BACKGROUND: Mortality rates in critically ill adult patients admitted to the intensive care unit (ICU) remains high, and numerous patient- and disease-related adverse prognostic factors have been identified. In recent years, studies in a variety of emergency conditions suggested that outcome is dependent on the time of hospital admission. The importance of out-of-hours admission to the ICU has been sparsely evaluated and with ambiguous findings. We assessed the association between out-of-hours (16:00 to 07:00) and weekend admission to the ICU, respectively, and 90-day mortality in a nationwide cohort.

METHODS: We included all Danish adult patients admitted to the ICU between 1 January 2011 and 30 June 2014, with an ICU stay > 24 h. The crude and adjusted association between out-of-hours and weekend admission and 90-day mortality was assessed (odds ratio (ORs) with 95% confidence intervals (CI)).

RESULTS: A total of 44,797 patients were included, 53.3% were admitted out-of-hours, and 22.6% during weekends. Median age was 67 years (interquartile range (IQR) 55-76), and median SAPS II was 42 (IQR 30-54). Patients admitted in-hours vs. out-of-hours displayed a 90-day mortality rate of 41.0% vs. 44.2%. The adjusted association (OR with 95% CI) between out-of-hours admission and 90-day mortality was 1.07 (1.02-1.11), and the adjusted association (OR with 95% CI) between weekend admission and 90-day mortality was 1.10 (1.05-1.15).

CONCLUSION: This nationwide study suggests that critically ill adult patients admitted to the ICU during weekends and out-of-hours, and with an ICU stay > 24 h are at slightly increased risk of mortality.