Vascular Access for Dialytic Therapies

C H A P T E R

87

 

Vascular Access for Dialytic Therapies Jan H. M. Tordoir

Functional vascular access is needed for all extracorporeal dialytic therapies and remains the lifeline for patients with endstage renal disease who need chronic intermittent hemodialysis (HD) therapy. The ideal HD access should have a long length of a suitable superficial vein for cannulation in two places more than 5 cm apart with a sufficient blood flow for effective dialysis, usually in excess of 400 ml/min. A vascular access should have good primary patency, have a low risk of complications and side effects, and leave opportunities for further procedures in the event of failure. Ideally, a first access should be an arteriovenous (AV) fistula placed peripherally at the wrist. However, upper arm and lower limb access sites are increasingly used because the aging dialysis population, with multiple comorbidities, has poor and diseased arm vessels that may be unsuitable for the creation of a simple wrist fistula. Vascular access should be performed with minimal delay by a surgeon experienced in vascular access creation and, wherever possible, in advance so that dialysis may start with permanent access rather than with use of a central venous catheter. Central venous catheter use should be minimized because of the increased risk of sepsis, the increased mortality, and the development of central venous stenosis or thrombosis, which compromises further access in the upper limbs. Unfortunately, many patients require a central venous catheter either to start dialysis or as a bridge between the failure of a permanent access and the creation of a new AV fistula.1 The need for revisional procedures because of access-related complications, including thrombosis, central venous obstruction, and ischemia, is increasing. A multidisciplinary approach to access creation and maintenance, involving nephrologists, interventional radiologists, access surgeons, and dialysis nurses, is mandatory to meet the burden of HD vascular access on health care facilities and costs.

EVALUATION OF THE PATIENT FOR VASCULAR ACCESS The earlier a patient with chronic kidney disease (CKD) is seen by a vascular access surgeon, the better the chance for the patient to have a well-functioning access at the initiation of HD. An early decision on the type, side, and site of the first vascular access will be based on the following: n Clinical examination with careful palpation of arterial pulses and venous vasculature. Particular attention is paid to the venous filling capacity, with use of a blood pressure cuff and variable pressures, and to the presence of venous

collaterals and swelling. The dominant arm is not necessarily the preferred side, and the decision should be based on the quality of the vessels. n Vascular mapping by Doppler ultrasound. This provides information about the venous vasculature, particularly in obese patients and in the upper arm, and about the diameter of the brachial, radial, and ulnar arteries; detects vascular calcifications; and reveals the blood flow volume in the brachial artery. The resistance index, a measure of arterial compliance, can be calculated from the differences between the high-resistance triphasic Doppler signal with clenched fist and the low-resistance biphasic waveform after the fist is released. A preoperative resistance index of 0.7 or higher in the feeding artery indicates insufficient arterial compliance (often associated with arterial calcification) so that the chance of successful creation of an AV fistula is reduced. Current guidelines recommend ultrasound mapping in all patients. Additional angiography is needed only in very difficult cases; the use of radiocontrast media should be minimized. Preservation of veins during the earlier stages of CKD is crucial for the success of vascular access. Patients should be instructed to protect their veins, restricting blood sampling to the dorsum of the hand whenever possible.

PRIMARY AUTOGENOUS VASCULAR ACCESS Radiocephalic AV Fistula A well-functioning distal radiocephalic AV fistula in the nondominant arm is the ideal permanent access for HD. This usually gives an adequate blood flow and a long length of superficial vein for needling. It also leaves proximal sites for further procedures in the event of failure. A distal radiocephalic AV fistula should be possible in a majority of incident patients but may be compromised if the cephalic and antecubital fossa veins are unusable because of thrombophlebitis from previous intravenous cannulae or venipunctures. For this reason, it is essential that these veins be avoided for intravenous cannulae, which should be restricted to the dorsum of the hand in all patients with CKD, except in the emergency situation when rapid access to the circulation is required. A radiocephalic AV fistula is usually created at the wrist (Fig. 87.1) but can be performed more proximally in the forearm if distal vessels are inadequate. On occasion, three or four radiocephalic AV fistulas can be created at progressively more proximal sites in the forearm before resorting to a brachiocephalic AV 1031

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fistula. The radiocephalic AV fistula at the wrist was initially described by Brescia and Cimino in 1966 as a side-to-side anastomosis, but an end-to-side configuration is preferred by most to reduce the risk of venous hypertension in the radial aspect of the hand. An end-to-end anastomosis is advocated by some surgeons to eliminate the small risk of steal. The primary patency of radiocephalic fistulas varies from center to center, but recent publications report high primary failure rates varying from of 5% to 41% and 1-year primary patencies from 52% to 71% (Fig. 87.2).2-7 Early thrombosis and nonmaturation of an AV fistula in the older comorbid population, who have poor upper limb vessels, are the major causes of these high primary failure and low patency rates. The patency of radiocephalic AV fistulas is poorer in women, so a proximal AV fistula might be preferable if the cephalic vein or radial artery is small. Nonmaturation of Radiocephalic AV Fistula The autogenous radiocephalic AV fistula needs time to mature and for the vein to enlarge to a size at which it can be needled for dialysis. Usually 6 weeks for maturation is advised. Earlier cannulation can damage the thin veins. Nonmaturation rates vary from 25% to 33%. The essential components of a successful AV fistula are a sufficient vein diameter of 4 to 5 mm for needling and a high blood flow so that blood can be drawn from the fistula at between 300 and 400 ml/min. In reality, this requires a fistula flow of about 600 ml/min to prevent excessive recirculation and to permit adequate dialysis within the usual 4-hour time

