Validation study of thoracic fluid bioimpedance for assessing the haemodialysis-induced changes in total body fluids

Thoracic fluid bioimpedance (TFB) has been proposed as a noninvasive technique for monitoring both haemodynamics and fluid homeostasis in patients on regular dialysis. To validate the reliability of TFB in assessing the haemodialysis (HD)-induced changes in plasma volume (PV) in these patients, we examined the changes of TFB during and after HD in relation to those in total plasma protein (TP) concentration, haematocrit (Ht), heart rate (HR), total body water (TBW) and plasma angiotensin II (A-II) concentration. Data were recorded in 13 HD patients with a wide range of interdialytic weight gains before, at the end, and 4, 8, 24, 48 h after the HD session. We found that the percent TFB changes were closely and inversely related with those of TP, Ht and TBW (r = -0.54, r = -0.45 and -0.68, respectively, p < 0.001 for all). Similar relations were found between the percent changes in TFB and those in absolute TP and Ht. In addition, a direct relation was found between the percent changes of TFB and those of HR and of A-II (r = 0.33 and r = 0.31, respectively, p < 0.01 for both). These data indicate that TFB is a reliable method for evaluating the HD-induced changes of intra- and extravascular fluids and, with respect to the conventional techniques, has the advantage of providing this information dynamically, and in conjunction with the haemodynamic data of patients.