title: Intraperitoneal fluid overestimates hydration status assessment by bioimpedance spectroscopy.
abstract: 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.
authors.affiliation: Nephrology Department, Hospital General Universitario Gregorio Marañón, Madrid, Spain.
authors.forename: David
authors.initials: D
authors.lastname: Arroyo
authors.affiliation: Nephrology Department, Hospital General Universitario Gregorio Marañón, Madrid, Spain.
authors.forename: Nayara
authors.initials: N
authors.lastname: Panizo
authors.affiliation: Nephrology Department, Hospital General Universitario Gregorio Marañón, Madrid, Spain.
authors.forename: Soraya
authors.initials: S
authors.lastname: Abad
authors.affiliation: Nephrology Department, Hospital General Universitario Gregorio Marañón, Madrid, Spain.
authors.forename: Almudena
authors.initials: A
authors.lastname: Vega
authors.affiliation: Nephrology Department, Hospital General Universitario Gregorio Marañón, Madrid, Spain.
authors.forename: Abraham
authors.initials: A
authors.lastname: Rincón
authors.affiliation: Nephrology Department, Hospital General Universitario Gregorio Marañón, Madrid, Spain.
authors.forename: Ana Pérez
authors.initials: AP
authors.lastname: de José
authors.affiliation: Nephrology Department, Hospital General Universitario Gregorio Marañón, Madrid, Spain.
authors.forename: Juan M
authors.initials: JM
authors.lastname: López-Gómez
mesh_terms: D000328:Adult; D000368:Aged; D001202:Ascitic Fluid / Q000378:metabolism*; D001823:Body Composition; D015331:Cohort Studies; D058266:Dielectric Spectroscopy / Q000379:methods*; D005260:Female; D006801:Humans; D007676:Kidney Failure, Chronic / Q000175:diagnosis / Q000628:therapy*; D008297:Male; D008875:Middle Aged; D010530:Peritoneal Dialysis / Q000009:adverse effects / Q000379:methods*; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D016896:Treatment Outcome; D014883:Water-Electrolyte Imbalance / Q000175:diagnosis*
keywords: Bioimpedance spectroscopy; body composition