Access for Renal Replacement Therapy

Temporary Dialysis Catheters

Central venous catheters (CVCs) are an option in patients with renal failure to provide dialysis. Catheters are either cuffed or uncuffed. Uncuffed CVCs are used as a temporizing measure in patients who require immediate or emergent hemodialysis. About 40% of patients with renal failure present acutely and require short-term vascular access and dialysis. These patients include the “acute presenter” and the “crash lander.” Acute presenters require short-term RRT to allow renal recovery, and crash landers, those who present suddenly with new ESRF, require short-term access during planning for a long-term option. In both instances a temporary uncuffed CVC may be placed to facilitate dialysis. Temporary catheters can be inserted at the bedside and can remain in situ for up to 3 weeks depending on the site of insertion.

The three most common locations for temporary vascular access are the internal jugular vein (IJV), subclavian vein (SCV), and common femoral vein (CFV). Upper limb catheters can remain in situ for up to 3 weeks, patients can remain fully ambulatory, infection rates are lowest, and they are therefore preferred to groin CVCs. Currently the favored site for temporary venous access is the right IJV, although some patients find the visibility of the catheter in the neck above the collar unsightly. The advantages of IJV placement are lower risk of infection, higher patency rates, and lower risk of insertion-related complications.

Permanent Dialysis Catheters

Patients requiring long-term dialysis and in whom there has not been an opportunity to create a fistula, AVG, or peritoneal dialysis catheter in a timely fashion will require a permanent dialysis catheter. In the US the incidence of patients starting dialysis on a tunneled catheter remains high at around 70%. The UK incidence is not much better with 48% of new starters initiating hemodialysis via a CVC. The current indications for central venous catheter insertion are displayed in Box 5.1 . Permanent catheters are always tunneled, dual-lumen, large-diameter (14 to 16 French) polyurethane catheters that have an annular fibrous cuff that holds that catheter in place within the tunnel tract. CVCs are composed of biologically neutral material that should not induce catheter lumen thrombosis or a perivascular reaction and subsequent venous thrombosis. The catheter should be soft and compliant, easy to insert, durable, and should be coated with an agent that reduces bacterial proliferation and biofilm formation. Furthermore it should be inexpensive and permit blood flow of >350 mL/min to facilitate efficient dialysis. Numerous catheters are available for use, and they can be differentiated by the design of the distal tip and the presence of side holes and flow dividers. The hemodynamic effects of these design variations are regularly debated and remain largely unknown and are influenced by numerous factors such as insertion technique, site of insertion, and position of the catheter tip. Although interesting, catheter design and insertion principles are less important than providing efficient dialysis. This includes the ability of the catheter to be able to process at least 50 L of fluid during a standard 4-hour dialysis session with favorable arterial and venous pump pressures and minimal recirculation.

The right IJV is the most favored site of placement of a permanent catheter, which is then tunneled to an exit site on the anterior chest wall. Care should always be taken to ensure that the cuff is at least 4 cm from the exit site to minimize the risk of cuff extrusion and minimize infection rates. Internal jugular vein catheter placement can be performed surgically using a cut down at the medial border of sternocleidomastoid. However, the Seldinger technique using ultrasound to guide the needle into the vessel is more frequently performed. It is essential to place catheters under fluoroscopic control, to ensure that the tip of the catheter is placed in the superior vena cava (SVC). The malposition rate of catheters when placed without fluoroscopic control has been shown to be as high as 29%. The tip of the catheter should be at the junction of the SVC and right atrium as this affords the most optimal blood flow through the catheter. A list of complications associated with central venous catheter insertion is displayed in Box 5.2 .

Tunneled catheters can provide access for months and even years, particularly in those patients in whom all native venous conduits for AVF or AVG formation have been exhausted or where arteriovenous strategies are likely to induce risks of limb loss from steal syndrome or precipitating heart failure from the high volume venous return. Indeed, in such patients who become dependent on a tunneled catheter, placement is becoming more adventurous with reports of transhepatic, translumbar and even transmediastinal approaches being used as last resort procedures.

