Hemodialysis Catheters: Update on Types, Outcomes, Designs and Complications

Abstract

Hemodialysis catheters (HDCs) are an essential part of kidney replacement therapy. While these catheters are considered only the bridge to long-term vascular access such as arteriovenous fistulas and grafts, they are associated with significant morbidity and mortality and subsequent increased health care expenditures. However, despite these risks, a large proportion of end stage kidney disease population initiates dialysis using these catheters. The pathogenicity of HDCs stems from its invasive nature to the venous vasculature tree resulting in both mechanical and infectious complications. Therefore, the wide use these catheters in dialysis population and the associated complications necessitated continuous innovations in the catheter material, design, and placement techniques. This review provides an update on the catheter types, catheter tip designs, and the new technologies and innovations aimed to improve the catheter functionality and mitigate its related complications.

Hemodialysis catheters (HDC) are essential part of kidney replacement therapy. The clinical considerations are evolving as more new data and devices are becoming available. Since 1970s, Central venous catheters (CVCs) have provided central venous access, especially for hemodialysis. In 1976, to secure catheters, the subcutaneous tunnel creation was invented, and later a cuffed silicone catheter was developed for patients on hemodialysis. ¹ The percentage of end-stage-renal-disease (ESRD) patients using hemodialysis varies depending on several parameters, including the time of pre-ESRD care. According to the 2019 US Renal Data System annual data report, 80% of patients with ESRD receive hemodialysis via catheter. ² The use of these catheters is not without a risk. Some of the catheter related complications may lead to major morbidity and mortality in ESRD patient. Therefore, it is vital to investigate and improve the HDC designs and placement techniques to reduce these unfavorable outcomes in ESRD patients. This review discusses the different types of HDCs, the most recent developments in catheter designs, placement techniques, and outcomes. Additionally, catheter complications and subsequent catheter design changes to minimize these complications are discussed.

Types of Hemodialysis Catheters

Despite the efforts to decrease the frequency and duration of HDC requirement, most ESRD patients will need HDC for kidney replacement therapy. HDC placement, utilization and removal are associated with many risks and complications. The catheters have constantly been evolving to minimize the complication rates, improve the catheter patency, optimize blood flow, minimize intraluminal thrombosis, increase biocompatibility, and decrease the rate of catheter infection, kinking, collapse, or breakdown.

The most commonly used tip shapes include; step tip, split-tip, symmetric tip, and curved tip. ³ More recently, heparin-or antibiotic-coated catheters and self-centering catheters have been added to the toolbox. Currently, most of the HD catheters are dual-lumen and use the “DD” internal lumen design, which has low hydraulic resistance and small caliber. ⁴

HDCs provides vascular access for both short-term and long-term use and can be classified into two groups, non-tunneled and tunneled (cuffed) catheters.

Short Term Use Hemodialysis Catheters (Non-Tunneled Catheters)

Short-term use catheters are tapered, stiff and introduced over a guidewire. They are mostly used in an inpatient setting, where they can be placed at bedside using Seldinger technique without the need for fluoroscopy. Notably, these catheters are usually made from polyurethane or silicone. Polyurethane non-tunneled HDCs are stiff at room temperature, and they becomes less rigid after placement as they reach body temperature; a property that minimizes the risk of vessel injury. ⁵ The ports of the short-term catheters may be either straight or pre-curved to allow the external portion to adjust to the ergonomics of the neck and lie on the anterior chest. Pre-curved catheters are more comfortable for patients than straight catheters. Additionally, pre-curved catheters are associated with a reduced likelihood of kinking.

