Background
Large population studies on predictors of post-appendectomy abscess are lacking. Using a large patient database, we sought to find the strongest preoperative and intraoperative predictors of post-appendectomy abscess.

Method
This was a retrospective cohort study utilizing the ACS-NSQIP database in the years 2016 to 2020. All adult patients undergoing an emergent appendectomy for appendicitis were eligible for inclusion. Preoperative predictors assessed were sex, age, BMI, diabetes, smoking, hypertension, and white blood cell (WBC) count. Intraoperative predictors assessed were operative time, operative approach, and perforated appendicitis with or without an abscess. The primary outcome assessed was post-appendectomy abscess. Univariable and multivariable logistic regression models with backward elimination process were built to evaluate the association between post-appendectomy abscess as the outcome variable and the chosen predictors as the independent variables.

Results
100 CleanCision and 170 Alexis cases were enrolled with a mean ages of 64.9 and 62.9 years, respectively. There were no significant differences between the two groups in demographics and preoperative comorbidities. There were also no significant differences in diagnosis, resection type, length of operation, estimated blood loss, surgical technique, and elective versus emergent status. CleanCision cases had a significantly larger mean length of incision (6.4 vs. 4.9 cm, p = 0.04).
SSI rates were significantly lower in the CleanCision group (1% vs. 9.4%, p = 0.006). There were no significant differences in Clavien-Dindo classification, hospital LOS, and 30-day readmission. Multivariable logistic regression with backward elimination showed that the use of CleanCision was significantly more protective against SSI by 91.3% compared to the use of Alexis.

Conclusion
A total of 35,530 patients were enrolled with a mean age of 39.5 (18-89) years, with 48.9% being female. 5% of patients were diabetic, 15.2% were smokers, and 4.3% had open surgery. The mean preoperative WBC count was 13.1 and mean operative time was 54.2 minutes. 8.6% of patients had intraoperative findings of abscess and perforation, 12.6% had perforation only, and 4.7% had abscess only. 1187 patients (3.3%) had post-appendectomy abscess. Multivariable logistic regression analysis revealed the following predictors of post-appendectomy abscess: intraoperative findings of perforation and abscess (12.36, 10.55-14.49, P < 0.001), intraoperative perforation only (7.08, 6.04-8.29, P < 0.001), intraoperative abscess only (3.6, 2.81-4.78, P < 0.001), open surgery (1.44, 1.12-1.75, P < 0.001), diabetes (1.26, 1.56-1.01, P = 0.04), smoking (1.19, 1.39-1.02, P = 0.03), WBC count (1.05, 1.04-1.06, P < 0.001), and operative time (1, 1-1, P < 0.001) (Table 1). For every unit (1 WBC/cc) rise in WBC count over normal, there was a 5.1% increased odds of post-appendectomy abscess. For every additional 30 minutes of operative time over the mean operative time, there was a 6% increased odds of post-appendectomy abscess.