Phase angle as a prognostic factor for postoperative outcomes in major abdominal surgery: a single-center prospective observational study

Purpose: Phase angle (PA), derived from bioelectrical impedance-analysis (BIA) has emerged as a reliable marker predicting clinical outcomes. This prospective observational study investigated the association between PA and a composite in-hospital outcome in major abdominal surgery. Methods: Each patient underwent BIA before surgery (PA_pre), immediately postoperatively (PA_post), and 1 day postoperatively (PA_POD1). Specific assessment for frailty and nutrition status was performed before surgery. Patient outcomes were assessed using a composite adverse outcome comprising death, myocardial infarction, revascularization, stroke, hemodynamic instability, acute kidney injury, pulmonary complications, delirium, ileus, and surgical complications during hospitalization. One-year complication, including all-cause mortality, myocardial infarction, stroke, surgical complications, and readmission after discharge within the year were also assessed. Results: A total of 122 adults who underwent major abdominal surgery were enrolled from July 2019 and April 2021. Twenty-three patients (53.5%) in the lower PA group (PA < 5) experienced in-hospital complications compared to 38 patients (34.2%) in the higher PA group (PA ≥ 5) (relative risk, 1.6; 95% confidence interval [CI], 1.0 to 2.4; p = 0.038). PA_pre was significantly associated with in-hospital complications (odds ratio, 0.491; 95% CI, 0.279 to 0.862; p < 0.001). Patients with lower PA_pre had a higher degree of frailty, and poor nutritional status. However, PA_pre was not significantly associated with 1-year composite complications. Conclusion: Low PA_pre was associated with adverse postoperative outcomes after major abdominal surgery. PA can be a reliable prognostic factor to predict in-hospital complications in patients undergoing major abdominal surgery, serving as an alternative surrogate to frailty indices and nutritional markers. Trial registration: Clinical Research Information Services of the Republic of Korea (CRIS identifier: KCT0004160).