Major abdominal surgeries (e.g., gastrectomy, pancreatectomy, colectomy) carry a high risk of life-threatening postoperative complications, including multiorgan disfunction syndrome (MODS), acute kidney injur (AKI), miocardial injury after non-cardiac surgery (MINS) and severe infections. These complications are driven by ischemia-reperfusion injury, leading to oxidative stress and a systemic inflammatory response. Despite advances in surgical and anesthetic techniques, there are no effective pharmacological strategies for personalized prevention of these events, which adversely affect recovery and survival.

In this context, opioid receptor agonist, particularly senthetic analogs of Leu-enkephalin such as Dalargin, have emerged as promising agents for pharmacologica preconditioning. Preclinical evidence suggests their ability to mitigate oxidative stress and inflammation by moduating key signaling pathways . The potential for these peptides to protect andothelial function and reduce organ damage presents a novel therapeutic avenue.

This study aims to clinically test the hypothesis that perioperative intravenous infusion of Dalargin reduce the incidence and severity of postoperative organ dysfunction. Patients undergoing high-risk abdominal surgery will be randomized to receive either a 72-hour continuous of Dalargin (following a defined dosage regimen) or an identical placebo infusion. the study will also integrate an assessment of genetic polymorphism ( e.g., in NRF2, OLR1, TLR9 genes) to explore personalized approaches to risk stratification and prevention.

This is a prospective, randomized, double-blind, placebo-controlled clinical trial. The study investigates the effects of a synthetic leucine-enkephalin analog (Dalargin) on oxidative distress, systemic inflammatory response, organ failure, and infectious complications in patients undergoing high-risk abdominal surgery (e.g. on the stomach, pancreas, or colon).

Objectives: The primary objective is to evaluate whether perioperative infusion of Dalargin reduces the incidence of a composite endpoint of postoperative organ dysfunction (including acute respiratory destress syndrome, acute kidney injury, and sepsis) . Secondary objectives include assessing its effects on biomarkers of oxidative stress (malondialdehyde, carbonylated proteins), inflammation (procalcitonin, interleukin-6, HMGB-1), and myocardial injury (high-sensitivity troponin T), as well asthe length of ICU and hospital stay.

Methods: A total of 200 patients aged 18-85 years (ASA I-III) scheduled for elective high-risk abdominal surgery ander general anesthesia will be randomized to recieve either Dalargin or placebo (0,9% sodium chloride). The study drug will be administered as a continious intravenous: 8 ml/hour for the first 24 hour, followed be 4 ml/hour for the next 48 hours, startinf after anesthesia induction. Patient outcomes will be evaluated using clinical scales (e.g., CPIS, KDIGO, APACHE II) and laboratory assessments. Additionally, genetic polymorphismis (NRF2, OLR1, TLR9, AGTR1, AQP1) will be analyzed to identify predictors of organ dysfunction and enable personalized risk stratification.

Scientific Navelty: This is the first study to comprehensively evaluate the organoprotective potential a synthetic enkephalin analog via pharmacological preconditioning in high-risk non-cardiac surgery, combining clinical endpoints with biomarker and genetic analysis to develop a personalized prevention strategy.

Sample Size Justification: The sample size of 200 participants (100/group) was calculated based on the anticipated incidence of the primary composite endpoint (postoperative organ dysfunction) in the control group. Based on previous similar studies and meta-analyses, we assume an event rate of 35% in the placebo group. We hypothesize that Dalargin will reduce this incidence to 20% (absolut risk reduction of 15%). With a two-sided alpha of 0.05 and 80% power, using a chisquared test, the required sample size is 178 participants. To account for a potential dropout rate of approximately 10%, the total sample size was increased to 200 partipitants. This sample size also provides adequate power (>80%) to detect clinically meaningful differences in key secondary endpoints, including the incidence of MINS (Myocardial Injury after non-cardiac Surgery) and changes in biomarker levels (e.g., interleukin-6)

Inclusion Criteria:

• Male or female patients aged 18 to 85 years.
• Scheduled for elective high-risk abdominal surgery (e.g., gastrectome, pancreatectomy, colectomy) under general anesthesia.
• American Society of Anesthesiologists (ASA) physical status class I-III.
• Able to provide written informed consent.

Exclusion Criteria:

• ASA physical status class IV or V.
• Acute myocardial infarction within the past 6 month.
• Acute stroke within the past 6 month.
• Chronic heart failure NYHA class IV.
• Chronic kidney disease stage 3a or higher (according KDIGO)
• Active infectious disease.
• Any diagnosed phychiatric disorder (according ICD-10) confirmed be a psychiatrist.
• Any neuromuscular disease (according to ICD-10)
• Pregnancy or breastfeeding.
• Inability to undergo preoperative assessment.
• Previous enrollment in this trial.