Dialysis catheters are artificial indwelling transcutaneous conduits that are used to access the intravascular space or the intraperitoneal space for renal replacement therapy (RRT). Different types of catheters used for extracorporeal RRT for patients with end-stage renal disease(ESRD)– which includes hemodialysis, hemofiltration, hemodiafiltration and ultrafiltration – and for peritoneal dialysis (PD). Catheters for extracorporeal RRT are essentially wide-bore central vascular catheters that allow blood withdrawal from and returned to the patient efficiently. Thus the blood can be processed in an extracorporeal RRT machine; the catheter may pass directly into the target vein, or may first pass through a short subcutaneous tunnel with a felt cuff securing it to the local tissue. PD catheters allow dialysate fluid to be instilled into and removed from the intraperitoneal space, where the dialysis occurs across the peritoneal membrane.
Non-tunneled catheters for extracorporeal RRT are preferentially inserted under ultrasound guidance, as this allows subcutaneous structures to be visualized and reduces the complication rates, but they can also be placed using only surface anatomical landmarks. Potential placement sites include the internal jugular vein, subclavian vein, and femoral vein. Tunneled cuffed catheters get inserted under fluoroscopic guidance into the subclavian vein. For catheters placed through the internal jugular vein or subclavian vein, the optimal tip location is at the junction of the superior vena cava and right atrium, and catheters around 15cm in length are appropriate. The subclavian vein is less commonly used in the acute or emergency setting, as flow rates may be more reduced, and this site carries associations with subsequent subclavian vein stenosis, which may make placement of a tunneled cuffed catheter or a surgical arteriovenous fistula more difficult should the patient go on to require this. Femoral vein catheters should be at least 20cm in length so that the tip of the catheter passes through the common iliac vein and reaches the inferior vena cava.
When correctly placed, peritoneal dialysis catheters should traverse the anterior abdominal wall, with the distal tip resting superficial to the visceral peritoneum and deep to the parietal peritoneum, pointed in the direction of the pelvis. The borders of the rectus muscle are preferred insertion sites, away from the paths of the superficial and inferior epigastric arteries. With the use of a Tenckhoff catheter with two cuffs, the deeper cuff should rest within the pre-peritoneal space in the rectus sheath, and the superficial cuff should lie 2 to 3cm medial to the superficial wound. Placing the deeper cuff outside the rectus muscle may lead to less tissue ingrowth, increasing the likelihood of leakage and herniation. If the superficial cuff placement is too deep, serous fluid may collect in the space outside of the cuff, leading to skin irritation and infection.
Placement of a dialysis catheter is invariably necessary for extracorporeal renal replacement therapy (RRT) in the emergency or acute settings. Non-tunneled catheters are appropriate for temporary, emergency or short-term use, and tunneled cuffed catheters may be more appropriate for medium-term to long-term use where there is the anticipation of ongoing need for RRT. However, hemodialysis for patients with chronic renal failure is preferentially carried out using an arteriovenous (AV) fistula, which consists of a suitable artery and vein that have been surgically attached, creating an “arterialized” vein that is more amenable to repeated venipuncture over protracted periods with wide-bore needles. AV fistulas require a surgical procedure and may take weeks to months to mature to the point where they are ready for use. By contrast, catheters can be used immediately after insertion, so they are often required for patients with subacute or chronic renal failure where it is not feasible to establish another means of vascular access in advance. Contraindications include local infection over the insertion site, thrombosis or stenosis within the target vein, distorted anatomy, or vascular injury.
For peritoneal dialysis, the placement of a catheter is always necessary. Peritoneal dialysis may be particularly appropriate where vascular access is difficult, in hemodynamically labile patients with poor cardiovascular function who may tolerate hemodialysis poorly, or in pediatric patients.
Contraindications for extracorporeal renal replacement therapy catheters include local infection over the insertion site, thrombosis or stenosis within the target vein, distorted anatomy, or local vascular injury. Peritoneal dialysis catheters may be contraindicated where the peritoneum is not intact, such as where there has been recent trauma, sepsis or surgery to the abdomen. Peritoneal dialysis itself may be inappropriate where the metabolic derangements are too extreme (such as in severe hyperkalemia), or in severe acute respiratory distress syndrome (ARDS) where the peritoneal fluid may splint the diaphragm and interfere with the work of breathing. It is unclear whether peritoneal dialysis or extracorporeal renal replacement therapy correlates with fewer risks in the presence of coagulopathy.
