Temporary Vascular Access for Extracorporeal Therapies

Therapeutic Apheresis 4(3):249–255, Blackwell Science, Inc. © 2000 International Society for Apheresis

Temporary Vascular Access for Extracorporeal Therapies Bernard Canaud, He´le`ne Leray-Moragues, Khaola Kamoun, and Vale´rie Garrigue Nephrology Department, Lapeyronie University Hospital Dialysis Research and Training Institute, Montpellier, France

Abstract: Central venous catheters provide at the present time the basic and ideal method to perform acute extracorporeal blood purification. Rapid launch of extracorporeal therapy is indicated in two situations: first, renal conditions presenting as a recognized acute organic renal failure (ARF) and acute decompensation of end stage renal disease (ESRD) without permanent vascular access; second, non-renal conditions presenting as urgent clinical situations requiring isolated ultrafiltration for chronic congestive heart failure, plasmapheresis or selective immunoadsorption for immune diseases, cytapheresis for hematological disease, and selective detoxification for certain types of poisoning. Central venous catheters are classified into 2 categories according to the duration of use: temporary catheter (less than 90 days) and permanent catheter (more than 90 days). A temporary catheter, including rigid (polyethylene, teflon) and semirigid (polyurethane) ma-

terial, is indicated in emergency situations and for shortterm use. A permanent catheter, made usually of soft silicone rubber with a subcutaneous anchoring system, has a subcutaneous tunnel and is indicated in medium and longterm use. Catheter design has benefited greatly from technical advances and material hemocompatability. However, catheter-related morbidity still remains high and is associated with an unacceptable incidence rate of infection and/ or vein thrombosis. This article covers our present knowledge regarding catheter indications, technical aspects of catheter insertion and care, functional limitation of central venous catheters, and catheter-related complications. It is also our intent to provide the reader with optimal indication and catheter care in order to prevent and reduce the burden of catheter-related morbidity. Key Words: Hemodialysis—Hemapheresis—Temporary vascular access.

Access to the vascular system is the cornerstone of all extracorporeal therapy (1). Rapid launch of extracorporeal dialysis is indicated in two categories: first, renal conditions, presented as a recognized acute organic renal failure (ARF) and acute decompensation of end-stage renal disease (ESRD) without permanent renal access, and second, non-renal conditions, presented as urgent clinical situations requiring an adjunct extracorporeal therapy such as isolated ultrafiltration for chronic congestive heart failure, plasmapheresis or selective immunoadsorption for immune diseases, cytapheresis for hematological disease, and selective detoxification for certain types of poisoning. Faced with these emergencies, one must recognize that the ideal vascular access should have the following characteristics: easy and rapid insertion proce-

dure, immediately available for use, low risk of complications or dysfunction, hemocompatible to minimize thrombosis risk, performance-adapted to requirements, low risk of infection, and possibility of prolonged use (from a few days to several weeks) thus reducing costs. Access to bloodstream indicated for these categories of patients are deep central venous catheters. External arteriovenous shunts and permanent arteriovenous fistula access using the patient’s native blood vessels or synthetic grafts (PTFE) are not covered in this chapter, even though they may be used occasionally. DEEP PERCUTANEOUS CATHETERS General points The percutaneous catheter (KT) is the simplest and most rapid way to set up the extracorporeal blood circulation necessary for any method of extracorporeal dialysis. KT is suitable for both high-flow and low-flow dialysis methods. Usually this KT is implanted percutaneously in

Received October 1999; revised December 1999. Presented in part at the 2nd International Society for Apheresis Congress, held April 15–18, 1999, in Saarbrucken, Germany. Address correspondence and reprint requests to Dr. Bernard Canaud, Nephrology Department, Lapeyronie University Hospital, 34295 Montpellier, France.

