Surgical Site Infection: Conditional Influence of Surgery Duration and ASA Classification in Major Procedures

Surgical site infection (SSI) is a major complication in surgical patients. This study aimed to investigate predictors of SSI in cardiac, neurological and orthopaedic surgeries. A total of 28,803 procedures (2015-2021) were analysed. Predictive variables included age, sex, ASA score, wound classification, operative duration and preoperative stay. Logistic regression was applied. Overall SSI rate was 7.2% (2062 cases): 47% neurological, 39% cardiac and 15% orthopaedic. Infected patients had longer preoperative stays (median 6 [IQR: 2-13] vs. 3 days [IQR: 1-9], p < 0.001), extended operative times (median difference: 70 min, 95% CI: 60-79, p < 0.001), and prolonged hospitalizations (median difference: 14 days, 95% CI: 14-15, p < 0.001). Mortality was higher among infected patients (15% vs. 8.2%). Despite lower SSI incidence, orthopaedic patients had a 3.0-fold increase in median stay and 5.3-fold increased odds of death. A significant duration × ASA (> 3) interaction indicated that SSI risk increased with surgical time in high-severity patients. Model adequacy was confirmed by the Hosmer-Lemeshow test (p = 0.481). Higher ASA scores, prolonged surgeries, and extended preoperative stays are significant contributors to SSI risk in major procedures.