ORIGINAL ARTICLE
J Vasc Access 2014 ; 15 ( Suppl 7 ): S140- S146 DOI: 10.5301/jva.5000262
Dialysis central venous catheter types and performance Maurizio Gallieni1,2, Irene Brenna1,2, Francesca Brunini1,2, Nicoletta Mezzina1,2, Sabina Pasho1,2, Antonino Giordano1 1 2
Nephrology and Dialysis Unit, Ospedale San Carlo Borromeo, Milan - Italy Specialty School of Nephrology, University of Milan, Milan - Italy
ABSTRACT The choice of both short-term (nontunneled) and long-term (tunneled) central venous catheters (CVCs) for hemodialysis is a difficult one, due to the large number of available catheters, with very different characteristics and cost. CVC-related complications (in particular infections, thrombosis and inefficient dialysis) can determine ominous consequences and death, with extremely elevated costs due to prolonged hospitalization and expensive procedures. Thus, the correct balance between cost and quality of CVC is required when deciding which kind of CVC should be adopted. In this regard, the design of CVCs has become a very active area of industrial and clinical research, with the ultimate goal of improving the long-term function of the catheter and of reducing complication rates, because even small improvements in the complication or reintervention rates have a positive impact on individual patient care and cost to society. In this article we review the general features of CVCs, including differences between tunneled and nontunneled CVCs, materials and their compatibility with lock solutions, the implications of straight versus precurved design in nontunneled CVCs, lumen and tip features with their clinical implications, catheter coatings and their effect on infection and thrombosis. Key words: Central venous catheter, Complications, Hemodialysis, Materials, Vascular access Accepted: March 14, 2014
INTRODUCTION In their seminal article of 1999, Schwab and Beathard (1) highlighted one of the most important clinical issues of hemodialysis, the necessity of using central venous catheters (CVCs) and the consequent dilemmas that have become even more relevant in recent years. In fact, a progressive increase in the use of CVCs has been observed in most countries, despite major efforts worldwide to maintain or increase the number of patients dialyzing with an arteriovenous fistula. Catheter use rose 1.5- to 3-fold among prevalent patients in many countries from 1996 to 2007, even among nondiabetic patients 18-70 years old. Furthermore, 58% to 73% of patients newly diagnosed with end-stage renal disease used a catheter for the initiation of hemodialysis (2). Thus, hemodialysis CVCs continue to play an important role in the delivery of hemodialysis and the conundrum described by Schwab and Beathard is still valid: nephrologists hate having to deal with the problems inherent in catheter usage, but the enormous utility of these devices has forced them to accept the fact that they cannot live without them in their current practice (1). The main problems associated with long-term catheterization S140
include thrombosis, vascular stenosis and infection. Major efforts by the industry in providing new CVC designs with technical innovations aimed at resolving or attenuating patient safety issues, as well as improving CVC performance (3). Other CVC design modifications provide improvements for the insertion procedure. GENERAL FEATURES OF CVC A broad classification of dialysis CVC refers to the distinction between nontunneled and tunneled catheters (Tab. I). Totally implantable dialysis CVCs were available in the past, but they have been put out of the market (4). In oncology patients, the subcutaneous port is clearly the best CVC for the reduced number of complications and for patient preferences, with catheter-associated infections as low as 0.087 per 1,000 catheter days (5, 6). Thus, the appealing idea of a fully implantable dialysis port, durable and providing high blood flows, led to the development of two products, which were commercially available from the late 1990s (7, 8). Despite some difficulties in their management, especially the need for specific needles for
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TABLE I - MAIN CHARACTERISTICS OF HEMODIALYSIS CENTRAL VENOUS CATHETERS
TABLE II - DIALYSIS CENTRAL VENOUS CATHETER PROPERTIES THAT MAY INFLUENCE THEIR SELECTION
Types
• Ease and safety of insertion (minimal trauma, easy tunneling, valved introducer for prevention of air embolism, radiopaque appearance on X-ray)
- Non-tunneled (short term, noncuffed) - Tunneled catheters (long term, cuffed) - Totally implantable dialysis venous access devices (e.g., LifeSite and Dialock systems): no longer manufactured
• Flexibility to banding, avoidance of lumen collapse, kinking and breaks • In vivo delivered blood flow rates with moderately negative pressures, achieved by inner lumens as large as possible and small wall thickness
Design - Single, double or triple lumen - Straight or precurved
• Catheter thrombosis and resistance to occlusion by fibrous sheathing
- Tip configuration (staggered, split, symmetric) - Stabilization cuff in tunneled models
• Catheter weakening, rupture and embolization
- Retrograde vs antegrade tunneling system
• Vein trauma (mechanical phlebitis, vein thrombosis)
Composition
• Resistance to infection, biofilm formation
- Polyurethane
• Resistance to dissolution by chemicals, in particular those used in antimicrobial locking solutions
- Polyurethane/polycarbonate (CarbothaneTM) - Silicone
• Catheter maintenance requirements
Coatings - May have antimicrobial or antiseptic coating to protect against bacterial seeding - May have heparin coating to reduce fibrin formation - Radiopaque to confirm tip placement by X-ray