Standard Radiocephalic AV Fistula at the Wrist Cephalic vein

Radial artery Figure 87.1  Standard radiocephalic AV fistula at the wrist. Anastomosis of end of vein to side of artery.

frame of a HD treatment. Fistulas that fail immediately are the consequence of poor selection of vessels or poor technique. Regular duplex ultrasound investigation early after AV fistula formation, especially in fistulas that are not maturing, can detect poor flow, stenosis, and accessory branches, guiding the interventional radiologist and surgeon to the appropriate treatment.

SECONDARY AUTOGENOUS VASCULAR ACCESS Although a primary radiocephalic AV fistula is preferable, the first-choice procedure is increasingly an upper arm AV fistula with use of an autogenous deeply located arm vein, especially in the dialysis population with associated comorbidities such as diabetes mellitus, coronary artery disease, and peripheral arterial occlusive disease.1 The upper limb is preferred to the lower limb for vascular access because of the ease of cannulation, comfort for the patient, and considerably lower incidence of complications. Similarly, autogenous conduits are preferable to the use of prosthetic grafts because of improved patency and lower risk of infection.

Forearm Cephalic and Basilic Vein Transposition and Elevation Superficial vein transposition or elevation increases the possibilities of creating a forearm fistula. The cephalic vein is preferred, but if it is unsuitable, the basilic vein can be transposed from the ulnar to the radial side along a straight subcutaneous course from the elbow to the radial artery. Alternatively, a basilic vein to ulnar artery anastomosis can be performed with additional volar transposition to facilitate needling for dialysis. Different surgical techniques, with or without transposition, have been advocated according to the forearm artery and vein location. In one study,8 91% fistula maturation was achieved with a range of techniques; 15% were suitable for a straightforward AV fistula, 33% required vein transposition from dorsal to volar for anastomosis to the appropriate artery, and the remaining 52% required superficial transposition of a vein on the volar aspect of the forearm before arterial anastomosis. Primary patency rates were 84% at 1 year and 69% at 2 years. Needle cannulation may be difficult, particularly in obese patients. A forearm cephalic vein that is too deeply located may be made accessible for cannulation by transposition or elevation. In one study, the elevation technique was applied in obese patients with radiocephalic AV fistulas and cannulation difficulties; primary failure rate was 15%, with a 1-year patency rate of 84%. After operation, all patients could be successfully cannulated for dialysis.9

Early Failure and 1-Year Patency Rates of Radiocephalic AVF

Figure 87.2  Early failure and 1-year patency rates of radiocephalic AV fistulas.

Author

Year

No. Fistulae

Early Failure (%)

1-Year Patency (%)

Wolowczyk et. al.

2000

208

20

65

Gibson et. al.

2001

130

23

56

Allon et. al.

2001

139

46

42

Ravani et. al.

2002

197

5

71

Roijens et. al.

2005

86

41

52

Biuckians et. al.

2008

80

37

63



CHAPTER

Elbow and Upper Arm Cephalic Vein AV Fistula The brachiocephalic and antecubital fistulas are two possible AV anastomoses in the elbow region. In addition, anastomosis between the transposed cephalic vein and brachial artery 2 cm proximal to the elbow may be executed, which provides an optimal situation for cannulation along the cephalic vein (Fig. 87.3). The outcome of the brachiocephalic AV fistula is usually good, with a high primary function rate and good long-term patency; studies showed a 10% early failure rate due to nonmaturation and an 80% 1-year patency rate.10,11 Two-year primary, assisted primary, and secondary patency rates were 40%, 59%, and 67%, respectively. (Primary patency is functioning access without any intervention; assisted primary patency is functioning access after preemptive intervention for flow decline; secondary patency is functioning access after intervention for thrombosis.) Predictors of failure include diabetes mellitus and a history of contralateral forearm AV graft (indicating poor vessels). Therefore, the primary patency of brachiocephalic fistulas is

87  Vascular Access for Dialytic Therapies

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comparable to that of radiocephalic fistulas. The early failure and 1-year patency rates of brachiocephalic AV fistulas are shown in Figure 87.4.10-14

Upper Arm Basilic Vein AV Fistula The upper arm basilic vein is usually inaccessible for dialysis cannulation because of its medial and deep position. Therefore, the basilic vein needs to be superficialized and transposed to an anterolateral position. The original technique of brachiobasilic AV fistula construction is a two-step approach. First, a brachiobasilic anastomosis is constructed, and in the second operation, usually after 6 weeks, the arterialized vein is mobilized into a subcutaneous position, becoming accessible for needling (Fig. 87.5); nowadays, the brachiobasilic AV fistula may be performed as a one-stage surgical procedure, with elevation or transposition of the vein to a subcutaneous and anterolateral position at the time of creation of the AV anastomosis. A nonrandomized study comparing the different techniques of brachiobasilic AV fistula

Options for the Creation of Elbow AV Fistulas

Median cubital vein

Accessory cephalic vein

Basilic vein Perforating vein

Cephalic vein

Figure 87.3  Options for the creation of elbow AV fistulas. A, Brachiocubital AV fistula. B, Brachiocubital AV fistula with ligation of proximal cubital vein. C, Brachiocephalic AV fistula.