Catheter Dysfunction

Catheter dysfunction was historically defined as “failure to attain and maintain adequate extracorporeal blood flow sufficient to perform dialysis in a timely fashion.” A recent collaboration of transplant surgeons and physicians, the North American Vascular Access Consortium (NAVAC), introduced a new definition in an attempt to create a uniform standard. Dysfunction was defined as the first occurrence of either (1) peak blood flow of 200 mL ⁄ min or less for 30 minutes during a dialysis treatment, (2) mean blood flow of 250 mL ⁄ min or less during two consecutive dialysis treatments, or (3) inability to initiate dialysis owing to inadequate blood flow, after attempts to restore patency have been attempted.

Dysfunction accounts for 17% to 33% of all catheter removals and can be either early or late. Early dysfunction is due to technical error such as kinking of the catheter in the subcutaneous tunnel or catheter malpositioning. Late dysfunction is due to central vein occlusion, catheter thrombosis, and fibrin sheath formation ( Fig. 5.1 ). Catheter thrombosis has an estimated frequency of 0.5 to 3 episodes per 1000 days and an incidence of 46% and is the major cause of catheter dysfunction. Antifibrinolytic therapy introduced via the catheter is the treatment of choice and first-line therapy is usually 5000 IU/mL of urokinase of sufficient volume to fill the lumen. This can be repeated immediately and if bolus dosing fails can be followed by a systemic infusion of 20,000 IU/mL/hr over 6 hours or a continuous infusion during dialysis of 250,000 IU. An RCT of tenecteplase versus placebo in patients with catheter dysfunction demonstrated that patients treated with tenecteplase had significantly increased flow rates (>300 mL/min). Patients within the study with <1 day of catheter dysfunction had the greatest benefit with 35% of tenecteplase-treated patients gaining adequate dialysis flow rates compared with 8% in the placebo group. If thrombolysis fails then imaging of the catheter to obtain further information is indicated. Direct injection of contrast via the arterial port can help elucidate the presence of a fibrin sheath. Treatment of a fibrin sheath usually involves replacement of the catheter at a new location although there is some evidence to support mechanical stripping, which is carried out using a snare around the catheter.

Catheter-Related Central Vein Stenosis

The long-term presence of any device within the central venous system is associated with the development of venous stenosis. The exact mechanism by which this happens is unclear; however, catheter-related thrombosis or infection along with progressive trauma to the endothelium is the most likely cause. The incidence of CVC-induced stenosis is reportedly as high as 50% although there are values as low as 18% in the literature. The rate of stenosis after subclavian vein cannulation is higher than that seen when the catheter is placed in the IJV, and catheters placed on the left side of the neck have a higher reported incidence of associated stenosis compared with those placed on the right. Fig. 5.2 shows an example of a right arm venogram in a patient with a central venous stenosis as a result of a CVC.

Central Vein Occlusion

The presence of occlusive thrombus in the central veins, in particular the SVC, is asymptomatic in about 30% of cases. Although it can manifest as catheter dysfunction, the presence of arm and facial edema or prominent superficial vessels should raise suspicion of central venous occlusion or stenosis. Thrombus is usually detected by angiography; however, transesophageal Doppler and contrast-enhanced cross sectional imaging are also useful diagnostic tools. The treatment of central vein thrombus depends on the chronicity of the thrombus. Acute thrombus may respond to fibrinolytic therapy. However, fibrinolytic therapy will not have any effect on older, organized thrombus. Percutaneous angioplasty and stenting have an increasing role in maintaining central venous catheter patency and recanalization of stenosed or occluded vessels. In addition, the advent of novel technology such as the Surfacer Inside-Out device (Merit Medical) has provided a potential means to persist with upper limb access in the presence of SVC occlusion. The details of the device are covered in the Advances in Access section later in the chapter.

