Relationship between Intraoperative Hypotension and Postoperative Venous Thromboembolism in Elderly Patients Undergoing Hip Surgery and Construction of a Risk Prediction Model

Abstract Objective To investigate the dose-response relationship between intraoperative hypotension (IOH) and postoperative venous thromboembolism (VTE) in elderly patients undergoing hip surgery under combined spinal-epidural anesthesia, and to construct and validate a VTE risk prediction nomogram model suitable for this population, so as to provide evidence-based basis for precise perioperative VTE prevention and refined blood pressure management. Methods A single-center retrospective cohort study was conducted, enrolling 680 patients aged 65 years and above who underwent primary hip surgery (internal fixation for periacetabular fractures, total hip arthroplasty) under combined spinal-epidural anesthesia in our hospital from January 2020 to December 2025. Intraoperative minute-by-minute mean arterial pressure (MAP) was extracted from the hospital anesthesia information system. With MAP < 65 mmHg as the hypotension threshold, three quantitative indicators including time-weighted average hypotension amplitude (TWA), area under the hypotension curve (AUC) and cumulative duration of IOH were calculated. Postoperative VTE within 14 days was set as the primary outcome indicator. Clinical data including demographic characteristics, underlying diseases, surgery-related indicators and perioperative preventive measures were collected through the electronic medical record system. Univariate Logistic regression analysis was used to screen candidate risk factors for VTE, and variables with P < 0.1 were included in multivariate Logistic regression analysis to identify independent risk factors. A VTE risk prediction nomogram model was constructed based on the independent risk factors. The discriminative ability, calibration and clinical utility of the model were verified by receiver operating characteristic (ROC) curve, calibration curve and decision curve analysis (DCA), and risk stratification analysis was performed according to the nomogram scores. Results The overall incidence of VTE within 14 days after surgery was 4.20% (28/680) in the 680 elderly patients undergoing hip surgery. Multivariate Logistic regression analysis showed that TWA (OR=1.125, 95%CI: 1.058-1.196, P<0.001), AUC (OR=1.098, 95%CI: 1.045-1.154, P<0.001), cumulative duration of IOH (OR=1.036, 95%CI: 1.012-1.061, P=0.003), age≥75 years (OR=2.895, 95%CI: 1.216-6.887, P=0.016), history of diabetes mellitus (OR=2.563, 95%CI: 1.082-6.079, P=0.032), operation time ≥120 min (OR=3.102, 95%CI: 1.305-7.376, P=0.010) and non-standard use of mechanical prophylaxis after surgery (OR=4.018, 95%CI: 1.695-9.523, P=0.001) were independent risk factors for postoperative VTE in elderly patients undergoing hip surgery, and the three quantitative indicators of IOH showed a significant dose-response relationship with the risk of VTE (P for trend <0.001). For the nomogram model constructed based on the above 7 independent risk factors, ROC curve analysis showed an AUC of 0.816 (95%CI: 0.725-0.907), indicating good discriminative ability of the model; the calibration curve showed a high consistency between the predicted probability and the actual incidence probability of the model (Hosmer-Lemeshow test, χ²=6.895, P=0.542); DCA confirmed that the model had significant clinical net benefit within the threshold probability of 5%-40%. According to the nomogram scores, patients were divided into the low-risk group (≤100 points), moderate-risk group (101~150 points) and high-risk group (>150 points), with the VTE incidences of 1.1% (3/325), 7.6% (22/286) and 22.7% (15/69) respectively, and the inter-group difference was statistically significant (χ²=45.865, P<0.001). Conclusion Under combined spinal-epidural anesthesia, the depth, load and duration of IOH in elderly patients undergoing hip surgery have a dose-response relationship with the risk of postoperative VTE, and IOH is an independent risk factor for postoperative VTE. The nomogram model integrating IOH quantitative indicators and clinical characteristics has good predictive efficacy and clinical utility, which can achieve precise risk stratification of postoperative VTE in elderly patients undergoing hip surgery, and provide a scientific basis for formulating individualized perioperative VTE prevention strategies and refined blood pressure management plans.