one of these products and the need for technical skills in puncturing the devices, they gained some popularity and showed clinical advantages, such as a reduced need in the use of antibiotics for a reduced rate of cutaneous infections, although no significant differences emerged as regards bacteremia incidence (9). Since episodes of infection did occur, inevitably, these devices did not meet the very high expectation generated by their marketing. Following adverse incident reports to the Food and Drug Administration, both companies were targeted by product liability litigations that resulted in their demise (4). It appears unlikely that other totally implantable models will be tested and introduced in clinical practice, despite the fact that this approach might reduce the morbidity associated with CVCs and increase patient comfort. Implanted dialysis ports cannot eliminate infections, because infections are the consequence of different mechanisms, not only the type of device. Table I also describes the main design characteristics of hemodialysis CVCs, which will be addressed in the present article. In addition to specific design features, other properties of CVCs may influence their selection by the nephrologist (Tab. II). We undertake a mainly descriptive approach, because controlled trials comparing the performance of different biomaterials and catheter designs on rates of infection or thrombosis are lacking. In tunneled dialysis catheters, a polyester (Dacron) cuff positioned at about 2 cm from the skin exit site allows
tissue ingrowth for anchoring and for preventing bacterial migration. This feature is associated with a marked reduction of short- and long-term complications (10) and of the risk of catheter-related bacteremia by 44% to 77% (11). BIOMATERIALS FOR CVC Requirements for materials aimed at CVC production are very challenging. They should be biocompatible, biostable, flexible, resistant, chemically neutral, not affected by administered drugs, deformable and resistant to sterilization (12). The two traditional biomaterials for CVC construction are polyurethane and silicone, but copolymers, such as the polyurethane/polycarbonate copolymer Carbothane™, are also common (Tab. I). Due to its more rigid nature, polyurethane is preferred for nontunneled CVCs, which can be introduced over a guidewire with the Seldinger technique of CVC insertion. On the other hand, traditionally silicone, being intrinsically soft and flexible, was the preferred material for long-term, tunneled CVCs. Compared with the newer polyurethane/polycarbonate-based CVCs, silicone catheters have a thicker wall for avoiding kinking, while polyurethane catheters of the same French size can have larger internal diameters and increased blood flow rates. In addition, silicone is weakened by iodine, slightly degraded by povidone–iodine solutions or to peroxide, while it is compatible with most alcohols and ointments (13). The use of several antibiotic ointments can damage polyurethane-based CVCs. Tunneled dialysis catheters made of polyurethane/polycarbonate copolymers, such as Carbothane™, are now the most commonly employed, coupling strength for CVC durability and softness
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for flexibility and patient comfort. They have the advantages of polyurethane, but they can be made with thinner walls having a greater strength. In addition, they are also resistant to iodine, peroxide and alcohols (3, 13). The issue of resistance to contact with chemicals is particularly important because of the increasingly used practice of CVC locking with antimicrobials. Mechanical integrity of dialysis CVCs should be preserved after exposure to catheter lock solutions. Some studies have examined the effect of 30% ethanol-based lock solutions on polyurethane CVCs (14, 15). In an experimental setting for determining the mechanical properties of CVCs, including Carbothane™, the average force required to break CVCs tended to be smaller in the catheters exposed to ethanol compared with saline controls. The degree of the effect of ethanol on CVCs does not prevent its use in the clinical setting, because forces produced during dialysis are many times smaller than the force required to break the catheters examined in these studies. However, considering that some CVCs may stay in place for years, an increased tendency to break during the procedure of CVC removal, when force is applied by the operator, should be taken into consideration. Thus, further studies could be useful in determining the long-term safety and efficacy of alcohol-based locking solution. Silicone-based CVCs appear to be more resistant to alcohol exposure, as indicated by a mass spectrometry and scanning electron microscopy study, showing integrity after an exposure of 15 days to 60% ethanol solution (16). NONTUNNELED STRAIGHT VS PRECURVED CVCS Nontunneled CVCs are available as straight or precurved. CVCs with curved extensions represent an intermediate solution. The precurved design offers advantages in minimizing catheter kinking and by facilitating a less invasive dressing on the patients’ neck, while nontunneled straight catheters are uncomfortable for dialysis patients and cannot be well fixated. A prospective analysis comparing 104 straight and 65 precurved dialysis CVC found that a lower rate of CVC removal (15% vs 53%) and a lower rate of CVC-related bacteremia (0 vs 5.6 per 1,000 catheter days) were observed in precurved compared with straight CVCs (17). LUMEN AND TIP DESIGN Many lumen and tip designs are also available. Larger lumens guarantee better flows, while tip design is mainly directed at minimizing recirculation of blood during dialysis, that is, direct re-entry of blood in the aspirating lumen from the blood restitution lumen. This is generally achieved separating the proximal and distal catheter S142
