In the April 2005 issue of Nephrology Dialysis Transplantation, Brunori et al. [1] and Saran et al. [2] expressed personal opinions about the proper timing of first cannulation of haemodialysis arteriovenous fistulae (AVFs): the former stressed once more the importance of waiting for a given time period between the creation of the AVF and its first cannulation [1]; the latter were more flexible about this issue, underlining the need for a proper assessment prior to first cannulation, e.g. by objective techniques, such as Doppler ultrasound [2]. The cause of the discrepancy in these personal opinions certainly lies in the unsatisfactory NKF-K/DOQI guidelines on this issue: if, on the one hand, they recommend the monthly surveillance of blood flow rate (Qb) of the vascular access by means of saline ultrasound dilution, conductance dilution, thermal dilution, Doppler ultrasonography and other techniques, paradoxically, on the other hand, the maturation of an AVF is still committed to a clinical assessment [3]. Clinically, there are some AVFs that are obviously mature. These clinically mature AVFs usually have an easily palpable, relatively straight and >10 cm long superficial vein, which is of adequate diameter and with a uniform thrill to palpation [4]. The real problem in clinical evaluation is in predicting the ultimate outcome of those AVFs that are not clearly mature. Thus, the ability to predict whether an AVF is going to mature eventually is important.
Therefore, we conducted a feasibility study aimed at developing objective quantitative criteria in order to evaluate AVF maturity prior to first cannulation [5]. Our choice fell on duplex Doppler ultrasonography of the brachial artery feeding the radio-cephalic wrist AVF, because the brachial artery has been suggested to be the best site for the evaluation of Qb of an AVF [6]. Brachial artery Qb was measured just before AVF construction and uniformly 1, 7 and 28 days afterwards in 18 incident uraemic patients [5]. Brachial artery Qb was 56.1±19.2 ml/min at baseline. A new AVF was constructed in that patient whose brachial artery Qb was 80.0 ml/min at day 28. When excluding this AVF, the mean brachial artery Qb of the 17 AVFs was 720.4±132.8 ml/min (median 750, range 480890) at day 28. When analysing the percentage increase in brachial artery Qb of the 17 AVFs at the different time points, the most dramatic increase occurred at day 1 compared with baseline (549.0%; mean Qb at day 1 = 365.0±129.3 ml/min). Thus, the Qb at day 1 represents already more than half (50.7%) of the Qb which will be measured at day 28. The first cannulation occurred 56.2±12.1 days after the creation of the AVFs; the mean brachial artery Qb of the 17 AVFs was 997.6±259.7 ml/min 258.0±63.0 days after AVF creation [5].
There are at least two other reports that drew conclusions quite similar to ours: Robbin et al. measured Qb at the level of the draining vein within 4 months after AVF placement [4]. AVF adequacy for dialysis was nearly doubled if Qb was 500 ml/min (84%) vs <500 ml/min (43%) [4]. Interestingly enough, no significant difference in Qb was found during 24 post-operative months, thus allowing the authors to suggest that measurements obtained at 48 weeks can be used to predict AVF outcome [4]. Furthermore, Wong et al. performed measurements at the level of the cephalic vein and radial artery pre-operatively, and at the level of the cephalic vein, radial artery and the anastomotic region at day 1, and at 2, 4, 6 and 12 weeks post-operatively [7]: most of the increase in Qb occurred at day 1; individual AVF Qb did not increase substantially at the 4, 6 and 12 week time points when compared with the 2 week time point [7]. Finally, the mean Qb at the level of the cephalic vein was 710±318 ml/min at the 12 weeks time point and was roughly the same both at the 4 and 6 week time points [7].
To summarize, we share the conclusions drawn by Saran et al., with the addition of the following personal opinions (expressed in italics):
Conflict of interest statement. None declared.
Division of Nephrology Miulli General Hospital Acquaviva delle Fonti Italy Email: basile.miulli{at}libero.it
References
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