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 The needle is now withdrawn 5–10 mm into the cannula, so that the point no longer protrudes from the end.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)
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