Chapter 8. Vascular access
Intravenous access allows fluids or drugs to be administered. In children, the intraosseous (IO) route is often used. This route is increasingly being used in shocked adults in whom intravenous access may be difficult or impossible.
Technique of intravenous cannulation
The largest cannula which can successfully be inserted into the vein should always be chosen. As with any procedure where there is a risk of contact with body fluids, gloves should be worn by the operator, then:
1. Choose a vein capable of accommodating the size of cannula needed, preferably one that is both visible and palpable. The junction of two veins is often a good site as the ‘target’ is larger and the veins tend to be less mobile
2. The vein should be allowed to dilate as this increases the success rate of cannulation. In the limb veins, this is usually achieved by using a proximal tourniquet. Further dilation can be encouraged by gently tapping the skin over the vein. When cannulating the external jugular vein, if it is safe to do so, the patient can be tipped slightly head down to encourage the vein to dilate. Turning the patient’s head to the opposite side will also facilitate cannula insertion
3. The skin over the vein should be cleaned. If alcohol-based agents are used, they must be given time to work (2–3 minutes), ensuring that the skin is dry before proceeding further
4. The vein should now be immobilised in order to prevent it being displaced by the advancing cannula. This is achieved by pulling the skin over the vein tight, with the operator’s free hand
5. Holding the cannula firmly, at an angle of 10–15° to the skin, it should be advanced through the skin and into the vein. Often a slight loss of resistance is felt as the vein is entered. This should be accompanied by the appearance of blood in the flashback chamber of the cannula
6. While keeping the skin taut, the angle of the cannula is reduced slightly and advance it a further 2–3 mm into the vein. This is to ensure that the first part of the plastic cannula lies within the vein. Care must be taken at this point not to push the needle out of the back of the vein
7. The needle is now withdrawn 5–10 mm into the cannula, so that the point no longer protrudes from the end. As this is done, blood will often be seen to flow between the needle body and the cannula, confirming that the tip of the cannula is within the vein
8. The cannula and needle are advanced along the vein together. The needle is retained within the cannula to provide support and prevent kinking at the point of skin puncture
9. Once the cannula is inserted as far as the hub, the tourniquet should be released and the needle completely removed and disposed of safely
10. Confirmation that the cannula lies within the vein should be made by injection of a saline flush
11. Finally, the cannula should be secured using adhesive tape or a specific cannula dressing.
Complications
Early
• Failure of cannulation
• Haematoma
• Extravasation
• Damage to local structures
• Air embolus (rare)
• Breakage of the cannula.
Late
• Infection and inflammation (thrombophlebitis)
• Irritation can be caused by high concentration drugs or fluids.
Intraosseous access
The intraosseous route allows the administration of fluids and drugs, with circulating levels of drugs being comparable with those achieved when given via a central vein.
In children, access is generally gained in the limbs, in adults the sternum and pelvis can also be used.
Sites for intraosseous access
Four peripheral sites can be used for intraosseous access:
• The anteromedial surface of the tibia, 2–3 cm below the tibial tuberosity
• The distal tibia, just proximal to the medial malleolus
• The anterior surface of the femur, 3 cm above the lateral condyle
• The humeral head at the shoulder.
These sites are relatively free of other local important structures. The most relevant feature to be borne in mind is the proximity of the epiphyses (growth plates). Damage to these could interfere with subsequent bone growth and development.
The main site for central IO access is the manubrium sterni which should only be used for adults.
Standard IO devices (hand inserted)
The needles have a short shaft, with a central solid trocar, which has a large handle for manual insertion. The trocar must be unscrewed before it can be removed from the needle. The external end of the needle has a standard Luer fitting. Some needles have a screw thread to improve their security in the bone.
Intraosseous needles come in a range of sizes:
• 6–20 gauge for children younger than 18 months
• 12–16 gauge for children older than 18 months.
Technique (conventional hand-inserted IO needle)
1. An appropriate site is chosen, taking care to avoid placing the needle in a fractured bone. Placement of a needle in a distal bone (e.g. the tibia) in the presence of a proximal fracture (e.g. of the femur) is acceptable. If the proximal tibia is used, it may help to place a firm support behind the knee
2. The skin over the site should be thoroughly cleaned. Ideally, local anaesthetic solution should be infiltrated into the skin and underlying periosteum
3. The needle is introduced at 90° through the skin to make contact with the bone and then advanced using a screwing action with threaded needles or a ‘bradawl’-type action with unthreaded needles, at the same time applying firm pressure
4. A loss of resistance is felt as the cortex is penetrated by an unthreaded needle and the marrow cavity entered. The needle should feel as if it is ‘gripped’ by the bone and should hold its position once released
5. The trocar is unscrewed and removed and correct placement confirmed by the ability to aspirate bone marrow. This should always be used to check blood glucose levels. Further confirmation is provided by being able to flush 5 mL of saline through the needle without resistance or signs of extravasation.
Never place an IO needle in a fractured bone.
EZ-IO® power driver
This device uses a battery powered motor to insert the intraosseous needles in a similar way to a hand-held drill.
The device is very effective and easy to use but requires the use of specially designed IO needles (pink for paediatrics; blue or yellow for adults).
A longer needle is available for use in the head of the humerus when lower limb insertion is inappropriate or has failed.
Sternal IO injection device (e.g. FAST®)
Specially designed to insert a needle into the manubrium of the adult sternum.
The device fires a spring-loaded needle through the outer table of the sternum.
The device activates when equal pressure is applied to the stabilisation points around the needle to ensure entry at 90° to the skin.
Bone injection gun
May be used in any of the conventional insertion sites IN ADULTS but NOT in the sternum. A paediatric version is available.
Intraosseous fluid administration
All drugs and fluids that can be given via peripheral intravenous cannulae can be administered via the IO route.
All IO routes will require fluids to be administered under pressure – by hand, using a pressure bag or a pressure infusion device – gravity alone will not be effective.
Forcing fluid into bone spaces under pressure is painful, often more painful than the insertion of the needle. If time is available, 2–3 mL of 1% lignocaine can be infused first to reduce the pain stimulus.
Fluid administration via an intraosseous line in children is most safely and effectively achieved by the administration of boluses by injection using a syringe and a three-way tap.
Complications
Complications, which are rare, include:
• Failure to enter the bone marrow cavity – the most common problem
• Extravasation of fluid
• Compartment syndrome
• Leakage from the hole left by a previous attempt
• Infection in the skin, abscess formation and ultimately osteomyelitis
• Damage to the growth plate of the bone could occur as a result of careless placement and in very young children (rare)
• Fracture might occur if excessive force is used (rare).
Fluid flow through cannulae and catheters
The diameter and length of the cannula as well as the viscosity of the fluid and the pressure applied combine to affect the rate at which fluid will flow through the cannula.
| Colour | Diameter (mm) | Gauge | Length (mm) | Flow (mL/min) |
|---|---|---|---|---|
| Pink | 1.0 | 20 | 32 | 54 |
| Green | 1.2 | 18 | 45 | 80 |
| Grey | 1.7 | 16 | 45 | 180 |
| Brown | 2.0 | 14 | 45 | 270 |
For further information, see Ch. 8 in Emergency Care: A Textbook for Paramedics.
