Which action is best for preventing air embolism in a patient with a central vascular access device CVAD )?

Karen Cowley, DipHE, RGN.

Practice Development Nurse at York Hospitals NHS Trust

Vascular access devices (VADs) are inserted into veins via peripheral or central vessels for diagnostic or therapeutic reasons, such as blood sampling, central venous pressure readings, administration of medication, fluids, total parenteral nutrition (TPN) and blood transfusions.

The choice of VAD should be based on the needs of the patient, the reason the line is required, the length of time it needs to remain in situ and the skills of the operator. The size, the material it is made of and the manufacturer’s guidelines must also be considered.

It is important to ensure that operators are suitably trained to use VADs. Standardising devices across a trust will avoid the confusion that can occur if many types of VAD are available. This will increase staff familiarity with a particular device and increase competence in its use.

VADs, particularly multiple-lumen devices, have been increasingly linked to a higher infection risk (Jones, 1998), so lumens should be kept to a minimum where possible. VADs should be inserted and accessed using aseptic technique.

Dressings used to cover the site should be semipermeable to promote evaporation of moisture, which will prevent the site becoming macerated and infected, and prolong the time the VAD can be left in place. Maintenance of all the lines described in this review should be based on RCN standards for infusion therapy (2003) and NICE guidance (2003).

There are several types of VAD, which can be inserted peripherally or centrally. Peripheral lines are cannulae and midlines. Centrally inserted devices are peripherally inserted central catheters (PICCs), non-tunnelled central venous catheters (CVCs), tunnelled central venous catheters, and implantable ports.

The Medicines and Healthcare products Regulatory Agency states that operators of any piece of equipment must be trained to use it and must be able to prove they are competent to do so. This is becoming increasingly important since the launch of the Clinical Negligence Scheme for Trusts, which requires proof of training and competence in the light of litigation claims (NHS Litigation Authority, 2004).

Peripheral cannulae

Peripheral cannulae are the most commonly used type of VAD in secondary care settings. They are used for short-term (one to five days) infusions of fluids, blood products and medication, and are inserted by health-care professionals with very few problems.

The cannula is a flexible tube containing a needle that can be inserted into a vein (Anderson and Anderson, 1995), usually those on the dorsal and ventral surfaces of the upper extremities.

The most commonly used veins for peripheral cannulation are the metacarpal, cephalic and basilic (Dougherty, 1999; 2000; Hadaway 2001; Centers for Disease Control and Prevention, 2002). It is possible to use veins in the lower extremities (feet), but this is best avoided in adults owing to increased risk of thrombophlebitis.

The advantage of using this type of VAD is that it is usually easy to insert and has few associated complications. However, peripheral cannulae are associated with phlebitis, which may require them to be resited.

Site selection should involve a thorough assessment of the patient’s veins to establish suitability. Veins that are inflamed, fibrosed, thrombosed, bruised or have been venepunctured previously should be avoided.

A number of types of peripheral cannula is x available. Evidence suggests that the incidence of complications increases as the ratio of the cannula’s external diameter to vessel lumen increases. The use of the smallest, shortest gauge cannula is therefore recommended (Millam, 1992; Perucca, 1995; Weinstein, 1997; Fuller and Winn, 1999).

Standard wire gauge is the measurement used for needles and cannulae. This measures the internal diameter of the cannula, so the smaller the gauge size, the larger the diameter of the cannulae.

The over-the-needle cannula is the type most widely used - it is available in a range of gauge sizes, lengths, materials and designs. A thin, smooth-walled cannula, tapering to a scalloped end will cause less damage on insertion than one that is abruptly cut off (Dougherty, 1999).

Cannulae should be thin walled, to provide the largest internal diameter without increasing the external diameter. Using the thinnest walled cannula will reduce mechanical irritation to the vein wall, enable blood to flow around the line and increase the uptake of medication, fluids and blood products, thus decreasing the risk of chemical irritation.

The largest internal diameter also aids maximum flow rates. Cannula flow rates vary according to manufacturer, material and device length.