openings by at least 2 cm with a staggered tip design or by using a split catheter design, but new approaches are now available, such as the symmetric tip Palindrome CVC. In this design, the arterial and venous tracts have the same length. While inflow occurs through the side slot and the most proximal portion of the end hole, outflow occurs as a jet directed away from the catheter tip, avoiding recirculation (18). Primary assisted patency of this catheter is also remarkable, being 94% at 180 days (19). Another peculiar design is a self-centering CVC, with a built-in curvature designed to push the tip of the catheter away from the wall of the vessel or heart chamber (20). Side holes design, or the absence of side holes, has been a controversial issue. The presence of side holes should guarantee blood flow by avoiding suction effects against the vein or the atrial wall. However, side holes with irregularity of their cut surfaces may favor thrombosis and infection (21). In addition, when multiple side holes are present, the first available hole is primarily employed, especially from the aspirating lumen, determining a low flow zone at the tip of the catheter at increased risk for thrombosis (22). When a nontunneled dialysis CVCs is needed in the intensive care unit, a triple lumen CVC may be useful. A third, smaller medial lumen may be useful in several specific circumstances: blood transfusions, blood sampling in patients with poor peripheral veins, need for injection of contrast media during radiology studies and infusion of total parenteral nutrition (TPN). The latter often requires a dedicated lumen to avoid precipitation of the infused solutions: when using TPN, nothing else should be administered through that lumen. In chronic kidney disease patients who will need continuing dialysis and preparing an arteriovenous fistula, a triple lumen CVC might help in preserving the integrity of veins. A randomized trial showed that CVC-related bloodstream infections (about 7/1,000 catheter days for jugular sites) were similar for triple and double lumen nontunneled catheters (23). Nontunneled dialysis CVCs have a conically shaped tip, which is relatively rigid at room temperature to facilitate insertion, but then softens at body temperature to minimize the potential for vessel trauma. Both atrial and cava vein perforations have been reported, during the insertion procedure but also in the medium to long term (24). Although very rare, vascular or cardiac perforations are the most feared complication related to CVCs. Case reports of atrial perforation by CVCs have led to the recommendation of placing the tip of nontunneled dialysis CVC in the superior vena cava (25), while tunneled CVCs should have their tip positioned in the right atrium (26). Catheter tips in the superior vena cava or the innominate vein often lead to poor flows, as the tip may lie against a vessel wall. This is true for both tunneled and nontunneled CVCs. In addition, cases of superior vena cava perforation have been reported, especially for catheters inserted on the left side (27, 28), and thrombosis of the superior vena
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cava appears to be more common when the CVC tip is in the vein, compared with the position in the right atrium. Thus, vascular erosion or perforation can occur with the catheter tip in any location (29, 30). With the availability of softer silicone nontunneled CVCs, reports on the safety of tip positioning in the right atrium have been published (31) with the aim of improving dialysis efficiency, compared with inserting a shorter dialysis catheter targeting tip placement in the superior vena cava, for continuous renal replacement therapy. Placing the longer (20-25 cm) dialysis catheters was associated with an increased average dialyzer life span of 6.5 hours and improved delivered daily dialysis dose. The incidence of atrial arrhythmias was similar between groups (28% vs 21%). Thus, the use of longer soft silicone short-term dialysis CVCs targeting right atrial placement appeared to be safe and could improve dialysis performance compared with the use of shorter CVCs targeting superior vena cava placement (31). The inner lumen diameter is of crucial importance in determining the blood flow rate of a specific catheter, because according to Poiseuille’s law resistance to flow in a tube is proportional to its length and inversely proportional to the fourth power of the radius. Thus, minimal changes in the internal diameter may greatly affect the flow capacity (13). CATHETER COATINGS Polyurethane/polycarbonate CVCs are more resistant to attack by biological enzymes and hydrolysis than the traditional polyurethanes. In addition, some catheter materials can be modified and coated with antibacterial and/or antithrombotic agents. Catheter coatings such as heparin, antibiotics and silver ion have been proposed to minimize thrombosis and infection. Antimicrobial coatings may decrease microorganism adhesion and biofilm formation, thus reducing the risk of infection (32). The possibility of the development of resistance should be considered, especially in the case of antibiotics. The ideal coated catheter should combine low-cost coating technology, wide-spectrum and long-lasting or permanent antimicrobial properties and safe utilization. Sousa et al (33) reviewed recent advances and strategies for the development of new CVCs with antimicrobial properties. The ultimate goal in CVC development is to create a catheter that combines low-cost coating technology, wide-spectrum and long-lasting antimicrobial properties and secure utilization. A key issue, and a sort of “mission impossible,” is avoiding the development of the biofilm on the catheter surface, minimizing protein adsorption and subsequent microbial adhesion (34). In the intensive care unit, CVCs coated with antimicrobial agents are often employed for preventing CVC-related