There are conflicts on duration safety in the literature, and recommendations vary from one to a few weeks. ⁶ The most commonly used short-term central venous catheters in the United States market are Niagara (BD Bard, Covington, Georgia, USA), Mahurkar (Medtronic,Dublin, Ireland), Duo Flow (MedComp, Harleysville, PA, USA), Power-Trialysis (BD Bard, Covington, Georgia, USA), Schon XL (AngioDynamics, Latham, NY USA), and Hemocath (MedComp, Harleysville, PA, USA). The last two are made from silicone and include insertion stylet to provide rigidity during insertion, while the others are made from polyurethane. ⁷ Silicone catheters are more flexible which decreases vascular damage during insertion, however, makes the catheter insertion theoretically harder. While these catheters are biocompatible and, thus less thrombogenic, their main disadvantage is the thicker wall, which decreases the internal lumen. Although blood flow rates are generally lower in non-tunneled as compared with tunneled HDC the blood flows are usually acceptable to achieve the desired clearance. It is worth mentioning that both silicone and polyurethane can be affected by antiseptic solutions. Whereas iodine deteriorates silicone, both alcohol and polyethylene glycol deteriorate polyurethane. ⁸

Long-term Hemodialysis Catheters (Tunneled Catheters)

The tunneled catheters are used to provide vascular access until the creation or maturation of a long-term dialysis access, such as arteriovenous fistula (AVF) or arteriovenous grafty (AVG). They are also used in patients who exhausted all access options for long term dialysis access. They are ideally placed under fluoroscopic guidance into the jugular vein and terminate in the right atrium. Tunneled catheters are made of pliable materials such as polyurethane–polycarbonate copolymer or silicone to minimize catheter breakdown, vascular damage, and catheter-related complications. Polyurethane-polycarbonate copolymers are systematically biocompatible. ⁸

It is well known that infection is the most common complication encountered with long term HDC and usually associated with significant morbidity, mortality and hospitalization in hemodialysis patients. ⁹ Most of these catheter-related blood-borne infections are often the result of colonization from the neighboring skin flora. ⁶ Subsequently, the tunneled cuffed catheters were developed in which the cuff is intended to form a fibrous tissue that could create a barrier against infection. Moreover, the cuff and its associated fibrous tissue could also provide more stable access by preventing displacement. Currently, all long-term catheters contain a polyester cuff that helps in positioning the catheters in the subcutaneous tract. As such, these catheters are described as tunneled or cuffed catheters. ⁴

In terms of design, the long-term HDC are made with side holes to maintain continuous blood flow during the dialysis process. ⁴ However, the presence of these side holes is associated with increased turbulence and subsequent intra-luminal thrombosis. The use of dialysis catheters that have no side holes has been reported to have a lower catheter infection rate. ¹⁰

In practice, there are five different tip designs for the long-term HDC available in the market; step-tip, split-tip, symmetrical, self-centering, and Y-Tip ( Fig. 1 ). The most commonly used long-term catheters are Palindrome (Medtronic), HemoStar (BD Bard), PermCath (Medtronic), Hemo-Cath (MedComp), Hemo-Flow (MedComp), Hemo-Split (BD Bard), Cannon (Teleflex, Wayne, Pennsylvania), CentrosFLO (Merit), and Glidpath (BD Bard) . Permcath, Hemo-Cath and Hemo-Flow catheters are made of silicone.

Fig. 1.

Comparison of contemporary design of various hemodialysis catheters, ( a ) Medtronic MAHURKAR step-tip type catheter. ( b ) Medtronic Palindrome symmetric-tip type catheter. ( c ) Medcomp Split Cath split-tip type catheter. ( d ) Merit CentrosFLO self-centering split-tip type catheter. ( e ) BD Bard Pristine Y-tip type catheter. (Illustration by Juri Bassuner).

