Effect of vascular access type and blood draw method on recirculation and rebound in the HEMO study.
ASN 30th Annual Meeting, San Antonio
J Am Soc Nephrol (Sep) 8:280A 1997
The post-dialysis blood sample is normally drawn after 20 seconds of slow blood flow. This is to allow any recirculated blood to clear the fistula. Without this 20 second delay, there is a risk of significant overestimation of Kt/V if the patient has access recirculation. However, there is normally some post-dialysis rebound during this 20 seconds which will result in an underestimation of Kt/V.
This study analyzed blood urea concentrations after 1 hour of dialysis, at the end of dialysis and 30 minutes after dialysis. The 1hr and postdialysis samples were drawn at full flow and after a 20 second delay. Over 700 patients were studied as part of the HEMO study.
The results show that, as expected, the 20 second delay results in a slight overestimation of Kt/V in patients without recirculation. This overestimation is around 4% and is probably not clinically important. The study also shows that the arterial and venous rate equations predict the rebound well.
In my view, the clinical message from the study is that Kt/V is best measured using a post-dialysis blood sample taken at full-flow at the end of dialysis and corrected for the expected rebound. This measurement must be combined with an independent measurement of recirculation such as the saline or thermal dilution methods. If recirculation cannot be independently measured, a sample taken after 20 seconds of slow flow is acceptable but will result in a slight but predictable underestimation of Kt/V. (James Tattersall, M.D., United Kingdom)
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ASN 30th Annual Meeting, San Antonio
Basic hemodialysis : Adequacy, prescription, urea kinetics