infections. Catheters impregnated with chlorhexidine and silver sulfadiazine or with minocycline and rifampicin are the most frequently used (35, 36). Because silver sulfadiazine can generate allergic reactions, silver or silver nanoparticles have been increasingly used, due to their good antimicrobial action and low toxicity (34). The clinical effectiveness of CVCs coated with anti-infective agents in preventing catheter-related bloodstream infections was assessed by a systematic review (37). Meta-analyses of data from 27 trials assessing CVC-related infections showed a strong treatment effect in favor of coated CVCs (odds ratio 0.49, 95% confidence interval 0.37-0.64). Importantly, the article conclusions included a warning on the opportunity of establishing whether this favorable effect of coated CVCs remains in settings where infection prevention bundles of care are routine practice. Another study compared cost-effectiveness of four major types of antimicrobial-coated CVCs: minocycline and rifampicin coated; silver, platinum and carbon impregnated; and two chlorhexidine and silver sulfadiazine-coated catheters: one on the external surface and the other on both internal and external surfaces (38). The baseline cost-effectiveness analysis indicated all four types of antimicrobial-coated CVCs were cost saving relative to uncoated catheters, but when uncertainty arising from data estimates, data quality and heterogeneity was considered, the cost-effectiveness of using antimicrobial-coated CVCs within the intensive care unit became uncertain (38). In another review of 37 randomized controlled trials, Gilbert and Harden (39) found significant reductions of CVC-related infections for heparin-coated and antibiotic-impregnated catheters and only a marginal effect for chlorhexidine- and silver-coated catheters. Again, these results refer to short-term permanence of CVCs, as most of the studies included in the systematic review were less than 2 weeks long. Thus, these results might not apply to tunneled dialysis catheters. An interesting new approach is coating with the antimetabolite drug 5-fluorouracil, which can effectively inhibit microbial growth. Walz et al (40) compared the safety and efficacy of 5-fluorouracil-coated CVCs with those coated with chlorhexidine and silver sulfadiazine in a multicenter randomized trial conducted in 960 intensive care patients. Observation was carried out for up to 28 days. The primary antimicrobial outcome was catheter colonization, and secondary antimicrobial outcomes were local site infection and catheter-related bloodstream infection. CVCs coated with 5-fluorouracil were noninferior to chlorhexidine- and silver sulfadiazine-coated CVCs with respect to the incidence of catheter colonization (2.9% vs 5.3%, respectively). Local site infections were also similar (1.4% vs 0.9%) and catheter-related bloodstream infections were very rare in both groups (0 vs 2 episodes). Interestingly, only Gram-positive organisms were cultured from 5-fluorouracil catheters, whereas Grampositive bacteria, Gram-negative bacteria and Candida
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were cultured from the chlorhexidine and silver sulfadiazine CVCs (40). No hard outcome data are available, such as mortality and illness severity, limiting the prospect of large use of this coated catheter. More safety data are also needed for this new approach. In the dialysis setting, few studies are available. Bambauer et al (41) showed in an in vivo study that tunneled silver-coated catheters had lower bacterial colonization than uncoated catheters (11% vs 44%). However, a seminal randomized trial by Trerotola et al (42) failed to demonstrate a benefit against clinical infection or catheter colonization by silver sulfadiazine-coated tunneled CVCs with mean permanence of 92 days. In addition, silvercoated catheters had to be removed in 4% of patients due to skin reaction to the coating. With nontunneled CVCs results have been more encouraging, with a decreased incidence of catheter-related infections in the short term (43, 44). A recent Cochrane review also addressed the issue of CVC coatings and infections (45), confirming the effectiveness of antimicrobial CVCs in improving the rates of CVC-related infections and colonization. However, it concluded that significant benefits were mainly observed in studies conducted in the intensive care setting and that antimicrobial CVCs do not appear to significantly reduce clinically diagnosed sepsis or mortality. Thus, most experts would not recommend the use of coated tunneled CVCs because of insufficient evidence of clinical benefits. However, further research is warranted with more technologically advanced materials, such as silver nanoparticles.
Antithrombotic coatings should reduce platelet adhesion, inhibit the inflammatory response and reduce thrombus formation (44, 46). In vitro, coagulase-negative Staphylococci had lower adherence to heparin-coated CVCs (46). Two studies in critically ill children using heparin-coated CVCs have found fewer thrombotic complications and a reduced incidence of infection (47, 48). Currently, heparin-coated tunneled CVCs for dialysis are available in the market. Two retrospective studies of heparin-coated tunneled CVCs found a similar frequency of malfunction and overall catheter survival (49, 50), but in one of them coated catheters had a decreased frequency of CVC-related infection (49). Catheter and vein thrombosis is a very relevant clinical problem in the hemodialysis patient population, and more studies are needed to assess and demonstrate a clinically significant effect of the coating protection, whose longevity should match the length of the intended catheter placement (months to years, in the case of tunneled dialysis CVCs).
