This study adopts a combination of retrospective and prospective cohort research methods to explore the composition of preoperative oropharyngeal and gut microbiota in elderly patients undergoing elective upper abdominal surgery, aiming to analyze the correlation between preoperative oropharyngeal and intestinal microbiota composition and metabolite levels and the occurrence of postoperative pulmonary complications (PPCs). The research subjects of the retrospective cohort study were participants (ClinicalTrials.gov No. NCT05679661) included in the prospective RCT on the effects of perioperative immune nutrition intervention and oral hygiene on postoperative complications in elderly patients, which was conducted at Peking Union Medical College Hospital from January 2023 to present. The prospective cohort study plans to continue enrolling elderly patients aged ≥ 65 who underwent elective upper abdominal surgery.

This study collects preoperative oropharyngeal and fecal samples, as well as preoperative plasma from patients for microbial sequencing and untargeted metabolomics analysis. The main outcome measurement is PPCs, which include pneumonia, atelectasis, and hypoxemia within 7 days after surgery. Inflammatory cells and cytokines in peripheral blood are secondary outcomes.

Inclusion Criteria:

1. Age: ≥ 65 years old;
2. Surgery: Upper abdominal surgery (expected duration ≥ 2 hours);
3. Anesthesia methods: general anesthesia, tracheal intubation;
4. ASA classification: I-IV levels;
5. Postoperative Pulmonary Complications Risk Score (ARISCAT): Medium to High Risk
6. Patients or their families are able to understand the research protocol and are willing to participate in this study, providing written informed consent

Exclusion Criteria:

1. Emergency surgery;
2. This is the second surgery within the past month;
3. Preoperative presence of pulmonary infection or other serious pulmonary complications
4. Patients who have used antibiotics, probiotics, and acid suppressants within one month before surgery

Elderly patients over 65 years old who plan to undergo elective upper abdominal surgery