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Central venous catheters: some common clinical questions

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VOL: 97, ISSUE: 19, PAGE NO: 34

Liz Simcock, BA, RGN, is clinical nurse specialist for central venous access, Meyerstein Institute of Oncology, Middlesex Hospital, London

There are several confusing and controversial clinical issues surrounding the use of central venous catheters (CVCs), not all of which have been addressed by research. Different management solutions are covered here under a series of topic headings and common questions.

Use of gloves

Should gloves be worn when accessing the catheter during dressing changes and, if so, do they need to be sterile?

The exact procedure and equipment used when handling the catheter is probably less important than following the principles of asepsis. Rowley (2001) argues that gloves should be worn to prevent descaling of bacteria onto key parts, but that the gloves need not be sterile as long as a no-touch technique is used.

When is it safe to use a CVC?

How soon after insertion can a CVC be used?

CVCs can be used immediately after insertion (including implantable ports), as long as the position of the catheter has been verified by X-ray.

Why is a chest X-ray necessary even though a tunnelled line or port has been inserted under X-ray guidance?

The function of this X-ray is to screen for pneumothorax. If the correct tip position in the superior vena cava has already been verified, many clinicians are happy for the catheter to be used for the infusion of intravenous fluids and drugs without waiting for the chest X-ray, as long as the patient shows no sign of breathlessness. However, it is suggested that complex treatments such as chemotherapy should not be started until the chest X-ray has been carried out.

How can I verify that the catheter is functioning properly and is safe to use?

Each time the catheter is used to administer therapeutic drugs or fluids, the patency and correct functioning of the line should be established. Signs of catheter occlusion, whether partial or complete, should be taken seriously, and action taken earlier rather than later to restore full patency. Ignoring the early signs may lead to the development of more serious problems, such as complete blockage or thrombosis (Hadaway, 1998).

Nurses can be confident of correct functioning if all three of the following apply (though they should note that, with implantable ports, this technique assumes correct needle placement in the port):

- Infusion fluids run freely into the line under gravity (although sometimes a flush with a 10ml syringe may be needed to achieve this). In paediatric care, however, free flowing of infusion fluids is not considered good practice because of the uncontrolled infusion of unknown volumes of fluid. In such cases, it is acceptable to assess this aspect by estimating resistance to flushing;

- Blood can be withdrawn from the catheter, or backflows into an infusion line when the infusion bag is lowered briefly below the level of the patient’s heart (Fig 1);

- The patient experiences no discomfort during infusion of fluids and there are no other complications - for example, leakage of fluids around the exit site.

If any of these criteria is not met, doubts are raised about the patency of the line and the safety of using it. Part four in this series explores the management of patency problems.

Flushing procedures

How often should the catheter be flushed when not in use and what solution should be used?

It is generally agreed that any unused lumen should be flushed regularly (even when other lumens are in use), but there is no clear evidence to suggest how often this should take place. Informal questioning of nurses expert in caring for patients with tunnelled CVCs and peripherally inserted central catheters (PICCs) revealed differences of opinion. However, the consensus is that twice a week is sufficient to prevent occlusion problems.

Is heparinised saline preferable to saline to maintain patency and at what concentration?

A review of the literature offers no clear answers, but the consensus is that a low concentration of heparinised saline (which should be prescribed by a doctor) is the preferred flush for unused tunnelled CVCs and PICCs (Mayo et al, 1996; Gabriel, 1996; Hadaway, 1998; Weatherill, 1999). However, there may be exceptions to this.

Hanson et al (1976) concludes, ‘only heparin solutions containing at least 10 units per ml prevented the formation of clots within the catheter’, and suggests that this lowest effective dose should be used.

With implantable ports, less frequent flushing with a stronger concentration of heparinised saline is recommended if the port is left unused for lengthy periods (flush once every four weeks with 5ml heparinised saline, 100 units per ml).

NB: if blood is present in the line, flush the lumen with 5-10ml 0.9% saline before the heparinised saline flush. If there are infusional vasoactive drugs in the lumen then these must be be withdrawn before flushing, otherwise the drug will be administered rapidly as a bolus dose.

Is there any need to withdraw and discard 3ml of blood before flushing the line?

This practice aims to avoid flushing micro-organisms (which might have been building up within an unused catheter) into the patient’s bloodstream and therefore, theoretically, reduces the risk of septicaemia. This is considered to be good practice by some expert practitioners, but it is not research-based. It is probably a good idea but is not always possible - sometimes an unused lumen needs a flush before blood can be withdrawn.

Dressings

Immediately after insertion, what dressing should be used for the exit site and how frequently should it be changed?

As with any surgical wound, the exit site should ideally be left undisturbed for several days. Routine taking down of the dressing to inspect the site merely exposes the patient to increased risk of infection. On the other hand, if the exit site bleeds and exudate/blood/serous fluid is observed on the outside of the dressing, then the dressing should be changed immediately as a wet surface provides a liquid pathway for bacteria to travel to the wound. For this reason, the ideal dressing immediately after insertion is a dry dressing, covered and sealed with a transparent dressing; in most cases this will absorb the slight ooze but will not require the dressing to be changed. If bleeding is excessive, the dressing should be changed for a more absorbent one and pressure applied to the site. The patient should also be encouraged to lie still until the bleeding settles.