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Financial support: None. Conflict of interest: None. Address for correspondence: Maurizio Gallieni, MD Nephrology and Dialysis Unit Ospedale San Carlo Borromeo Via Pio II 320153 Milan, Italy [email protected]
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J Vasc Access 2014 ; 15 ( Suppl 7 ): S140- S146 DOI: 10.5301/jva.5000262
Dialysis central venous catheter types and performance Maurizio Gallieni1,2, Irene Brenna1,2, Francesca Brunini1,2, Nicoletta Mezzina1,2, Sabina Pasho1,2, Antonino Giordano1 1 2
Nephrology and Dialysis Unit, Ospedale San Carlo Borromeo, Milan - Italy Specialty School of Nephrology, University of Milan, Milan - Italy
ABSTRACT The choice of both short-term (nontunneled) and long-term (tunneled) central venous catheters (CVCs) for hemodialysis is a difficult one, due to the large number of available catheters, with very different characteristics and cost. CVC-related complications (in particular infections, thrombosis and inefficient dialysis) can determine ominous consequences and death, with extremely elevated costs due to prolonged hospitalization and expensive procedures. Thus, the correct balance between cost and quality of CVC is required when deciding which kind of CVC should be adopted. In this regard, the design of CVCs has become a very active area of industrial and clinical research, with the ultimate goal of improving the long-term function of the catheter and of reducing complication rates, because even small improvements in the complication or reintervention rates have a positive impact on individual patient care and cost to society. In this article we review the general features of CVCs, including differences between tunneled and nontunneled CVCs, materials and their compatibility with lock solutions, the implications of straight versus precurved design in nontunneled CVCs, lumen and tip features with their clinical implications, catheter coatings and their effect on infection and thrombosis. Key words: Central venous catheter, Complications, Hemodialysis, Materials, Vascular access Accepted: March 14, 2014
INTRODUCTION In their seminal article of 1999, Schwab and Beathard (1) highlighted one of the most important clinical issues of hemodialysis, the necessity of using central venous catheters (CVCs) and the consequent dilemmas that have become even more relevant in recent years. In fact, a progressive increase in the use of CVCs has been observed in most countries, despite major efforts worldwide to maintain or increase the number of patients dialyzing with an arteriovenous fistula. Catheter use rose 1.5- to 3-fold among prevalent patients in many countries from 1996 to 2007, even among nondiabetic patients 18-70 years old. Furthermore, 58% to 73% of patients newly diagnosed with end-stage renal disease used a catheter for the initiation of hemodialysis (2). Thus, hemodialysis CVCs continue to play an important role in the delivery of hemodialysis and the conundrum described by Schwab and Beathard is still valid: nephrologists hate having to deal with the problems inherent in catheter usage, but the enormous utility of these devices has forced them to accept the fact that they cannot live without them in their current practice (1). The main problems associated with long-term catheterization S140
include thrombosis, vascular stenosis and infection. Major efforts by the industry in providing new CVC designs with technical innovations aimed at resolving or attenuating patient safety issues, as well as improving CVC performance (3). Other CVC design modifications provide improvements for the insertion procedure. GENERAL FEATURES OF CVC A broad classification of dialysis CVC refers to the distinction between nontunneled and tunneled catheters (Tab. I). Totally implantable dialysis CVCs were available in the past, but they have been put out of the market (4). In oncology patients, the subcutaneous port is clearly the best CVC for the reduced number of complications and for patient preferences, with catheter-associated infections as low as 0.087 per 1,000 catheter days (5, 6). Thus, the appealing idea of a fully implantable dialysis port, durable and providing high blood flows, led to the development of two products, which were commercially available from the late 1990s (7, 8). Despite some difficulties in their management, especially the need for specific needles for
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TABLE I - MAIN CHARACTERISTICS OF HEMODIALYSIS CENTRAL VENOUS CATHETERS
TABLE II - DIALYSIS CENTRAL VENOUS CATHETER PROPERTIES THAT MAY INFLUENCE THEIR SELECTION
Types
• Ease and safety of insertion (minimal trauma, easy tunneling, valved introducer for prevention of air embolism, radiopaque appearance on X-ray)
- Non-tunneled (short term, noncuffed) - Tunneled catheters (long term, cuffed) - Totally implantable dialysis venous access devices (e.g., LifeSite and Dialock systems): no longer manufactured
• Flexibility to banding, avoidance of lumen collapse, kinking and breaks • In vivo delivered blood flow rates with moderately negative pressures, achieved by inner lumens as large as possible and small wall thickness
Design - Single, double or triple lumen - Straight or precurved
• Catheter thrombosis and resistance to occlusion by fibrous sheathing
- Tip configuration (staggered, split, symmetric) - Stabilization cuff in tunneled models
• Catheter weakening, rupture and embolization
- Retrograde vs antegrade tunneling system
• Vein trauma (mechanical phlebitis, vein thrombosis)
Composition
• Resistance to infection, biofilm formation
- Polyurethane
• Resistance to dissolution by chemicals, in particular those used in antimicrobial locking solutions
- Polyurethane/polycarbonate (CarbothaneTM) - Silicone
• Catheter maintenance requirements
Coatings - May have antimicrobial or antiseptic coating to protect against bacterial seeding - May have heparin coating to reduce fibrin formation - Radiopaque to confirm tip placement by X-ray
