Electric impedance for evaluation of body fluid balance in cardiac surgical patients

Objective: To evaluate whether electric impedance can be used to monitor bo dy fluid balance and fluid distribution in cardiac surgical patients. Design: Prospective clinical study. Setting: Heart Center, Rigshospital, Copenhagen. Participants: Sixteen consecutive patients scheduled for cardiac surgery. Measurements and Main Results: Body weight, fluid balance, central hemodyna mics, and total and segmental body impedance were examined perioperatively. During semisupine rest before surgery, changes in impedance indicated relo cation of fluid from the legs to the thorax, mostly in the extracellular sp ace. After surgery, weight and fluid balance increased by 3.87 +/- 0.35 kg and 1.86 +/- 0.16 L (mean +/- SE, p < 0.01) and remained elevated through t he next 2 days. Impedance decreased by 30% over the thorax, by 24% over the abdomen, by 2% over the leg, and by 4% over the entire body. Changes in to tal and thoracoabdominal impedances had the highest correlation to the flui d balance (r = -0.86 and r = -0.87). After correction of impedance values b y the constant from the regression model, the mean difference in estimation of fluid changes obtained by electric impedance and by fluid balance was 0 +/- 0.1 L at the range of changes of 4.6 L. Conclusion: Alterations in electric impedance closely follow changes in flu id balance during the perioperative period. This method can be used in clin ical practice to control postoperative body fluid balance in cardiac surgic al patients. Copyright (C) 2001 by W.B. Saunders Company.