Catheters for Extracorporeal Renal Replacement Therapy (RRT)
The catheters used for extracorporeal renal replacement therapy are central vascular access devices with wide internal lumens. Blood is withdrawn from the patient and undergoes dialysis and/or filtration before being returned. The wide bores allow high blood flow rates, meaning that the desired RRT targets can be reached within a reasonable timeframe while reducing the shear stress on blood cells as they pass through the circuit. Externally, the catheter is attached to the renal replacement therapy machine using color-coded Luer taper connectors: the side where blood gets withdrawn from the patient is typically colored red, with the side where blood is returned being blue. Rates of blood flow through each connector are modifiable by adjusting the adjacent clamps. Most catheters are dual-lumen, incorporating both access and return limbs in the one device, but single-lumen catheters also exist; if these are used, two will be required. There are also triple-lumen catheters which include a third narrow lumen that can be used for other purposes while RRT is ongoing, such as right atrial pressure monitoring or administering medications.
Early dual-lumen catheters had a coaxial design, with blood removal through a large outer cannula and returned down the center through a narrow removable inner cannula; the inner cannula was replaced anew for each session of dialysis. Most contemporary catheters instead have the two lumens sitting in parallel side by side. Inside the patient, the return lumen opens at the distal tip of the catheter (that is, at the end closer to the heart), and the opening of the withdrawal lumen is physically separated from the return lumen by a short distance. This setup reduces the likelihood that purified blood returning to the patient will immediately be sucked back out into the extracorporeal RRT machine, a phenomenon known as “recirculation” which decreases the efficiency of the RRT session.
Both non-tunneled catheters and tunneled cuffed catheters exist. (A third category – implantable vascular access devices, with subcutaneous ports – saw limited use in the 1990s, but are no longer on the market.) Insertion of non-tunneled catheters is directly through the skin into the target vein. Tunneled cuffed catheters are different in that they have a longer shaft incorporating a synthetic felt cuff; they are also inserted through the skin, but they are then passed through a short subcutaneous tunnel before entering the target vein. The cuff ends up under the skin near the entry point and stimulates a local fibroblastic response, leading to ingrowth of the surrounding tissue over time which secures the device more firmly. Together, the cuff and tunnel act as barriers to microbial migration along the outside of the catheter, reducing the risk of catheter-associated bloodstream infections compared to non-tunneled catheters.
When correctly placed, the tip of the catheter should rest in the middle of a large central vein away from the vessel wall, so that the opening of the withdrawal lumen – which is under negative pressure – does not become occluded by the vessel wall gets sucked across it. The clinician placing the catheter should consider how its position may change when the patient moves. By the Hagen-Poiseuille equation, flow is inversely proportional to length, so the chosen catheter should be long enough that the tip can reach the intended target site, but should otherwise be as short as possible to minimize resistance to flow. Some dual-lumen catheters replace the single withdrawal opening near the tip with multiple side holes along the length of the catheter; this allows more flexibility in positioning the catheter near the vessel wall but may increase turbulence, leading to poorer flow rates. Alternatively, if the lumens are in parallel, the two end holes may be arranged so that the withdrawal lumen is on the inside of the catheter’s curve, further from the vessel wall.
The following equipment is required to place a non-tunneled catheter for extracorporeal renal replacement therapy:
If using ultrasound, the machine will require a linear probe, sterile probe cover, and sterile aqueous gel.
Catheters for Peritoneal Dialysis
Peritoneal dialysis catheters are single-lumen indwelling transcutaneous cannulas which allow dialysate fluid to be instilled into and removed from the intraperitoneal space. They have a single lumen, with multiple side holes present on the intraperitoneal section. Rigid catheters are usable in the acute setting; however, for chronic renal failure or patients with multiple organ failure, the most common type in contemporary use are Tenckhoff catheters (named for Henry Tenckhoff who pioneered their use). They differ in that their composition is of soft, flexible silicone, they incorporate one or two synthetic felt cuffs along the shaft (similar to those seen on the tunneled cuffed catheters used for extracorporeal RRT), and they are inserted using a special trocar or by the Seldinger technique. They can be placed by an open surgical technique or by laparoscopy; percutaneous techniques with or without fluoroscopy are less invasive but may have correlations with more complications. The tips of Tenckhoff catheters may be straight or coiled, with coiled catheters potentially being less susceptible to blockage.
For acute intermittent peritoneal dialysis, the dialysate fluid (approximately 2000mL for an adult, or 20 to 50mL/kg for a child) is instilled through the catheter into the peritoneal cavity and is left there for 30 to 60 minutes before being drained out by gravity. Some newer techniques like continuous-flow peritoneal dialysis require the presence of separate catheters for simultaneous inflow and outflow of fluid.
The following equipment is required to place a Tenckhoff peritoneal dialysis catheter using the Seldinger technique:
The presence of a skilled assistant during catheter insertion is beneficial but is not strictly necessary as long as patient positioning is correct, and all required equipment is available.
