Dinwiddie LC, Frauman AC, Jaques PF, Mauro MA, Hogan SL, Falk
RJ
Comparison of two measures for prospective identification of
venous stenoses in high risk PTFE grafts
Am Soc Nephrol
J Am Soc Nephrol (abstract)
(Sep) 7:1405 1996
Two methods of monitoring access failure via pressures have been
proposed: one by Schwab using pressures measured at 200 or 150 ml/min
blood flow (VPF), and one by Besarab, measuring intra-access pressures
normalized to blood pressure at zero flow (VP0). Importantly, with
the Schwab method, VPF is not normalized to mean BP, whereas it is
with the Besarab method. VP0/MBP levels of 0.4 or 0.5 are viewed
as critical thresholds for impending access failure. The criteria for
a positive VPF test was a pressure > 150 mm Hg at a flow of 200
ml/min.
In this paper, VPF and VP0/MBP were measured in 20 patients who were
considered at high risk for access failure (how risk was identified
was not stated). Nineteen of these were then sent for angiography,
and a positive angiographic test was considered a > 50% stenosis.
The number of positive tests by VPF and VP0/MBP were quite different;
5/20 by VPF (e.g., VPF > 150 mm Hg), and 16/20 by VP0/MBP (>
0.4). Of the 16 positive patients by VP0/MBP, 14 had > 50%
stenosis by angiography. All 5 of the patients with VPF > 150 mm
Hg had > 50% stenoses, but VPF missed 10 patients with angiographic
stenosis, whereas VP0/MBP missed only two. The conclusions of the
authors are, that VP0/MBP is a better predictor of angiographic
stenosis than VPF.
Comment: This is one of many abstracts at this meeting and at
last year's ASN suggesting that monitoring VP0/MBP is a better strategy
than VPF. VPF is confounded by needle resistance, which is a function
of Qb, needle size, and hematocrit/viscosity, and possibly also needle
placement. For a practical method of measuring VP0/MBP, see Besarab et al..
(John T. Daugirdas, M.D., University of IL at Chicago)
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Am Soc Nephrol
Basic hemodialysis :
Vascular Access: graft/fistula