Definition of a vascular access device

For the purposes of prehospital care, a vascular access device is a device that is inserted into a peripheral or central vein (intravenous), or into the marrow cavity of selected bones (intraosseous). The devices may be used to administer drugs or fluids, or as a prophylactic measure. They may be used for sampling blood for diagnostic tests although this is not currently within the remit of UK paramedics.

There is a variety of vascular access devices available and each has its own requirements; however, there are certain principles that are applicable to all devices.

Anatomy of veins

The superficial veins of the upper limbs are normally selected for siting a peripheral cannula in prehospital care. Use of the lower limbs may be indicated in very small children and where injury prevents the use of the upper limbs but cannulation of the lower limbs is associated with an increased risk of venous thromboembolism.¹

Veins consist of three layers:²

Tunica adventitia – the outer layer of fibrous connective tissue.
Tunica media – the middle layer comprising of smooth muscle and elastic fibres.
Tunica intima – the thin inner layer of endothelium.

The skin consists of two layers:²

Epidermis – the superficial thinner layer of the skin composed of keratinised stratified squamous epithelium.
Dermis – a layer of dense, irregular connective tissue lying deep to the epidermis. Blood vessels, nerves, glands and hair follicles are embedded in dermal tissue.

The structure and appearance of the skin alters with age as the dermal layers become thinner and elasticity is lost. The number of cells producing collagen and elastic fibres decrease leading to the development of wrinkles. The veins of older people may be easier to see as a result of these changes but they are more mobile, more fragile, and often tortuous and thrombosed.³ It is perhaps best to avoid the dorsum of the hand in older people due to their fragile nature.⁵

Peripheral cannulas

There are two commonly used peripheral cannulas; a peripheral cannula, and a hollow-needle infusion device, often called a ‘butterfly’ (see Figures 13.1 and 13.2). The peripheral cannula is usually a catheter-over-needle design; the needle is withdrawn after the venepuncture whilst the flexible plastic catheter remains in the vascular compartment. The needle of the butterfly remains in the vein thereby causing increased risk of damage to the vein.⁴

Peripheral cannulas are available to paramedics in various sizes ranging from 22 gauge (smallest) through to 14 gauge (largest). Each device is colour-coded and information regarding flow rates and catheter diameters can be found on the device packaging. Modern catheters tend to be made from polyurethane, which is more flexible, less traumatic and less irritating on the intimal layer of the vein than earlier polyvinyl chloride (PVC) models.^5,6

Figure 13.1 Intravenous cannulas.

Figure 13.2 Butterfly cannula.

Indications for peripheral cannulation

Peripheral cannulas are indicated for:

Drug therapy
Fluid therapy
Prophylaxis.

There are potential complications associated with intravenous cannulation so care should be taken to perform cannulation only on patients who are likely to benefit from the procedure. The risks associated with prophylactic cannulation probably outweigh the benefits so cannulation for this purpose is to be discouraged.

Selection of device for peripheral cannulation

The choice of cannula will be dependent upon several factors:

Purpose of cannulation. A larger bore cannula will be required for rapid infusion of fluids whilst a smaller gauge will be adequate for drugs or for prophylactic purposes.
Size of veins. Smaller veins will only tolerate a small cannula so irrespective of the purpose of cannulation, a small cannula may be required.
Shocked patients. Shock leads to peripheral shutdown and may restrict the size of cannula that can be inserted.
Practitioner skill and confidence. A newly qualified practitioner may be less confident at placing a large bore cannula so may take a pragmatic view that something is better than nothing.

Selection of vein

An advantage of peripheral venous cannulation is that the veins are normally visible; however, there may be occasions where this is not the case so palpation and familiarity with venous topography are useful. Figures 13.3 and 13.4 illustrate venous anatomy in the hand and forearm.

The vein should be selected before the device so that only an appropriate device is selected. The vein should be straight, free of valves and should feel ‘bouncy’ when palpated. It is best to avoid joints as there is increased risk of mechanical phlebitis and intermittent flow of fluids or drugs created by the patient’ s movements.

Vein selection will be dependent upon a number of factors including the reason for the cannulation, accessibility of the veins, injuries to the patient, and previous cannulation attempts. The initial attempt should be undertaken at the distal end of the limb as an unsuccessful attempt hinders the use of veins distal to the original site. A cannula should not be placed in areas of localised oedema, dermatitis, cellulitis, arteriovenous fistulae, wounds, skin grafts, fractures, stroke, planned limb surgery and previous cannulation.⁵ It may also be beneficial to patient independence if the cannula is placed in the non-dominant limb.