B

Brachial artery

C

A

Early Failure and 1-Year Patency Rates of Brachiocephalic AVF Author

Year

No. Fistulae

Early Failure (%)

1-Year Patency (%)

Murphy et. al.

2002

208

16

75

Zeebregts et. al.

2005

100

11

79

Lok et. al.

2005

186

9

78

Woo et. al.

2007

71

12

66

Koksoy et. al.

2009

50

10

87

Figure 87.4  Early failure and 1-year patency rates of brachiocephalic AV fistulas.

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Transposed Brachiobasilic AV Fistula

Figure 87.5  Transposed brachiobasilic AV fistula. A, Dissection of the basilic vein. B, Anterolateral transposition and brachial artery anastomosis.

Basilic vein Median cubital vein

A

Basilic vein

Brachial artery

B

Early Failure and 1-Year Patency Rates of Brachiobasilic AVF

Figure 87.6  Early failure and 1-year patency rates of brachiobasilic AV fistulas.

Author

Year

No. Fistulae

Early Failure (%)

1-Year Patency (%)

Segal et. al.

2003

99

23

64

Wolford et. al.

2005

100

20

47

Harper et. al.

2008

168

23

66

Keuter et. al.

2008

52

2

89

Koksoy et. al.

2009

50

4

86

creation reported 86% to 90% 1-year patencies in all groups, with only 5% to 7% nonmaturation rates.15 Primary failure rates of 2% to 23% with 1-year patencies varying from 55% to 89% have been reported (Fig. 87.6).12,16-19 In comparison with brachiocephalic fistulas, brachiobasilic AV fistulas are more likely to mature, although they are more susceptible to late thrombosis. However, a randomized study showed similar patencies of brachiocephalic and brachiobasilic AV fistulas.12 The technique of subcutaneous placement of the basilic vein has several advantages over forearm or upper arm graft implan­ tation, with less infection and thrombosis. A meta-analysis

comparing brachiobasilic AV fistulas with prosthetic grafts has shown superiority of the brachiobasilic AV fistula in primary and secondary patency rates, and it should therefore be used early in difficult access cases before the use of prosthetic grafts.20

NONAUTOGENOUS PROSTHETIC VASCULAR ACCESS When autogenous AV fistula creation is impossible or the fistulas have failed, graft implantation should be considered as a vascular



CHAPTER

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Non-Autogenous Prosthetic Graft (PTFE) Vascular Access

Brachial vein

Brachial artery

Cephalic vein

Axillary artery PTFE

Axillary vein

PTFE Axillary artery

Radial artery

PTFE

PTFE

Ulnar artery

Figure 87.7  Nonautogenous prosthetic graft (PTFE) vascular access. Straight and loop configuration in upper limb.

access conduit. Xenografts such as the ovine sheep (Omniflow) and bovine cow ureter graft (SynerGraft) are popular materials as an alternative access conduit, with acceptable patency and low infection rates. The most frequently used implants are prosthetic grafts made of either polyurethane (Vectra) or polytetrafluoroethylene (PTFE). These prosthetic grafts can be implanted in a wide variety of locations and configurations in the upper limb (Fig. 87.7). Short-term functional patency is usually good, but stenosis (mostly at the graft-vein anastomosis) may lead to thrombotic occlusion within 12 to 24 months. The primary patency rates of prosthetic AV grafts vary from 60% to 80% at 1 year and from 30% to 40% at 2 years of follow-up. Secondary patency ranges from 70% to 90% and from 50% to 70% at 1 and 2 years, respectively.21-24 Intimal hyperplasia, with smooth muscle cell migration and proliferation and matrix deposition, is the major cause of stenosis formation and thrombosis. The etiology of the intimal hyperplasia is uncertain, although the high wall shear stress, caused by the access flow, may denude the endothelial cell layer, resulting in platelet adhesion and initiation of a cascade of proteins that stimulate the smooth muscle cells to proliferate and to migrate.