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a deep vein via the femoral, subclavian, or jugular route. Very occasionally, arterial catheters will be used for low-flow continous arteriovenous renal replacement methods. In this case, the arterial catheter is always inserted in the femoral artery while the venous catheter carrying the return blood supply is inserted in the ipsilateral femoral vein. TYPES OF CATHETERS AND INDICATIONS FOR USE There is a large choice of disposable hemodialysis catheters on the market (Fig. 1). The properties and performance characteristics of a dialysis catheter are the functions of its physical features; the type of material used (Polyethylene, Teflon, Polyurethane polymer, Silicone polymer); the flexibility of the catheter; the length and diameter of the lines; the number and position of the internal lumen (single lumen, double lumen with coaxial positioning, or double D); split catheters; existence, number, and arrangement of distal outlets; distance of the tip from the arterial and venous ends; and whether or not there is a means of subcutaneous anchoring system (Dacron cuff, subcutaneous suture, ceramic, etc.). The medical indications, the clinical context, and the experience of the operator using the device will dictate the choice of catheter material. In practice, hemodialysis catheters are classified by flexibility (rigid, semi-rigid, and flexible) and by the expected

duration of use (short-term, less than 10 days; longterm, from 10 days to several weeks). However, in all of these cases, it should be remembered that the performance of, and complications with, catheters depend as much on their characteristics as the conditions of use and maintenance. Rigid catheters for short-term use are usually made of Teflon or polyethylene or occasionally polyurethane. Rigid catheters are indicated for use with the Seldinger technique in which insertion is carried out using a flexible metallic guidewire. The catheter used (Desilet) is comprised of 2 parts, a core introducer and a soft catheter that is introduced over the introducer. As insertion procedures for catheters of this type are rapid and simple, they are particularly useful in acute critical situations. Semirigid catheters for medium-term use are usually made of flexible polyurethane polymers. Their relative rigidity allows direct insertion using a metallic guidewire, either with or without using an introducer and a vein catheter dilator. If a single lumen catheter is used, two catheters can be inserted into the same vein. Currently, double-lumen catheters are more likely to be used (Fig. 2). When using this type of catheter, the site of choice should always be the internal femoral or jugular site; the subclavian route should only be used if these are unavailable, as there is an increased risk of venous stenosis and thrombosis associated with this route. The performance and, more importantly, the recirculation rate depend on the length of the catheter: 30 to 35 cm

FIG. 1. Shown are the different types of hemodialysis catheters: single lumen (A); coaxial double lumen (cuffed type) (B); coaxial double lumen (opposing double D) (C); Desilet: central introducer, ringed dilator (D); and concentric double lumen (E).

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FIG. 2. A semi-rigid (polyurethane polymer) double lumen Duo Cath catheter is installed in the right subclavicular vein.

seems to be the optimum length for femoral catheters, and 20 to 25 cm for jugular and subclavian catheters. Catheters with a J-shaped bend are the preferred choice for insertion into internal jugular sites as they are more comfortable for the patient and less exposed to infection risks. This type of catheter can be kept in position for between 8 to 30 days. In the case of dysfunction, replacement of the catheter over a metallic guidewire is strongly advised against, as it carries a serious risk of endoluminal bacterial contamination. Flexible catheters for long-term use are a considerable advance in the field of temporary vascular access (2–4). These catheters are usually made of silicone polymers; occasionally they are flexible polyurethane polymers (Fig. 3). The common characteristics of these catheters are flexibility, nontraumatic properties, hemocompatibility, and the ability to be tunnelled (5). Percutaneous insertion of these types of material, using the Seldinger technique and Desilet catheters, will facilitate procedures in acute patients. Subcutaneous tunneling is essential with this type of catheter, ensuring greater stability and better protection from bacterial contamination. Long-term catheters are normally inserted into the superior vena cava (also called atrial catheters) through the internal (sometimes external) jugular route and, more rarely, the subclavian route (6). Recent work indicates that good results have been obtained when this type of catheter is inserted in the inferior vena cava system by the femoral route or, occasionally, by the trans-cava route (7–9). Venous insertion sites Conventional insertion sites for venous percutaneous catheters fall into three categories: femoral, internal jugular, and subclavian.

FIG. 3. Permanent flexible Dual Cath double-winged catheters (silicone polymer) are installed in the internal right jugular vein.