Hemodialysis Catheter Access Sites

The most preferred HDC access site is the right internal jugular vein (IJV) due to its short distance to the right atrium, which provides a straight trajectory ( Fig. 2 ). Other venous options include left IJV and common femoral veins. Importantly, left IJV access is technically more challenging; has higher immediate complications during insertion such as venous lacerations and hemorrhage; and central vein stenosis related to the anatomic curves of the vein ( Fig. 3 ). Although the ideal catheter tip position of the femoral vein HDC is at the junction of the inferior vena cava (IVC) and the right atrium, this tip position is associated with increased flow resistance. Accordingly, a catheter tip within the IVC is enough to obtain adequate flow, which usually correlates with catheter length >24 cm. Of particular importance, no significant difference between the femoral and IJV HDC was found in the catheter infection rates among patients with body mass index (BMI) < 28Kg/m. ⁸

Fig. 2.

Radiograph image of right internal jugular tunneled hemodialysis catheter, showing the straight course of the catheter.

Fig. 3.

Radiographic image of left internal jugular tunneled hemodialysis catheter, showing the anatomic curves taken by the catheter.

After insertion, HDC often require repeated interventions to maintain its utility. In fact, it is estimated that the rates of primary patency failure, and HDC removal in the first year are 91% and 52%, respectively. ¹¹ Optimal catheter tip positioning for IJV catheters is recommended to be within the right atrium, a location that decreases the fibrin cap formation. ⁴

It is well recognized that the use of HDC in dialysis population is associated with multiple catheter placement, exchange, and removal procedures leading to central venous stenosis and eventually thrombosis, which ultimately limit future vascular access options.

In the subset of dialysis patients who exhausted the traditional venous access sites to perform therapy, other unusual routes have been utilized such as transhepatic and translumbar sites. Po et al. was first to describe the use of transhepatic hemodialysis route to perform dialysis among those who ran out of conventional vascular access sites ( Fig. 4 ). ¹² Further, Younes et al reviewed 22 patients who underwent a total of 127 transhepatic catheter placements at 24 transhepatic access sites and concluded that transhepatic hemodialysis catheter placement is associated with low rates of morbidity and provides a viable access for dialysis in this group of patients. ¹³

Fig. 4.

Radiographic image of transhepatic tunneled hemodialysis catheter.

On the other hand, percutaneous translumbar catheterization of the IVC was first reported in the 1980s ¹⁴ and then progressed to HDC placement using this approach ( Fig. 5 ). The main complications of translumbar hemodialysis catheters are poor blood flow (40%) and catheter related infection (36%). ¹⁵ Concerns were raised by some authors about the safety and effectiveness of translumbar tunneled HDC, especially in overweight and obese patients, who may be prone to catheter migration/malposition and retroperitoneal hemorrhage. However, these concerns were addressed by Nadolski et al. who found that translumbar tunneled HDC in patients with limited venous access is safe, and effective procedure regardless of the patient's body mass index. Further, the authors found that catheter-related central venous thrombosis rate was 0.01 per 100 catheter days, and catheter-associated infection rate was 0.51 per 100 catheter days, which is within the acceptable range according to National Kidney Foundation Kidney Disease Outcomes Quality Initiative guidelines for tunneled HDC (0.16 - 0.55 per 100 days). ¹⁶

Fig. 5.

Radiographic image of translumbar tunneled hemodialysis catheter.

It is worth noting that studies of tunneled femoral hemodialysis catheters have reported ipsilateral lower extremity deep venous thrombosis (DVT) rates ranging from 14% to 25% with substantially shorter primary patency in comparison to IJV hemodialysis catheters. ¹⁷ As a result, some interventionalists may favor translumbar access over the transfemoral approach to mitigate the risk of femoral-iliac DVT, a complication that could potentially delay or preclude surgical access creation or renal transplantation. ¹⁶

Hemodialysis Catheter Complications

The use of HDCs carry several risks and is associated with significant morbidity and mortality. These complications are classified into two groups: short-and long-term complications ( Table 1 ). Short-term complications can be related to the procedure itself including; provider inexperience, site of access, placement technique, or the patient's illness severity and comorbidities. Catheter-related bloodstream infection (CRBSI), thrombosis, central venous stenosis, and mechanical dysfunction comprise the long-term complications of HDC.

