Intraperitoneal fluid overestimates hydration status assessment by bioimpedance spectroscopy

Background: Bioimpedance spectroscopy (BIS) is a valuable tool to assess nutrition and volume status in peritoneal dialysis (PD) patients. However, data about the influence of intraperitoneal fluid on body composition measures are conflicting, and there is no clear consensus about whether the abdomen should be drained before the procedure. We designed a comparison study to detect the influence of intra-abdominal fluid on BIS results.

Methods: We performed 73 pairs of BIS measurements in 34 stable PD patients, first with the peritoneum filled with a 1.36% glucose dialysate solution and then after the solution was drained. Patients stayed in the supine position for 10 minutes before the BIS procedure, and the electrodes were not moved between measures. Clinical and demographic data were collected, as were analytic parameters of nutrition and volume status.

Results: Fluid overload is overestimated when BIS is performed with a full abdomen (1.82 ± 1.73 L vs 1.64 ± 1.68 L, p = 0.043). We also found a spurious overestimation in extracellular water (16.40 ± 3.21 L vs 16.24 ± 3.16 L, p < 0.001) and in relative overhydration (8.29% ± 6.96% vs 7.14% ± 6.79%, p = 0.017). No differences in intracellular water or parameters of nutrition were found. We observed negative correlations for the extracellular water overestimation with age (r = -0.245, p = 0.037), serum B-type natriuretic peptide (r = -0.366, p = 0.036), body mass index (r = -0.248, p = 0.035), and lean tissue index (r = -0.427, p = 0.001). The difference in extracellular water correlated only with body mass index (r = -0.259, p = 0.039). We also found that, assessed at 50 KHz, whole-body impedance (-4.52 ± 8.37, p = 0.001) and phase angle (-0.08 ± 0.23 degrees, p = 0.002) were both lower when BIS was performed in patients with a full abdomen.

Conclusions: Fluid overload is overestimated by BIS when performed in patients with dialysate in the peritoneum. The observed differences are greater in younger, more poorly nourished, or less overhydrated patients. If more precise results are required, we suggest that the abdomen be drained before BIS is performed.