Surgery is performed at the weekend for risk to life or limb, when mandated by clinical guidelines, or depending on resource availability. Weekend healthcare interventions have been associated with increased mortality and adverse clinical outcomes in the majority of the literature examining the weekend effect, but these findings are not consistent. Results from recent observational studies argue against a true weekend effect. Higher rates of adverse outcomes associated with hospital activity at weekends do not appear to be due to altered medical staffing as commonly hypothesized, but are thought to be in part a result of data artefact and confounding by severity or indication. For this study, we hypothesized that patients who are admitted to hospital at the weekend and require surgery have an increased risk of death compared with patients who are admitted and undergo surgery on weekdays. The primary aim was to examine whether patients who underwent surgery and were admitted at the weekend had an increased risk of 30 day all-cause mortality compared with patients who were admitted and underwent surgery on weekdays; secondary aim was to examine whether the timing of surgery (i.e., surgery on the same weekend or surgery on a subsequent weekday) for patients admitted at the weekend is associated with increased risk of 30 day all-cause mortality.

Inclusion Criteria:

• any hospital admission associated with an eligible surgical procedure in the Ontario discharge abstract database
• between 2005 and 2015

Exclusion Criteria:

• cardiothoracic or cardiology therapeutic procedures
• non-surgical therapeutic interventions (e.g. dialysis)
• obstetric procedures.

Any hospital admission in Ontario, Canada, between 2005 and 2015 for noncardiac surgery.

Study data used are housed at the Institute for Clinical Evaluative Sciences