Infection

Septic complications from CVCs are well documented, and the longevity of modern cuffed and tunneled catheters is still limited by infection. Catheter-related bacteremia rates for cuffed, tunneled catheters ranges from 1.5 to 5.5 per 1000 days. Catheter-related infections include exit site infection, tunnel infections, and catheter-associated bacteremia. Sepsis is the most significant cause of catheter-associated morbidity and mortality ( Fig. 5.3 ). Catheter infection is responsible for between 6% and 28% of catheter failure. Gram-positive skin dwelling bacteria, in particular Staphylococcus species, account for 40% to 80% of infections with gram-negative organisms accounting for 20% to 40%. Polymicrobial (10%) and rare causes such as fungal infection (<5%) make up the remainder. The route of infection is twofold, either tracking along the external surface of the catheter or via the lumen. Exit-site infections present with localized erythema with or without discharge and often respond to topical or oral antibiotics. Unresponsive infections or those with discharge and no signs of systemic sepsis and no bacterial growth on blood culture should be treated with parenteral antibiotic therapy. The Kidney Disease Outcomes Quality Initiative (KDOQI) guidelines recommend treatment for 3 weeks. However, if the patient is hemodynamically unstable or fails to improve after 36 hours of parenteral antibiotics, with bactericidal serum levels of an appropriate antibiotic, the catheter should be removed. Serious complications from catheter-associated infections occur in 3% to 44% of cases and include endocarditis, osteomyelitis, thrombophlebitis, septic arthritis, spinal epidural abscess, and large atrial thrombi. Mortality from catheter-associated infections is greatest when Staphylococcus aureus is the culprit with a reported rate of up to 30% in some units. Methicillin-resistant Staphylococcus aureus (MRSA) has three to five times higher mortality compared with methicillin-sensitive strains and is considerably more costly to treat and manage.

Wrist Fistula

The initial procedure of choice, in patients with suitable vessels, is a radiocephalic AVF at the wrist. The operation is performed under LA as a day case procedure. The original Brescia-Cimino AVF involved a side-to-side radial artery to cephalic vein anastomosis although more recently an end of cephalic vein to side of radial artery has come into favor. The original Brescia-Cimino AVF often led to venous hypertension in the hand, whereas the end-to-side variation does not. The disadvantages of radiocephalic AVFs are the high primary failure rate and failure to mature. Mean primary patency rates at 1 year are 55% (46%–63%) and secondary patency rates are 71% (65%–77%). At 1 year, 23% (17%–29%) of fistulas will have been abandoned without use.

The surgical technique for formation of radiocephalic fistulas follows. The cephalic vein and radial artery are exposed via a longitudinal, oblique, or S -shaped incision depending on the proximity of the vessels and the preference of the surgeon. The cephalic vein is mobilized for 3 cm from beneath the lateral skin flap ensuring preservation of the sensory dorsal branch of the radial nerve. The artery is located lateral to the tendon of the flexor carpi radialis and lies underneath the fibers of the deep fascia, which must be divided. Between 2 to 3 cm of artery should be mobilized and branches of the vessel can be ligated and divided. The vein and artery are controlled proximally and distally with vascular slings and microvascular clamps. In an end-to-side anastomosis the cephalic vein is ligated distally and divided obliquely to leave a spatulated end for anastomosis. An arteriotomy is then performed on the anterolateral surface of the radial artery. In a side-to-side anastomosis an arteriotomy (1–1.5 cm) is performed on the lateral aspect of the vessel, and afterwards a venotomy of equal length is performed on the medial side of the cephalic vein. A 6-0 or 7-0 nonabsorbable, monofilament suture with two needles is then used to perform a continuous anastomosis. Once the anastomosis has been completed and in the presence of an acceptable thrill within the vein, the distal cephalic artery can be ligated and divided. In a successful procedure there should be a thrill present once the clamps have been released and the slings loosened. In the absence of a thrill one must ensure the patient is not hypotensive, there are no adventitial bands constricting the vein, and there are no errors, such as an intimal flap, twisting of the vein, or presence of thrombus.

Elbow Fistulas

In the presence of failed radiocephalic fistulas or inadequate forearm vessels, an autogenous elbow fistula should be the next procedure of choice. A brachiocephalic AVF is usually the first procedure of choice at the elbow and is a straightforward procedure performed under LA.