VOL: 97, ISSUE: 18, PAGE NO: 34
Liz Simcock, BA, RGN, is clinical nurse specialist for central venous access, Meyerstein Institute of Oncology, Middlesex Hospital, London
Central venous catheters (CVCs) are used in a wide variety of settings. In acute care, they enable rapid and reliable intravenous administration of drugs and fluids and are used to monitor central venous pressure. In other areas, such as cancer care, they may be used for patients undergoing long-term, continuous or repeated intravenous treatments, such as chemotherapy, and for blood sampling.
The term CVC refers to any intravenous catheter whose tip lies in a large central vein, giving what is termed ‘central access’. The tip of the catheter should be placed in the superior vena cava, just above the right atrium (Todd, 1998), where the blood flow around the catheter is far greater than in a peripheral vein. This means that irritant drugs or fluids can be easily infused without damaging the vein wall.
This series discusses four types of CVC: centrally inserted CVCs, tunnelled CVCs, peripherally inserted central catheters (PICCs) and implantable ports. The choice of device depends on the purpose for which it is intended, although patient preference may be a key factor with long-term catheters. Most CVCs come in different sizes with single or multiple lumens.
With multiple lumen lines, each lumen provides independent access to the venous circulation. This allows two incompatible drugs or fluids to be infused simultaneously. As a general principle the lumen diameter and number of lumens should be kept to a minimum as larger bore catheters and multiple lumens are associated with higher risks of infection and thrombosis (Jones, 1998). However, in high-dependency settings, large bore lines and multiple lumens tend to be used because they are essential for the management of acutely ill patients.
Another issue facing those who purchase and select CVCs is the material they are made of. Research suggests a possible advantage in using catheters impregnated with an antiseptic or antimicrobial coating (Pearson and Abrutyn, 1997), although this is controversial. Department of Health guidelines (2001) suggest the use of antimicrobial-impregnated catheters, but only in the short term for patients at high risk of infection.
Centrally inserted non-tunnelled CVCs
Centrally inserted non-tunnelled CVCs are most commonly used for patients in acute settings where the catheter will be needed only for a few days or weeks. Insertion may be in response to an emergency or a planned event. These lines are usually inserted via the subclavian, jugular or femoral veins (Todd, 1998) and secured to the patient’s skin using non-dissoluble sutures. They may have single or multiple lumens and each lumen is fitted with a clamp.
Tunnelled CVCs are often referred to as Hickman lines, although Hickman is a trade name. They are large-bore silicon catheters intended for longer term use in patients requiring multiple infusions of fluids, blood products, drugs or total parenteral nutrition (TPN). They provide access for routine blood sampling.
When inserted, one end of the catheter is introduced into a vein (usually the cephalic, subclavian, internal or external jugular vein) and threaded into the superior vena cava. The other end is tunnelled under the skin and pulled through, so the exit site is some distance from the point of insertion, reducing the risk of bacteria from the skin contaminating the bloodstream.
Most tunnelled CVCs are equipped with a fibrous cuff that sits under the skin about 1.5cm from the exit site. The patient’s tissues gradually grow around the cuff, which has two functions. First, it holds the catheter in place so the sutures can be removed seven to 21 days after insertion of the line. Second, it acts as a mechanical barrier to bacteria (Wilson, 1994).
Each lumen is equipped with a clamp or other type of sealing device. For example, Bard’s Groshong catheters have a three-way valve at the proximal end of each lumen instead of a clamp. Patients are often prescribed low-dose maintenance warfarin while the tunnelled CVC is in situ, to reduce the risk of thrombosis (Krzywda, 1999).
People with tunnelled CVCs often return home between treatments, so patient education on the recognition and reporting of complications is of great importance. Where possible, hospital care should aim to promote independence in managing the tunnelled CVC, but liaison with the primary health care team remains vital.
When assessing the suitability of this type of device for a patient, other long-term catheters, such as PICCs and implantable ports may be considered.
Peripherally inserted central catheters
A PICC is a fine-bore CVC inserted into a peripheral vein (usually the basilic or cephalic) and threaded towards the heart. The position of the tip needs to be verified by chest X-ray after insertion. PICCs may have single or multiple lumens. Each lumen is fitted with a clamp or other sealing device.
PICCs perform a similar function to tunnelled CVCs but differ in a few key aspects:
- They can be inserted relatively easily, without requiring a surgeon or theatre space, so they may be more cost-effective;
- They are associated with lower rates of thrombosis and sepsis (Wilson, 1994), as well as reduced risks of pneumothorax, great vessel perforation and ‘pinch-off’ (Todd, 1998);
- PICCs do not have a cuff to secure the line. There is nothing to keep the catheter in place unless it is secured by sutures, tape or a dedicated fixing device;
- The PICC exits onto the patient’s arm, so it may be difficult for patients to care for it themselves unless a conscious effort is made to leave an adequate length of line exposed for two-handed access. Dressing changes may also be awkward for the patient so, again, liaison with the primary health care team is vital;
- Some patients may find PICCs more acceptable than tunnelled CVCs, which exit onto the chest.
PICCs should not be confused with midline catheters, which are ‘usually 20cm in length … and are designed for short-term peripheral drug delivery’ (Todd, 1999). A midline catheter is not a CVC as its tip lies not in a central vein but in the region of the axillary vein.
PICC placement is contraindicated after axillary node dissection or irradiation or, in the case of lymphoedema of the arm, axillary node disease or skin infection at the insertion site (Todd, 1998).
The implantable port differs from other types of CVC because it has no external parts. Instead of protruding from the patient’s skin, the end of the catheter is attached to a self-sealing injection port implanted under the skin on the patient’s chest. Access is gained through the skin using a dedicated non-coring needle. Double-lumen catheters are available, each lumen terminating in its own port.
Some implantable ports are designed for intra-arterial access. The care for such devices differs significantly from that of intravenous ports, mainly because they include a one-way valve to prevent pressure from the arterial system resulting in back-flow into the port. Assessment of the port’s patency is slightly different, as is the frequency of flushing when not in use.
Some patients find an implantable port more discreet and less intrusive than a tunnelled CVC (Camp-Sorrell, 1992). They require less maintenance and may have a lower risk of infection (Camp-Sorrell, 1992; Krzywda, 1999).
Implantable ports are suitable for patients in need of long-term, frequent and intermittent venous access. Arguably, they are less than ideal for long-running, continuous infusions, because of the risk of the needle being dislodged (Schulmeister, 1989).
Ports may also be used as alternatives to subcutaneous administration of long-term maintenance therapies when the subcutaneous route has become unacceptable to the patient or is unreliable, for example, because of the formation of subcutaneous nodules.
As with tunnelled CVCs and PICCs, patients are often prescribed low-dose maintenance warfarin while the port is in situ to reduce the risk of thrombosis (Krzywda, 1999).
The patient may return home with the port in situ, so patient education on the recognition and reporting of complications is important, as is liaison with the primary health care team.
They are not recommended for obese or cachexic patients, before or after chest irradiation or at mastectomy sites (Camp-Sorrell, 1992).
- Next week, the series continues with a practical guide to the management of CVCs.