Objective:To investigate the risk factors that were associated with the death of elderly patients who were admitted to the intensive care unit (ICU) after elective abdominal surgery, and to find reliable and sensitive predictive indicators for early interventions and reducing the mortality.Methods:A retrospective case-control study was conducted. The clinical data of elderly (age≥65 years old) patients after elective abdominal surgery admitted to the ICU of the Affiliated Hospital of Guizhou Medical University from January 1st 2016 to December 31st 2020 were collected, including the patient's gender, age, body mass index (BMI), medical history, American Society of Anesthesiologists (ASA) grades, surgical classification, intraoperative blood loss, duration of operation, interval time between end of operation and admission to the ICU, acute physiology and chronic health evaluationⅡ(APACHEⅡ) score and the worst laboratory examination results within 24 hours of ICU admission, the first blood gas analysis in ICU, the duration of invasive mechanical ventilation, and the length of ICU stay. Postoperative abdominal infection was evaluated by the pathogenic culture of peritoneal drainage fluid and clinical symptoms and signs. The patients were divided into death group and survival group based on clinical outcomes, and clinical data were compared between the two groups. Binary multivariate Logistic regression analysis was used to screen the risk factors of death, and the receiver operator characteristic curve (ROC curve) was plotted to analyze the predictive values of these risk factors.Results:A total of 226 elderly patients with elective abdominal surgery were admitted to the ICU of our hospital during the past 5 years, of whom, two patients who did not undergo laboratory examinations within 24 hours of admission to the ICU were excluded. Finally, 224 patients met the criteria, with 158 survivors and 66 deaths. Univariate analysis showed that: compared with survival group, APACHEⅡscore, blood lactate acid (Lac) and the proportion of postoperative abdominal infection were higher in death group [APACHEⅡ score: 27.5 (25.0, 31.3) vs. 23.0 (18.0, 27.0), Lac (mmol/L): 2.9 (1.8, 6.6) vs. 1.8 (1.1, 2.8), the proportion of postoperative abdominal infection: 65.2% (43/66) vs. 35.4% (56/158), all P < 0.01], prothrombin time (PT), activated partial thromboplastin time (APTT) and interval time between end of surgery and admission to ICU were longer [PT (s): 17.20 (14.50, 18.63) vs. 14.65 (13.90, 16.23), APTT (s): 45.15 (38.68, 55.15) vs. 39.45 (36.40, 45.70), interval time between end of surgery and admission to ICU (hours): 39.2 (0.7, 128.9) vs. 0.7 (0.3, 2.0), all P <0.01], postoperative hemoglobin (Hb), platelet count (PLT), prealbumin (PA), mean arterial pressure (MAP) and oxygenation index (PaO 2/FiO 2) were lower in death group [Hb (g/L): 95.79±23.64 vs. 105.58±19.82, PLT (×10 9/L): 138.5 (101.0, 177.5) vs. 160.5 (118.5, 232.3), PA (g/L): 80.88±43.63 vs. 116.54±50.80, MAP (mmHg, 1 mmHg = 0.133 kPa): 76.8±19.1 vs. 91.6±19.8, PaO 2/FiO 2 (mmHg): 180.0 (123.5, 242.5) vs. 223.5 (174.8, 310.0), all P < 0.05]. Binary multivariate Logistic regression analysis showed that APACHEⅡscore [odds ratio ( OR) = 1.187, 95% confidence interval (95% CI) =1.008-1.294, P < 0.001], interval time between end of operation and admission to ICU ( OR = 1.005, 95% CI = 1.001-1.009, P = 0.016) and postoperative abdominal infection ( OR = 2.630, 95% CI = 1.148-6.024, P = 0.022) were independent risk factors for prognosis in these patients. MAP ( OR = 0.978, 95% CI = 0.957-0.999, P = 0.041) and PaO 2/FiO 2 ( OR = 0.994, 95% CI = 0.990-0.998, P = 0.003) were protective factors for the patients' prognosis. Lac, Hb, PLT, PA, PT and APTT had no predictive value for the prognosis of elderly patients admitted to ICU after elective abdominal surgery [ OR value and 95% CI were 1.075 (0.945-1.223), 1.011 (0.99-1.032), 1.000 (0.995-1.005), 0.998 (0.989-1.007), 1.051 (0.927-1.192) and 1.003 (0.991-1.016), respectively, all P > 0.05. ROC curve analysis showed that APACHEⅡscore, interval time between end of operation and admission to the ICU and the postoperative abdominal infection had certain predictive values for the prognosis of elderly patients, the area under ROC curve (AUC) were 0.755, 0.732 and 0.649 respectively, all P < 0.001; When the cut-off of APACHEⅡscore and interval time between end of operation and admission to the ICU were 24.5 scores and 2.15 hours, the sensitivity were 78.8% and 66.7%, respectively, and the specificity were 62.0% and 76.6%, respectively. The combined predictive value of the three variables was the highest, which AUC was 0.846, the joint prediction probability was 0.27, the sensitivity was 83.3%, and the specificity was 75.3%. Conclusion:APACHEⅡscore, interval time between end of surgery and admission to ICU, and postoperative abdominal infection may be independent risk factors for the death of elderly patients who were admitted to the ICU after elective abdominal surgery, there would be far greater predictive values when the three variables were combined.