Table 1. Complications of hemodialysis catheters.

Acute, periprocedural complications  • Bleeding  • Hematoma, Hemothorax, Hemopericardium, Hemomediastinum  • Pneumothorax, pneumomediastinum  • Atrial perforation  • Cardiac arrhythmias  • Cardiac arrest  • Trachial laceration  • Air embolism  • Improper placement Chronic complications  • Infection (localized catheter infection, catheter-related bloodstream infection [CRBSI])  • Mechanical dysfunction (kinking, bending, breakage)  • Thrombosis (intraluminal, mural, atrial)  • Fibrin sheath formation  • Central venous stenosis  • Inadequate dialysis

Many guidelines have been developed to decrease the acute and chronic complications of HDC use in the dialysis population, with suboptimal success. Unfortunately, patients with HDC are at higher risk for hospitalization than those with AVF, and more likely to contract a CRBSI. ¹⁶

Peri-procedural and Acute Complications

The acute periprocedural complications that occur during HDC placement include arterial punctures, venous laceration, bleeding, hematoma (hemothorax, hemopericardium, hemomediastinum), pneumothorax, pneumopericardium, cardiac arrhythmias, and air embolisms. The following paragraphs shed some light on these complications.

Vascular Injury and Bleeding

The incidence of periprocedural arterial and venous injury associated with HDC placement is relatively low (<1%) but can be life-threatening, requiring emergency surgery when the injury involves lacerations to the superior vena cava, mediastinal vessels, or the right atrium ( Figs. 6 and 7 ). ⁶ On the other hand, the risk of periprocedural bleeding and hematoma formation is higher among those who have coagulopathies, thrombocytopenia, and hematological malignancies, or are using blood thinners. To lower these procedure-related complications, the use of ultrasonography guidance during HDC placement is advised, a practice that is associated with better outcomes. In terms of management, post placement oozing at the HDC site can be addressed by manual pressure, Gelfoam pledgets, or placing a simple stitch at the catheter exit. While symptomatic hematomas is usually treated with warm compresses, surgical evacuation is rarely indicated in clinical practice.

Fig. 6.

A case of difficult left internal jugular tunneled dialysis catheter placement, with no blood return on aspiration. The radiographic image shows contrast injection through the catheter with extravasation into the pericardium (white arrow) and right pleural space (black arrowhead) indicating vascular injury.

Fig. 7.

56-year-old woman who underwent traumatic left internal jugular non-tunneled hemodialysis catheter placement complicated by hemopericardium and hemothorax. ( a ) and ( b ) coronal maximum intensity projection (MIP) and axial contrast enhanced CT scan images respectively, showing misplaced left internal jugular non-tunneled hemodialysis catheter (thin arrow), Extracorporeal membrane oxygenation (ECMO) canula (thick arrow), bilateral chest tubes (white stars), hemopericardium (arrowhead), left hemothorax (curved arrow). ( c ) Central venogram showing extravasation at the site of misplaced catheter (thin arrow). ( d ) Central venogram following removal of the catheter and deployment of 2 Amplatzer II plugs at the extravascular catheter tract (thin arrow) showing no evidence of contrast extravasation.

Pneumothorax and Pneumopericardium

Pneumothorax and pneumopericardium are rare complications that are often seen with subclavian vein HDC placement. With the use of sonographic guidance, and proper technique, these complications are rarely encountered. Whereas high flow oxygen is usually sufficient to manage small size pneumothorax (<15%) in asymptomatic patient, chest tube placement is indicated to treat large pneumothorax with hemodynamic instability or hypoxia. ¹⁸

Cardiac Arrhythmias

Arrhythmias are often caused by the guidewire manipulation in the right heart, which is, mostly benign and temporary, and usually disappear after wire retraction or removal. ⁶