one of these products and the need for technical skills in puncturing the devices, they gained some popularity and showed clinical advantages, such as a reduced need in the use of antibiotics for a reduced rate of cutaneous infections, although no significant differences emerged as regards bacteremia incidence (9). Since episodes of infection did occur, inevitably, these devices did not meet the very high expectation generated by their marketing. Following adverse incident reports to the Food and Drug Administration, both companies were targeted by product liability litigations that resulted in their demise (4). It appears unlikely that other totally implantable models will be tested and introduced in clinical practice, despite the fact that this approach might reduce the morbidity associated with CVCs and increase patient comfort. Implanted dialysis ports cannot eliminate infections, because infections are the consequence of different mechanisms, not only the type of device. Table I also describes the main design characteristics of hemodialysis CVCs, which will be addressed in the present article. In addition to specific design features, other properties of CVCs may influence their selection by the nephrologist (Tab. II). We undertake a mainly descriptive approach, because controlled trials comparing the performance of different biomaterials and catheter designs on rates of infection or thrombosis are lacking. In tunneled dialysis catheters, a polyester (Dacron) cuff positioned at about 2 cm from the skin exit site allows
tissue ingrowth for anchoring and for preventing bacterial migration. This feature is associated with a marked reduction of short- and long-term complications (10) and of the risk of catheter-related bacteremia by 44% to 77% (11). BIOMATERIALS FOR CVC Requirements for materials aimed at CVC production are very challenging. They should be biocompatible, biostable, flexible, resistant, chemically neutral, not affected by administered drugs, deformable and resistant to sterilization (12). The two traditional biomaterials for CVC construction are polyurethane and silicone, but copolymers, such as the polyurethane/polycarbonate copolymer Carbothane™, are also common (Tab. I). Due to its more rigid nature, polyurethane is preferred for nontunneled CVCs, which can be introduced over a guidewire with the Seldinger technique of CVC insertion. On the other hand, traditionally silicone, being intrinsically soft and flexible, was the preferred material for long-term, tunneled CVCs. Compared with the newer polyurethane/polycarbonate-based CVCs, silicone catheters have a thicker wall for avoiding kinking, while polyurethane catheters of the same French size can have larger internal diameters and increased blood flow rates. In addition, silicone is weakened by iodine, slightly degraded by povidone–iodine solutions or to peroxide, while it is compatible with most alcohols and ointments (13). The use of several antibiotic ointments can damage polyurethane-based CVCs. Tunneled dialysis catheters made of polyurethane/polycarbonate copolymers, such as Carbothane™, are now the most commonly employed, coupling strength for CVC durability and softness
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for flexibility and patient comfort. They have the advantages of polyurethane, but they can be made with thinner walls having a greater strength. In addition, they are also resistant to iodine, peroxide and alcohols (3, 13). The issue of resistance to contact with chemicals is particularly important because of the increasingly used practice of CVC locking with antimicrobials. Mechanical integrity of dialysis CVCs should be preserved after exposure to catheter lock solutions. Some studies have examined the effect of 30% ethanol-based lock solutions on polyurethane CVCs (14, 15). In an experimental setting for determining the mechanical properties of CVCs, including Carbothane™, the average force required to break CVCs tended to be smaller in the catheters exposed to ethanol compared with saline controls. The degree of the effect of ethanol on CVCs does not prevent its use in the clinical setting, because forces produced during dialysis are many times smaller than the force required to break the catheters examined in these studies. However, considering that some CVCs may stay in place for years, an increased tendency to break during the procedure of CVC removal, when force is applied by the operator, should be taken into consideration. Thus, further studies could be useful in determining the long-term safety and efficacy of alcohol-based locking solution. Silicone-based CVCs appear to be more resistant to alcohol exposure, as indicated by a mass spectrometry and scanning electron microscopy study, showing integrity after an exposure of 15 days to 60% ethanol solution (16). NONTUNNELED STRAIGHT VS PRECURVED CVCS Nontunneled CVCs are available as straight or precurved. CVCs with curved extensions represent an intermediate solution. The precurved design offers advantages in minimizing catheter kinking and by facilitating a less invasive dressing on the patients’ neck, while nontunneled straight catheters are uncomfortable for dialysis patients and cannot be well fixated. A prospective analysis comparing 104 straight and 65 precurved dialysis CVC found that a lower rate of CVC removal (15% vs 53%) and a lower rate of CVC-related bacteremia (0 vs 5.6 per 1,000 catheter days) were observed in precurved compared with straight CVCs (17). LUMEN AND TIP DESIGN Many lumen and tip designs are also available. Larger lumens guarantee better flows, while tip design is mainly directed at minimizing recirculation of blood during dialysis, that is, direct re-entry of blood in the aspirating lumen from the blood restitution lumen. This is generally achieved separating the proximal and distal catheter S142
