Correlation Between Changes in Bioelectrical Impedance Phase Angle During Cardiopulmonary Bypass and ICU Length of Stay After Cardiac Surgery

CAO Lu; LI Yonghua; MO Shaoyan; XIAO Jiefei; WU Xiaomei; JIANG Yumei; RONG Jian

doi:10.13498/j.cnki.chin.j.ecls.2025.06.03

Abstract：Objective This study aimed to investigate the dynamic changes in bioelectrical impedance phase angle(PhA)during the peri-cardiopulmonary bypass(CPB)period and its predictive value for ICU length of stay(LOS)following cardiac surgery.Methods Sixty patients undergoing CPB cardiac surgery between May and July 2023 were prospectively en-rolled.Whole-body and segmental PhA and edema index(EI)were measured using a multifrequency bioelectrical impedance analyzer(InBody S10)pre-CPB(post-anesthesia)and post-CPB.Patients were stratified into low-PhA(≤5.85°,n=30)and high-PhA(>5.85°,n=30)groups based on preoperative PhA median.Intergroup comparisons of baseline characteristics,intra-operative parameters,and clinical outcomes were performed.Linear regression identified independent predictors of ICU LOS.Results Post-CPB PhA decreased significantly compared with pre-CPB values(5.46°±1.16° vs.5.85°±1.05°,P=0.0035),with elevated upper-limb EI(P<0.05).The low PhA group exhibited poorer baseline status:lower BMI(21.34±3.47 kg/m2 vs.23.80±3.12 kg/m2),reduced preoperative albumin(36.93±3.35 g/L vs.39.63±4.25 g/L),and higher APACHEⅡ scores(7.70±4.16 vs.4.93±2.18)(all P<0.01).This group required higher intraoperative RBC transfusion[3.2(2.0-4.0)U vs.2.0(0.0-2.9)U,P=0.029],prolonged mechanical ventilation[10.8(7.2-21.5)h vs.7.5(5.0-10.0)h],and extended ICU LOS[32.0(21.2-67.0)h vs.21.0(19.2-24.0)h](all P<0.05).Linear regression identified preoperative PhA(β=-39.48,95%CI:-68.05 to-10.92,P=0.009),intraoperative fluid balance(β=0.02,95%CI:0.01-0.04,P=0.047),and mechanical ventilation du-ration(β=0.90,95%CI:0.72-1.09,P<0.001)as independent predictors of ICU LOS.Each 1° increase in preoperative PhA was associated with a reduction in ICU LOS of 39.48 hours.Conclusion Significant reduction in PhA and increased upper-limb hy-dration during CPB suggest CPB-induced cellular membrane dysfunction and regional fluid redistribution.Preoperative low PhA independently predicts prolonged postoperative ICU LOS.Segmental bioelectrical impedance analysis of the upper limbs may serve as a targeted monitoring metric for goal-directed fluid management during CPB.