Air Embolism

Air embolism (AE) is a rare but potentially deadly complication that can occur during the insertion or the removal of HDCs. The exact incidence of AE is difficult to estimate due to the nonspecific symptoms, which makes the diagnosis difficult, and the lack of routine reporting. In a retrospective analysis, Vesely et al found that the rate of AE was 0.12% and mainly seen with tunneled catheter insertion that uses peal-away sheath. ¹⁹ The severity of AE ranges from asymptomatic or transient mild symptoms to severe organ ischemia, hemodynamic failure or rarely death. ²⁰ The awareness of this complication, the use of sonographic guidance during HDC placement, careful techniques and meticulous care during insertion, utilization, and removal of the HDC, help to mitigate this potentially fatal complication. During catheter removal, placing the patient in Trendelenburg position with breath holding is recommended.

Management of AE includes securing the airway by implementing the ABC of emergency (airway, breathing and circulation), placing the patient in in left lateral decubitus and Trendelenburg position to trap the air within the right atrium or right ventricular apex, and providing 100% oxygen by mask. In rare occasions when these measures are unsuccessful, the use of hyperbaric oxygen, chest compressions and manual removal of the air through a catheter should be considered.

Chronic Complications

Infection

Infection is overwhelmingly the most common long-term complication associated with HDC use. The risk factors include old age, diabetes, malnutrition, frequent catheter manipulation, longer duration of catheter use, bacterial colonization, and dialysis solution contamination. ^{6 21} For most patients with a HDC, the question is when will an infection occur. As the number of catheter days increases, the likelihood of bacteremia rises. In one study, 16.4% of patients developed a CRBSI within one year of catheter placement ²² with most of these cultures dominated by the skin flora microorganisms, such as S. aureus and S. epidermidis . ²³ Importantly, these organisms can result in further havoc on the patient's health through the hematogenous spread of the infection resulting in endocarditis, osteomyelitis, septic arthritis, epidural abscess, septic shock, and even death. ⁶ It is worth mentioning that the lifelong mortality risk among those who contracted CRBSI remains higher than the baseline risk of patients who did not have bacteremia or sepsis, even after CRBSI full recovery. ²⁴

With such high incidence rates and associated mortality, several guidelines and recommendations have been developed to prevent catheter-related infections. In 2011, the Center for Disease Control (CDC) published recommendations for dialysis staff and patients that emphasized hand hygiene, and mask and glove-wearing when accessing the CVC, as well as the use of either chlorhexidine >0.5% with alcohol, 70% alcohol, or 10% povidone-iodine solution before accessing the catheter hub. ²⁵ Although applying a topical antibiotic ointment at the CVC exit site was initially advocated during HDC placement, CDC in 2017 recommended the use of chlorhexidine impregnated sponge dressings as an alternative to antibiotic ointments at the exit site. ²⁵ Significant reduction in CRBSI was reported in a quality improvement project when chlorhexidine transparent dressing ( Fig. 8 ) was used, compared with dry gauze dressing and antibiotic ointment. ²⁶ A systematic review found that the use of exit-site antimicrobials may reduce the incidence of CRBSI. However, the use of the antimicrobial impregnated catheters and perioperative systemic antimicrobial administration was not associated with any benefit. ²⁷

Fig. 8.

( a ) Tegaderm CHG, Chlorhexidine Gluconate I.V. Securement Dressing. ( b ) The transparent chlorhexidine containing dressing applied at the tunneled hemodialysis catheter entry site.

