similar to hospitalized patients: 48.7% vs 48.8% (adjusted PR, 0.97; 95% CI, 0.95-0.99; P<.001) but were higher than the general population (33.2%; adjusted PR, 1.40; 95% CI, 1.38-1.42; P<.001). Among the 9912 critical illness survivors with no psychiatric history, the absolute risk of new psychiatric diagnoses was low but higher than hospitalized patients: 0.5% vs 0.2% over the first 3 months (adjusted HR, 3.42; 95% CI, 1.96-5.99; P <.001), and the general population cohort (0.02%; adjusted HR, 21.77; 95% CI, 9.23-51.36; P<.001). Risk of new psychoactive medication prescriptions was also increased in the first 3 months: 12.7% vs 5.0% for the hospital cohort (adjusted HR, 2.45; 95% CI, 2.19-2.74; P<.001) and 0.7% for the general population (adjusted HR, 21.09; 95% CI, 17.92-24.82; P<.001). These differences had largely resolved by 9 to 12 months after discharge.
Conclusions and relevance: Prior psychiatric diagnoses are more common in critically ill patients than in hospital and general population cohorts. Among survivors of critical illness, new psychiatric diagnoses and psychoactive medication use is increased in the months after discharge. Our data suggest both a possible role of psychiatric disease in predisposing patients to critical illness and an increased but transient risk of new psychiatric diagnoses and treatment after critical illness.