**2. Anatomical considerations**

VA can be divided in to three types:

Arterio venous fistula (AVF), where anastomosis is surgically formed between artery and vein.

Arterio venous Graft (AVG), where a graft made of poly tetrafluoroethylele (PTFE) is placed between artery and vein.

Central venous catheters (CVC), where a double lumen tube is placed within the central vein usually terminating at or within the right atrium.

The upper extremities are most commonly used for VA. AVF or AVG is made by connecting a vein with artery or interposition of synthetic graft between them which provides a high flow circuit for percutaneous cannulation for hemodialysis. A mature AVF is better than AVG in given higher patency rates, lesser infection chances and reduced maintainace. Generally, the upper limb is used to create such communication. The Non dominant upper limb is the first choice to facilitate daily activities with

**Figure 1.** *Upper limb vascular anatomy (a) and (b) various types of AVF [3, 4].*

*Hemodialysis AV Fistula: What a Radiologist Should Know? DOI: http://dx.doi.org/10.5772/intechopen.100485*

dominant limb while providing adequate time to VA for maturation. Usually, AVF is considered in forearm to preserve the proximal vessels for future if required. Likewise, AVG is preferred in non dominant arm rather than forearm. AVF can be created through a surgical anastomosis between vessels where both the vessels may be in their normal position or the distal end of vein may be transpositioned more superficially to facilitate cannulation, while in Translocation, the entire vein is moved and anastomosis is done.

So, the preferred type and sites of anastomosis would be - forearm AVF > arm AVF > arm AVG > thigh AVG in respect to available vessels.

The most preferred type of AVF which is *Radio-cephalic fistula* made in forearm near wrist can also fail to mature in elder patients with underlying vascular or diabetic etiology [2]. *Brachio cephalic AVF* is usually made in antecubital fossa providing benefits of ease of cannulation due to larger surface area (**Figure 1**) [3, 4]. However it poses a major complication – steal syndrome (*will be discussed later*). As basilic vein is less commonly accessed for venipuncture, it is usually better preserved and is less commonly involved in post venipuncture phlebitis in comparison to cephalic vein. However, Brachio-basilic AVF in arm involves dual surgical procedure, difficult to cannulate due to medial location of basilic vein and more prone to infections.

Central venous catheters (CVC) provide short term access in emergency conditions, but they are associated with higher rates of failure, infection and mortality. Patients switching to AVF or AVG from CVCs have almost 50% reduction in mortality [5]. Moreover, previous CVC placement poses a risk of central venous stenosis due to endothelial injury and thrombosis caused by them.

## **3. Role of radiology**

According to Dialysis Outcome Quality Initiative (DOQI) guidelines, AVF is preferred over AVG due to its greater lifespan and reduced incidence of infection. Detailed imaging of vascular anatomy prior to AVF creation provides good evaluation of veins that may be suitable for the creation of AVF, particularly in patients with previous failed AVF and/or history of CVC placement. Detailed preoperative imaging helps the surgeon to choose suitable efferent vein and surgical technique (in the form of AVF or AVG and transposition or translocation in AVF). Also, it helps to select the most functional vein which helps in decreasing postoperative failure and complications (**Figure 2**). However, a considerable number of AVFs fail to mature and in those patients, Ultrasonography can evaluate the etiology of immaturity. If the exact etiology is known, the role of Intervention (angioplasty of a stenosis) or Surgery (AVF revision or accessory vein ligation) can be cleared. VAs are commonly imaged by Ultrasonography and color doppler study (CDI); however other modalities like DSA, MRI and CT scan can also be used as and when necessary. But, we will focus on various aspects related to Ultrasonography and color doppler study in pre and postoperative imaging of VAs. Catheters in situ, overlying dressing, open wounds, Severe Edema and hematoma can hinder the visibility in USG.

#### **Figure 2.**

*Gray mode USG image showing minimal intimal wall thickening and multiple tiny flecks of calcification within the wall of brachial artery.*

#### **3.1 Preoperative evaluation of AVF/AVG**

High resolution linear transducer (≥ 9 MHz) is used for vascular mapping. For ease of description, vessels towards shoulder will be considered proximal and towards the wrist will be considered distal vessels. The scanning is done at room temperature to avoid vasoconstriction in cooler temperature. Warm blankets or warm compression can be used if necessary. The patient should be relaxed and rested in sitting or supine position whichever is comfortable with proximal tourniquet binding. The non dominant arm is assessed first and is placed in extended position along his sides or on any support (like pillow) according to patient's position. The upper limb should be abducted and externally rotated for better visualization.

