title: Post to predialysis plasma urea nitrogen ratio, ultrafiltration and weight to estimate K.t/V. Use in auditing the amount of dialysis being administered.
abstract: The formula -In (R - 0.03 - UF/W), where R is the ratio of the postdialysis to predialysis plasma urea nitrogen level, UF the ultrafiltrate volume per session, and W the postdialysis weight, has been shown by us to estimate K.t/V accurately. We audited the amount of dialysis being administered in a moderate size outpatient unit in which urea kinetic modeling was not being done and in which 4 hr dialysis at a 250 or 300 ml/min blood flow rate was routinely prescribed. R was determined once per month on each of six successive months, and standard three point urea kinetic modeling was done on all patients once. R was quite reproducible in each patient, with a coefficient of variation of 6.6% +/- 3.2 standard deviation (SD). The R:UF:W-derived K.t/V averaged 0.91 +/- 0.19; the R:UF:W-derived K.t/V correlated with the modeled K.t/V (r = 0.98), with a mean percent error of only 0.12% +/- 3.6. A negative correlation (r = -0.56) was present between the R:UF:W-derived K.t/V and postdialysis weight; 9 of 40 patients had K.t/V values below 0.8 and 7 of these 9 weighed more than 85 kg. In 13 other patients, K.t/V was between 0.8 and 0.9. After inclusion of residual renal function (Kru) to calculate KT, KT was still below 0.9 in 19 patients. The main cause of underdialysis was inadequate prescription. The results suggest that monthly monitoring of R, with inclusion of UF and W to estimate K.t/V, is one useful quality assurance tool to assess the amount of dialysis being administered.
authors.affiliation: Department of Medicine and Research, Veterans Administration Hospital, Hines, Illinois.
authors.forename: F J
authors.initials: FJ
authors.lastname: Manahan
authors.forename: L
authors.initials: L
authors.lastname: Ramanujam
authors.forename: M
authors.initials: M
authors.lastname: Ajam
authors.forename: T S
authors.initials: TS
authors.lastname: Ing
authors.forename: V C
authors.initials: VC
authors.lastname: Gandhi
authors.forename: J T
authors.initials: JT
authors.lastname: Daugirdas
mesh_terms: D001806:Blood Urea Nitrogen; D001810:Blood Volume / Q000502:physiology; D001835:Body Weight / Q000502:physiology*; D006440:Hemofiltration / Q000379:methods*; D006801:Humans; D007676:Kidney Failure, Chronic / Q000097:blood*; D008962:Models, Theoretical; D006435:Renal Dialysis / Q000379:methods*