Intraoperative hypoxemia is a common and serious complication during monitored anesthesia care for elective endoscopic retrograde cholangiopancreatography (ERCP), especially in older adults. Frail patients have reduced physiologic reserve and are at increased risk of life-threatening events including unplanned intubation, hemodynamic collapse, and hypoxic brain injury. However, the independent relationship between frailty and intraoperative hypoxemia during sedated ERCP remains poorly defined, and no validated risk prediction model exists for this high-risk population. This single-center, dual-cohort study will be conducted at China-Japan Friendship Hospital to evaluate whether preoperative frailty can predict intraoperative hypoxemia in patients aged 65 years and older undergoing elective ERCP. Frailty will be assessed primarily using the Frailty Index (FI), with secondary screening by the Modified Frailty Index-11 (mFI-11), Edmonton Frail Scale (EFS), Clinical Frailty Scale (CFS), FRAIL scale, and Fried phenotype. The primary outcome is intraoperative hypoxemia, defined as SpO₂ < 90% for 5 seconds or longer. In the retrospective phase (n = 313), investigators will identify risk factors and develop a preliminary prediction model. In the prospective phase (n = 388), the model will be validated, refined, and internally tested for discrimination, calibration, and clinical utility. This study aims to establish frailty as a reliable preoperative risk marker and provide a clinically practical prediction tool to support risk stratification, personalized sedation strategies, and perioperative safety in elderly patients undergoing ERCP.

This dual-cohort study investigates the predictive value of preoperative frailty for intraoperative hypoxemia in patients aged 65 years and older undergoing elective endoscopic retrograde cholangiopancreatography (ERCP) under monitored anesthesia care at China-Japan Friendship Hospital, with a total target enrollment of 701 patients (313 retrospective and 388 prospective). Intraoperative hypoxemia, defined as pulse oxygen saturation (SpO₂) < 90% for 5 seconds or longer from anesthesia induction to procedure completion, serves as the primary outcome, while secondary outcomes include severe hypoxemia, postoperative hypoxemia, time to oxygen discontinuation, hemodynamic instability, anesthesia- and procedure-related adverse events, respiratory depression, and apnea. Frailty will be assessed primarily using the Frailty Index (FI) as the core instrument, with additional secondary screening performed using the Modified Frailty Index-11 (mFI-11), Edmonton Frail Scale (EFS), Clinical Frailty Scale (CFS), FRAIL questionnaire, and Fried frailty phenotype. Eligible patients are aged 65 years or older with ASA class II-IV status, scheduled for elective ERCP with a planned procedure duration of less than 60 minutes and complete intraoperative SpO₂ monitoring data; those requiring emergency surgery, severe anemia, pre-existing severe respiratory or hemodynamic instability, or impaired consciousness will be excluded. The retrospective phase will use existing electronic health records to identify risk factors and construct a preliminary prediction model, with propensity score matching, univariate and multivariable logistic regression, bootstrap internal validation, and random forest for feature importance ranking. The prospective phase will prospectively collect standardized data, validate the association between frailty and hypoxemia using adjusted logistic regression, refine the prediction model, compare the performance of different frailty scales using Delong's test, and evaluate machine learning models with SHapley Additive exPlanations (SHAP) values for interpretability. The final model will be tested in an internal validation cohort for discriminative ability, calibration, and clinical utility. All statistical analyses will be performed using R and SPSS software at a two-sided significance level of α = 0.05, with multiple imputation for missing data and Holm-Bonferroni correction for multiple comparisons.

Inclusion Criteria:

1. Age 65 years or older
2. Elective endoscopic retrograde cholangiopancreatography (ERCP) under anesthesia sedation
3. American Society of Anesthesiologists (ASA) physical status II-IV
4. Expected procedure duration less than 60 minutes
5. Available and complete intraoperative pulse oximetry (SpO₂) monitoring data

Exclusion Criteria:

1. Emergency ERCP
2. Severe anemia (hemoglobin < 60 g/L) or conditions interfering with accurate 3. SpO₂ measurement

4. Pre-existing severe respiratory insufficiency requiring long-term oxygen therapy 5. Unstable hemodynamics requiring continuous vasopressor infusion Impaired consciousness, delirium, or cognitive dysfunction that prevents reliable frailty assessment

This observational cohort study will enroll elderly patients aged 65 years and older who are scheduled for elective endoscopic retrograde cholangiopancreatography (ERCP) under anesthesia sedation at China-Japan Friendship Hospital. The study population consists of two sequential cohorts: a retrospective cohort of 313 patients with complete electronic health record data and a prospective cohort of 388 patients to be recruited prospectively. Eligible participants include those with American Society of Anesthesiologists (ASA) physical status II-IV and an expected procedure duration of less than 60 minutes, with adequate intraoperative pulse oximetry monitoring.

Individual participant data (IPD) will be shared with qualified researchers upon reasonable request, following publication of the study results. Shared data will include de-identified clinical information (baseline characteristics, intraoperative parameters, postoperative outcomes) and biomarker data, excluding direct identifiers to protect participant privacy. Data access will require approval from the institutional review board of China-Japan Friendship Hospital and a signed data use agreement specifying the purpose of use and confidentiality obligations. The data will be shared via a secure research data repository for up to 5 years after study completion

Individual participant data (IPD) and supporting information will be made available within 1 month after the publication of study results, with access maintained for 5 years after study completion.

Eligible researchers must submit a research application specifying the purpose of data use and research plan, which will be reviewed and approved by the Institutional Review Board of China-Japan Friendship Hospital.A data use agreement must be signed, committing to use the data solely for scientific research, protect participants' privacy, refrain from unauthorized data transfer, and cite this study in published outcomes.De-identified data will be accessible through the hospital's designated secure data repository.