In an attempt to reduce the incidence of CRBSI, catheter antimicrobial locks (AML) have been developed. Overall, the ideal AML should be able to prevent CRBSI, inhibit biofilm formation, and have a broad spectrum of activity, without causing catheter dysfunction or microbial resistance. ²⁵ These locks contain highly concentrated antiseptic, antibiotic or anticoagulant solutions that fill the catheter when it is not in use to prevent the formation of biofilms and CRBSI. ²⁵ Mai et al. evaluated the efficacy of AMLs and found that citrate based locks could reduce the risk of CRBSI as compared with heparin-based locks. Additionally, citrate locks were effective in reducing exit site infection in non-tunneled HDC. ²⁸

Several devices are developed to reduce CRSBI such as ClearGuard HD cap and GRIP-LOK™. ClearGuard HD Antimicrobial Barrier Cap (ICU Medical) is a hemodialysis catheter cap, which includes a rod that extends into the catheter hub. The rod and cap threads are coated with chlorhexidine acetate that is released from the rod into the catheter lock solution. The use of ClearGuard HD cap has been shown to be associated with lower rates of CRBSI in comparison to standard caps. ²⁹

GRIP-LOK™ (TIDI Products, Neenah, WI, USA) is a sutureless adhesive catheter securement device. A recent single-center retrospective observational study investigated this device and found a reduced risk of CRBSI in the non-tunneled HDC mainly via suppressing the catheter-exit site infection. ³⁰

CRBSIs are initially treated empirically with broad spectrum antibiotics, which can be modified based on the final pathogen identity and its antimicrobial sensitivities. In uncomplicated cases of CRBSI, catheter exchange over a wire can be considered in addition to antibiotic therapy. However, HDC should be removed in complicated CRBSI cases such as severe sepsis, osteomyelitis, endocarditis, persistent positive blood cultures after 72 hours of appropriate antibiotics therapy and fungal infections. ⁶

Thrombosis

Thrombosis is a frequent complication of HDC that can be classified into extrinsic (mural, central venous and atrial thrombus), and intrinsic (intraluminal, catheter tip thrombus and fibrin sheath) ( Fig. 9 ). ⁵ The pathogenesis of thrombosis is ascribed to the endothelial trauma during catheter placement as well as the catheter induced turbulent blood flow, which activate the coagulation cascade, leading to thrombus formation and subsequent occlusion ( Fig. 10 ). Early detection and treatment of HDC thrombi are crucial in preventing permanent vascular access loss and in lowering overall patient morbidity. Management of catheter dysfunction related to thrombotic occlusion include patient repositioning and forceful saline flush. If unsuccessful, intraluminal thrombolytic therapy with recombinant tissue plasminogen activator and systemic anticoagulation with warfarin, or direct oral anticoagulation with unfractionated heparin bridge can be used. ³¹ It is worth mentioning that the success rate of restoring patency with these treatment options have been variable. Furthermore, the threshold for what qualifies as adequate dialysis blood flow, and the maximum duration of an HD session varies widely among different hemodialysis centers. This variability may explain the difference in the rate of HDC exchange due to catheter dysfunction caused by thrombus formation/occlusion locally, regionally and globally. ³²

Fig. 9.

Types of catheter related thrombosis (Illustration by Husameddin El Khudari).

Fig. 10.

Virchow's triad (Illustration by Husameddin El Khudari).

Fibrin Sheath Formation

Fibrin sheath (FS) is composed of a smooth muscle cell–collagen matrix that is covered by endothelial cells. Starting within days of insertion, FS forms a sleeve that encase the catheter starting at the blood vessel entry point. ⁴ Once the catheter tip is involved, the FS act as one way valve, allowing catheter flushing and fluid administration, and preventing blood aspiration. The diagnosis is usually clinical and confirmed by injecting contrast under radiographic imaging ( Fig. 11 ). Management of FS formation includes catheter exchange with or without balloon angioplasty, and rarely FS stripping. All three techniques were found to be equivalent in terms of immediate technical success, complication rates, and durability of catheter function. ³³

Fig. 11.

( a ) Catheter injection through the tunneled hemodialysis catheter showing fibrin sheath formation (arrows). ( b ) Disruption of the fibrin sheath by angioplasty using 12mm × 4 mm balloon catheter (arrow). ( c ) Venogram showing successful disruption of the fibrin sheath. ( d ) Placement of a new tunneled hemodialysis catheter following fibrin sheath disruption.