The femoral route was first proposed in the 1960s as an alternative to peripheral arteriovenous shunts and remains the access of choice in situations of extreme urgency. It is particularly suitable for acute patients with respiratory distress, impending hyperkalemia, or highly agitated patients. A double catheter or double-lumen catheter can be inserted into the femoral vein for as long as it takes to deal with the emergency. To reduce the recirculation rate, the distal end of this type of catheter should be placed in the central area of the inferior vena cava. The subclavian site, introduced in the 1970s, was widely used during the last decade. In has been almost abandoned by nephrologists because it is associated with an increase risk of stenosis and thrombosis complications. However, its use is still indicated as a secondary option when using longterm hemocompatible and nontraumatic catheters. There are also contra-indications in cases of respiratory distress or when stenosis or superior thoracic vein thrombosis (collateral thoracic circulation) is suspected. The optimum position for the distal end of semi-rigid catheters is the junction of the superior vena cava and the right atrium. The interior jugular site for hemodialysis introduced in the 1980s is becoming increasingly indicated as the most suitable procedure for acute patients. Semirigid catheters are inserted percutaneously in the upper part of the internal jugular vein. However, they expose the patient to the risk of bacterial infection and thrombosis of the host vein. Precurved catheters facilitate the use of occlusive dressings, are more comfortable for the patient, and appear to be the most effective way of preventing Ther Apher, Vol. 4, No. 3, 2000

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infections. For anatomical reasons, the use of the right jugular vein is preferred to the left jugular vein. This reduces the risk of trauma (perforation of vessels) and thrombosis. On the other hand, catheters for long-term use should be inserted lower, down into the internal jugular to optimize the flow. They will also be more efficient using a long (10 to 12 cm) subcutaneous tunnel, which will increase the stability and protect more effectively the catheter. This type of catheter can be inserted in either the right or left jugular. Ideally, the distal end of the catheter should be placed at the junction of the superior vena cava and the right atrium. Other, nonconventional, routes are also possible. These can be used to resolve some problems where vascular access has become difficult. We will just mention tunnelled femoral catheters into the thigh or abdomen and the inferior trans-cava catheters inserted using echolocation by the posterior percutaneous route (7,8). These routes are specific cases that deserve more in-depth analysis and must not be suggested as a first-choice procedure for acute patients. INSERTION, CARE, MONITORING, AND EVALUATION OF PERCUTANEOUS CATHETERS Currently, percutaneous insertion of deep vein catheters is the standard method. Normally, after the appropriate skin preparation, a blind puncture of the vein is performed under local anaesthesia using anatomical landmarks. Nowadays there is a tendency toward ensuring the success of this procedure by carrying out preliminary or continuous ultrasound guiding to the vein. The best functioning of the catheter depends essentially on the position of the distal tip. Fluoroscopic marking also facilitates proper positioning of the distal tip (10). Strict attention to procedure during set up, use, and handling can considerably reduce complications caused by catheters. The insertion of venous catheters must not be thought of as a simple routine procedure, as it is just the reverse and should therefore only be done by qualified doctors. Adequate skin preparation and careful aseptic procedures can avoid the risk of initial infections. Post-insertion infections will be avoided by restricting the use of percutaneous catheters to dialysis and by applying strict antiseptic procedures at each handling operation. The appearance of the catheter, puncture site, and subcutaneous path should be checked visually at each dialysis session. Blood cultures and cultures from the distal clot of the catheter should be carried out if there are concerns over the appearance of the Ther Apher, Vol. 4, No. 3, 2000

skin or if the patient appears to be in a subfebrile state. Quality care procedures and continuous vigilance by all members of the care team is imperative to reduce complications using hemodialysis catheters. Unfortunately, the ideal catheter, whose intrinsic qualities would ensure complete success without nursing care, does not exist; therefore, the quality of care given to the upkeep and monitoring of catheters will directly affect their performance and the incidence of complications. To prevent thrombosis, catheters should be locked at the end of the dialysis session with a standard heparin solution (5,000–7,500 IU); low molecular weight heparin or sodium citrate can also be used if heparin is contraindicated or responsible for bleeding. In case of catheter dysfunction due to partial endoluminal fibrin clotting, insufficient flow, or high venous pressure, the obstruction can be cleared either by chemical methods (fibrinolysis; Urokinase) or by mechanical methods (e.g. endoluminal brushing using a metallic guidewire). A plastic dressing will protect catheters during the interdialytic interval. At each dialysis session, the catheter must be checked to ensure that it is operating adequately. A useful and a simple method is to calculate the resistance index of the catheter. This can be obtained by measuring the arterial and/or venous pressure displayed on the dialysis machine as a function of the blood flow used. The recirculation rate (R) must also be known in order to avoid inadequate dialysis efficiency. R can be estimated by taking a blood urea sample (arterial, venous, and equilibrated arterial 2 min after stopping flow) or by direct measurement using on-line doppler probes (HD Monitor, Transonics). The overall effectiveness of the session should be checked periodically by taking pre- and post-dialysis blood samples to assess the dialysis dose (percentage of urea reduction, Kt/V) delivered during the session (11,12). Morphological assessment of catheters is necessary when malfunctions reoccur. The ultrasound method is used to detect deep vein stenosis or thrombosis. Auricular thrombosis can be detected using either transthoracic or preferably endoesophagic echocardiography. However, phlebography of the upper or lower limbs (depending on requirements) and the catheterogram are still the only imaging methods capable of confirming the existence of venous stenosis or thrombosis and, in some cases, enabling treatment. Systemic fibrinolysis should be considered in the case of a recent thrombosis, and transluminal angioplasty involving recanalization or