openings by at least 2 cm with a staggered tip design or by using a split catheter design, but new approaches are now available, such as the symmetric tip Palindrome CVC. In this design, the arterial and venous tracts have the same length. While inflow occurs through the side slot and the most proximal portion of the end hole, outflow occurs as a jet directed away from the catheter tip, avoiding recirculation (18). Primary assisted patency of this catheter is also remarkable, being 94% at 180 days (19). Another peculiar design is a self-centering CVC, with a built-in curvature designed to push the tip of the catheter away from the wall of the vessel or heart chamber (20). Side holes design, or the absence of side holes, has been a controversial issue. The presence of side holes should guarantee blood flow by avoiding suction effects against the vein or the atrial wall. However, side holes with irregularity of their cut surfaces may favor thrombosis and infection (21). In addition, when multiple side holes are present, the first available hole is primarily employed, especially from the aspirating lumen, determining a low flow zone at the tip of the catheter at increased risk for thrombosis (22). When a nontunneled dialysis CVCs is needed in the intensive care unit, a triple lumen CVC may be useful. A third, smaller medial lumen may be useful in several specific circumstances: blood transfusions, blood sampling in patients with poor peripheral veins, need for injection of contrast media during radiology studies and infusion of total parenteral nutrition (TPN). The latter often requires a dedicated lumen to avoid precipitation of the infused solutions: when using TPN, nothing else should be administered through that lumen. In chronic kidney disease patients who will need continuing dialysis and preparing an arteriovenous fistula, a triple lumen CVC might help in preserving the integrity of veins. A randomized trial showed that CVC-related bloodstream infections (about 7/1,000 catheter days for jugular sites) were similar for triple and double lumen nontunneled catheters (23). Nontunneled dialysis CVCs have a conically shaped tip, which is relatively rigid at room temperature to facilitate insertion, but then softens at body temperature to minimize the potential for vessel trauma. Both atrial and cava vein perforations have been reported, during the insertion procedure but also in the medium to long term (24). Although very rare, vascular or cardiac perforations are the most feared complication related to CVCs. Case reports of atrial perforation by CVCs have led to the recommendation of placing the tip of nontunneled dialysis CVC in the superior vena cava (25), while tunneled CVCs should have their tip positioned in the right atrium (26). Catheter tips in the superior vena cava or the innominate vein often lead to poor flows, as the tip may lie against a vessel wall. This is true for both tunneled and nontunneled CVCs. In addition, cases of superior vena cava perforation have been reported, especially for catheters inserted on the left side (27, 28), and thrombosis of the superior vena
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cava appears to be more common when the CVC tip is in the vein, compared with the position in the right atrium. Thus, vascular erosion or perforation can occur with the catheter tip in any location (29, 30). With the availability of softer silicone nontunneled CVCs, reports on the safety of tip positioning in the right atrium have been published (31) with the aim of improving dialysis efficiency, compared with inserting a shorter dialysis catheter targeting tip placement in the superior vena cava, for continuous renal replacement therapy. Placing the longer (20-25 cm) dialysis catheters was associated with an increased average dialyzer life span of 6.5 hours and improved delivered daily dialysis dose. The incidence of atrial arrhythmias was similar between groups (28% vs 21%). Thus, the use of longer soft silicone short-term dialysis CVCs targeting right atrial placement appeared to be safe and could improve dialysis performance compared with the use of shorter CVCs targeting superior vena cava placement (31). The inner lumen diameter is of crucial importance in determining the blood flow rate of a specific catheter, because according to Poiseuille’s law resistance to flow in a tube is proportional to its length and inversely proportional to the fourth power of the radius. Thus, minimal changes in the internal diameter may greatly affect the flow capacity (13). CATHETER COATINGS Polyurethane/polycarbonate CVCs are more resistant to attack by biological enzymes and hydrolysis than the traditional polyurethanes. In addition, some catheter materials can be modified and coated with antibacterial and/or antithrombotic agents. Catheter coatings such as heparin, antibiotics and silver ion have been proposed to minimize thrombosis and infection. Antimicrobial coatings may decrease microorganism adhesion and biofilm formation, thus reducing the risk of infection (32). The possibility of the development of resistance should be considered, especially in the case of antibiotics. The ideal coated catheter should combine low-cost coating technology, wide-spectrum and long-lasting or permanent antimicrobial properties and safe utilization. Sousa et al (33) reviewed recent advances and strategies for the development of new CVCs with antimicrobial properties. The ultimate goal in CVC development is to create a catheter that combines low-cost coating technology, wide-spectrum and long-lasting antimicrobial properties and secure utilization. A key issue, and a sort of “mission impossible,” is avoiding the development of the biofilm on the catheter surface, minimizing protein adsorption and subsequent microbial adhesion (34). In the intensive care unit, CVCs coated with antimicrobial agents are often employed for preventing CVC-related