Materials used to manufacture cannulae are non-irritant and should not predispose to thrombus formation (Payne-James et al, 1991). Teflon material is quite rigid, therefore polyurethane-based cannulae are preferable due to the flexibility of the material and because smaller gauge cannulae can be used. This in turn reduces phlebitis. Ideally, the cannula should be radio-opaque to aid detection should part of it shear off and cause an embolus.

Midlines

A midline catheter provides venous access in a large peripheral vein but does not enter the central venous system. Midlines are usually inserted into a vein situated in the antecubital fossa area of the arm and the tip extends into the vein of the upper arm up to 20cm. Midlines should not be extended past the axilla.

Midline catheters are used when patients do not have accessible peripheral veins or have a minimal number of adequate vessels available for administration of therapy for moderate duration (less than six months) (Oncology Nursing Society, 1996). If they are used for longer periods for IV antibiotics, for example, it is better to use a midline rather than repeatedly cannulating patients.

Midlines can be inserted to provide venous access in patients who have poor peripheral veins or in whom insertion of a CVC is contraindicated.

Midlines are fairly easy and less complicated to insert in the antecubital fossa (Goetz et al, 1998). Radiological confirmation is not required, as the tip does not proceed beyond the proximal aspect of the arm (RCN, 2003).

However, the Intravenous Nursing Society (1998) supports radiological confirmation in certain clinical situations, for example, if vesicant infusions are to be administered. Should that be the case, check with the manufacturer of the device that it is safe to do so and keep a vigilant eye on the line because of the risk of damage should the infusion extravasate. Health-care professionals can be trained to insert midlines with the support of the manufacturers.

Silicone and polyurethane are the most common materials used to make midlines, which are available as single- or double-lumen catheters with a length of 20cm. The line can be cut to the desired length after measuring the patient’s arm from the selected site of insertion.

The vein of choice for insertion is the basilic, as it is large, straight, and the lines tend to last longer than if they are sited in the cephalic vein.

Central venous catheters

A CVC is a device whose tip is positioned into the superior vena cava or right atrium by direct entry into the antecubital fossa, jugular or subclavian veins.

CVCs are used to monitor central venous pressure, administer large amounts of fluid or blood products, provide long-term access for administration of vesicant drugs, such as cytotoxic and antibiotic infusions, for repeated specimen collection and TPN.

Insertion is potentially hazardous (Speer, 1990). Because of the likelihood of complications, doctors tend to insert CVCs, but appropriately trained nurses can insert peripheral central lines.

Four types of CVC are available: peripherally inserted central catheters (PICCs), centrally inserted catheters (non-tunnelled and tunnelled), and implantable ports.

The choice of which device to use will depend on how ill the patient is, the reason for insertion and patient preference.

CVCs come in different sizes, with single or multiple lumens. Multiple lumens allow numerous drugs to be administered simultaneously without the risk of interaction. However, multiple lumens are documented as increasing the risk of thrombus and infection.

Multiple-lumen catheters are used in acutely ill patients in nurse-enhanced units, high-dependency units and intensive care units. Every lumen must have an external clamp to minimise the risk of air embolism; the use of needle-free devices such as a ‘Bionector’ (Vygon) will reduce the risk of infection and prevent air embolism compared to three-way taps.

Peripherally inserted central lines

A peripherally inserted central line is a catheter that is inserted into an antecubital fossa vein - the basilic or cephalic - which is advanced into the superior vena cava. The tip position is usually confirmed radiologically.

PICC lines are used when there is a lack of peripheral access for infusion of vesicant and irritant drugs/fluids, TPN and hyperosmolar solutions. They are also used when long-term access is required.

Peripheral lines have a number of advantages: they are relatively easy to insert and do not require the procedure to be done in theatre, making them also potentially a more cost-effective option. While some nurse-led PICC insertion services have been established across the UK, such lines are generally inserted by doctors.

PICCs are associated with lower rates of thrombosis and sepsis (Wilson, 1994); there is also a reduced risk of pneumothorax, large vein perforation and ‘pinch off’ (Todd, 1998), which are risks associated with centrally inserted catheters.