TEMPORARY VASCULAR ACCESS dilation should be discussed if there is a stenosis or symptoms of an old thrombosis. The presence of a thrombus forming a fibrin sleeve covering the distal end of the catheter is commonly reported. The obstruction can be removed by external stripping of the catheter via the femoral transcutaneous route using an appropriate snare probe and/or fibrinolysis (13,14). If this fails, the catheter should be removed, and anticoagulation therapy should be given. COMPLICATIONS OF HEMODIALYSIS CATHETERS There will always be risks involved in inserting and using catheters (15). Strict observance of the rules and appropriate procedures will reduce the risk incidence. At the moment, there are no catheters that do not carry some risk. Complications observed during the use of catheters fall into two categories: early or immediate complications and late or delayed complications. Immediate complications Immediate complications occur within minutes or hours of insertion of the catheter. The severity of the symptoms will distinguish minor forms from the major forms that could jeopardize the medical prognosis. Prior, detailed evaluation of the patient, taking into account the risk factors and carrying out the appropriate techniques using a trained operator, will minimize the incidence of complications. Table 1 lists the main forms of immediate complications. Delayed complications The onset of delayed complications normally happens after several days’ use of the catheter. Any venous hemodialysis catheter carries a higher risk of infection (16,17). These infections are a result of foreign materials carrying infectious micro-organisms being introduced into a vein. Fifty to seventy percent of all catheter losses are caused by infections. Two TABLE 1. Early complications of hemodialysis catheters Minor complications Difficulties with insertion (anatomic anomalies, previous thrombosis, or stenosis in vein) Persistent pain (head, shoulders, legs) Hemorrhage, localized hematomas Inflammation or infection of the skin puncture site Early malfunction (malposition) Major complications Trauma (pneumothorax, hemothorax, hemopneumothorax, hemomediastin) Anaphylactic reactions (allergy to the material or disinfectant) Arrhythmia (extra ventricular systole, ventricular fibrillation) Air embolism Perforation of anatomical structure (atrium, venous trunk, inferior vena cava)

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types of infections are observed with the use of catheters: local infection and generalized or systemic infections. Localized infections of the skin puncture wound and/or the subcutaneous pathway are the most frequent. The incidence of localized infection is estimated to be between 3 and 9 episodes per 1,000 patient days. Localized infections can act as an entry point for systemic infections. The infections are frequently caused by skin bacteria moving along the subcutaneous pathway from the exit site of the catheter. The puncture wound infection can be cleared up using appropriate local treatment and a systemic antibiotic (18). Tunnel infections spread along the subcutaneous pathway. They require immediate removal of the catheter and systemic antibiotic treatment. In two-thirds of all cases, the bacteria found are Staphylococcus aureus or epidermidis. Other, mainly gram-negative, bacteria are much more rarely found. Therefore, first-choice antibiotic therapy should act on Staphyloccocal and grampositive bacteria. Systemic infections, bacteremia or septicemia, present as serious and acute septic episodes. One day bacteremias usually have transient (24 to 48 h) febrile episodes corresponding to the endoluminal passage of the bacteria through the circulation. The incidence is around 3 to 5 episodes per 1,000 patient days (0.27–39). In this case, with suitable treatment, the catheter can be left in place. However, the catheter is often covered by a biofilm that confines the colonizing bacteria. For this reason a 3-pronged approach is required: The internal lumen of the catheter should be cleaned by fibrinolysis and, at the same time, an in situ strong antibiotic treatment (antibiotic lock) should be used and finally systemic antibiotics. Some authors suggest that satisfactory results can be obtained by replacing the line over a metallic guidewire as well as using systemic antibiotic treatment (19). On the other hand, if a septicemia is confirmed, with or without secondary local infections, the catheter must be removed immediately, and a suitable dual course of systemic antibiotics and bactericides should be given. The same applies in the case of infected thrombi, which cause catheter dysfunction and septicemia. In this case, the systemic antibiotic treatment must be complemented by effective anticoagulant therapy. Careful handling of the catheters by the dialysis care team, improvement in the catheters and materials design, and the use of preventive measures, such as the antibiotic lock, will greatly reduce the infection risk. Venous thrombosis is a common problem to all vascular prostheses. Introducing a foreign body into Ther Apher, Vol. 4, No. 3, 2000