Where feasible, informed consent should be obtained from the patient after explaining the benefits and risk of the procedure, and this should be documented appropriately in the medical notes. IV access should be obtained, and monitoring commenced by ECG, blood pressure, and pulse oximetry. For peritoneal dialysis catheters, the patient should empty their bowels and bladder before the procedure. The patient should then lie supine on the treatment bed. Internal jugular or subclavian vein catheters should be placed with the patient in the Trendelenburg position, and with the head facing forward neutrally. Femoral vein catheters require exposure to the inguinal area. The chosen insertion site is painted as for a surgical procedure with an antiseptic such as povidone-iodine or 2% chlorhexidine. The clinician should don a hat and face mask (preferably with an eye shield or goggles), perform proper hand hygiene, and put on a sterile gown and gloves. A sterile drape is placed on the patient so that the aperture exposes the chosen site.
Catheters for Extracorporeal Renal Replacement Therapy (RRT)
Insertion of a hemodialysis catheter largely follows the same principles as for other forms of central venous access. The local surface anatomy is identified; if ultrasound is available, gel and a sterile cover are applied over the probe, and the device is used to visualize the subcutaneous structures to determine the route to the target vein. A local anesthetic is injected at the insertion site, first superficially to raise a subcutaneous wheal, and then more deeply to anesthetize tissues in the direction of the vein.
The introducer needle is attached to a syringe and then inserted through the skin towards the vein, applying constant negative pressure to the plunger of the syringe. When a flash of blood is aspirated, the clinician stops advancing the needle and detaches the syringe, covering the aperture of the needle to prevent air from entering. An alternative version of this process involves a cannula loaded over the needle; if using this technique, the cannula is threaded into the vein at this point, and the needle and syringe are both removed. The guidewire is then gently advanced through the needle (or cannula); if resistance is encountered, the operator should stop and confirm the position of the needle tip before repeating. Another variation of the procedure uses a special commercially-available syringe with a built-in channel through the center of the plunger, through which the guidewire can be inserted directly into the needle without needing to detach the syringe.
When the guidewire is in place, the needle or cannula is removed. The clinician next uses a scalpel to make a small nick in the skin at the site of the guidewire, and the skin dilator is then advanced over the guidewire through the skin into the target vein to open up a tract for the catheter, using constant rotation while advancing it to reduce the likelihood of kinking the wire. The dilator is removed while keeping gentle pressure over the site, and the dialysis catheter is then advanced over the wire into the desired depth, making sure to keep hold of the wire at all times to avoid accidental inward migration. The wire is then removed and the catheter secured to the skin using suture material and a dressing. For internal jugular or subclavian lines, a chest radiograph should be obtained to confirm the position and rule out pneumothorax.
Catheters for Peritoneal Dialysis
In the percutaneous Seldinger technique, a local anesthetic is first injected at the chosen midline insertion site, approximately 1 to 2cm below the umbilicus, through the full depth of the skin and abdominal wall down to the parietal peritoneum. A scalpel is used to make a nick at the insertion site, and a mosquito forceps is used to dissect bluntly down to the linea alba. Gripping onto the rectus sheath with the forceps, the abdominal wall is lifted to hold it taut away from the underlying bowel, and the cannula and needle are passed through the linea alba, stopping when there is a loss of resistance. The cannula is advanced, and the needle removed. The peritoneal space is then primed by instillation of warmed fluid (such as 500mL of normal saline), which should run in smoothly if the cannula tip is in the intraperitoneal space and is not kinked. This creates a fluid-filled space into which the catheter can be passed. The guidewire is then gently advanced, and the cannula is withdrawn. A specially-designed perforated sheath is inserted in its place using a special introducer before the guidewire and introducer are then removed.
After lubricating the catheter tip with gel and soaking the cuffs in saline, the catheter is slowly inserted into the abdomen through the sheath until the first cuff is in the pre-peritoneal space; the sheath is progressively split open along its perforations while the catheter is inserted before it is eventually broken away entirely and removed. Dialysate should flow freely into the intraperitoneal space if the catheter tip positioning is correct.
A more local anesthetic is injected under the skin laterally to the midline wound, and a small nick is made with a scalpel at this site. A subcutaneous tunnel is fashioned by passing a special tool into the midline wound, through the subcutaneous tissue, and exiting at the lateral wound. The proximal end of the catheter is then passed back through the tunnel; when correctly positioned, the second cuff should come to rest under the skin about 2 to 3cm medial to the exit site. The two wounds are then closed and dressed, and the catheter is fixed to the skin with suture material.
