title: A non-invasive, on-line deuterium dilution technique for the measurement of total body water in haemodialysis patients.
abstract: BACKGROUND
  Despite its importance, total body water (TBW) is usually estimated rather than measured due to the complexity of isotope dilution methods. The aim of this study was to demonstrate the applicability in haemodialysis (HD) patients of a recently developed on-line breath test, previously validated in healthy subjects, that uses the gold standard deuterium dilution method to measure TBW. In particular we wished to show that a pre-dialysis estimation was as good as a post-dialysis equilibrated measurement in order to avoid patients needing to remain behind after dialysis treatment.
  
  
  METHODS
  The dispersal kinetics of breath HDO, measured using a flowing afterglow mass spectrometer (FA-MS) following ingestion of D(2)O immediately post-dialysis, were determined in 12 haemodialysis patients and used to calculate the absolute TBW(PostHD) after full equilibration. TBW(PreHD) was then determined from breath samples taken immediately prior to the next dialysis. This measurement was adjusted for the interdialytic weight change and urine output (TBW(PreHD-adjusted)) and compared to the TBW(PostHD). The accuracy and precision of FA-MS was also assessed using known concentrations of deuterium-enriched water samples.
  
  
  RESULTS
  Mean TBW(PostHD) was 50.0 +/- 9.3 L and TBW(PreHD-adjusted) was 50.7 +/- 9.0 L. They were highly correlated (R = 0.99, P < 0.001) with a CV of 2.6%. The mean difference was +0.74 L (SEM 0.35, 95% CI -0.03 to 1.51 L, P = 0.059), compatible with a daily insensible loss of 0.37 L. Accuracy and precision of FA-MS were comparable to the previous validation work.
  
  
  CONCLUSIONS
  This non-invasive adaptation of the D isotope dilution method for determining TBW can be applied to haemodialysis patients who show deuterium equilibration kinetics identical to normal subjects; a pre-dialysis estimation may be used to determine TBW, and so avoiding the necessity to remain behind after dialysis making this suitable for application in the clinical setting.
authors.affiliation: Department of Nephrology, University Hospital of North Staffordshire, Stoke-on-Trent ST4 7LN, UK.
authors.forename: Cian
authors.initials: C
authors.lastname: Chan
authors.forename: David
authors.initials: D
authors.lastname: Smith
authors.forename: Patrik
authors.initials: P
authors.lastname: Spanel
authors.forename: Christopher W
authors.initials: CW
authors.lastname: McIntyre
authors.forename: Simon J
authors.initials: SJ
authors.lastname: Davies
mesh_terms: D000368:Aged; D001834:Body Water / Q000502:physiology*; D001944:Breath Tests; D003903:Deuterium / Q000493:pharmacokinetics*; D017097:Electric Impedance; D005260:Female; D006801:Humans; D007201:Indicator Dilution Techniques; D007676:Kidney Failure, Chronic / Q000175:diagnosis / Q000628:therapy; D008297:Male; D013058:Mass Spectrometry / Q000379:methods; D008875:Middle Aged; D006435:Renal Dialysis / Q000009:adverse effects / Q000379:methods*; D015203:Reproducibility of Results; D012494:Sampling Studies; D012680:Sensitivity and Specificity; D014883:Water-Electrolyte Imbalance / Q000517:prevention & control
chemical_list: D003903:Deuterium