Bioelectric impedance predicts total body water, blood pressure, and heart rate during hemodialysis in children and adolescents.

OBJECTIVE: The purposes of our study were to: (1) assess if changes in the volemic status of children and adolescents over the course of standard dialysis could be observed using bioelectric impedance (BIA); and (2) evaluate whether the variability of blood pressure (systolic blood pressure, SBP; diastolic blood pressure, DBP) and heart rate (HR) could be explained by independent variables from BIA data.

DESIGN: We used a randomized, single-blinded treatment and repeated-measures design.

SETTING: This study took place at the DaVita Children's Dialysis Center (Chicago, IL).

PATIENTS: There were 7 subjects, aged 10 to 16 years.

INTERVENTION: Two identical standard hemodialysis (HD) sessions were completed, with data collected five times during each HD session: pre-HD, intra-HD (hours 1, 2, and 3), and post-HD. Endpoints included total body water (TBW), resistance (R), reactance (Xc), bioimpedance vector |Z|, supine and sitting SBP, DBP, and HR. Standing SBP, DBP, and HR were collected pre-HD and post-HD.

RESULTS: No differences were observed in TBW between HD sessions for all subjects. However, TBW decreased throughout the HD sessions for all subjects (although no significant differences were seen between hour 3 and post-HD). Reactance (representative of extracellular water) correlated with supine, sitting, and standing SBP (r = 0.55, 0.59, and 0.51, respectively; P < or = .008). The bioimpedance vector increased beginning at hour 1 (P < .001), reflective of a decline in tissue hydration over the course of HD.

CONCLUSIONS: Weight gain in end-stage kidney disease patients is largely fluid. Thus, the use of BIA during HD may aid in the prediction of cardiovascular instability before the development of symptoms, because intravascular hypovolemia and hypotension can result from excessive ultrafiltration below the critical dry weight. In addition, BIA explains, in part, the variability of SBP, DBP, and HR during HD. We suggest that our data also demonstrates the delay in mobilization of fluid from the interstitial space for plasma refill, as evidenced by the delayed change in |Z| over HD. Bioelectric impedance is useful for explaining changes in volemic status and, in part, the variability of SBP, DBP, and HR during HD.