B mode axial plane imaging is ideal for evaluating vascular anatomy and to evaluate their diameter as well as wall thickness. Arteries are evaluated for presence of any intimo-medial thickening, wall calcification or stenosis. Presence of calcification in arterial wall hinders its distensibility and may contribute towards dysfunction (**Figure 3**). Veins are evaluated for compressibility (denoting to patency) and the depth of anterior venous wall from the level of skin. Color doppler study of arteries evaluates color filling of lumen and excludes luminal narrowing or thrombosis. Spectral waveform excludes any distal occlusion or vascular disease. Color doppler study of veins evaluates venous phasicity and respiratory variations.

Usually the imaging is started from Radial artery. The vessel wall and internal diameter of radial artery at forearm are assessed. If the diameter is not at least 2 mm at wrist, the radial artery is not used for creation of AVF. If the radial artery is satisfactory, cephalic vein at wrist is evaluated. Brachial artery is also evaluated for possible

*Hemodialysis AV Fistula: What a Radiologist Should Know? DOI: http://dx.doi.org/10.5772/intechopen.100485*

#### **Figure 3.**

*(a) Gray mode image showing brachial artery at elbow with internal lumen diameter 3.2 mm, (b) CDI study showing normal color flow with triphasic waveform.*

arm fistula placement. All the peripheral arteries show Triphasic waveform on CDI study (**Figure 4**). For evaluation of cephalic vein at wrist, tourniquet is tightened in proximal forearm and the distal limb is percussed for about 3 minutes. The main idea behind tourniquet and percussion is that the veins capable of distending up to 2.5 mm will be preferred for AVF due to their distensibility during higher venous pressures. Veins with diameter smaller than 2 mm will not distend up to adequate diameter in most cases. Cephalic vein is then assessed for continuity up to proximal forearm and if its adequate, then the tourniquet is shifted to a more proximal level. If the cephalic vein is narrow in caliber, discontinuous, stenotic or shows thrombus or thick wall, it is not adequate for AVF creation. Branch points must be thoroughly imaged, as they may show narrowing below 2.5 mm in veins. After the forearm is assessed, the vein should be traced up to axilla to evaluate the sites of deep venous communication. Evaluation of neck veins should also a routine practice in upper limb mapping as any abnormality in neck veins can contribute to future AVF failure. If cephalic vein is not adequate for AVF, basilic vein is assessed in the same manner (**Figures 5** and **6**).

If forearm vessels are not promising for wrist AVF creation, AVF at elbow is considered and brachial artery is imaged. Brachial artery internal diameter is measured above its bifurcation in to radial and ulnar arteries, which must be ≥2 mm. The cephalic vein is then assessed at antecubital fossa. Cephalic vein must be at least 2.5 mm in diameter and must extend about 2 cm distal to antecubital fossa. If cephalic vein is not suitable, basilic vein is considered and it must extend to about 4 cm proximal to antecubital fossa for AVF formation. Chronically thrombosed cephalic vein is a very frequent finding in ESRD patients due to frequent venipuncture. Cephalic vein appears narrow with thick walls and appears cord like with no internal color flow in such cases (**Figure 7**). However, sometimes median cubital vein may also be used as

### *Multidisciplinary Experiences in Renal Replacement Therapy*

#### **Figure 4.**

*(a) Gray mode image showing narrow Cephalic vein in forearm with internal lumen diameter 1.8 mm and depth from skin level measuring about 4.7 mm and (b) patent lumen on color doppler study.*

#### **Figure 5.**

*(a) Gray mode image showing basilic vein at elbow with internal lumen diameter 2.8 mm and depth from skin level measuring about 5.0 mm, (b) CDI study showing normal color flow, (c) gray scale image showing normal median cubital vein in cubital fossa.*

*Hemodialysis AV Fistula: What a Radiologist Should Know? DOI: http://dx.doi.org/10.5772/intechopen.100485*

**Figure 6.** *Gray mode image showing chronically thrombosed narrow cord like Cephalic vein (\*).*

**Figure 7.** *(a) Gray mode image showing AVF (b) CDI study showing normal aliasing color flow within the AVF.*

an alternative as it courses close to brachial artery. In any case, considerable length of patent vein is needed for the surgical procedure as well as during dialysis.
