Fluid status after cardiac surgery assessed by bioelectrical impedance vector analysis (BIVA) and the effects of extracorporeal circulation

Abstract Objective Hydration status after cardiac surgery can be difficult to assess, often requiring invasive measurements. Bioelectrical impedance vector analysis (BIVA) is based on patterns of resistance (R) and reactance (Xc) corrected by height and has been used in various clinical scenarios to determine body composition and monitor its changes over time. Our purpose was to apply this method in cardiac surgery patients to assess the variation in hydration status and to compare its changes according to the use of extracorporeal circulation. Design Single-center, observational, prospective study including patients over 18 years old undergoing elective or urgent cardiac surgery. Setting Intensive cardiac care unit of a tertiary center in a metropolitan area. Participants In 76 patients, with a median age of 60 years and mostly undergoing coronary-artery by-pass grafting (CABG) (n = 47, 61.8%) with extracorporeal circulation (n = 54, 73%). Interventions Bioimpedance was measured with a standard tetrapolar single-frequency bioimpedance meter using a standardized procedure and plotted in an R–Xc graph. Measurements & Main Results We found an increase in total body water immediately after surgery, that was sustained until producing hyperhydration 24 hours later. Off-pump CABG was associated with a normal hydration status after surgery, while on-pump CABG produced a significant increase in total body water. Conclusions Fluid status assessment with BIVA in cardiac surgery showed an increase in total body water up to 24 hours after surgery. Off-pump surgery avoided overhydration, which could partially explain the reduction in some of the postoperative complications. BIVA could pose as a useful method for monitoring fluid status in the setting of goal-directed therapy to assist in maintaining euvolemia in cardiac surgical patients.