Measures to Improve Graft Patency Numerous experimental and clinical studies have defined the influence of graft material and graft design on AV graft patency. Modulating the geometry of the arterial inlet or venous outlet of the graft may have a beneficial effect on intimal hyperplasia. Clinical studies using tapered (at the arterial side of the graft) grafts did not improve patency rates, nor did cuff implantation at the venous anastomosis.25,26 However, primary patency did improve with the use of a cuff-shaped prosthesis (Venaflo).27 Grafts such as polyurethane, which are more distensible, could in principle influence intimal hyperplasia by the better matching of the stiff prosthesis with the compliant vein at the anastomotic site; however, in clinical studies, this feature was not of proven benefit.28

PHARMACOLOGIC APPROACHES FOR ACCESS PATENCY Aspirin, ticlopidine, and dipyridamole have some beneficial effect in maintaining patency of AV fistulas and grafts but increase the risk of hemorrhage.29 Clopidogrel may also be effective in reducing thrombosis of AV grafts and fistulas. Warfarin reduces AV graft thrombosis but increases the risk of hemorrhage.30 A recent large trial showed that dipyridamole plus aspirin had a significant but modest effect in reducing the risk of stenosis and improving the duration of primary unassisted patency of newly created AV grafts.31 In a large randomized study, clopidogrel improved primary radiocephalic fistula function but not maturation.32 On the available evidence, antiplatelet agents should be used routinely in patients with AV grafts but not fistula. Warfarin should be considered only when there is recurrent thrombosis in the absence of anatomic stenosis. There have been suggestions that other drugs, such as calcium channel blockers and angiotensin-converting enzyme inhibitors, might be associated with improved AV fistula patency, but this requires confirmation with randomized studies.33 Fish oil reduced AV graft thrombosis in one randomized trial.34 Efforts have been made to inhibit the development of intimal hyperplasia pharmacologically with the cytotoxic agent paclitaxel. Paclitaxel wraps have been shown to reduce prosthetic graft intimal hyperplasia in animal models but have yet to be clinically evaluated.

LOWER LIMB VASCULAR ACCESS Probably the only indication for lower limb vascular access is bilateral central venous or caval obstruction, which endangers the outflow of upper limb AV fistulas. Saphenous and superficial femoral vein transposition is a primary option for thigh AV fistulas, although this carries a relatively high risk of distal ischemia. If clinical evaluation indicates incipient ischemia, primary flow

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reduction by tapering of the anastomosis is indicated to prevent ischemia.35 Prosthetic graft implantation in the thigh bears a high risk of infection and septicemia.

VASCULAR ACCESS COMPLICATIONS Nonmaturation of AV Fistulas Fistulas that fail immediately are the consequence of poor selection of vessels, poor technique, or postoperative hemodynamic instability. Vascular abnormalities, including stenoses, occlusions, and accessory veins, will be identified in virtually all early failures, and more than half of the stenoses are in the perianastomotic area of nonmatured fistulas. Arterial inflow stenoses of more than 50% coupled with poor flows are seen in less than 10% of nonmaturing fistulas, but if identified, they should undergo angioplasty. If this fails to improve fistula flow rates, it is unlikely that surgical bypass will be of help. Anastomotic and swing segment (where the vein has been mobilized and swung over to the artery) stenosis may be treated percutaneously or surgically, depending on local expertise. The diameter of the angioplasty balloon is chosen to correspond to the diameter of the vessel next to the stenotic or occlusive lesion and is usually not smaller than 5 mm for venous stenoses and not smaller than 4 mm for arterial or anastomotic stenoses. Ultrahigh-pressure balloons inflatable up to 30 atm are used when necessary to abolish the waist of the stenosis on the balloon. Apart from local infection, contraindications to balloon angioplasty are anastomotic stenoses in fistulas less than 4 to 6 weeks after surgical construction, which increases the risk of anastomotic disruption at angioplasty. Percutaneous balloon angioplasty is further discussed in Chapter 88. The surgical approach is to reconstruct the AV fistula, usually under local anesthesia. The anastomosis is exposed and ligated; the vein can then be divided, mobilized proximally, and reanastomosed to the proximal radial artery. A prospective nonrandomized study of 64 patients showed that outcomes were similar with angioplasty or surgery.36 Restenosis rates were significantly higher after angioplasty, but overall costs of treatment were similar. Nonmatured fistulas are rescued by angioplasty of stenoses or occlusions, ligation of accessory veins, or both. Accessory veins can be obliterated through coil embolization, percutaneous ligation, or surgical ligation. The use of coils with a diameter of 1 mm in excess of the target vessel diameter will prevent coil dislocation. Although ligation of accessory veins is usually performed in a single surgical intervention, three variants of vein ligation in a stepped approach have also been described.37 By use of this approach, surgery is limited to ligation of the accessory veins if the AV fistula appears to be of adequate size to allow cannulation. If the fistula is still considered to be too small, the median cubital vein is ligated. If the AV fistula is still believed inadequate, temporary banding of the main venous channel is performed. Apart from surgical ligation, accessory veins can also be ligated percutaneously.

