New-onset mental illness and long-term survival in survivors of critical illness: population-based cohort study in South Korea

Background Critical care unit (CCU) survivors have a high risk of developing mental illness. Aims We aimed to examine the incidence and associated factors of newly developed mental illness among CCU survivors of critical illness. Moreover, we examined the association between newly developed mental illness and 2-year all-cause mortality. Method All adult patients (≥20 years) who were admitted to the CCU during hospitalisation between 2010 and 2018 and survived for 1 year were defined as CCU survivors and were included in this nationwide population-based cohort study. CCU survivors with a history of mental illness before CCU admission were excluded from the study. Results A total of 1 353 722 CCU survivors were included in the analysis; of these, 33 743 survivors (2.5%) had newly developed mental illness within 1 year of CCU admission. Old age, longer CCU stay, hospital admission through the emergency room, increased total cost of hospitalisation, mechanical ventilatory support, extracorporeal membrane oxygenation support and continuous renal replacement therapy were associated with an increased incidence of newly developed mental illness. Moreover, the newly developed mental illness group showed a 2.36-fold higher 2-year all-cause mortality rate than the no mental illness group (hazard ratio: 2.36; 95% CI: 2.30–2.42; P < 0.001). Conclusions In South Korea, 2.5% of CCU survivors had newly developed mental illness within 1 year of CCU admission. Moreover, newly developed mental illness was associated with an increased 2-year all-cause mortality.