infections. Catheters impregnated with chlorhexidine and silver sulfadiazine or with minocycline and rifampicin are the most frequently used (35, 36). Because silver sulfadiazine can generate allergic reactions, silver or silver nanoparticles have been increasingly used, due to their good antimicrobial action and low toxicity (34). The clinical effectiveness of CVCs coated with anti-infective agents in preventing catheter-related bloodstream infections was assessed by a systematic review (37). Meta-analyses of data from 27 trials assessing CVC-related infections showed a strong treatment effect in favor of coated CVCs (odds ratio 0.49, 95% confidence interval 0.37-0.64). Importantly, the article conclusions included a warning on the opportunity of establishing whether this favorable effect of coated CVCs remains in settings where infection prevention bundles of care are routine practice. Another study compared cost-effectiveness of four major types of antimicrobial-coated CVCs: minocycline and rifampicin coated; silver, platinum and carbon impregnated; and two chlorhexidine and silver sulfadiazine-coated catheters: one on the external surface and the other on both internal and external surfaces (38). The baseline cost-effectiveness analysis indicated all four types of antimicrobial-coated CVCs were cost saving relative to uncoated catheters, but when uncertainty arising from data estimates, data quality and heterogeneity was considered, the cost-effectiveness of using antimicrobial-coated CVCs within the intensive care unit became uncertain (38). In another review of 37 randomized controlled trials, Gilbert and Harden (39) found significant reductions of CVC-related infections for heparin-coated and antibiotic-impregnated catheters and only a marginal effect for chlorhexidine- and silver-coated catheters. Again, these results refer to short-term permanence of CVCs, as most of the studies included in the systematic review were less than 2 weeks long. Thus, these results might not apply to tunneled dialysis catheters. An interesting new approach is coating with the antimetabolite drug 5-fluorouracil, which can effectively inhibit microbial growth. Walz et al (40) compared the safety and efficacy of 5-fluorouracil-coated CVCs with those coated with chlorhexidine and silver sulfadiazine in a multicenter randomized trial conducted in 960 intensive care patients. Observation was carried out for up to 28 days. The primary antimicrobial outcome was catheter colonization, and secondary antimicrobial outcomes were local site infection and catheter-related bloodstream infection. CVCs coated with 5-fluorouracil were noninferior to chlorhexidine- and silver sulfadiazine-coated CVCs with respect to the incidence of catheter colonization (2.9% vs 5.3%, respectively). Local site infections were also similar (1.4% vs 0.9%) and catheter-related bloodstream infections were very rare in both groups (0 vs 2 episodes). Interestingly, only Gram-positive organisms were cultured from 5-fluorouracil catheters, whereas Grampositive bacteria, Gram-negative bacteria and Candida
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were cultured from the chlorhexidine and silver sulfadiazine CVCs (40). No hard outcome data are available, such as mortality and illness severity, limiting the prospect of large use of this coated catheter. More safety data are also needed for this new approach. In the dialysis setting, few studies are available. Bambauer et al (41) showed in an in vivo study that tunneled silver-coated catheters had lower bacterial colonization than uncoated catheters (11% vs 44%). However, a seminal randomized trial by Trerotola et al (42) failed to demonstrate a benefit against clinical infection or catheter colonization by silver sulfadiazine-coated tunneled CVCs with mean permanence of 92 days. In addition, silvercoated catheters had to be removed in 4% of patients due to skin reaction to the coating. With nontunneled CVCs results have been more encouraging, with a decreased incidence of catheter-related infections in the short term (43, 44). A recent Cochrane review also addressed the issue of CVC coatings and infections (45), confirming the effectiveness of antimicrobial CVCs in improving the rates of CVC-related infections and colonization. However, it concluded that significant benefits were mainly observed in studies conducted in the intensive care setting and that antimicrobial CVCs do not appear to significantly reduce clinically diagnosed sepsis or mortality. Thus, most experts would not recommend the use of coated tunneled CVCs because of insufficient evidence of clinical benefits. However, further research is warranted with more technologically advanced materials, such as silver nanoparticles.
Antithrombotic coatings should reduce platelet adhesion, inhibit the inflammatory response and reduce thrombus formation (44, 46). In vitro, coagulase-negative Staphylococci had lower adherence to heparin-coated CVCs (46). Two studies in critically ill children using heparin-coated CVCs have found fewer thrombotic complications and a reduced incidence of infection (47, 48). Currently, heparin-coated tunneled CVCs for dialysis are available in the market. Two retrospective studies of heparin-coated tunneled CVCs found a similar frequency of malfunction and overall catheter survival (49, 50), but in one of them coated catheters had a decreased frequency of CVC-related infection (49). Catheter and vein thrombosis is a very relevant clinical problem in the hemodialysis patient population, and more studies are needed to assess and demonstrate a clinically significant effect of the coating protection, whose longevity should match the length of the intended catheter placement (months to years, in the case of tunneled dialysis CVCs).
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Financial support: None. Conflict of interest: None. Address for correspondence: Maurizio Gallieni, MD Nephrology and Dialysis Unit Ospedale San Carlo Borromeo Via Pio II 320153 Milan, Italy [email protected]
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