Rigid catheters are also inserted in the midline. The abdomen must first be primed with a bolus of dialysate fluid – approximately 2000mL for an adult – that is instilled through a wide-bore needle inserted at the midline wound site below the umbilicus. After priming, the needle is removed, and the catheter with its trocar is inserted through the abdominal wall with a rotatory motion. The trocar is slightly withdrawn, and the rest of the catheter is then advanced along the midline in the direction of the coccyx, with the catheter’s external bead coming to rest on the skin. The trocar is withdrawn before warmed dialysate fluid, and a collection bag is attached to the three-way tap, and fluid is then instilled to confirm patency. The catheter is then sutured to the skin and dressed.
Catheters for extracorporeal renal replacement therapy share the complications of other central venous catheters, and include morbidity and mortality from thrombosis and infection, trauma to adjacent structures such as the pleura (causing pneumothorax) or arteries, stenosis of the central veins, and failure of the device leading to lower blood flow rates and a shorter functional survival life in the patient. Dialysis catheter dysfunction may arise due to poor placement (such as kinking at the point of entering the vein, poor position of the tip within the blood vessel, or choosing a blood vessel that is too narrow for the device), stasis of blood; and hypercoagulability conditions of the blood. These can all predispose to the formation of a fibrin sheath around a catheter, greatly reducing its functionality. Various surgical techniques have been developed to restore patency and functionality in failing tunneled cuffed catheters. These include an over-the-wire exchange of one catheter for another, stripping of the fibrin sheath from around the device (by entering the vasculature via the femoral artery), and removal of the catheter followed by balloon dilatation of the fibrin sheath and re-implantation of another catheter in the same location. Reversing the bloodlines in the circuit – so that blood gets removed through the return lumen, and returned through the withdrawal lumen – may improve flow rates in a failing catheter, but at the expense of higher recirculation reducing the efficiency of RRT.
When placing catheters for peritoneal dialysis, misplacement of the needle during priming of the peritoneal cavity may result in dialysate instilling into the bowel or bladder, which may give rise to the sudden onset of diarrhea or sudden increase in urine flow respectively. Bowel perforation occurs in approximately 1% of cases, and damage to intraabdominal structures may reveal itself by the presence of fecal matter or significant amounts of blood in the effluent fluid. Infection of the cutaneous wound is less common early on, but peritonitis may occur, which may require treatment with antibiotics, discontinuation of peritoneal dialysis and switching the patient to extracorporeal RRT. Catheters may become obstructed over time due to malposition, kinking, adhesions, clots or formation of a fibrin sheath. Irrigation with saline or urokinase, or repositioning of the catheter, may restore flow. Laparoscopy and omentectomy may ultimately be required. Fluid may leak through the cutaneous wound; this is more common with rigid catheters than tunneled Tenckhoff catheters.
Catheters inserted for chronic renal failure may need to remain functional for several months and should be cleaned and cared for using appropriate substances. Many dialysis catheters are made from polyurethane, which is a thermoplastic and becomes softer at body temperature while retaining tensile strength. However, it is weakened by alcohol (a commonly-used disinfectant), by most antibiotics except for triple antibiotic ointment, and by polyethylene glycol which is a common component in ointments. Some newer catheters are made from silicone, which is more flexible and softer than polyurethane, and consequently requires that the catheter have thicker walls to avoid collapse or kinking of the line. It is more compatible with ointments but is weakened by exposure to iodine, another commonly used disinfectant.
The nephrologist and dialysis nurses need to know the different types of dialysis catheters available on the market. While they all function similarly, they all are also prone to a wide range of complications. The dialysis nurse is usually in charge of the care of the catheter.
Complications arising from vascular access in dialysis patients are a significant cause of morbidity and mortality, particularly when comparing the long-term use of transcutaneous central venous catheters to other modalities of vascular access. In the United States, the number of dialysis patients requiring hospitalization for infections related to vascular access more than doubled between 1993 and 2006, although the number has since plateaued. A high proportion of end-stage renal disease – in excess of 50% in some series – end up requiring renal replacement therapy to be started urgently by a central venous catheter. The Kidney Disease Outcome Quality Initiative currently recommends that less than 10% of chronic hemodialysis patients should receive treatment through central venous catheters and that this modality should be a consideration only if alternative modalities such as AV fistulas and grafts are inappropriate, or have failed. In healthcare organizations providing dialysis services, where the case mix includes a lower proportion of patients using catheter-based dialysis, those patients may experience higher rates of catheter-associated infections. Infection control measures may be stronger in organizations dealing with higher proportions of this patient group.
Overall, peritoneal dialysis appears to correlate with lower requirements for hospitalization than hemodialysis. Success for peritoneal dialysis may be optimized by good multidisciplinary communication, monitoring of renal function, careful patient selection and early placement of the catheter; immediate initiation of dialysis after placement should be avoided.
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