Mechanical Catheter Dysfunction

These include catheter kinking, bending, fracture, dislodgment, migration, and improper catheter tip positioning. Catheter exchange is usually required to address these complications.

Central Venous Stenosis and Occlusion

While the subclavian vein, brachiocephalic (innominate) vein, and superior vena cava (SVC) are considered the central veins in the upper extremity, both the iliac vein and the IVC veins form the central veins of the lower extremity ( Fig. 12 ). HDC is often associated with central venous stenosis (CVS) and central venous occlusion (CVO), with an incidence of 20 to 50%. Importantly, both the number of the inserted catheters and catheter exposure are associated with increased CVS and CVO incidence. ⁶ Further, the rate of CVS and CVO tends to be higher with subclavian vein and left IJV catheters. Consequently, the presence of CVS may limit the availability of access options for future AVF or AVG creation in both upper and lower extremities and may preclude kidney transplant when it affects the iliac veins. Although the exact mechanism of CVS and CVO is unknown, several factors have been implicated in CVS and CVO pathogenesis such as the position of the catheter within the vessel, turbulent flow, uremic milieu with consequent inflammation, and multiple catheter insertions. ³⁴ Detailed endovascular management of CVS and CVO including recanalization techniques ( Fig. 13 ) and HeRo graft placement are discussed in other articles in this issue.

Fig. 12.

Central veins anatomy (Illustration by Husameddin El Khudari).

Fig. 13.

ESRD patient with right internal jugular tunneled hemodialysis catheter complaining of right arm and breast swelling. ( a ) Central venogram showing severe stenosis to almost complete occlusion of the superior vena cava (SVC) (arrow). ( b ) Angioplasty of the SVC stenosis using 12 mm × 40 mm balloon catheter with constriction at the middle of the balloon (arrow). ( c ) Release of the constriction ring after balloon angioplasty. ( d ) Central venogram showing successful angioplasty with patent SVC and free flow of contrast into the right atrium. A new tunneled hemodialysis catheter was placed at the end of the procedure (not shown).

Hemodialysis Catheter Lumen and Tip Design

The popular double-D lumen design was initially introduced in the Mahurkar (Medtronic) catheter, which maximizes the internal cross-section of the arterial and venous ports. Despite its low profile, this design provides a high blood flow rate necessary to perform hemodialysis.

Both non-tunneled and tunneled catheter types may have arterial and venous side ports that are staggered in position, usually by a few centimeters, with the arterial port proximal to the venous port. This design is characterized by step-tip and split-tip catheters like the Mahurkar (Medtronic) and Split Cath (Medcomp), respectively ( Fig. 1 a and c ). It is believed that this design minimizes the recirculation of blood from the venous tip to the arterial tip of the catheter. Conversely, symmetric-tip catheters have end lumens that are aligned and can be used as arterial or venous ports. In the case of the Palindrome (Medtronic) catheter, the symmetric tip has slanted cut-away in a spiral configuration that allows propulsion of venous blood downstream from the catheter, away from the arterial inflow ( Fig. 1 b ). ⁴ Unexpectedly, the lowest rate of recirculation is noted in catheters with symmetric tip (1%). In comparison, the rate of recirculation in the step-tip and split-tip catheters is reported to be 7% during the forward flow direction and 10–30% in the reverse direction. ³ This phenomenon is significant as the dialysis ports are frequently mixed up. ³⁵ Although split-tip catheters have longer patency rates than step-tip catheters, both types provide comparable blood flow rates. ⁴ In comparison, two randomized controlled studies showed greater catheter patency of the symmetric-tip catheters and lower dysfunction rates and recirculation with reversed blood lines compared with the step-tip catheters. ^{36 37}

