Do Pre-Hemodialysis Estimates of Extracellular Volume Excess Using Bioimpedance and N-Terminal Brain Natriuretic Peptide Correlate With Cardiac Chamber Size Measured by Magnetic Resonance Imaging?

Bioimpedance can be used to measure extracellular water (ECW) and total body water in hemodialysis (HD) patients and estimate ECW excess. However, ECW excess potentially includes both an increase in the plasma volume and also the extravascular volume. Overestimating the amount of fluid to be removed during HD risks intra-dialytic hypotension. We wished to determine the association between estimates of ECW excess comparing several different equations using bioimpedance, brain N-terminal pro-brain natriuretic peptide (NT-proBNP) with cardiac chamber volumes and function as determined by cardiac magnetic resonance imaging pre-HD measurements of ECW and total body water were made using multifrequency bioimpedance and cardiac chamber sizes and function were determined by magnetic resonance imaging. Thirty patients, 20 males (66.7%), mean age 64.4 ± 15.3 years were studied. ECW and ECW/height were positively associated with indexed right ventricular end-systolic (RVESVi) and end-diastolic volume (RVEDVi) (RVESi r = 0.46, r = 0.43; RVEDi r = 0.50, r = 0.44, all P < 0.05), but not with left sided cardiac volumes. Whereas NT-proBNP was associated with indexed left atrial and ventricular size (r = 0.47, r = 0.58, P < 0.05), but not right sided cardiac volumes. Pre-HD NT-proBNP was associated with left sided cardiac chamber sizes, but not with right sided chamber sizes, whereas ECW/height was associated with right sided cardiac chamber sizes. As right-sided cardiac chamber size is more responsive to and reflective of changes in intravascular volume than the left atrium and ventricle, then bioimpedance measured ECW is potentially more reliable in estimating plasma volume expansion.