Surgery Is in Itself a Risk Factor for the Patient.

(1) Background: Adverse events (AE) affect about 1 in 10 hospitalised patients, and almost half are related to surgical care. The aim of this study is to determine the prevalence of AE in operated and non-operated patients in surgical departments in order to determine whether surgical treatment is a risk factor for AE. (2) Methods: A cross-sectional design that included 3123 patients of 34 public hospitals in the Community of Madrid determining the prevalence of AEs in operated and non-operated patients in surgical departments. (3) Results: The prevalence of AE in non-operated patients was 8.7% and in those operated was 15.8%. The frequency of AE was higher in emergency surgery (20.6% vs. 12.4%). The 48.3% of AEs led to an increase in hospital stay, and surgery was involved in 92.4% of cases. The most frequent AEs were related to hospital-acquired infection (42.63%), followed by those related to a procedure (37.72%). In the multivariate analysis, being operated on represented 2.3 times the risk of developing an AE. (4) Conclusions: Surgical sites are particularly vulnerable to AE. Surgical intervention alone is a risk factor for AE, and we must continue to work to improve the safety of both patient care and the working environment of surgical professionals.