Another symmetric catheter tip design involves the distal lumens angled on opposing sides of the catheter, so that blood exiting the venous port is deflected away from blood entering the arterial port of the catheter, and thereby reducing recirculation. This unique catheter tip also produce spiral laminar flow resulting in less platelet activation during dialysis and subsequently longer catheter patency rates ( Fig. 14 ). ³⁸ Using this design, the VectorFlow catheter (Teleflex, Wayne, Pennsylvania) was cleared for clinical use by the US Food and Drug Administration (FDA) in 2015. A recent multicenter randomized trial found that both Palindrome and VectorFlow catheters with symmetric catheter tips have similar 90-day primary patency rate although dialysis adequacy, measured by Kt/V ([dialyzer urea clearance × total treatment time]/total volume of urea distribution), was significantly higher in the VectorFlow catheter group compared with the Palindrome catheter group. ³⁹

Fig. 14.

Illustration showing the tip of the VectorFlow catheter with the spiral laminar flow of the returning blood (Illustration by Husameddin El Khudari).

In a continuous effort to improve catheter patency rate and reduce complications, the self-centering CentrosFLO catheter was developed. ⁴⁰ This catheter is an iteration of the split-tip prototype in which both the arterial and venous limbs of the catheter are curved, forming an oval shaped configuration. The side ports are directed inward to prevent contact with the vessel wall, a merit that hinders fibrin sheath formation and encasement of the side ports ( Fig. 1 d ). Prospective clinical trials demonstrated ∼90% patency of the self-centering catheters at 3 months of use. ³³

Another innovation in the catheter design was the recent introduction of Pristine catheter (BD Bard, Covington, Georgia, USA), which is characterized by the presence of the Y-tip with slots and the absence of the side holes ( Fig. 15 ). This design is claimed to prolong primary patency and decrease the rates of catheter thrombosis and infection. Preliminary clinical data demonstrated good patency and low complication rates. ¹⁰

Fig. 15.

( a ) PRISTINE catheter (BD Bard, Covington, Georgia, USA), ( b ) Y-tip design with slots in the tip wall and no side holes, ( c ) Radiographic image showing placement of 15.5 Fr PRISTINE tunneled hemodialysis catheter (arrow) through the right internal jugular vein. Note the simultaneous placement of a 6 Fr PRO-LINE tunneled central catheter (arrowhead) (Medcomp).

Other Designs of the Catheter Surface Materials

Various coatings and impregnated materials have been developed to enhance the performance of HDCs. For instance, BioFlo DuraMax catheter (Angiodynamics) used heparin on the catheter surface as anti-adhesive coatings to prevent the thrombus and fibrin sheath formation and consequently improve the HDC patency and functionality. Of a particular importance, the use of the anti-adhesive coatings could potentially decrease the long-term sequela of indwelling catheters such as central venous stenosis and, as such, preserves the vascular access real estate. ⁴¹

One the other hand, antimicrobial coated catheters commonly employ silver coating to decrease CRBSI. As an example, the Palindrome Precision SI-Silver Ion has a silver coating along the external portion of the catheter, between the cuff and the hub.

However, there is a concern about the development of antibiotic resistance associated with the use of catheter anti-bacterial coatings. Accordingly, an engineering technique called micropatterning, which mimics various natural surface patterns (such as the surface of shark skin or lotus leaves), is under development. The premise of micropatterning is that changing the HDC surface could potentially block the adhesion of bacteria and platelets and thus reduce the rate of colonization and fibrin sheath formation. ⁴²

Conclusion

Despite the efforts to decrease its use, HDC remains the main dialysis vascular access utilized in the ESRD population. These catheters are associated with significant morbidity and mortality related their mechanical and infectious complications. These complications are responsible for high economic burden encountered in this sick population and usually compromises the future creation of permanent vascular accesses. It is within this context that several innovations have developed in the catheter design and placement techniques to improve the overall catheter patency and functionality. Although several strides in the catheter design and material have been accomplished, several hurdles and challenges to reduce infectious complications and central venous stenosis sequalae remain unresolved.