Questions under study/principles: The objective was to assess observed-to-expected in-hospital postoperative 30-day mortality and to identify associated risks.

Methods: A single centre, retrospective study was performed in Geneva University Hospitals, Switzerland. Hospitalised adult surgical patients who received anaesthesia and stayed in the Post Anaesthesia Care Unit - Intermediate Care Unit (PACU-IMC) between July 2008 and June 2011 were included. Outcome measure was in-hospital 30-day mortality. Expected probabilities of in-hospital death were estimated with the surgical mortality probability model (S-MPM). Descriptive statistics were calculated. Univariate and multivariate logistic regressions (odds ratio [OR] with 95% confidence interval [95% CI]) were used to identify risk factors of mortality.

Results: Overall in-hospital mortality was 0.8% (176/24 160 patients). Observed 30-day in-hospital mortality was 0.7%; expected mortality from the S-MPM was 1.2%. Independent risk factors were age (OR 1.05, 95% CI 1.03-1.06), American Society of Anesthesiologists Physical Status score (ASA PS 3-5 vs ASA PS 1-2: OR 5.48, 95% CI 3.12-9.63), nonelective surgery (vs elective surgery) (OR 3.15, 95% CI 2.04-4.86), head surgery (OR 2.83, 95% CI 1.41-5.67) and duration of PACU-IMC stay (OR 1.00, 95% CI 1.00-1.00). A protective factor was a high body mass index (OR 0.92, 95% CI 0.89-0.96). The procedural risk, type and time of anaesthesia and day of intervention were not independent risk factors of mortality.

Conclusion: The postoperative observed-to-expected mortality ratio was favourable. Independent postoperative risk factors for mortality were well-established factors such as age, ASA PS, non elective surgery but also duration of PACU-IMC stay which was considered as a surrogate of postoperative complications.