Techniques of venodilatation

Tourniquet and Gravity

Apply venous tourniquet to limb and tightened to between the patient’ s systolic and diastolic pressures. If veins are not readily apparent or appear small in calibre, place the limb below the level of the heart.⁸ Gravity serves to slow venous return, leading to increased venous volume and distention of veins of the upper extremity.¹¹

Fist clenching

Opening and closing of the fist augments venous return by virtue of muscular compressive forces exerted on vessels to enhance arterial blood flow,⁷ which results in local venous distention.⁸ Increased blood velocity from fist clenching also increases venous flow to the basilic and cephalic veins.⁹ Research has shown that this form of isometric activity also results in vasodilatation.¹⁰

Vein ‘tap’ and ‘milking’

Tapping a superficial vein once or twice augments vein distention¹¹ although the mechanism by which this occurs is unclear.⁸ Applying a mild, sliding pressure (‘milking’) along a short length of vein, from proximal to distal, displaces blood distally resulting in vein distention.⁸ Care must be taken not to apply overly vigorous stimuli, especially to those with fragile superficial veins (e.g., elderly, those chronically on steroids) so as not to injure the veins or to result in pain related reflex vasoconstriction. 8 ‘Slapping’ the vein is painful and causes the release of histamine – this technique should not be used.

Local warmth

Blood flow in human skin increases greatly in response to direct heating¹² although care has to be taken not to induce thermal damage to the extremity. Applying local warmth in the prehospital environment may be difficult but consideration may be made to immersing the upper extremity in warm water for a few minutes, or applying a warm, moist compress.¹³

Dilatation of the external jugular vein (EJV)

The Valsalva manoeuvre (forced expiration through a closed glottis) for 30 sec (at a pressure of 40 mmHg) has been shown to result in an 86% increase in the area and 41% increase in the circumference of the right EJV.¹⁴ Similarly, use of the Trendelenburg position augments venous return towards the right atrium and can result in EJV distention.^15,16

Complications of peripheral venous cannulation

No clinical intervention is risk free but the benefits of appropriate intravenous cannulation are normally considered to outweigh the complications. One of the key concerns in prehospital care is the time delay for undertaking the task. Studies suggest that intravenous cannulation with no therapeutic treatment can increase on-scene times by an average of between 8 and 13 minutes,^17,18 this needs to be considered when making the clinical decision to cannulate as should the number of attempts that should be made.

Intravenous cannulation provides a direct portal of entry for infectious pathogens and is a considerable source of morbidity and mortality in hospital.^19,20 The incidence of infection secondary to intravenous cannulation by paramedics is not known but the nature of the work and the practice environment mean that it could be even higher. An increased risk of infection during emergency insertion has been noted as strict adherence to aseptic techniques may be less rigorous.²¹ Places, people and equipment can all serve as reservoirs for infection.²² For this reason infection prevention and control should consider not only patients, but also staff and bystanders as well as the environment and any equipment in use.²³ Whilst the paramedic may have limited control over the environment, they can minimise the risk of infection from equipment by ensuring that any packaging is intact and in date. When opening packaging, aseptic techniques should be employed. Compliance with hand hygiene and personal protective equipment policies is imperative in order to minimise the risks of contamination through this portal and, although there is debate regarding the efficacy of skin cleansing prior to insertion, current recommendations advocate the use of 2% chlorhexidine gluconate in 70% isopropyl alcohol, which should be allowed to dry.²⁴

The incidence of vascular complications increases as the ratio of the external diameter of the cannula to vessel lumen increases;²⁵ therefore the smallest cannula for the prescribed therapy should be used.^5,26,27 Phlebitis related to intravenous cannulation has three underlying factors; mechanical (caused by friction and movement of the device within the vein), chemical (relating to infusates), and physical (related to the properties of the cannula).²⁸

THINK

Identify common sources of contamination during intravenous cannulation and describe how to minimise these risks.

Other potential complications and their solutions are presented in Table 13.1

Management in situ

Once sited, the peripheral cannula should be flushed with 0.9% sodium chloride or a heparin solution. The exact volume of fluid required to maintain patency is unclear but between 2 and 5 mL is adequate providing correct technique is used; i.e. a pulsatile flush ending with positive pressure.²⁵

Once the cannula is in situ it should be taped into place for security. Non-sterile tape should not cover the site; it should be treated as an open wound. Specific cannula dressings are supplied and should be used as they are sterile and allow vision of the site during fluid/medication administration.

