HDCN Article Review/Hyperlink

Wu MJ, Feng YF, Shu KH, Cheng CH, Lian JD

Another simpler bypassing dialysate technique for measuring post-haemodialysis BUN

Nephrol Dial Transplant (Oct) 12:2124-2127 1997

Although DOQI guidelines suggest drawing the BUN within 10-15 sec postdialysis to obviate phase I of postdialysis rebound, an argument can be made for waiting about 2 min postdialysis: (a) adequacy with venous and arterial accesses is measured using the same yardstick (postdialysis venous urea concentration), whereas A/V equilibration is not accounted for at the 10-15 sec sampling time, and (b) if cardiac output falls markedly at the end of dialysis, the A/V urea gradient can be large, and the second phase of rebound (cardiopulmonary recirculation) can be unexpectedly pronounced. However, using a slow flow method, it is problematic to keep the blood flow at 50-100 ml/min for 2 min, as clotting might be engendered, even if the UF rate is appropriately set to zero at the start of the slow flow period. Wu et al here present an alternative method; keeping the blood flow high, but putting the dialysate into bypass and waiting for 3 min.

With such methods, as with venous catheters, the standard arterial "rate equation"

delta Kt/V = (Kt/Vsp)/h x 0.60 - 0.03
to compute equilibrated Kt/V cannot be used. The proper slope coefficient would then be closer to 0.40 (rather than 0.60) and the intercept closer to 0.02 (rather than 0.03) with such delayed 2-3 min postdialysis sampling times. The venous rate equation slope is 0.47 (cited in the same paper). This value may be a bit too steep when 2-3 min postdialysis specimens are used, as considerable "3rd phase" rebound occurs during the first 3 min after dialysis. (John T. Daugirdas, M.D., University of Illinois at Chicago)

The abstract of this paper is available from Oxford Press at this site.
(Full text available in .pdf format, free until Jan 1, 1998!)