**2. Types of central venous catheters**

There are two main categories of hemodialysis catheters: (i) non-tunneled, uncuffed, designed for short-term venous access of up to three weeks and (ii) tunneled, cuffed catheters for longer use. An ideal CVC is biologically neutral and does not induce venous or catheter lumen thrombosis; its surface is coated with an agent, which prevents migration and multiplication of bacteria. It should enable continuous dialysis with the blood flow through the catheter > 350-400 ml/min. Moreover, it ought to be non-traumatic, soft, easy to insert, mechanically durable, bending-resistant, comfortable for the patient and inexpensive. A comparison of acute and chronic central venous catheters is shown in Table 3.

*i. Temporary acute catheters* 

Acute untunneled CVCs are used in emergency situations (dialysis, plasma exchange, hemofiltration or hemoperfusion) or as a short-term bridging access (ideally < 7 days). The advantages of these catheters are their ease of insertion (even by the bedside), the ability to insert them in multiple sites in almost any patient and the lack of hemodynamic compromise associated with their use. Internal jugular vein is the preferred site as

and infection compared with AVFs. As a result of this, maintaining CVCs is associated with high costs (Lacson et al 2007). The increased use of CVCs requires a maximal precaution in

Maturation time not required Lower blood flow rates requiring a longer dialysis time

its management and a stringent practice to reduce its risk and complications.

No venepuncture

Easy replacement Functional for months (chronic tunneled CVC) Ease of correcting thrombotic

complications

exhausted

*i. Temporary acute catheters* 

No hemodynamic consequences

Pending maturation of arteriovenous fistula

controlled and the peritoneum be rested Awaiting for living-related donor transplantation

Table 2. Indications for central venous hemodialysis catheters

planning of long-term access

**2. Types of central venous catheters** 

**Advantages Disadvantages**  High success rate High morbidity caused by thrombosis and infection Insertion into multiple sites Risks of permanent central venous stenosis or occlusion

Table 1. Advantages and disadvantages of central venous catheters for hemodialysis

 Providing temporary dialysis treatment for patients undergoing maintenance peritoneal dialysis but complicated by peritonitis such that the infection can be

"Bridging dialysis" followed failed previous vascular or peritoneal access allowing

Permanent vascular access when other sites for arteriovenous fistula or grafts are

There are two main categories of hemodialysis catheters: (i) non-tunneled, uncuffed, designed for short-term venous access of up to three weeks and (ii) tunneled, cuffed catheters for longer use. An ideal CVC is biologically neutral and does not induce venous or catheter lumen thrombosis; its surface is coated with an agent, which prevents migration and multiplication of bacteria. It should enable continuous dialysis with the blood flow through the catheter > 350-400 ml/min. Moreover, it ought to be non-traumatic, soft, easy to insert, mechanically durable, bending-resistant, comfortable for the patient and inexpensive.

Acute untunneled CVCs are used in emergency situations (dialysis, plasma exchange, hemofiltration or hemoperfusion) or as a short-term bridging access (ideally < 7 days). The advantages of these catheters are their ease of insertion (even by the bedside), the ability to insert them in multiple sites in almost any patient and the lack of hemodynamic compromise associated with their use. Internal jugular vein is the preferred site as

A comparison of acute and chronic central venous catheters is shown in Table 3.

anatomically this provides the most direct route to the superior vena cava and right atrium. The vein should be localized by ultrasound (+/- Doppler). Insertion into the left internal jugular vein is associated with a higher incidence of central stenosis and poorer patency. For selected cases requiring short-term dialysis, the femoral vein can also be used. Subclavian vein should be discouraged as it may jeopardize the long-term arteriovenous access options with complication of subclavian stenosis. The catheters are usually inserted using the Seldinger technique. The catheter can be used immediately after confirming correct placement with fluoroscopy.


Table 3. Comparison between acute and chronic central venous catheters

To ensure continuous, independent blood flow, catheters are double–lumen. The distal part has two separate openings; one collecting the patient`s blood − "arterial", located 2-3 cm from the catheter end and the second one pumping the blood to the patient − "venous", placed at its end. Temporary catheters are usually made of stiff materials: polyurethane or polyvinyl, and thus are easier to introduce along the guidewire and a hemostasis valve is not needed. The sharp distal tip facilitates the insertion through the subcutaneous tissues. Compared to soft catheters, they are more resistant to bending in the vessel. At body temperature, after contact with the bloodstream, they become plastic, which reduces the risk of vessel damage. Temporary CVCs have no cuffsbut are quipped with dacron muffs. The insertion doe not require "tunnelization", thus fast access to the circulatory system can be provided. They vary in length, therefore the proper choice is easier depending the puncture site and availability of a central vessel. They may be used for several days or up to three weeks. Their main advantage is easy insertion into the vessel using the Seldinger technique with easy replacement not requiring expensive accessory devices, (which may not be always available) such as fluoroscopy or ultrasound. Generally, the blood flow through temporary CVCs is limited to 200-250 ml/min.

