Electrochemical Evaluation of Polymer-Based Microelectrode Arrays: Analytical Performance on Oxygen and Hydrogen Peroxide.

Major Abdominal Surgery (MAS) refers to intra-abdominal procedures via open or minimally invasive approaches, involving resection of gastrointestinal, hepatobiliary, pancreatic, or renal organs (). Laparoscopic surgeries with total incision length ≥5 centimeters (cm) are included, along with operation time expected to last >2 hours (h) or involved blood loss >500 milliliters (mL) (, ). A relevant study has confirmed that preoperative pulmonary function tests (including forced expiratory volume in one second, FEV₁) are associated with postoperative pulmonary complications (). In addition, the patients undergoing MAS often experience restricted respiratory function due to factors like advanced age, preoperative comorbidities, significant surgical trauma, residual anesthetic effects, and postoperative pain, which can trigger hypoxemia (, ). The postoperative hypoxemia may lead to impaired wound healing, brain dysfunction, arrhythmias, myocardial ischemia, and even cardiopulmonary arrest (, ). Moreover, it prolongs post-anesthesia care unit (PACU) stays, increases costs, and consumes valuable medical resources (). Emerging evidences suggest that signs of respiratory depression during early anesthesia recovery may increase the risk of severe adverse events (). Postoperative hypoxemia is one of the most common and potentially dangerous complications in the PACU. Some studies have investigated risk factors for PACU hypoxemia; however, most of these investigations have been restricted to specific surgical populations. Wang et al. () focused on patients with Stanford type A acute aortic dissection, a procedure requiring cardiopulmonary bypass with deep hypothermic circulatory arrest, where the mechanisms of postoperative hypoxemia are primarily driven by systemic inflammation and myocardial injury. Duan et al. () concentrated on elderly patients (≥65 years) with femoral neck fractures, in whom advanced age, reduced cardiopulmonary reserve, prolonged recumbency, and pulmonary infection are the main triggers of hypoxemia; moreover, that study simultaneously developed a dedicated nomogram prediction model. Li et al. () included pediatric patients undergoing general anesthesia; owing to developmental airway characteristics and a lower burden of baseline comorbidities, the risk factor profile for hypoxemia in children differs substantially from that in adults, and their study only performed risk factor analysis without establishing a predictive model. Taye et al. () and Andualem et al. () enrolled mixed adult surgical cohorts in high-altitude Ethiopian healthcare settings, where limited oxygen resources served as a unique confounding factor; both studies only screened for risk factors and did not develop predictive tools. To our knowledge, no studies have reported a predictive model of hypoxemia in PACU patients after MAS. In this study, we retrospectively analyzed patients undergoing MAS and aimed to construct a nomogram that clinicians can use to identify high-risk patients in the PACU. All consecutive patients who met the inclusion criteria during the study period were enrolled. The training group included 378 patients treated between June 1, 2024, and December 31, 2024; the validation group included 189 patients treated between April 1, 2025, and May 31, 2025. The sample size was calculated using the events per variable (EPV) method, with EPV > 10 considered necessary to ensure stable estimates (). The final multivariable model included 4 predictors. Based on the previous experiment, the incidence of hypoxemia in the PACU after MAS was approximately 33.0%. With EPV set at 10, the required sample size was calculated as: (4 × 10) /0.33 ≈ 121 cases. After adding 10% to account for missing data, approximately 134 cases were needed. The inclusion criteria for this study were as follows: (i) adults aged ≥18 years who underwent elective MAS under general anesthesia; (ii) BMI ranging from 18 to 30 kg/m; (iii) American Society of Anesthesiologists (ASA) physical status II to III; and (iv) patients transported to the PACU with an endotracheal tube in place. Exclusion criteria were as follows: (i) unplanned transfer to the intensive care unit (ICU); (ii) preoperative severe respiratory disease (such as chronic obstructive pulmonary disease, asthma, respiratory failure, etc.) or pulse oximetry oxygen saturation (SpO) less than 90% without oxygen inhalation; (iii) history of severe upper respiratory tract infection; (iv) severe obstructive sleep apnea syndrome (OSAS). The study was approved by the Ethics Committee of the First Affiliated Hospital of Naval Medical University (Approval No.: CHEC2025-317). The patient screening process is shown in .