Yafang Li Chuang Nie Na Li Jieying Liang Ning Su ^* Chunhua Yang ^*

• The Sixth Affiliated Hospital of Sun Yat-sen University, Guangzhou, China

Background: Postoperative pulmonary complications (PPCs) significantly impact surgical outcomes, and Controlling Nutritional Status (CONUT) score, a simple and easily available nutritional score, has been demonstrated to be significantly associated with postoperative patient outcomes and complications, including PPCs. However, there are few studies that specifically focus on patients undergoing radical surgery for colorectal cancer (CRC). Methods: We retrospectively analyzed the clinical data of 2,553 patients who underwent radical surgery for CRC at the Sixth Affiliated Hospital of Sun Yat-sen University. Patients were divided into three groups: normal nutrition group (CONUT≤1), mild malnutrition group (2≤CONUT≤4), and moderate-to-severe malnutrition group (CONUT≥5). Risk factors for PPCs and all-cause mortality were evaluated by multivariate regression. In addition, we assessed surgical outcomes including ICU admission, hospital stay, 1-year mortality and tumor-related mortality. Results: The incidence of PPCs was 9.0% (n = 230). Multiple regression showed that the higher the CONUT score, the higher the risk of PPCs (mild malnutrition group vs. normal nutrition group, OR: 1.61, 95% CI: 1.18 -2.20, p = 0.003; moderate-to-severe malnutrition group vs. normal nutrition group, OR: 2.41, 95% CI: 1.51 -3.84, p < 0.001). All-cause mortality was significantly higher in moderate-to-severe malnutrition group than that in normal nutrition group, HR: 1.88, 95% CI: 1.34 -2.62, p < 0.001). Older age, male sex, chronic heart disease, open surgery, blood transfusion during surgery, distant metastasis of tumor and colon tumor were all risk factors for PPCs. Furthermore, the malnutrition groups had poor surgical outcomes including postoperative pneumonia (mild vs.