Rapid bedside method to assess changes in postoperative fluid status with bioelectrical impedance analysis

Estimates of daily postoperative fluid balance usually rely on properly recorded inputs, outputs, and daily weights or clinical signs. These may be imprecise (when poorly done) and are often considered tedious to perform.

We used bioelectric impedance analysis (BIA) to assess changes in body water shifts in cardiac patients after surgery. Nine consecutively admitted patients undergoing coronary artery bypass (seven men and two women; age range, 43 to 67 years) were studied. Body weight, fluid intake and output, and BIA variables (resistance and reactance) were measured daily. Relationships between body weight and changes in resistance and reactance and net change in fluid balance (in liters per day) were evaluated statistically by regression analysis.

Mean body weights changed significantly, reflecting early operative fluid accumulation and later postoperative diuresis; net fluid balance correlated poorly (r = 0.48; p less than 0.05) with body weight, whereas both resistance (r = -0.82; p less than 0.001) and reactance (r = -0.92; p less than 0.0001) correlated highly with net fluid balance.

BIA is useful as an accurate, rapid bedside method for assessing changes in hydration status sequentially after surgery in cardiac patients with complicated fluid shifts.