Introduction/Aim. Currently, there is no classification reflecting the severity of complicated intra-abdominal infections (cIAIs). Therefore, we aimed to create one and facilitate the prognostic assessment of cIAIs in clinical practice.
Methods. This was a single-center study conducted at a University Hospital Stara Zagora including 140 patients with cIAIs. Retrospectively, for the period January 2017 – October 2018, we divided the patients with cIAIs into three groups according to their sequential organ failure assessment (SOFA) score and World Society of Emergency Surgery Sepsis Severity Score (WSES SSS) – mild cIAIs (SOFA < 2 points), severe cIAIs (SOFA ≥ 2) and severe complicated intra-abdominal sepsis (SCIAS) – WSES SSS ≥ 8 or septic shock. Prospectively, we validated the created classification in 62 patients with cIAIs between November 2018 and August 2021.  
Results. For the retrospective and prospective group, respectively, death rate among patients with mild cIAIs was 3.1% and 3.6%, with severe cIAIs – 26.8% and 19%, and with SCIAS we observed the highest mortality – 68.8% and 30.8%. Prognostic scores that differed significantly according to severity for both time periods were SOFA, Mannheim Peritonitis Index, and WSES SSS.
Conclusion. The proposed classification has the potential to be a reliable predictor of severity in patients with cIAIs.

 Keywords: intra-abdominal infections, mortality, severity classification, SOFA, WSES SSS

 Corresponding author:
Evgeni Dimitrov
e-mail: evgeni_d1984@yahoo.com