PICCs are fine-bore lines which are available as single and double-lumen catheters. The choice of the number of lumens must be made on the basis of the reason the line is required, the type of fluid and medication that will be infused, and the condition of the patient with regards to risk of susceptibility to infections.

PICCs are manufactured either open ended or valved, and are made of polyurethane or silicone. Valved PICCs have the advantage of not blocking off as easily as open-ended lines. They are usually fixed to the patient’s skin with adhesive strips or sutures.

PICC placement is contraindicated after axillary node dissection or irradiation, in lymphoedema of the arm, axillary node disease or skin infection at the insertion site (Todd, 1998).

Centrally inserted catheters

Tunnelled lines

Tunnelled CVCs are often referred to as Hickmann lines. They are used when the patient requires long-term infusional therapy, such as chemotherapy, and TPN. They also provide access for blood sampling.

This type of line is usually manufactured as a large-bore silicone line with single or double lumen. This type of material ensures that vesicant infusions do not erode the line, causing complications. Tunnelled lines can be used for long-term infusional therapy for periods ranging from months to years.

The tip of the catheter is inserted directly into the jugular or subclavian vein (as with non-tunnelled lines) and is then threaded through to end up in the superior vena cava. The other end is tunnelled about 2cm under the skin and then pulled out on to the patient’s chest, creating an exit site, which is usually 1.5cm away from the entry point.

Many tunnelled CVCs are equipped with a fibrous (Dacron) cuff, which sits in the skin tunnel. This enables the patient’s tissue to bond with the line, to create a secure fix, and will act as a mechanical barrier to stop infection travelling down the line into the patient’s bloodstream to cause sepsis. These CVCs may be open-ended or valved.

This type of line is usually inserted in theatre or radiology using an image intensifier to ensure correct positioning. Patients are usually lightly sedated. Some nurses are being trained to insert this type of line and many hospitals provide a nurse-led tunnelled line removal service.

Tunnelled lines are easy to care for, so patients are often educated to care for their line.

Non-tunnelled

This type of CVC is often referred to as a short-term percutaneous central venous catheter (non-tunnelled) and is the most commonly used CVC in secondary care. It is inserted directly into a central vein.

Non-tunnelled CVCs are used in patients who are acutely unwell. They provide access for intravenous therapy lasting from a few days to several weeks, to measure central venous pressure, for emergency use - for example, fluid replacement - and when there is an absence of peripheral access (Henderson, 1997).

A doctor in theatre, radiology, high-dependency areas, or occasionally the ward, usually inserts this type of device using a strict sterile technique. NICE has produced guidance (2002) recommending the use of ultrasound imagery when inserting CVCs. The positioning of non-tunnelled CVCs is generally confirmed radiologically. Jugular sites are more prone to infection due to the difficulty of securing the catheter to the patient’s neck securely.

Implantable ports

Implantable ports are VADs inserted into the chest, abdomen or antecubital area. They are used for long-term intravenous therapy, bolus injections, blood sampling and TPN. The development of more sophisticated devices such as CVCs and PICCs has meant they are not as widely used as in the past.

Ports are inserted by doctors under subcutaneous skin. Patients often prefer implantable ports because they are less visible; medical staff opt to use them because they are associated with fewer risks and are easily accessed using a non-coring needle, which can remain in situ for up to seven days.

Ports can be used as an alternative for subcutaneous infusions and have been used for epidural pain relief. Patency is maintained by regular flushing with heparin-based solutions. They require minimal care and manipulation.

Conclusion

The choice of the most appropriate VAD for an individual patient is not easy, as any single device may not meet all requirements. However, an understanding of how each system works, along with its limitations and risks, can support the decision.

Consideration should be given to the reason a patient requires the line, medical history, vascular accessibility, the type of therapy to be provided and the length of time the line is required.

It is vital to draw up local protocols for care and maintenance of VADs, based on national guidance. Procurement groups should be set up at hospital, regional and national levels to identify and standardise devices, based on the best up-to-date evidence available.

