The Scourges of the Hemodialysis Catheter

The first scourge: maintaining patency

The standard procedure for maintaining patency between dialysis treatments, the instillation of heparin into the lumens in a volume sufficient to fill to the lumen tip (the lock) is being replaced by the substitution of a trisodium citrate (TSC) 4 percent lock at many centers. One large Canadian study (6) showed a lower rate of TDC exchange and tissue plasminogen activator (tPA) use without a change in hospitalization for TSC 4 percent versus heparin. On the basis of available evidence, the American Society of Diagnostic and Interventional Nephrology Clinical Practice Committee (7) recommends using a locking solution of heparin 1000 U/mL or TSC 4 percent to maintain TDC patency.

Although a larger-bore catheter design allows an initial rate of blood flow above 400 mL/min to be achieved, virtually all catheters show eventual flow dysfunction manifested as progressive blood flow reductions at prepump pressures considered safe: 200–250 mm Hg.

Prospective monitoring for blood flow dysfunction through systematic monitoring of blood flow and prepump negative arterial pressure (Pa) during HD should be a routine part of the management of patients using TDCs (8) but in many centers it is not. Most large-gauge catheters have a conductance (Qb/Pa) of 2 mL/min/mm Hg. When prescribed blood flow rate (e.g., 350–400 mL/min) is examined serially over time, an increasing negative prepump pressure over time to achieve the prescribed flow reflects alterations in inlet orifice and suggests impending access dysfunction, which may warrant intervention.

Dysfunction manifests as thrombus formation within or at the tip of an HD catheter or by its entrapment within a fibrin sleeve. Systemic anticoagulants and antiplatelet agents have proved to be ineffective in preventing such dysfunction while adding a risk of bleeding. Noninvasive pharmacotherapy with thrombolytic agents has proved to be effective in restoring catheter patency over the short term. All too often, however, adequate flow function can be restored only by catheter replacement with balloon disruption of the fibrin sheath (9), an invasive and costly procedure.

Various protocols for thrombolytic dwells are used by dialysis centers to restore TDC blood flow, usually when the situation is urgent. I favor the slow advancement of the thrombolytic by the injection of saline solution 0.2 mL/lumen behind it every 10–15 minutes to advance the lytic to the catheter tip during a 1-hour dwell, because this strategy decreases the need for repeat lytic dwells by 81 percent (10). Two alternative strategies attempt to improve flow before the development of an “emergency” TDC flow problem: so-called preemptive postdialysis thrombolytic lock or intradialysis lytic infusions. I favor the use of a thrombolytic agent as a prolonged lock of 44–68 hours, both to restore flow and to prevent flow dysfunction. Regular once-weekly use of a tPA agent as a catheter lock solution may be the most effective technique to reduce the risk of vessel occlusion between HD sessions, avoid bleeding risk, and may incur the additional benefit of lower catheter-related bloodstream infection (CRBSI) (11). However, there have been no comparative efficacy or cost studies of the various strategies.

The second scourge: CBRSI

TDCs are responsible for almost half of all infections in HD patients. The infection rates of TDC are 15- and 25-fold higher than those for grafts and native fistulas, respectively. Infection is the leading cause of catheter removal, and CRBSI is a major reason for the loss of anatomic sites for vascular access. CRBSI is associated with substantial morbidity, including metastatic infection. One can estimate from the U.S. Renal Data System and Medicare reimbursement data that there are approximately 100,000 episodes of CRBSI per year in the United States at an average cost of $22,000 per episode (1). CRBSI usually requires catheter removal and 3 weeks of appropriate antibiotics. In some circumstances, catheter removal may be avoided by adding an antibiotic lock to the systemic antibiotic therapy.

Several approaches have been used to decrease the incidence of CRBSI: the use of intravenous antibiotics around the time of catheter implantation; the use of exit-site antimicrobial agents such as honey, mupirocin, and povidone-iodine combined with nasal mupirocin; and the use of antimicrobial-impregnated catheters and antimicrobial locks (AMLs) instilled into the catheter lumen.

Of these, only AMLs and exit-site antimicrobial agents significantly reduce the risk and rate of catheter-related infection and the risk of catheter loss from any complication (12). In a metaanalysis, the use of AMLs resulted in a 75 percent reduction in the risk of CRBSI (12) and only one published study showed the emergence of resistant organisms. Despite the demonstrated effectiveness of AMLs in reducing CRBSI, there is obvious reluctance to their use because of the potential for the development of bacterial drug resistance. Given that the U.S. Food and Drug Administration is unlikely to approve an antibiotic lock, current research focuses on the use of antimicrobial agents, usually combinations of several agents that prevent biofilm formation (13).

The third scourge: central vein stenosis and occlusion

The insertion of a large-bore catheter into a central vein is all too frequently associated with the development of stenosis within that vein. Central vein stenosis is catastrophic when it develops on the side of an established or maturing permanent access, graft, or native fistula, and it all too often precludes the placement of permanent access in the ipsilateral upper extremity. When such catheters are placed in the inferior vena cava, stenosis of the iliac vein can compromise the placement of a kidney graft. Strategies considered to reduce such stenosis include self-centering catheters and catheters configured to support themselves at opposite points of the superior vena cava. Inasmuch as longer catheter dwell times increase the development of central vein abnormalities, and catheter-related infection appears to promote stenosis, it is imperative to keep a TDC as short as possible and prevent infection.

Although catheters offer several advantages in the acute setting, acting as a bridge to more permanent vascular access, continued improvement in the design and performance of catheters is needed. Future studies should focus on better defining the prophylactic use of thrombolytic agents as locking solutions and the appropriate use of AMLs. Clearly, we need improvements in the process of care to reduce the fraction of patients in whom HD is begun with a TDC.