ESTIMATION OF TOTAL-BODY AND EXTRACELLULAR WATER IN POST-CORONARY ARTERY BYPASS GRAFT SURGICAL PATIENTS USING SINGLE AND MULTIPLE FREQUENCYBIOIMPEDANCE

Objective: To assess the value of bioimpedance as a clinical tool by d etermining the accuracy and bias of single and multiple frequency bioi mpedance estimates of total body and extracellular water in comparison with values established by criterion reference techniques, Design: Co ntrolled, prospective, single-blind investigation, Setting: Private, n ot-for-profit, university-affiliated, acute care hospital. Patients: E ight male, post-elective coronary artery bypass graft surgical patient s. Interventions: Within 6 hrs after surgery, estimates of total body and extracellular water volumes were determined using single and multi ple frequency bioimpedance techniques. These estimates were then compa red with the gold standard volumes measured by deuterium oxide and bro mine dilutional space determination, respectively. Measurements and Ma in Results: The mean multiple frequency bioimpedance estimate of total body water of 47.7 +/- 9.4 L was statistically different from the sin gle frequency bioimpedance and deuterium values of 52.5 +/- 9.4 (p <.0 06) and 53.3 +/- 11.6 L (p <.002), respectively, In comparison, the me an multiple and single frequency bioimpedance estimates of extracellul ar water, 26.3 +/- 5.4 and 29.2 +/- 5.4 L, respectively, were not stat istically different from the bromine value of 27.5 +/- 6.9 L. In addit ion, the mean errors for multiple and single frequency bioimpedance de terminations of extracellular water, -1.2 +/- 2.0 and 1.7 +/- 2.7 L, r espectively, were statistically different (p =.001). Conclusions: In m ale, post elective coronary artery bypass graft surgical patients, sin gle frequency bioimpedance was a more accurate and less biased predict or of total body water than multiple frequency bioimpedance. The accur acy and bias of multiple frequency bioimpedance was superior to single frequency bioimpedance for the prediction of extracellular water. Whe ther this observation remains true for other populations of critically ill patients remains to be investigated.