Author’s contact details

Karen Cowley, Practice Development Nurse, York Hospitals NHS Trust, Wiggington Road, York YO31 8HE; email:

Anderson, K.N., Anderson, L.E. (eds). (1995)Mosby’s Pocket Dictionary of Nursing, Medicine and Professions Allied to Medicine. London: Mosby.

Centers for Disease Control and Prevention. (2002)Guidelines for the prevention of intravascular catheter-related infections. Morbidity and Mortality Weekly Report 51: RR-10, 1-30.

Dougherty, L. (1999)Obtaining peripheral vascular access. In: Dougherty, L., Lamb, J. (eds). Intravenous Therapy in Nursing Practice. Edinburgh: Churchill Livingstone.

Dougherty, L. (2000)Vascular access devices. In: Mallet, J., Dougherty, L. (eds). Manual of Clinical Nursing Procedures. Oxford: Blackwell Science.

Fuller, A., Winn,, C. (1999)Selecting equipment for peripheral intravenous cannulation. Professional Nurse 14: 4, 233-236.

Goetz, A.M., Miller, J., Wagener, M.M., Muder, R.R. (1998)Complications related to Intravenous midline catheter usage. Journal of Intravenous Nursing 21: 2, 76-80.

Hadaway, L. (2001)Anatomy and physiology in infusion therapy. In: Infusion Therapy in Clinical Practice. Philadelphia, Pa: W.B. Saunders. 

Henderson, N. (1997)Central venous lines. Nursing Standard 11: 42, 49-56.

Hinson, E., Blough, L. (1996)Skilled IV therapy clinicians’ product evaluation of open-ended versus closed-ended valve PICC lines. Journal of Intravenous Nursing 19: 4, 198-210.

Intravenous Nursing Society. (1998)Revised intravenous nursing standards of practice. Journal of Intravenous Nursing 21: 15 (suppl).

Jones, G.R. (1998)A practical guide to evaluation and treatment of infections in patients with central venous catheters. Journal of Intravenous Nursing 21: (suppl), S134-S142.

Millam, D. (1992)Starting IVs: how to develop your venepuncture skills. Nursing 92: 33-46.

NICE. Ultrasound Locating Devices for Placing Central Venous Catheters (Interventional Procedure Guidance 49).London: NICE.

NHS Litigation Authority. (2004)Clinical Negligence Scheme for Trusts (Standard 5). London: NLA.

Oncology Nursing Society. (1996)Cancer Chemo-therapy Guidelines and Recommendations for Nursing Education and Practice. Pittsburgh, Pa: ONS.

Payne-James, J.J., Rogers, J., Bray, M.J. et al (1991)Development of thrombophlebitis in peripheral veins with Vialon and PTFE-Teflon cannulae: a double-blind RCT. Annals of the Royal College of Surgeons of England 73: 322-325.

Perucca, R. (1995)Intravenous complications. In: Terry, J., Baranowski, L., Lonsway, R.A., Hedrick, C. (eds). Intravenous Therapy: Clinical principles and practices. Philadelphia, Pa: W.B. Saunders.

Royal College of Nursing. (2003)Infusion Therapy Standards. London: RCN.

Speer, E.W. (1990)CVC issues associated with the use of single and multiple-lumen catheters. Journal of Intravenous Nursing 13: 1, 30-39.

Todd, J. (1998)Peripherally inserted central catheters. Professional Nurse 13: 5, 297-302.

Todd, J. (1997)Evaluation of the introduction of Groshong central venous catheter into the oncology/haematology department of a DGH. European Journal of Cancer Care 6: 215-221.

Weinstein, S.M. (1997)Plumer’s Principles and Practice of Intravenous Therapy. Philadelphia, Pa: J.B. Lippincott.

Wilson, J.A. (1994)Preventing infection during IV therapy. Professional Nurse 9: 6, 388-392.

How do you prevent an air embolism when a patient has a central line?

How can you reduce the risk of air embolism in Cvad?

What are some actions that prevent CVAD complications?

Which Cvad has lower risk of air embolism?