Table 13.1 Insertion and devices: complications and solutions

Risks with insertion of devices	Impact	Management
Failed technique	Delay in treatment and unable to use vein	Review technique, vein and equipment selection. Attempt again only if necessary and chances of success are high
Poor technique	Pain, nerve hit, overshot vein, bruising, increased risk of infection, patient anxiety, failed attempt	Refer to more experienced colleague; work to improve technique under supervision
Patient anxiety	Vein may be constricted, muscles may be tense so risk of pain	Reassure patient, select smallest suitable device, consider local anaesthetic, consider necessity of procedure in prehospital environment
Incorrect device	Device performs poorly, flow rate inadequate or fluid overload, causes mechanical phlebitis	Remove device and perform full assessment
Sharps disposal	Needlestick injury for staff or patient	Wash wound in running water and follow local policy
Plastic/air embolus	Risk of pulmonary embolism	Remove device and treat any symptoms, report on arrival at hospital and document incident
Patient compliance	Device removed or tampered with	Assess patient, ensure appropriate site selection and secure device
Haematoma	Bruising, pain, reduced access to vein	Remove device and apply pressure
Occluded cannula	Fails to allow fluid or medication delivery	Remove device and re-site

Adapted from Lavery and Smith 2007.⁶

Procedure for peripheral intravenous cannulation

Equipment required

Gloves
Selection of peripheral venous cannulas (select smallest for the intended purpose)
Venous tourniquet
2% chlorhexidine gluconate in 70% isopropyl alcohol
Sterile occlusive transparent semi-permeable membrane (e.g. Vecafix, Niko-Gard)
Intravenous administration set or 0.9% sodium chloride flush
Sharps box.

Procedure (Figures 13.5–13.13)	Additional information/rationale
Preparation
1. Explain the procedure and gain consent.	Legal requirement.
2. Select site for cannula placement.	Straight, wide veins; ‘bouncy’ on palpation; avoid joints and valves.
3. Prepare equipment. Check date and integrity of package.	Check all component parts are present.
Technique
1. Use a non-touch insertion technique²⁹	Minimises risk of infection.
2. Apply tourniquet.	To engorge veins the tourniquet should be tightened to between the patient’ s systolic and diastolic pressures.
3. Perform hand hygiene and, wearing gloves, disinfect the selected venepuncture site, allowing at least 30 seconds for the site to dry.²⁷	Minimises the risk of infection.
4. Inspect the chosen cannula to ensure product integrity. To avoid contamination do not touch the cannula shaft.	Ensure the package is intact and the expiry date has not been exceeded.
5. Hold the cannula in line with the vein at a 10–30° angle to the skin and insert the cannula through the skin.
6. As the cannula enters the vein, blood will be seen in the flashback chamber.	Return of blood into the cannula is required to confirm correct placement of cannula in the vein.³⁰
7. Lower the angle of the cannula slightly to ensure it enters the lumen of the vein and does not puncture the posterior wall of the vessel; advance the needle a little further.	The needle sits ahead of the catheter so the cannula may need to be advanced a little further to ensure that the catheter is in the vein.
8. Withdraw the stylet slightly and blood should be seen to enter the cannula. Slowly advance the cannula into the vein, ensuring that the vein remains anchored throughout the procedure. NB: The stylet must not be re-inserted as this can damage the cannula, resulting in plastic embolus.	Confirms the position in the vein.
9. Release the tourniquet Allows free flow of fluids/drugs and relieves pressure from patient’ s arm.	Prevents flow of blood out of the distal end of the cannula as the needle is removed.
10. Place pressure distal to the end of the catheter and remove needle; immediately place needle into sharps bin then replace bung onto the end of the cannula or connect giving set.	Drop sharps into container; do not push. Colleagues should NOT hold the sharps container so as to avoid risk of accidental needlestick injury.
11. Connect cannula to pre-prepared infusion giving set or flush with 0.9% sodium chloride (or heparin solution).	Confirms patency and ensures easy administration without pain, resistance or localised swelling.
12. Apply a sterile dressing.
13. Secure administration set tubing if an infusion is started.
14. Remove gloves and perform hand hygiene.
Post-procedure
1. Note the date and time of insertion on the case report form. Some cannula dressings may also have facility for documenting this information.	It is recommended that cannulas inserted in emergency conditions are replaced within 24 hours of insertion^21,32
2. Document the number of attempts and any other complications.	Allows hospital staff to monitor any untoward occurrences.
3. Splints should only be used when the cannula is placed in an area of flexion or is at risk of dislodgment.³¹	If a splint is used, removal to allow assessment of the circulatory status of the limb is required at established intervals.³¹