Healthcare and Medicine Reference
posterior wall of the vein, then advance the cannula a further
few millimetres. Figure 10.5 shows a diagrammatic representa-
tion of this.
Withdraw the needle gently and watch for the second fl ash-
Box 10.1 Equipment for intravenous cannulation
Tourniquet (disposable if available)
back in the cannula confi rming that it is in the correct position
Slowly advance the cannula fully into the vein holding the wings
2% chlorhexidine/alcohol wipe
of the cannula only (Figure 10.4f).
Remove the tourniquet.
5 mL 0.9% saline
Place a small piece of gauze underneath the open end of the
cannula to catch any drops of blood (Figure 10.4g).
Occlude the vein proximal to the tip of the cannula with
your fi nger while removing the needle from the cannula
Dispose of the sharp safely before screwing the cap securely on
the end of the cannula.
Secure the cannula safely with a purpose-made, sterile,
semi-permeable transparent dressing (Figure 10.4i).
If the dressing allows, label it with the insertion date and time.
Flush the cannula via the injection port with 5 mL 0.9% saline
(Figure 10.4j). Observe for any swelling or pain proximal to
the cannula site which could indicate that the cannula is not
Document the procedure, including the date and time, size of
cannula used, site, number of attempts, and any immediate
Taking blood from a cannula
It is possible to take blood out of a newly inserted cannula before
the cannula is fl ushed. This is done with either a purpose-designed
Vacutainer™ adapter or a syringe (Figure 10.6). Blood should be
taken before the tourniquet is released. Once the cannula has been
fl ushed, it should not be used for blood sampling.
Figure 10.3 Equipment required for intravenous cannulation.
1 Position the patient comfortably. It may be helpful to have the
arm resting on a pillow.
2 Apply the tourniquet to the upper arm (Figure 10.4a). It should
not be so tight as to obstruct arterial blood fl ow - check by
palpating the radial pulse.
Early complications of cannulation are often associated with
poor technique and inexperienced practitioners. If the pri-
mary fl ashback does not occur, the vein has probably not been
punctured. Re-palpate the vein and withdraw the cannula before
re-advancing again. If this is unsuccessful, start again and choose a
different site. For tips on fi nding a suitable vein, see 'Handy hints'
If the secondary fl ashback (as the needle is withdrawn through
the cannula) does not occur, the cannula is no longer in the vein.
This may be because the cannula entered the vein and then passed
through the posterior wall. By slowly withdrawing you may then
get a fl ashback as it re-enters the vein, in which case you can care-
fully advance the cannula into the vein. Once the needle has been
withdrawn it should not be re-inserted into the cannula. This prac-
tice may cause part of the catheter to be sheared off by the needle,
therefore entering the systemic circulation.
Cannulation is often a relatively painful experience for the
patient. This is more of a problem when larger cannulae are being
used or when cannulating children. In these circumstances subcu-
taneous or topical local anaesthetic can be used.
3 Ask the patient to clench and unclench the fi st. This will
promote venous fi lling.
Look and palpate for appropriate veins; they should feel full and
bouncy. The site of a vein bifurcation is often ideal as the vein is
tethered at this point.
Clean the area with an appropriate product: 2% chlorhexi-
dine gluconate in 70% isopropyl alcohol is recommended
(Figure 10.4b). Remember to let the solution dry and not to
palpate the skin further (no-touch technique).
Remove the cap from the cannula and put in a clean, safe, easily
accessible place (alternatively the cap can be left in place and
removed at the end of the procedure).
Hold the skin taut below your insertion site to tether and immo-
bilise the vein.
8 Holding the cannula at a 10-30º angle to the skin and in the
direction of the vein, gently advance the cannula through the
skin and into the vein (Figure 10.4c).
Once a fl ashback has been seen in the fl ashback chamber
(Figure 10.4d), lower the cannula slightly to ensure the tip is in
the lumen of the vein and that the needle does not puncture the