Protein malnutrition in critically ill patients is a global concern due to its association with prolonged hospital stays, and higher morbidity rates. Patients who undergo abdominal surgery are particularly vulnerable due to alterations in gastrointestinal function and prolonged fasting. Despite the significance of proper nutrition, the optimal target of protein supplementation remains controversial.

The investigators aimed to evaluate the effects of high protein provision, targeting a protein intake of at least 1.5 g/kg/day for the first 3 days after abdominal surgery, on 6-month mortality.

During the acute phase of critical illness, patients experience metabolic and physiological changes that affects their nutrition status. One prominent feature is the activation of stress hormones and inflammatory mediators, which contribute to a negative nitrogen balance, increased gluconeogenesis, and accelerated muscle proteolysis. Among these patients, those who undergo abdominal surgery are particularly vulnerable to malnutrition as they experience alterations in the structural barrier of the gastrointestinal tract, impaired nutrient absorption, and prolonged fasting due to concerns such as the integrity of an anastomosis. Thus, appropriate protein provision should be prioritized for critically ill patients following abdominal surgery, and it should include adequate nutritional support to preserve lean body mass and organ function. Despite the importance of nutritional supply, the recommendations for protein vary according to different guidelines, and this is the same for surgical patients. Recent randomized controlled trials reported conflicting results with current guidelines, with some suggesting that higher protein dose administrations did not significantly impact clinical outcomes and may even worsen the outcomes for certain patient groups. Thus, the optimal protein provision target during the acute phase of critical illness, particularly for surgical patients, remains controversial.

The investigators aimed to assess the effects of strict high protein provision between the high protein group (protein target supplemented with 1.5 g/kg/day) and the control group (protein target supplemented with less than 1.5 g/kg/day) using intravenous nutrient solution for the first 3 days after abdominal surgery. Additionally, the investigators investigated the appropriate target for protein provision in critically ill patients who undergo abdominal surgery.

Inclusion Criteria:

• Patients admitted after abdominal surgery to our institution's surgical ICU
• They were enrolled regardless of the surgical method, either open, laparoscopy, or robotic.

Exclusion Criteria:

• aged under 18 years
• underwent surgery under local or regional anesthesia
• pregnant
• readmitted to the ICU due to any cause
• diagnosed with renal failure and receiving renal replacement therapy
• patients diagnosed with multiorgan failure, represented by a high Sequential Organ Failure Assessment (SOFA) score (≥9) upon ICU admission
• failed to provide informed consent, or with 'do-not-resuscitate' status.