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Nephrol Dial Transplant (2004) 19: Editorial Comments

Nephrol Dial Transplant (2004) 19: 1956–1963 DOI: 10.1093/ndt/gfh244 Advance Access publication 15 June 2004

Colour Doppler ultrasound in dialysis access Patrick Wiese and Barbara Nonnast-Daniel Department of Medicine IV, Nephrology, University Erlangen-Nuernberg, Germany

Keywords: access stenosis; access thrombosis; colour Doppler ultrasound; hemodialysis; steal syndrome; vascular access

addition, CDU offers the advantage of a non-invasive bedside procedure with lower costs and with no need for radiocontrast. The aim of this article is to provide an update on CDU and to give some new information on preoperative evaluation and routine monitoring.

Introduction The native arteriovenous fistula (AVF) at the wrist [1] is generally accepted as the vascular access of choice in haemodialysis patients due to its low complication and high patency rates [2]. However, with an increasing number of elderly patients and patients with co-morbid conditions such as vascular disease and diabetes mellitus in the haemodialysis population, the creation and maintenance of a patent and well-functioning AVF has become a real challenge to nephrologists and vascular surgeons [3]. The DOQI guidelines state that creation of a primary AVF is possible in only 50% of the patients [4]. Therefore, in the US, synthetic polytetrafluoroethylene (PTFE) grafts are still the predominant form of permanent vascular access [5,6], despite the well known poorer outcome compared to AVFs [4,6,7]. To further increase the use of native AVFs, especially in the co-morbid patient group, a thorough preoperative evaluation with colour Doppler ultrasound (CDU) and mapping of the arterial and venous vascular system allows the placement of an AVF in a higher proportion of patients [8,9] and to achieve a better cumulative patency rate of fistulas [10]. After creation of access, periodic monitoring is recommended, since early detection of access dysfunction and subsequent intervention may help to reduce the rate of access failure [11,12]. Although angiography has been considered as the gold standard for imaging of vascular access abnormalities, duplex ultrasound may be superior in some aspects since it provides information both on the morphology and on the function of vascular access. In Correspondence and offprint requests to: P. Wiese MD, Department of Medicine IV, University Erlangen-Nuernberg, Klinikum Nuernberg, Breslaver Strasse 201, D-90471 Nuernberg, Germany. Email: [email protected]

Preoperative vascular evaluation Clinical criteria for the selection of veins and arteries for the successful placement of an AVF include a visible cephalic vein after tourniquet placement, a superficial course of the vein, absence of tortuous veins, an easily palpable radial pulse, a patent palmar arch (Allen’s test) and the absence of significant pressure differences (
20 mmHg) between both arms [13]. A more detailed identification of suitable upper extremity vessels to guide the surgeon is provided by preoperative vascular mapping using a linear CDU scanner with a 7.0 MHz imaging/5 MHz Doppler probe or higher. The patient should be studied in a supine position without angling of the elbow joint to avoid compression of the vessels under investigation. Both the superficial and the deep venous system of the left and right arm can be examined from the wrist to the central veins (that is axillary or distal subclavian vein) if this is technically possible. Silva et al. [10] identified certain sonographic criteria for the examination of veins before placement of a vascular access. Using a tourniquet, a venous luminal diameter of
2.5 mm is required for placement of an AVF and a diameter of
4.0 mm for grafts. Further criteria are the absence of segmental stenoses or occluded segments and a continuity with the deep venous system in the ipsilateral upper arm. In ultrasound measurements without the use of a tourniquet a minimal diameter of the cephalic vein of >2.0 mm results in a significantly higher proportion of well-matured fistulas [13]. The non-visualized part of the central veins can only be indirectly assessed sonographically by Doppler waveform analysis. Disturbances in respiratory venous filling, such as a missing increase of venous flow during deep inspiration, may point at a stenosis of

Nephrol Dial Transplant Vol. 19 No. 8 ß ERA–EDTA 2004; all rights reserved

Nephrol Dial Transplant (2004) 19: Editorial Comments

the central venous system. Although CDU is a valuable and accurate screening tool for detection of such lesions [14], phlebography or magnetic resonance venography might be considered if central vein stenosis is suspected. In elderly patients and patients with co-morbid conditions, e.g. diabetes or vascular disease, arterial problems with reduced arterial diameter and poor arterial flow become more important. Arterial wall calcifications can be detected well by ultrasound, which shows hyperechogenicity and wall irregularities. While these changes of wall structure influence outcome, they are difficult to quantify. Many authors postulate an arterial diameter
2.0 mm and a peak systolic velocity of at least 50 cm/s for AVF placement [10,15]. For a precise calculation of the vessel diameter, we recommend measuring the arterial lumen from inner edge to inner edge by a B-mode or M-mode technique. Using this method, Malovrh [16] demonstrated a significantly increased risk of AVF failure when the internal diameter of the radial artery was 1.6 mm. The feeding arteries dilate during access maturation. Consequently, it is obvious that not only the initial diameter but also the arterial compliance affect access outcome. The distensibility of the arterial wall can be assessed preoperatively by evaluating the Doppler waveform in the radial artery during reactive hyperaemia, induced by reopening a fist that was clenched for 2 min. The high-resistance triphasic Doppler ultrasound signal with clenched fist (regular signal of

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peripheral arteries) changes to a low-resistance biphasic waveform after releasing the fist (Figure 1) and the resistance index (RI) at reactive hyperaemia can be calculated using the formula ðpeak systolic flow velocity  end diastolic flow velocity) =peak systolic flow velocity ¼ RI: A preoperative RI of
0.7 in the feeding artery after release of the fist indicates that arterial blood flow will not increase sufficiently so that the chance of successful creation of an AVF is reduced [16]. We recommend preoperative screening to exclude an inappropriate response to reactive hyperaemia. This manoeuver is especially helpful in planning the location of the initial operation, i.e. selecting the wrist/forearm or elbow region. Table 1 summarizes the preoperative CDU criteria for the selection of suitable arteries and veins that predict AVF outcome.

Table 1. Preoperative colour Doppler ultrasound criteria for AVF outcome Arterial luminal diameter >1.6 mm (internal diameter) Venous luminal diameter >2.0 mm (without use of a tourniquet) Arterial resistance index 60 years and diabetes mellitus [38]. The steal syndrome is characterized by pain at rest, pain during haemodialysis sessions, ulcerations, mostly acral necrosis and even tissue loss. The challenge is to identify patients at high risk for an access-induced ischaemic steal syndrome by CDU prior to creation of the fistula. Preoperative investigation comprises assessment of flow patterns and the diameter of the brachial, radial and ulnar arteries to detect stenoses or occlusions. The Doppler spectrum, especially at reactive hyperaemia (Figure 1), is useful to predict the risk of low flow steal. Absent or low diastolic flow correlates with impaired capacity of the palmar arch arteries to vasodilate. Postoperative investigation comprises assessment of the access-feeding artery by investigating the parts proximal and distal to the anastomosis. The direction of flow is very easy to demonstrate by pw- or colour Doppler. If colour or spectral Doppler ultrasound show a change in flow direction, a steal situation is documented (Figure 5). Acknowledgements. We would like to thank Professor E. Ritz for having reviewed this editorial and given his suggestions and approval. Conflict of interest statement. None declared.

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