Comparison of bioimpedance and radioisotope methods in the estimation of extracellular water volume before and after coronary artery bypass grafting operation

To estimate extracellular water volume (ECW) changes in connection with cor onary artery bypass grafting operation, simultaneous ECW estimations by Cr- 51-EDTA dilution and whole-body bioimpedance techniques were performed in 1 5 patients. The assessments of ECW were compared with patients' weighing re sults. Whole-body bioimpedance-derived ECW correlated significantly with Cr -51-EDTA dilution-based ECW in the pre-operative period (r = 0.74; P < 0.00 5); the bias was 0.2 +/- 1.1 l (+/- SD). In the post-operative period, the agreement between these methods was poor, the bias being 0.5 +/- 2.5 l, and no significant correlation between the methods was found (r=0.38; P > 0.05 ). Whole-body bioimpedance-derived ECW changes correlated significantly wit h weight changes of the patient induced by the operation (r = 0.52; P < 0.0 5). Cr-51-EDTA dilution-based ECW changes correlated neither with weight ch anges (r = 0.33; P > 0.05) nor with bioimpedance-derived ECW changes (r = 0 .03; P > 0.05). Alterations in radioisotope tracer distribution and loss of it due to blood leakage in the post-operative period were presumed to expl ain the discrepancy between dilution technique and weighing results. The re sults suggest that bioimpedance is a useful non-invasive method for assessm ent of extracellular volume changes induced by coronary artery bypass graft ing operations. Cr-51-EDTA dilution-based ECW determination is not suitable in related conditions.