Survival analysis of weekend emergency medical admissions
Background
We previously reported weekend emergency admissions to have a higher mortality; we have now examined the time profile of deaths, by weekday or weekend admission, in all emergency medical patients admitted between 2002 and 2014.


Methods
We divided admissions by a weekday or weekend (After 17.00 Friday-Sunday) hospital arrival. We examined survival following an admission using Cox proportional hazard models and Kaplan-Meier time to event analysis.


Results
In total 82 368 admissions were recorded in 44, 628 patients. Weekend admissions had an increased mortality of 5.0% (95% CI 4.7, 5.4) compared with weekday admissions of 4.5% (95% CI 4.3, 4.7) ( P = 0.007). The univariate adjusted Odds Ratio (OR) of death for a weekend admission was significantly increased OR = 1.15 (95% CI 1.05, 1.24) ( P = 0.001). Mortality following an admission declined exponentially over time with a long tail, ∼25% of deaths occurred after day 28. Only 11.4% of deaths occurred on the weekend of the admission. Survival curves showed no mortality difference at 28 days ( P = 0.21) but a difference at 90 days ( P = 0.05). The higher mortality for a weekend admission was attributable to late deaths in the cohort with an extended stay; compared with weekday, these weekend admissions were more likely to be older and have greater co-morbidity.


Conclusion
Survival rates following a weekend or weekday admission were similar out to 28 days. The higher overall mortality for weekend admissions is due to divergence in survival between 28 and 90 days. Most deaths in weekend admissions occurred when the hospital was fully staffed.