Stenosis and Thrombosis The development of vessel stenosis in both autogenous AV fistulas and prosthetic AV grafts is usually initiated by intimal hyperplasia due to migrating and proliferating vessel smooth muscle cells, which form extracellular matrix. Progressive stenosis leads to access flow deterioration and subsequently

thrombotic occlusion. Prophylactic repair of access stenoses may prevent thrombosis and prolong access patency. Autogenous Fistula Stenosis or Thrombosis AV fistula stenosis should be treated if the vessel diameter is reduced by more than 50% and is accompanied by a reduction in access flow (25% flow decline between measurements or absolute flow below 500 ml/min) or in measured dialysis dose. Other indications for intervention are difficulties in cannulation and prolonged bleeding time after decannulation, indicating high intra-access pressure due to outflow vein stenosis. In AV fistulas, 55% to 75% of the stenoses are close to the AV anastomosis, 25% in the venous outflow tract and 15% in the arterial inflow. In brachiocephalic and brachiobasilic AV fistulas, the typical location for stenosis (besides the anastomosis) is at the junction of the cephalic with the subclavian vein and the basilic with the axillary vein (junctional stenosis). Endovascular treatment by percutaneous transluminal angioplasty (PTA) is the first option for arterial inflow and venous outflow stenoses and junctional stenoses, with the option of stent placement.38 These techniques are discussed further in Chapter 88. Some stenoses may not be sufficiently dilated by conventional balloons (12 to 16 atm), and in these patients, cutting balloons or ultrahigh-pressure balloons (up to 32 atm) may be applied. Anastomotic stenoses in forearm and upper arm fistulas are primarily treated with PTA; however, surgical revision with a more proximal reanastomosis for swing segment stenosis is indicated in failed PTA of radiocephalic AV fistula. Fistula thrombosis should be treated as soon as possible because timely declotting allows immediate use of the access without the need for a central venous catheter; fistula salvage usually requires intervention within 6 hours (grafts may be salvaged up to 24 hours). The duration and site of AV fistula thrombosis as well as the type of access are important determinants of treatment outcome. Thrombi become progressively fixed to the vein wall, which makes surgical removal more difficult. When the clot is localized at the anastomosis in radiocephalic and brachiocephalic fistulas, the outflow vein may remain patent because of continuing flow in its tributaries, making it possible to create a new proximal anastomosis.39 Thrombolysis can be performed mechanically or pharmacomechanically.40-42 Whereas the immediate success rate is higher in AV grafts than in autogenous AV fistulas (99% versus 93% in forearm fistulas), the primary patency rate of the forearm AV fistula at 1 year is much higher (49% versus 14%). One-year secondary patency rates are 80% in forearm and 50% in upper arm AV fistulas. In AV fistulas, the combination of a thrombolytic agent (urokinase or tissue plasminogen activator [tPA]) with balloon angioplasty resulted in an immediate success rate of 94%.41 AV Graft Stenosis or Thrombosis The most common cause of graft dysfunction and thrombosis is venous anastomotic stenosis. Because grafts should be implanted only in patients with exhausted peripheral veins, vein-saving procedures like PTA or patch angioplasty are preferred to graft extensions to more central venous segments. When a stent or a patch fails, graft extension is still possible. Graft monitoring by access flow measurement is recommended; with preemptive endovascular treatment, this may diminish graft thrombosis but does not extend graft patency. Intra-graft (or mid-graft) stenoses are found in the cannulation segment of grafts. They result from excessive ingrowth of

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fibrous tissue through puncture holes. These stenoses can be treated by PTA, graft curettage, or segmental graft replacement. When only a part of the cannulation segment is replaced, the access can be used for HD without the need of a central venous catheter. When restenosis occurs in a nonexchanged part of the graft, this can be replaced after healing of the new segment. Prosthetic graft thrombosis can be treated with various percutaneous techniques and tools, including combinations of thromboaspiration, thrombolytic agents such as tPA, and mechanical thrombectomy. An initial success rate of 73% and primary patency rates of 32% and 26% at 1 and 3 months, respectively, are reported.43-46 It is important to perform thrombolysis as soon as possible to avoid the need for a central venous catheter and as an outpatient procedure to decrease costs, whenever possible. Postprocedural angiography to detect and to correct inflow, intra-access, or venous outflow stenosis is mandatory. When endovascular treatment fails or is not possible, surgical thrombectomy may be performed with a Fogarty catheter after venotomy, with correction of the underlying obstruction. On-table angiography should be performed after completion of thrombectomy of both the arterial and venous limbs of the graft.

cava, it will not be possible to sustain upper limb access, and lower limb access will be required. Ultimately, ligation of the upper limb access can be considered, which will relieve local symptoms but loses a valuable dialysis access.