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the circulation will inevitably initiate complex prothrombin formation via the activation of coagulation cascade (platelets are activated and adhesion occurs), formation of a fibrin network (“biofilm”) which traps the circulating blood cells, activation of the complement cascade, and stimulation of the acute inflammation. The risk of thrombosis appears greater in certain circumstances: use of hemoincompatible materials, inflammatory state, previous thrombotic incidents, or increased blood coagulation (20). Thrombotic complications can occur in several ways. First, endoluminal thrombosis blocking the exit of the catheter is the most common. Recanalization of the line can be done by mechanical methods (metallic guidewire or endothelial brush) or chemical methods (such as fibrinolysis) (21). The catheter can be kept open by an anticoagulant plug (heparin or another anticoagulant). Second, external thrombosis of catheters caused by a fibrin clot covering the distal end of the catheter requires either fibrinolysis, catheter stripping through the intraluminal percutaneous route (22), or removing and replacing the catheter. Third, thrombosis in the host vein (subclavian, internal jugular, or femoroiliac vein) is the most dangerous major complication. It occurs either in the proximal area of the vein close to the insertion site or in the distal area of the deep vein (23). When this is the case, the clot can adhere to the vein wall causing partial obstruction, or it can be large enough to obstruct the entire vessel lumen (superior vena cava system or inferior vena cava system). In this case, there is serious risk of a massive pulmonary embolism. After fibrinolysis treatment to reopen the vessel, the catheter should be removed. Anticoagulation treatment should be prolonged and implemented with great care to avoid all risk of embolism. Thoracic catheters are particularly likely to cause thrombosis in the right atrium. This is a serious complication that is potentially lethal (24,25). This type of complication can be prevented by using flexible, hemocompatible catheters, positioning the distal tip at the junction of the superior vena cava and the right atrium, and using preventive anticoagulant treatments for high-risk patients (26). Stenosis in the host vein is a troublesome risk factor in the long term. It is more common with semirigid venous catheters than with flexible catheters. Nevertheless, to a greater or lesser degree, it is a risk in all catheter treaments, including long-term tunnelled catheters (27). The risk of thrombosis is greater in subclavian veins than in jugular or femoral veins (28). We should point out, however, that the Ther Apher, Vol. 4, No. 3, 2000

studies have only assessed this risk with regard to rigid or semi-rigid catheters with low hemocompatibility and serious trauma in the vascular endothelium. A percutaneous venous angioplasty should be considered if there is a venous stenosis producing physiological repercussions (29,30). If a line breaks, there is a possibility of the embolism migrating. However, it is possible to retrieve it from the pulmonary circulation using femoral catheterization and hooking it with a snare probe. CATHETER DEVELOPMENTS AND FUTURE PROSPECTS Despite the known risks, catheters for dialysis are a vital part of all methods of extracorporeal purification. However, strict attention to all relevant procedures during use of these catheters will considerably lessen the risks. Research in the biomaterial and technical development fields have indicated some solutions that may make the use of catheters safer in the near future. We will only mention the main developments. Current standard practice for catheter insertion uses ultrasound marking or continuous guiding to the vessel; this reduces the failure rate and early traumatic complications. Surface treatment of lines and catheters with ion bombardment, silver-impregnation, and anticoagulant or antibiotic absorption are intended to prevent platelet adhesion and localized activation of coagulation (anticoagulants) and bacterial colonization (antibiotics) thus reducing the risks of thrombosis and infections (31–33). A recent study comparing the incidence of infectious complications using catheters impregnated with antibiotics and catheters without antibiotics confirms the effectiveness of this type of surface treatment (34). Work done with implanted chambers seems particularly hopeful (35), and the preliminary clinical results obtained with chronic patients appears very promising (36,37). Finally, using a “mixed lock” (anticoagulant and antibiotic) to close catheters also appears effective, significantly reducing the risk of infection (38). All these advanced techniques need to be evaluated to justify their cost and confirm their place in the range of catheters currently available. CONCLUSIONS Temporary vascular access necessary for extracorporeal treatment has benefited from the progress made in the field of deep-vein catheters. Percutaneous insertion has improved bedside care of patients. However, the risks of catheter implants should always be taken into account. Stringent care and sur-

