Cannulation is a procedure regularly undertaken which involves threading a plastic tube into a vein to allow access to give fluids & other drugs. It is also possible to take bloods during the initial cannulation process, but once in & flushed with saline future samples are likely to be significantly contaminated. In addition to junior doctors, this procedure can be undertaken by some HCAs, most nurses (if signed off), outreach nurses & site managers if medically trained.

Due to the physics of fluid dynamics, a larger cannula even if only slightly wider, will allow the delivery of fluids significantly more quickly. Therefore larger bore cannulas are preferred in resuscitation – however, it is better to have achieved access with a smaller cannula than not have access at all as with resuscitation the peripheral veins will dilate allowing larger cannulas to be inserted.

When considering whether to re-cannulate a patient, consider whether it is necessary or whether IV drugs can be given orally. Generally, you should try at most twice before escalating. The reason for this is multiple failed cannulas can make those veins significantly more difficult to cannulate and so your seniors may have even less chance of success.

Equipment

• Gloves
• Hand sanitiser
• Tourniquet
• Appropriate size cannula 
• Alcohol swab
• Gauze
• Syringe 
• 0.9% sodium chloride vial
• Vacutainer/additional syringe if taking bloods too
• Cannula port/bung/octopus
• Cannula dressing
• Stickers to label cannula 
• Access to a sharps bin

Procedure

1. Introductions, handwashing, consent, check patient identifiers
2. Apply tourniquet
3. Identify suitable vein (as straight as possible & bounces when you palpate
4. Clean with an alcohol swab and let dry
5. Insert the needle of the cannula until a flash is seen, carefully insert a 1 mm further (be patient). This is because the plastic catheter is slightly shorter than the needle and you want to make sure both are in the vein
6. Advance the cannula over the needle, ensure you anchor the vein while you do this 
7. Once fully advanced, apply pressure to the vein proximally to the  cannula and remove the needle
8. If bloods are required attach syringe or vacutainer
9. Attach the bung/octopus port
10. Clean any blood from around the area
11. Flush the cannula with 0.9% sodium chloride. This should be painless and cause no swelling, otherwise, it suggests the cannula has “tissued” (which means it is now in the tissue rather than the vein)
12. Fix the cannula using the dressings
13. Label the cannula with the date
14. Document the cannula size and area inserted i.e. Left ACF 

Tips

• Always question whether a cannula is necessary before placing one
• Larger cannulas are better for giving a lot of fluids quickly. Radiographic contrast usually requires a cannula that’s pink or larger
• Try to go distally to allow more attempts to be had at the same vein proximally if unsuccessful
• Tapping the vein, gravity, submerging the hand in lukewarm water can all help improve your success rate
• Ensure you anchor the vein (particularly in the elderly) as it will otherwise roll away from the needlepoint
• Once you pierce the skin advance slowly until you get flashback, this stops you advancing through the vein. Once you achieve this, shallow your angle as you advance further by 1mm

Resources & References

• Demonstration video thanks to Geeky Medics

Written By Zana Martin (FY2)
Edited by Pratyush Pradeep