Central Venous Obstruction In the majority of patients, central vein obstruction is due to previously inserted central venous catheters or pacemaker wires. In 40% of patients with subclavian vein and 10% with jugular vein catheters, venous stenosis or occlusion will develop. Chronic swelling of the access arm is the most important sign, usually with prominent superficial collateral veins around the shoulder. The indications for intervention, by PTA and stent placement, are severe and disabling arm swelling, finger ulceration, and pain or inadequate HD. Contrast angiography of the access and complete venous outflow tract must be performed because the central veins can be difficult to examine with ultrasound in their retroclavicular position. Endovascular Intervention Endovascular intervention is the first option for central venous obstruction treatment. PTA alone results in low primary patency rates of 10% or less at 1 year, and numerous restenoses may develop. Primary or additional stent implantation gives much better outcome, with 1-year patency rates up to 56% or more.47,48 Reinterventions are usually required to maintain patency and to achieve long-term clinical success. Stent placement should avoid overlapping the ostium of the internal jugular vein because this vein is essential for future placement of central venous catheters. Similarly, a stent placed in the innominate vein should not overlap the ostium of the contralateral vein; otherwise, contralateral stenosis may occur and preclude future use of the contralateral limb for access creation. Surgical Intervention When interventional treatment of central venous obstruction fails, surgical revision with bypass grafting is indicated. Surgical bypass to the ipsilateral jugular vein or contralateral subclavian or jugular vein is the first option in these patients. Alternative surgical approaches for upper limb vascular accesses with compromised venous outflow are axillary vein to femoral, saphenous, or popliteal vein and right atrial bypasses.49 In case of bilateral obstruction of the mediastinal veins, including the superior vena

Vascular Access–Induced Ischemia Vascular access–induced upper limb ischemia is a serious complication that without prompt intervention may lead to amputation. The incidence of symptomatic ischemia varies from 2% to 8% of the HD population.50 Elderly patients, diabetics, and patients with peripheral or coronary arterial occlusive disease are most at risk of ischemia. In addition, previous ipsilateral vascular access increases the risk. Access-induced ischemia occurs more often with proximally located fistulas. These high-flow AV fistulas induce a steal phenomenon with lowering of distal perfusion pressures, and when collateral circulation is inadequate, symptoms may occur. Pain during HD is a characteristic early symptom. A grade 1 to 4 classification for access-induced ischemia can be used to outline the severity of the disease; this ranges from minor symptoms to finger necrosis. Grade 1: pale/blue or cold hand without pain Grade 2: pain during exercise or HD Grade 3: ischemic pain at rest Grade 4: ulceration, necrosis, and gangrene For grades 1 and 2, ischemia conservative treatment is advocated. With grades 3 and 4, interventional treatment is mandatory. Diagnosis of Ischemia Physical examination, including observation and palpation of peripheral vessels, may be inadequate and misleading for the diagnosis of symptomatic ischemia. Additional noninvasive testing with measurement of digital pressures and calculation of the digit to brachial index, transcutaneous oximetry, ultrasound of forearm arteries, and access blood flow measurement are important steps in the diagnosis and decision-making process. Finally, contrast angiography with visualization of the upper extremity arterial tree from the proximal subclavian artery to the distal palmar arches with and without AV fistula compression to enhance distal flow is obligatory to outline the strategy for treatment and to determine whether interventional or surgical options are preferred. Endovascular and Surgical Management of Ischemia The treatment strategy depends on the etiology of the ischemia. Inflow arterial obstruction and distal arterial lesions are recanalized with small-caliber balloons or stent placement51; high-flow AV fistulas are suitable for flow-reducing procedures like access banding (Fig. 87.8) and arterial inflow reduction by an interposition graft to a smaller forearm artery (revision using distal inflow).52,53 Steal in itself may be cured by ligation of the artery distal to the arteriovenous anastomosis (distal radial artery ligation). In most patients, it is necessary to add a saphenous vein or prosthetic graft bypass to the forearm arteries to augment distal hand perfusion (distal revascularization and interval ligation; Fig. 87.9). The results of these procedures are usually good, with relief of symptoms and preservation of the access site (Fig. 87.10).54-58 A simpler alternative to the distal revascularization–interval ligation procedure is the proximal arteriovenous anastomosis technique, in which the AV anastomosis at the elbow is disconnected and moved to the axilla, with

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Surgical Techniques for Banding of a High Flow Vascular Access

Figure 87.8  Surgical techniques for banding of a high-flow vascular access. A, Open venoplasty; B, Interrupted mattress suturing; C, Continuous mattress suturing; D, PTFE banding; E, PTFE interposition graft. The choice of technique is made by the surgeon on a case by case basis.

A

B

D

anastomosis to the axillary artery by means of a graft inter­ position.59 Recently, the minimally invasive limited ligation endoluminal-assisted revision procedure was described, using a minimally invasive percutaneous technique with banding of the access over a 4-mm balloon.60 Intraoperative digital pressure measurement or transcutaneous oximetry (TcPo2) is mandatory to guarantee an adequate surgical intervention with acceptable outcome. A digital-brachial pressure index above 0.60 or TcPO2 above 40 mm Hg is indicative of sufficient distal hand perfusion. In some patients, AV fistula ligation and transition to chronic catheter dialysis access or a change in renal replacement modality to peritoneal dialysis may be the only solution.

CENTRAL VENOUS CATHETER ACCESS Central venous catheters are still widely used as vascular access for HD. Data from the DOPPS study61 indicate that 25% of HD patients in the United States are dialyzed with catheters; in other countries, the use of catheters is even more common (Belgium, 41%; United Kingdom, 28%). Central venous catheters are the preferred vascular access for patients presenting with acute kidney injury and for chronic patients without permanent AV access or with failed vascular access. Two types of catheters are used in practice: nontunneled catheters for short-term dialysis, with a limited use and high morbidity; and tunneled cuffed catheters, which can be used up to several months or years with low morbidity. The physical characteristics (i.e., design and geometry) not only influence the performance (blood flow rate, recirculation, and resistance) but also affect the overall efficiency of the HD therapy and the morbidity risk (infection, thrombosis).

