**7. Arteriovenous fistulas complications**

Early causes include inflow problems due to small or atherosclerotic arteries, or juxtaanastomotic stenosis, so a preoperative evaluation for suitable access sites has to be performed [187]. Selective use of duplex ultrasonography appears to enhance AVF success rate, although agreed vessels criteria are needed [188]. It seems that the type of anesthesia plays a role in the fistula surgery, with regional anesthesia having a beneficial sympathectomy like effect that causes vasodilation with increased blood flow during surgery and in the AVF postoperatively that may prevent early thrombosis and potentially improve outcome [189], but more evidence are expected to establish this [190].

The etiology of this acquired lesion is not entirely clear but may be related to manipulating the free end of the vein, torsion, poor angulation or loss of the vasa vasorum during anatomic dissection. More often than not, this lesion can be effectively managed with angioplasty [191, 192] or surgical revision [193].

Accessory veins that divert blood flow from the intended superficial vessels to deeper conduits or central venous stenoses due to prior TCs placements may cause outflow problems. Vessels, smaller than one-fourth of the fistula diameter, are usually not hemodynamically relevant. Juxta-anastomotic stenosis and accessory veins are the most common causes for early failure AVFs when preoperative evaluations for suitable access sites have been performed [187]. In elderly population, there is an association of older age, female gender, black race, diabetes, cardiac failure and shorter pre-ESRD nephrology care with predialysis AVF failure [194].

heparin [180]. Nurse is also a key figure in the preventions of such infections with the adoption of standard precautions such as washing hands, managing HD rooms and other medical devices, managing vascular access, and providing educational support to patient [181].

There is conflicting evidence concerning the risk of infection based on the site of insertion [172, 182, 183]. Coagulase-negative staphylococci, *Staphylococcus aureus*, aerobic gram-negative bacilli, and *Candida albicans* most commonly cause catheter-related bloodstream infection. In most cases of nontunneled CVC-related bacteremia and fungemia, the CVC should be removed. The decision should be based on the severity of the patient's illness, documentation that the vascular-access device is infected, assessment of the specific pathogen involved and presence of complications, such as endocarditis, septic thrombosis, tunnel infection, or

Overall, compared with the subclavian vein, the internal jugular vein remains the preferred access site in ambulatory patients. In the intensive care unit, either femoral or internal jugular vein placement is satisfactory, with the use of ultrasound making internal jugular vein

The best solution is to prevent the infection by proper placement technique, optimal exit site care and management of the catheter within the HD facility [46, 185]. It is generally believed that CVC can adversely affect permanent VA ipsilateral placement outcomes due to central vein stenosis that they cause, but it seems that the primary failure rate of AVF and AVG is not affected by the presence of an ipsilateral catheter, but cumulative access

Early causes include inflow problems due to small or atherosclerotic arteries, or juxtaanastomotic stenosis, so a preoperative evaluation for suitable access sites has to be performed [187]. Selective use of duplex ultrasonography appears to enhance AVF success rate, although agreed vessels criteria are needed [188]. It seems that the type of anesthesia plays a role in the fistula surgery, with regional anesthesia having a beneficial sympathectomy like effect that causes vasodilation with increased blood flow during surgery and in the AVF postoperatively that may prevent early thrombosis and potentially improve outcome [189], but more evidence

The etiology of this acquired lesion is not entirely clear but may be related to manipulating the free end of the vein, torsion, poor angulation or loss of the vasa vasorum during anatomic dissection. More often than not, this lesion can be effectively managed with angioplasty [191,

Accessory veins that divert blood flow from the intended superficial vessels to deeper conduits or central venous stenoses due to prior TCs placements may cause outflow problems. Vessels, smaller than one-fourth of the fistula diameter, are usually not hemodynamically relevant. Juxta-anastomotic stenosis and accessory veins are the most common causes for early failure

metastatic seeding [184].

survival is inferior [186].

are expected to establish this [190].

192] or surgical revision [193].

**7. Arteriovenous fistulas complications**

placement safer.

260 Updates in Hemodialysis

A rather rare complication secondary to bleeding from a catheter-related puncture of an AVF is an acute forearm compartment syndrome [195].

Venous stenosis, thrombosis and attained arterial lesions like aneurysms or stenoses constitute late causes of AVFs' failure.

As blood flow decreases due to venous stenosis, weekly Kt/V ([dialyzer clearance time]/body volume) decreases and/or recirculation increases, constituting great clinical signs of VA dysfunction. AVF salvage surgery is of paramount importance in order to increase the patency rate, which prolongs survival and increases the patient's quality of life [196]. Balloon angio‐ plasty followed with stenting maintains the vessel lumen shape over time, as the stent is likely to reduce the risk of restenosis that can otherwise occur after balloon angioplasty because of the viscoelastic recoil of the vessel [197]. According to Aftab et al. [198], for AVF stenosis resistant to conventional percutaneous transluminal angioplasty (PTA), cutting balloon angioplasty may be a better second line treatment given its superior patency rates. It seems that the deficiency of circulating endothelial progenitor cells is associated with early and frequent restenosis after angioplasty of HD VA [199].

Native fistulas will not typically thrombose until flow is severely diminished. The thrombec‐ tomy of fistulas, although technically more challenging than in AVGs, is often successful and if flow is reestablished, primary patency is longer than in grafts [200]. Antiplatelet treatment protects fistula from thrombosis or loss of patency but has little or no effect on graft patency and uncertain effects on vascular access maturation for dialysis and major bleeding [201]. Elective repair of subclinical stenosis in AVFs with blood flow >500 ml/min cost-effectively reduces the risk of thrombosis and access loss [202]. Reconstructing the AVF by surgically removing venous neointimal hyperplasia is an effective technique for late hemodialysis access failure which preserves patients' vessels [203].

As AVF's size increases over time with increased blood flow, aneurysms may be formed, constituting rather a cosmetic than functional concern, unless stenotic lesions accompany them. If the overlying skin is atrophic or blanching, or there are signs of ulceration or bleeding, a surgical evaluation must be performed urgently [204]. Also, if there is a high association of venous outflow stenosis and AVF aneurysms, comprehensive therapy should encompass treatment of any venous outflow stenosis before open AVF aneurysm repair. A two-stage repair may decrease tunneled HD catheter use in patients with multiple aneurysms [205]. In order to maintain an autogenous access while conserving future dialysis sites, partial aneur‐ ysmectomy is recommended as a first-line choice for managing aneurysm associated compli‐ cations [206]. Also, autologous surgical reconstruction is feasible in the majority of AVF aneurysms. It preserves fistula function and keeps the advantages of an autogenous access [207]. The rupture of such aneurysms in high-flow fistulas can lead to exsanguination and death (Figure 14).

**Figure 14.** Aneurysm in forearm AVF.

Infections of AVFs are rare but must be treated properly due to patients' impaired immuno‐ logic status. Very rare infections of the AV anastomosis require surgery with resection of the infected tissue. More often, infections occur at cannulation sites and then the arm should be rested and cannulation cease [208]. In all cases of AVF infection, antibiotic therapy is initiated with broad-spectrum vancomycin plus an aminoglycoside and converting to appropriate one based on results of culture and sensitivities. Infections of primary AVFs should be treated for a total of 6 weeks, analogous to subacute bacterial endocarditis [209].
