Besarab A, Ross R, El-Ajel F, Deane C, Frinak S, Zasuwa G
The relation of intra-access pressure to intra-access flow
Am Soc Nephrol
J Am Soc Nephrol (abstract) (Nov) 6:483 1995

Besarab measured access blood flow by Doppler and the access pressure at zero extracorporeal flow divided by the blood pressure (VPo/BP) in 86 patients every 6 months. A VPo/BP ration > 0.45 was cause to perform angiography. In patients with no access events, flow remained at about 1L/min, VPo/BP at 0.35, with no change in VPo/BP over time. In 21 patients with intervention (a self-fulfilling prophecy, as intervention depended on VPo/BP), VPo/BP had increased by 0.15 to 0.53. Flow in this time was only 584 ml/min. In 6 patients with thrombosis, flow was 454 ml/min, VPo/BP was 0.66, and had increased by 0.12 units since baseline.

Comment: A nice study suggesting that one can monitor either pressure or flow to prevent thrombosis. However, data by Lavarias et al. suggest that venous pressure measurements during extracorporeal blood flow are not very useful. This is logical, as most of the venous resistance under flowing conditions is found in the venous needle. It appears that an access flow < 600 ml/min may be a cause for some concern. (Daugirdas)

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Am Soc Nephrol
Basic hemodialysis : Vascular Access: graft/fistula


Dr. Daugirdas misses the point that extracoporeal flow was zero during the venous pressure measurements. I don't see how Dr. Lavarias reference has any relationship to the measuremnts presented in this abstract.
Gerard Zasuwa (zasuwa@earthlink.net)
Detroit, MI USA-Friday, June 28, 1996 at 12:46:23 (CDT)

Gerry: I think the problem was that I didn't express myself clearly enough. In my comments section, I meant to say that the failure of Lavarias to show a predictive value for pressure measurements vs. the positive findings in this study were due precisely to the fact that pressure measurements were taken under different conditions. Under conditions of zero flow, the resistance in the needle is taken out of the equation. Needle resistance is a major determinant of outflow resistance under flowing conditions, and is a function both of needle size and blood flow rate. Hence the need for different guidelines when 16 gauge or 15 gauge needles are used. Also, not only blood flow but blood viscosity, namely hematocrit, then comes into the picture. So I strongly believe that pressure measurements under zero flow conditions are an advance, and am not surprised that they correlated with access flow.
John Daugirdas MD (jtdaugir@uic.edu)
Chicago, IL USA-Friday, June 28, 1996 at 13:04:11 (CDT)