This is a prospective, multicenter, real-world observational study to evaluate the impact of perioperative parenteral nutrition (PN) with fish oil-containing lipid emulsion on outcomes in adult patients with constipation undergoing elective colon surgery.

The study will compare two clinical nutrition strategies: (1) PN with fish oil-containing lipid emulsion started before surgery and continued after surgery, and (2) PN with fish oil-containing lipid emulsion started only after surgery. Eligible participants are adults (18-75 years) with slow-transit constipation (STC) or megacolon who are scheduled for elective colon surgery and have nutritional risk (NRS2002 score >=3).

The primary objective is to compare the incidence of postoperative complications between these two PN timing strategies. Secondary objectives include comparison of perioperative nutritional status, postoperative inflammatory status, prognosis, and safety outcomes.

This study will collect and analyze clinical data, laboratory indicators, perioperative recovery outcomes, follow-up assessments, and safety information in routine clinical practice. Outcomes include postoperative complication rates, changes in nutritional and inflammatory markers, bowel function recovery, length of hospital stay, constipation-related symptoms, quality of life, and adverse events. No experimental intervention will be assigned as part of this observational study.

The planned sample size is 306 participants. The findings may help optimize perioperative nutritional support strategies for patients with constipation undergoing surgery.

Inclusion Criteria:

1. Age 18 to 75 years.
2. Meets diagnostic criteria for slow-transit constipation (STC) or megacolon and is scheduled for elective colon surgery.
3. Nutritional Risk Screening 2002 (NRS2002) score >=3.
4. Receives fish oil-containing parenteral nutrition (PN) for >=3 days preoperatively or initiates PN for the first time postoperatively (according to the study cohort definition).
5. Voluntarily participates in the study and provides signed informed consent.

Exclusion Criteria:

1. Mental disorders or other conditions that prevent cooperation with treatment or follow-up.
2. Pregnant or breastfeeding women, women planning pregnancy / in a pre-pregnancy state, or women with a clear intention to become pregnant during the perioperative period or follow-up.
3. Contraindications to surgery or parenteral nutrition.
4. Concurrent enrollment in another study.
5. No baseline data available before initiation of nutritional support treatment.
6. Any other condition judged by the investigator to make the participant unsuitable for this study.

Adult patients (18-75 years) with slow-transit constipation (STC) or megacolon who meet clinical and diagnostic criteria, are scheduled for elective colon surgery, and have nutritional risk (NRS2002 score >=3). STC is identified based on Rome IV functional constipation criteria with objective evidence of delayed colonic transit and exclusion of outlet obstruction/pelvic floor dyssynergia. Megacolon is diagnosed based on clinical presentation and imaging evidence of colonic dilatation without mechanical obstruction, with exclusion of Hirschsprung disease and other obstructive causes. Participants are enrolled in a prospective multicenter real-world observational study comparing perioperative timing strategies of fish oil-containing parenteral nutrition.