Increased mortality associated with after-hours and weekend admission to the intensive care unit: a retrospective analysis

Objective: To study variation in mortality associated with time and day of admission to the intensive care unit (ICU). Design: Retrospective cohort analysis using the Australian and New Zealand Intensive Care Society Adult Patient Database. Setting and participants: 245 057 admissions to 41 Australian ICUs from January 2000 to December 2008. Main outcome measures: Observed mortality and standardised mortality ratio (SMR) based on Acute Physiology and Chronic Health Evaluation III, 10th iteration (APACHE III-j) scores. Subgroup analysis was performed on the basis of elective surgical or emergency admission to ICU. Results: 48% of patients were admitted after hours (18:00-05:59) and 20% of patients were admitted on weekends (Saturday and Sunday). Patients admitted after hours had a 17% hospital mortality rate compared with 14% of patients admitted in hours (P<0.001); and SMRs of 0.92 (95% CI, 0.91-0.93) and 0.83 (95% CI, 0.83-0.84), respectively. Weekend admissions had a 20% hospital mortality rate compared with 14% on weekdays (P <0.001), with SMRs of 0.95 (95% CI, 0.94-0.97) and 0.92 (95% CI, 0.92-0.93), respectively. Variation in outcome with time of admission to ICU was accounted for predominantly by elective surgical patients. Conclusions: Patients admitted to ICUs in Australia after hours and on weekends have a higher observed and risk-adjusted mortality than patients admitted at other times. Further research is required to determine the causes and relationship to resource availability and staffing.