C

E

Nontunneled Catheters Single- or double-lumen catheters are usually made of polymers (polyethylene, polyurethane), enabling a simple and direct implant possibility. The length of the catheter must be chosen in accordance with the insertion site. The femoral route requires catheters of 30 to 35 cm in length for the distal tip to be located in the inferior vena cava. The internal jugular vein route needs shorter catheters of 20 to 25 cm in length, with tip location at the inferior vena cava–right atrium junction. The subclavian vein should not be used because of the very high risk of subsequent venous stenosis. For sufficient blood flow rates to be achieved, the diameter of these catheters must be ideally between 12 and 14 French. It is recommended that the use of nontunneled catheters not exceed 7 days.

Tunneled Catheters Tunneled central venous catheters have two lumens, each having a length of 40 cm, 10 cm of which is tunneled under the skin; the cannulae are made of synthetic polymer with a large internal lumen and a Dacron cuff to ensure subcutaneous anchoring. The catheter characteristics rely on the type of polymer, design, and geometry (double-lumen catheters, dual catheters, split catheters). The use of a tunneled central venous catheter is associated with reduced morbidity as well as better and constant performance compared with uncuffed catheters.62 Both tunneled and nontunneled catheters are inserted percutaneously by the Seldinger technique and ultrasound guidance. These techniques are described in Chapter 88. The internal jugular vein (Fig. 87.11) and femoral vein routes are preferred

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CHAPTER

because of ease of implantation and low risk of complications, such as central vein stenosis.

that patients with central venous catheters have an increased relative mortality risk of 3.4 compared with patients with AV fistulas. Switching from central venous catheters to AV fistulas decreases the relative mortality risk to 1.4.63 The most likely explanation for this increased mortality risk is infection and sepsis related to the central venous catheter, including exit site infection. Typical infection rates are 3 episodes of infection per 1000 tunneled catheter–days and higher with nontunneled catheters.64 These localized infections can progress to metastatic complications of osteomyelitis, septic arthritis, epidural abscess, and endocarditis. Various societies have issued recommendations for the management of catheter infections.65 A recommended treatment algorithm is shown in Figure 87.12.

Catheter Infection Catheter-related blood stream infections are a significant cause of mortality in HD patients. Results of the HEMO study indicate

Distal Revascularisation-Interval Ligation (DRIL) for Ischemia in an Upper Arm Vascular Access

Infections Involving Temporary Catheters When a temporary dialysis catheter becomes infected, it should always be removed. There is no role for trying to salvage temporary catheters.65 Exit Site Versus Tunnel Track Infections An exit site infection is a localized cellulitis confined to the 1 to 2 cm where the catheter exits the skin. The majority of these cases respond well to systemic antibiotics and meticulous exit site care, and the removal of the catheter is generally not required.65 However, exit site infections can progress to tunnel track infections, which involve the potential space surrounding the catheter more than 2 cm from the exit site (Fig. 87.13). Patients with a tunnel track infection sometimes but not always have an associated exit site infection; untreated, they can rapidly develop bacteremia. Patients with a tunnel track infection present with fever as well as local signs of pain, swelling, fluctuance, and erythema along the track of the catheter. Because tunnel track infections involve a potential space, in an area with limited vascular supply, and an implanted synthetic material, they respond poorly to antibiotics alone and require catheter removal.65

AV graft

Arterial bypass

Catheter-Associated Bacteremia When a patient with a dialysis catheter has a fever, catheter infection must always be considered. If the patient does not have a clear and convincing alternative explanation for the fever, blood culture specimens should be obtained peripherally as well as through the catheter, and the patient should be started on antibiotic therapy, which is subsequently adjusted on the basis of culture results.65 The most common organism is Staphylococcus, although a wide range of gram-positive and gram-negative organisms have been reported (Fig. 87.14). The percentage of patients with methicillin-resistant Staphylococcus aureus (MRSA) varies greatly between centers, with higher rates associated with

Arterial ligature

Figure 87.9  Distal revascularization–interval ligation for ischemia in an upper arm vascular access.

Results of the DRIL Procedure for Angio-Access Related Ischemia Author

Year

No. fistulae

Ischemia cured (%)

Ischemia improved (%)

Ischemia not improved (%)

Access patency (%)

Haimov et. al.

1996

23

86

14

–

95

Knox et. al.

2002

55

55

25

11

86

Waltz et. al.

2007

36

100

–

–

54

Yu et. al.

2008

24

96

–

4

88

Huber et. al.

2008

64

78

–

NS

68

Figure 87.10  Results of the distal revascularization–interval ligation (DRIL) procedure for vascular access– related ischemia. NS, not stated.

