Secondary peritonitis is a frequent abdominal emergency that is still associated with a high morbidity and mortality rate due to surgical site infections (SSI) and sepsis. Early surgical source control is crucial to avoid sepsis and worse outcomes. The current randomized controlled trial aims to investigate the effect of peritoneal lavage with super-oxidized solution (SOS) on SSI and mortality in patients undergoing emergency abdominal surgery for secondary peritonitis. The investigators hypothesize that peritoneal lavage with SOS reduces the incidence of SSI and mortality in this patient population.

Secondary peritonitis is a frequent abdominal emergency that is associated with significant mortality and morbidity, especially surgical site infections (SSI). If not treated promptly and efficiently, secondary peritonitis may progress from a contained abdominal infection to systemic disease, i.e., sepsis and eventually septic shock. Early surgical source control is crucial to avoid sepsis and worse outcomes. Super-oxidized solution (SOS) has been shown to have a strong antimicrobial activity while being safe for medical use in humans.

This randomized controlled trial (RCT) will investigate the effect of peritoneal lavage with SOS vs. the current standard solution (Ringer) on SSI and mortality in patients undergoing emergency abdominal surgery (EAS) for secondary peritonitis. The hypothesis of this study is that peritoneal lavage with SOS during EAS will reduce the incidence of SSI and mortality.

Patients scheduled for open EAS with secondary peritonitis due to suspected hollow-viscus perforation, anastomotic insufficiency, or abdominal abscess, including patients with the named abdominal emergencies as a complication after elective surgery, will be assessed for eligibility. All patients included will be treated according to the current standard of care for secondary peritonitis. This includes the insertion of intravenous lines, start of antibiotic therapy, infusion of crystalloid solutions, monitoring of vital signs, and EAS.

Randomization will take place during EAS after the surgical procedure including regular peritoneal lavage have been performed. If a hollow-viscus perforation, anastomotic insufficiency, or an abdominal abscess is encountered intraoperatively, patients will be randomized and undergo additional peritoneal lavage with either SOS (SOS group) or Ringer's solution (control group).

In the SOS group, the abdominal cavity will be irrigated with 2 liters of SOS (Micodacyn60®), followed by aspiration of the product and abdominal closure. In the control group, the abdominal cavity will be irrigated with two liters of Ringer's solution, followed by aspiration of the solution and abdominal closure. The only difference in treatment between the two groups will be the additional peritoneal lavage with SOS or Ringer's solution at the end of the procedure. After surgery, there will be no difference in the management of the SOS and control group.

The primary outcome of this RCT will be the incidence of SSI and mortality as a composite outcome at 30 days postoperatively.

Secondary outcomes will be in-hospital and 30-day mortality, surgical site infections within 30 days, the time to occurrence of the primary outcome, sepsis as defined by the Sepsis-3 guidelines at 24 h, 48 h, and 7 days postoperatively, septic shock as defined by the Sepsis-3 guidelines at 24 h, 48 h, and 7 days postoperatively, organ dysfunction over time (14 days, as measured by SOFA and/or qSOFA scores), biomarkers of inflammation over time (14 days, including C-reactive protein, white blood cell count, and body temperature), postoperative fascial dehiscence at 30 days postoperatively, intestinal fistula at 30 days postoperatively, re-intervention for postoperative complications within 30 days postoperatively, days to first postoperative bowel movement, and total hospital and Intensive Care Unit length of stay.

Data will be collected during the hospital stay and a the follow-up visit 30 days postoperatively. Data assessors will be blinded for the study procedure.

Inclusion Criteria:

• Secondary peritonitis due to suspected hollow viscus perforation, anastomotic insufficiency, and/or abdominal abscess (including patients with the named abdominal emergencies as a complication after elective surgery)
• Scheduled emergency abdominal surgery by laparotomy with peritoneal lavage
• Age over 18 years
• Written informed consent

Exclusion Criteria

• Pregnancy (will be ruled out using beta-hCG testing in women of childbearing potential)
• Patients with primary or tertiary peritonitis