Electric Impedance for Evaluation of Body Fluid Balance in Cardiac Surgical Patients

Objective: To evaluate whether electric impedance can be used to monitor body 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 hemodynamics, and total and segmental body impedance were examined perioperatively. During semisupine rest before surgery, changes in impedance indicated relocation of fluid from the legs to the thorax, mostly in the extracellular space. 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 the 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 total and thoracoabdominal impedances had the highest correlation to the fluid balance (r = -0.86 and r = -0.87). After correction of impedance values by 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 fluid balance during the perioperative period. This method can be used in clinical practice to control postoperative body fluid balance in cardiac surgical patients.