The National Kidney Foundation Kidney Disease Outcomes Quality Initiative (NKF KDOQI) guidelines recommend vein mapping prior to access creation secondary to available evidence showing that preoperative vein mapping increases the rate of arteriovenous fistula creation [4, 5]. The American Institute of Ultrasound in Medicine (AIUM) in conjunction with the American College of Radiology (ACR) and Society of Radiologists in Ultrasound (SRU) recently published practice guidelines for the performance of preoperative vein mapping [6]. This formal exam is generally performed within the vascular laboratory and consists of an arterial exam documenting arterial size, aberrant arterial anatomy, calcification, and waveforms throughout the upper extremity and including a modified duplex Allen’s test for assessment of the palmar arch. A venous exam is also performed documenting the depth and diameters of the superficial veins (cephalic and basilic), any stenosis, as well as the phasicity and patency of the more central veins. If no suitable superficial vein is noted, then the diameter of the brachial vein and axillary vein should be documented to determine whether the patient is a candidate for arteriovenous graft (AVG) placement.

Point-of-care ultrasound examinations for preoperative assessment are less detailed and more focused. Localization of aberrant arterial anatomy can be used in both preoperative planning as well as in counseling the patient as to the risk of non-maturation or steal (Fig. 22.2). Similarly, depth assessment may lead to discussion with the patient about the potential need for a secondary procedure such as superficialization. Occasionally, the vascular lab exam is not as complete as suggested by the AIUM. In this case, point-of-care ultrasound can be used to answer focused questions to avoid sending the patient for a second trip to the vascular laboratory. For instance, the forearm basilic vein or the diameter of the brachial vein may not have been examined but may be suitable for arteriovenous fistula creation or graft placement. A patient may have an adequate forearm cephalic vein, but an inadequate upper-arm cephalic vein documented on the formal vein mapping. Point-of-care ultrasound can determine if the patient has a large communicating branch to the basilic vein or to the deep system, which will allow for radiocephalic fistula maturation in this situation or if radiocephalic fistula should not be attempted due to inadequate outflow. The clinic-based point-of-care exam is not intended to replace, but rather complement and supplement the information provided by the formal vein mapping.

Temperature, emotional state, and hydration status may affect measured vein diameter, a critical predictor for fistula maturation [5, 7]. It is also well recognized that regional and general anesthesia increase superficial venous diameter [8, 9]. Preoperative POC ultrasound may lead to an alteration in the operative plan. A POC exam may identify a vein of adequate size not seen or thought to be too small on preoperative vein mapping that can then be used for fistula creation as opposed to placing an arteriovenous graft. The vein diameter and compressibility should be checked throughout the length of the vein in this instance to confirm that the vein is adequate throughout its course into the deep system. The POC exam may also identify a suitable median antecubital branch communicating with either the upper-arm cephalic or the basilic vein. Preoperative identification of this may alter the medial or lateral extent of the antecubital incision necessary for upper-arm fistula creation. Large branch veins close to the arteriovenous anastomosis may also be identified and preemptively ligated to improve fistula maturation.

Occasionally, intraoperative POC ultrasound assessment can be helpful to identify technical problems with a newly created arteriovenous or graft anastomosis or an injury to the arterial system proximal or distal to the site of the newly placed access. For instance, loss of the radial pulse even with compression of the newly created access should prompt an intraoperative duplex exam or other evaluation such as angiography. Similarly, if the patient is noted to have symptoms of hand ischemia immediately postoperatively, especially after arteriovenous graft placement, a high-flow volume (>1400 ml/min) measured within the graft may prompt immediate banding or other revision as opposed to ligation of the access [10].

The Society for Vascular Surgery (SVS) published practice guidelines for hemodialysis access creation and maintenance in 2008 [11]. These guidelines correspond with the NKF KDOQI guidelines for adequate fistula maturation [4]. A mature fistula should have adequate length (ideally > 6 cm) and diameter for cannulation (ideally > 6 mm), a flow rate > 500 ml/min, and be superficial enough to be cannulated with the standard 12 mm long dialysis access needle (generally no deeper than 6 mm below the skin) [4, 11]. Primary failure rates for arteriovenous fistulas, as defined as inability to use the created access successfully for hemodialysis by 3 months after creation, have been reported to be as high as 30–70 % [12]. A recent meta-analysis reported a pooled estimate for primary failure to be 23 %, with increased rates in more recent publication dates [13]. Arteriovenous fistulas have higher patency rates than arteriovenous grafts only when primary failure rates are excluded [14]. Therefore, minimizing primary failure rates by aggressive reintervention in fistulas with marginal maturation is worthwhile [15–19].

POC ultrasound is helpful to assess fistulas with marginal maturation on clinical exam. Fistulas with a minimum diameter of 4 mm and flow rate >500 ml/min by 2 months postoperatively can be expected to have a 95 % chance of being usable for hemodialysis, whereas fistulas with a vein diameter below 4 mm and flow rate <500 ml/min only have a 33 % chance of becoming usable for hemodialysis [11, 20]. Mid-brachial artery flow volume can be used as a surrogate for fistula flow volume, with a brachial artery flow volume > 800 ml/min being associated with 98 % freedom from revision and 600–800 ml/min being associated with 90 % freedom from revision in a recent study. As the brachial artery is easily identifiable, has relatively constant diameter, and can be studied with a more appropriate Doppler angle then the more superficial fistula, a brachial artery flow volume can be performed within 5 min, making it ideal for POC study (Fig. 22.3) [3]. If the POC machine being used does not have the capability to measure flow volumes, a brachial artery diameter ≥ 4.5 mm, PSV > 150 cm/s, and EDV/PSV ratio > 0.4 are associated with a volume flow > 800 ml/min [3]. Figure 22.3 shows the brachial artery volume flow measurement in a young patient with a high-flow fistula.

Flow rates through the fistula increase within 2 weeks of access creation [21], with the increase in vein diameter stabilizing after 2 months [20]. Therefore, it is reasonable to assess fistulas at 4–6 weeks after the creation to determine whether a correctable problem exists that will improve the maturation rate [16]. POC ultrasound is well suited for this purpose, as the common correctable problems are easily identified with ultrasound. Special attention should be paid to the anastomosis and juxta-anastomotic vein as a frequent location of intimal hyperplasia/stenosis. The remainder of the venous outflow should be assessed for size; if it is diffusely small, then balloon-assisted maturation can be considered [22]. Focal stenoses can be treated either with endovascular or surgical angioplasty. Large accessory veins near the arteriovenous anastomosis should also be identified for possible ligation (Fig. 22.4). The depth of the fistula should be assessed to determine if superficialization is necessary. Inadequate arterial inflow is rarely the cause of failure of maturation, especially if the patient had adequate preoperative vein mapping, but should be checked as it may be correctable.

Individually, these problems may be identifiable with clinical exam alone; however, ultrasound is useful to evaluate the entire circuit; this is important as the prevalence of multiple lesions leading to failure of maturation has been reported to be between 34 and 71 % [17, 18]. All problems should be identified prior to revision to avoid failure of revision to lead to a functioning access. For instance, ligation of a large accessory branch will not assist with maturation if a venous outflow stenosis is also present. Clinical judgment is needed to determine whether a point-of-care examination is sufficient or if more formal evaluation of the access is needed via either the vascular lab or angiography. Correction of access-related problems can lead to a significantly higher rate of access maturation [15–19].