The newer catheters are made of silicone with bigger internal diameter which ensures the blood flow of 400 ml/min. Some of them are tunneled. Silicone is thermoset and thus the catheter is soft. Hence it has to be inserted using a dilator and peel-away sheath. Other materials include polyurethane which is thermoplastic and softens at body temperature. This reduces endothelial damage and thrombogenicity (Leblanc et al 1997). The tunneled catheters can be introduced either antegrade (skin to insertion site) or retrograde (insertion site to skin). The position of soft CVCs should be confirmed by fluoroscopy.

Acute and Chronic Catheter in Hemodialysis 111

veins or external iliac veins (Maya et al 2005). The vein should be localized by ultrasound and can be differentiated from the artery by Doppler. The probe should first be placed on the head of the sternomastoid muscle and then moves down towards the clavicle. The puncture site should be as low as possible but above the clavicle whereas the exit of the

Femoral and external iliac veins may be used for CVC insertion in bed-ridden patients or in the intensive care setting, particularly in patients requiring artificial lung ventilation, after head and neck trauma with numerous catheters and drains of the neck and thorax as well as those with tracheostomy (Zaleski et al 1999, Mathur et al 1993). Patients with kidney transplant potential should avoid femoral vein catheterization. With catheter insertion in the groin, meticulous hygiene of the puncture site is required. The patency period from the insertion to removal is markedly shorter in femoral vein access compared to catheters

Irrespective of the type (non-tunneled or tunneled) or design (straight or with formed shape), their use is likely to be associated with complications (Table 4) (Morgan 2001, Ross 2001).

**Early Late** 

The incidence of complications reaches 5.9% with catheter insertion based only on topographic anatomy even with experienced clinicians (McDowell et al 1993). In contrast, the incidence of procedure-related complications in central venous catheterization under ultrasound guidance is only 0.8% (Trerotola et al 1997). Ultrasound-guided catheterization also limits the incidence of failures related to catheter insertion and reduces complications and necessity of multiple punctures of a vessel (Randolph et al 1996). Early complications which are mainly "surgical" include pneumothorax, pleural or mediastinal hemotoma, air embolism, thoracic tract injury, damage to nervous structures within the neck and thoracic region, puncture of the cardiac cavities, or cardiac arrest (Feldman et al 1996) (Figure 1).

Non-surgical complications include cardiac arrhythmia and insertion site infection.

Hemothorax Central vein thrombosis

Pericardial tamponade Central vein stenosis Atrial perforation Catheter dysfunction

Table 4. Complications of central venous catheters insertion

Pneumothorax Catheter thrombosis formation

Dissection/occlusion of carotid artery Permanent vascular ingrowth

Infection

(can be early due to kinking)

subcutaneous tunnel should preferably be below the clavicle.

inserted through the internal jugular vein.

**4. Catheterization-related complications** 

Inadvertent arterial puncture and central

vessel perforation

Arrthymias Air embolism

Retroperitoneal hemorrhage (for femoral vein insertion) Primary failure – technical error

#### *ii. Long-term tunneled catheters*

Tunneled CVCs with cuffs are made of silicone, silastic or carbothane elastomer, polyurethane co-polymer and polycarbonate − these materials are softer and more plastic than those used in temporary catheters. Therefore, they are usually inserted using the Seldinger technique via peel-away sheath. Subcutaneous tunnelization and a cuff are to stabilize the catheter and prevent the spread of infections. The soft silastic elastomer enables the placement of the distal catheter tip in the right atrium, which should be confirmed by fluoroscopy. Bigger internal diameters (thicker catheters) provide better blood flows and a wider dilator or sequential dilator is frequently used.

The first model of a tunneled catheter was PermCath, an oval catheter with two circular canals. Subsequent models (e.g. Vas Cath) were designed with an internal septum dividing the internal lumen into two parts. The oval transverse section of the catheter facilitated its insertion through the peel-away sheath. The third popular option was the introduction of two catheters with a single lumen – Tesio or its modification. One collected the blood through the opening in the superior vena cava and the other one supplied blood through the opening in the right atrium. Other than the catheter body and lumen, the design of the shape of catheter tips is also emphasized for better blood flow, improved reliability and minimizing recirculation (Ash 2008).

The newest catheters implanted surgically are equipped with a subcutaneous port (Morgan 2001, Ross 2001), which reduces percutaneous device-related complications. In most cases, the port consists of a chamber made of a titanium, ceramics or other neutral plastic materials with silicone membrane and an attachable catheter. The silicone membrane enables repeated penetrations (about 1000-2000), depending on the product and size of the puncture needle. The entire system is placed under the skin, which prevents infections or accidental opening. There are different configurations of the catheter and port chamber from using two single catheters each attached to a single chamber port to a double-lumen catheter connected to a two-chamber port. The vascular port implantation is based on the same principles as those for central venous access except the ports are placed in a subcutaneous pocket. The port can be punctured with normal hemodialysis needles or needles with special make that does not cut an opening in the membrane. The main reason of low popularity of hemodialysis ports is their relatively high cost.
