A comparison of methods for the measurement of hemodialysis access recirculation.

BACKGROUND

NKF K-DOQI clinical practice guidelines recommend a regular monitoring of vascular access (VA) through several methods, such as VA recirculation (AR). Assessment of AR is crucial to avoid inefficiency of hemodialysis (HD). A non-urea based method has been developed (ultrasound dilution Transonics Hemodialysis Monitor--USM) which is considered the gold standard together with the two needle revised slow-stop-flow BUN recirculation method (S/SF). Furthermore, some other indicator dilution techniques, utilizing the dilution of serum potassium (K), glucose, hematocrit (Hct) and hemoglobin (Hb) have been recently described.

METHODS

Aim of the study was to compare some of these tests with the gold standards (the USM and the revised S/SF methods). One hundred-five adult HD patients were selected to participate; all had autogenous radiocephalic wrist arteriovenous fistulas (AVF). Studies included the assessment of AR by means of: A. non-urea based methods: 1. at the start of HD a blood sample was obtained from the arterial needle at the time of needle insertion for the measurement of serum K, Hb and Hct (respectively K1, Hb1 and Hct1). The blood circuit was connected and the pumping of blood was started at 200 mL/min. After 18 seconds, blood samples were drawn from the arterial line sampling port (K2, Hb2, Hct2). At this time, if AR is present, part of the saline entering the blood stream will dilute K2, Hb2, Hct2.AR (%) is =100 x (1 - Hb2/Hb1) in the case of Hb; 2. during the first 30 min USM was performed in triplicate (the blood pump rate was set to 300 mL/min); B. a urea based method: the revised S/SF method was performed at 30 min.

RESULTS

AR was absent when measured by means of the USM; it was absent even when cannulating the patients with the two needles placed as close as possible. AR measured by means of the USM was significantly different from AR measured by means of the other methods (means +/- SD, one-way analysis of variance, p < 0.0001).

CONCLUSIONS

AR in autogenous radiocephalic wrist AVFs was zero when measured by means of the USM; the revised S/SF method and the tests employing the dilution of Hb, Hct and serum K can be considered a valuable alternative to the USM.