TEMPORARY VASCULAR ACCESS veillance techniques will considerably reduce the risks. Semirigid polyurethane catheters are the first choice for short-term use (10 to 20 days). Catheters of flexible silicone are the best option for long-term use (several days to a few weeks). Technological advances in the catheter manufacturing are likely to reduce the risks even further. REFERENCES 1. Bander SJ, Schwab SJ. Central venous angioaccess for hemodialysis and its complications. Semin Dial 1992;5(2):121–8. 2. Canaud B, Be´raud JJ, Joyeux H, Mion C. Internal jugular vein cannulation with two silicone rubber catheters: A new and safe temporary vascular access for hemodialysis. Thirty months’ experience. Artif Organs 1986;10:397–403. 3. Shusterman NH, Kloss K, Mullen JL. Successful use of double-lumen, silicone rubber catheters for permanent hemodialysis access. Kidney Int 1989;5(3):887–90. 4. Gibson SP, Mosquera D. Five years experience with the Quinton Permcath for vascular access. Nephrol Dial Transplant 1991;6(4):269–74. 5. Moss AH, McLaughlin MM, Lempert KD, Holley JL. Use of a silicone catheter with a dacron cuff for dialysis short-term vascular access. Am J Kidney Dis 1988;12:492–8. 6. Johnson MS. Catheter access for hemodialysis. Semin Dial 1998;11(6):326–30. 7. Po CL, Koolpe HA, Allen S, Alvez LD, Raja RM. Transhepatic PermCath for hemodialysis. Am J Kidney Dis 1994; 24(4):590–1. 8. Gupta A, Karak PK, Saddekni S. Translumbar inferior vena cava catheter for long term hemodialysis. J Am Soc Nephrol 1995;5:2094–7. 9. Lund GB. Alternate access for catheter hemodialysis. Semin Dial 1998;11(6):331–5. 10. Selby JB, Tegtmeyer CJ, Amodeo C, Bittner L, Atuk NO. Insertion of subclavian hemodialysis catheters in difficult cases: Value of fluoroscopy and angiographic techniques. Am J Roentgenol 1989;152(3):641–3. 11. Kelber J, Delmez JA, Windus DW. Factors affecting delivery of high-efficiency dialysis using temporary vascular access. Am J Kidney Dis 1993;22(1):24–9. 12. Atherikul K, Schwab SJ, Conlon PJ. Adequacy of haemodialysis with cuffed central-vein catheters. Nephrol Dial Transplant 1998;13(3):745–9. 13. Crain M. Management of fibrin sheaths I: Percutaneous fibrin sheath stripping. Semin Dial 1998;11(6):336–41. 14. Lund GB. Management of fibrin sheaths II: Fibrinolytic therapy. Semin Dial 1998;11(6):342–6. 15. Tokars JI, Miller ER, Alter MJ, Arduino MJ. National surveillance of dialysis associated diseases in the United States, 1995. ASAIO J 1998;44(1):98–107. 16. Almirall J, Gonzalez J, Rello J, Campistol JM, Montoliu J, Puig de la Bellacasa J, Revert L, Gatell JM. Infection of hemodialysis catheters: Incidence and mechanisms. Am J Nephrol 1989;9:454–59. 17. Kessler M, Hoen B, Mayeux D, Hestin D, Fontenaille C. Bacteremia in patients on chronic hemodialysis. A multicenter prospective survey. Nephron 1993;64(1):95–100. 18. Levin A, Mason AJ, Jindal KK, Fong IW, Goldstein MB. Prevention of hemodialysis subclavian vein catheter infections by topical povidone-iodine. Kidney Int 1991;40(5):934–8. 19. Marr KA, Sexton DJ, Conlon PJ, Corey GR, Schwab SJ, Kirkland KB. Catheter-related bacteremia and outcome of attempted catheter salvage in patients undergoing hemodialysis. Ann Intern Med 1997;127(4):275–80. 20. D’amelio LF, Greco RS. Biologic properties of venous access devices. In: Wilson, SE, ed. Vascular access: principles and practice. St. Louis: Mosby, 1995:42–53.

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