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XVI  Dialytic Therapies

greater antibiotic use. An aminoglycoside or a cephalosporin is a good choice for gram-negative coverage; however, local microbiologic epidemiology must be taken into consideration, especially concerning antibiotic resistance. Catheter Removal The decision to remove a tunneled cuffed dialysis catheter for an episode of catheter-associated bacteremia is not straightforward. The clinical condition of the patient and response to initial therapy, the presence of metastatic complications, the infecting

Tunneled Cuffed Double-Lumen Central Venous Catheter Inserted in the Right Internal Jugular Vein

Figure 87.11  Tunneled cuffed double-lumen central venous catheter inserted in the right internal jugular vein.

organism, and the availability of other vascular access sites must all be taken into consideration before deciding on a treatment plan (see Fig. 87.12). The conventional approach is to remove the catheter with interval replacement at a different site after the infection has resolved. Although this is effective, it leads to an additional temporary catheter if dialysis is needed before the catheter can be replaced. Attempts to “salvage” an infected catheter with systemic antibiotic therapy lead to resolution of infection in only about 30% of cases. Another treatment option is to combine systemic antibiotics with antibiotic “lock” solutions. Many different cocktails of antibiotics mixed with either heparin or citrate have been tested; a popular regimen is vancomycin 2.5 mg/ml, gentamicin 1 mg/ml, and heparin 2500 U/ml. Infection clearance rates of between 50% and 70% are reported with antibiotic locking. Several studies have reported that exchange of the catheter over a guide wire 48 hours after initial antibiotic treatment is more effective then treatment with antibiotics alone and is as effective as removal of the catheter and delayed replacement, with the advantages of only one invasive procedure and preservation of the venous access site. Randomized trials of antibiotic locking and catheter exchange over a guide wire are not yet available. Prevention of Infection The most important measure to prevent catheter infection is meticulous handling of the catheter at all times. The catheter should be inserted with use of maximal sterile precautions. The dialysis nurses need procedures for accessing the catheters under strict sterile conditions, and it is of the utmost importance that these catheters are never accessed by untrained personnel. Preliminary data suggest that antibiotic lock solutions significantly reduce the incidence of infection, but large randomized trials demonstrating both safety and efficacy are awaited before this can be recommended. Topical application of mupirocin

Management of Central Venous Dialysis Catheter Infections Clinical suspicion of infection

Obtain cultures and start antibiotics

Figure 87.12  Algorithm for the management of central venous dialysis catheter infections. (Modified with permission from reference 65.)

Temporary catheter

Remove catheter

Type of catheter

Tunneled catheter

Yes

Tunnel tract infection or Metastatic infection or Poor clinical response to treatment

May proceed with antibiotic lock or exchange over guidewire

No



CHAPTER

87  Vascular Access for Dialytic Therapies

1041

catheter clot formation while increasing risk of hemorrhage. Regular use of low-dose warfarin or antiplatelet agents has failed to improve catheter function in dialysis patients in randomized trials. To prevent or to correct catheter dysfunction, it is recommended that the catheter lumen be cleaned periodically by applying a fibrinolytic agent (urokinase or tPA) as a lock solution or by continuous infusion on both arterial and venous lines. Occluded catheters are reopened either by means of a mechanical method (brush) or pharmacologically (urokinase or tPA). Removal of the fibrin sleeve may be achieved by lasso wire stripping or by infusion of a fibrinolytic solution (urokinase, tPA) during 3 to 6 hours. Alternatively, the catheter may be exchanged over a guide wire.

Figure 87.13  Dialysis catheter tunnel infection. (Courtesy Dr. I. M. Leidig, University Hospital Erlangen, Germany.)

Causative Organisms in Dialysis Catheter Infections Polymicrobial Gram positive

Gram negative

16% Staphylococcus aureus Staphylococcus epidermidis Enterococcus Corynebacterium

89% 30% 37% 17% 49%

Enterobacter Pseudomonas Acinetobacter Citrobacter Serratia Klebsiella Other Gram negative

33% 11% 7% 4% 4% 2% 3% 3%

Mycobacteria

2%

Figure 87.14  Causative organisms in dialysis catheter infections. Numbers do not add up to 100% because 16% of infections were polymicrobial. (Modified with permission from reference 66.)

ointment to tunneled exit sites has been reported to reduce the incidence of catheter-associated bacteremia.

Catheter Obstruction Catheter obstruction may be due to endoluminal fibrin deposits, restricting the catheter lumen or obstructing catheter side holes at the tip, or external fibrin sleeves surrounding the catheter, resulting in inadequate flow and excessive extracorporeal blood pressure alarms during the dialysis session. Depending on the location of the fibrin clot (arterial or venous line), there may be high negative arterial pressure (obstruction at the arterial catheter line) or high positive venous pressure (obstruction at the venous catheter line). Prevention of clot formation in the catheter tip during the interdialytic period is crucial. This is achieved by installing an antithrombotic lock solution (sodium citrate is superior to standard heparin or low-molecular-weight heparin). A certain amount of the antithrombotic lock solution may leak into the circulation through side and central catheter holes, facilitating

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