Because of the infection risk, it is not acceptable to add more dressings on top of blood-soaked dry dressings that have been in contact with a moist outer surface. Nurses concerned about the risk of frequent dressing changes for these patients may be able to devise a system of using an occlusive waterproof dressing on top of a layered absorbent dressing, so that when it becomes blood-soaked, the gauze immediately over the insertion site can be left undisturbed.

What on-going dressing regimes should be used after the first two to four days?

There is no clear evidence to help decide on a dressing for exit sites. The following principles are generally agreed:

- Any dressing should be inspected regularly and renewed immediately should it become soiled, wet or detached (Cornock, 1996);

- If the exit site is red, painful, exudating or infected, the entry site should be inspected at least once a day (part three of this series discusses the care of infected entry sites).

The advantages and disadvantages of different dressings are given in Table 1.

With implantable ports, no dressing is required unless the port is accessed, and then a dry dressing or a transparent IV-dedicated dressing are recommended. Tape may be used to secure the edges of the transparent dressing (Oncology Nursing Society, 1989). The infusion set should be firmly taped to the skin to prevent pulling on the needle (ONS, 1989), and the needle site should be inspected daily while the port is accessed.

Cleaning of the exit site

How often should the exit site be cleaned and what solution should be used?

Evidence about exit site care advocates regular cleaning with antiseptics (Cornock, 1996; Maki et al, 1991; Todd, 1998), but this is difficult to justify in terms of modern principles of wound care. Fletcher (1997) regards the routine cleaning of wounds as questionable unless it is justified in terms of removing foreign bodies or debris. There is general agreement among wound care experts that antiseptics should not be used indiscriminately as they may impair wound healing and encourage resistant organisms (Oliver, 1997).

Most research with antiseptics on exit sites compares one type of antiseptic with another, rather than with saline. The most convincing research in favour of chlorhexidine (Maki et al, 1991) uses a solution that is not available in the UK in a sterile form. More research is needed, but in the absence of uncontested data it is proposed that:

- Routine cleaning of the exit site and surrounding skin at dressing changes may be justified to avoid odours and discomfort and to aid dressing adherence;

- Cleaning, when it occurs, should be carried out using sterile gauze and sterile 0.9% saline with an outward ‘single-swipe’ motion to avoid transferring bacteria to the exit site;

- Loose blood, exudate or other debris, which might provide a focus for infection or impair inspection of the wound, should be gently removed in the same manner (Oliver, 1997);

- The exit site should be allowed to air dry or may be dried gently using sterile gauze before applying a fresh dressing.

Washing and swimming guidelines

Can patients with long-term catheters shower, bathe and swim?

There is little literature to support any guidelines. The following principles may be taken into account when advising patients:

- Tunnelled CVCs

Twenty-one days after insertion, the patient’s tissues should have adhered to the cuff, creating a physical barrier to ascending bacteria (Wickham et al, 1992; Wilson, 1994). Patients may shower after this time as long as they remove any dry gauze-type dressing immediately before or after showering and dry the skin thoroughly afterwards using sterile gauze and a no-touch technique. Cleaning of the exit site in the usual way should follow, and if a dressing is used a new one should be applied.

If the patient is using an IV-dedicated transparent dressing, there is no need to change the dressing after showering as long as it remains occlusive. If the dressing has come adrift, it must be removed immediately and the exit site cleaned and redressed in the usual manner. If the patient wishes to have a bath, he/she should be advised to keep the exit site out of the water, even if it is covered with an occlusive dressing.

Swimming probably constitutes a considerable infection risk. Therefore, if the patient is keen to do so, a way must be found to cover the exit site completely with a waterproof dressing, leaving no chance of water coming into contact with the site. Anecdotal reports suggest that stoma bags may be used for this purpose. The patient’s own motivation and inventiveness may be important factors.

- PICCs

Because the PICC enters the vein at the point where the catheter exits from the body (that is, there is no tunnelling), the exit site should not be allowed to come into contact with unsterile water. So an IV-dedicated transparent dressing, if properly applied, will allow showering, but immersing the site while bathing or swimming should be discouraged.

- Implantable ports

Non-accessed ports do not require dressings and present no obstacle to bathing, showering or swimming as the skin is intact.

When a port is accessed with a needle (Fig 2) the patient should only shower if the needle site is completely covered with an occlusive dressing, and should then take care to ensure that the needle is not dislodged by vigorous movement. If he/she wishes to bathe, he/she should be advised against immersing the needle site in water. Swimming is not advisable because of the risk of dislodging the needle as well as the infection risk.

Replacement practice

Should centrally inserted non-tunnelled CVCs be replaced (over a guide wire) every seven days?

Some authors state that regular changing of the catheter may reduce the incidence of catheter-related sepsis, arguing that the risk of sepsis increases markedly after seven days (Cunha, 1995; Wilson, 1994). However, other authors dispute this and recent Department of Health guidelines (2001) argue against this practice.

- Next week, the series continues with the management of complications of CVCs

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