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IV Cannulas

IV Cannulation

February 15th, 2021


Intravenous cannulas are inserted every day into hospitalised patients in order to provide IV fluids and medications. IVCs should be inserted using a no-touch technique and assessed regularly in order to avoid complications.
  • Indications for IV Cannulation

  • Fluid administration
  • Medications
  • Blood products
  • IV contrast
IV cannulas cannot be used for certain therapeutic reasons, such as certain chemotherapeutic agents, vasopressors, total parenteral nutrition, or intravenous potassium running at a rate >10mmol/hour.
Avoid taking blood from a peripheral cannula that is already in situ as this may collapse / damage the vein or affect the sample through haemolysis, dilution or contamination.

Equipment and Preparation

  • The equipment required for inserting a cannula includes:
  • Choosing the appropriate cannula size

    A variety of cannula sizes are available for different uses. These include:
  • 24 - paediatrics, fragile veins
  • 22 - paediatrics, fragile veins
  • 20 - everyday use, fluids, antibiotics, analgesia
  • 18 - everyday use, blood products, potassium, large volumes, surgery, IV contrast
  • 16 - trauma, major surgery, obstetrics, GI bleeds, large volumes
  • 14 - trauma, rapid infusion of large volumes

Identifying a Vein

When identifying a vein, there are multiple factors to take into account. Ideally the vein should be large and the placement of the cannula should not limit movement.
A useful first step is to ask patient where they have been cannulated in the past, or where their best veins are found.
Apply the tourniquet to the patient's limb and feel for a straight, firm, round, elastic vein. This should be non-pulsatile.
  • Places to Look

  • The ideal location for an IV cannula is the cephalic vein in the lateral forearm, as this is a large vein and insertion here doesn't limit patient movement. 
The basilic vein in the medial forearm is another good option, however this can be more difficult to access during insertion. 
The dorsum of the hand has smaller veins and IVCs here are more likely to clot, so this should be used as a backup option. 
The veins in the antecubital fossa should be avoided, as insertion here will limit the movement of the patient's arm and the cannula would be at a high risk of extravasating.
  • Places to Avoid

    Certain sites should be avoided in order to prevent complications. These include:
  • The same arm as an AV fistula - you may blow the fistula
  • The same arm as a past mastectomy or lymph node dissection, as the drainage of such limbs is poor and the patient may develop severe oedema that is difficult to reverse
  • A limb affected by stroke
  • An area that is affected by burns, oedema or infection
  • A limb that has a deep venous thrombosis
Avoid inserting a cannula into the lower limb if possible, due to the risk of deep venous thrombosis and the fact that lower limb IVCs limit mobility.
  • Difficulty Finding a Vein

    If you are having trouble finding a vein, certain methods can assist. These include:
  • Asking the patient to pump their fist
  • Warm the area using a blanket or heat pack
  • Tap the area repeatedly
  • Hang the limb over the bed
  • Use an ultrasound (this requires extra training)
  • Use a vein viewer, if available

IVC Insertion

  • Introduction

  • Preparation

  • Insertion

  • Finishing Up


Several issues occur commonly when inserting a cannula.
  • No Flashback is Seen

  • The cannula is unlikely to be in the vein, or has penetrated through the vein to the other side. Try advancing further or pulling back and inserting slightly medially or laterally. Don't pull the cannula all the way out or you'll have to start again.
  • There is Flashback, But No Blood is Coming Out

  • The cannula has penetrated through the vein, or the vein has collapsed. Pull back slightly, adjust the angle of the needle against the skin, pull back and try again.
  • Bright Red Blood is Pulsating Out

  • The cannula is likely in an artery. Remove the needle immediately and apply pressure to the area for at least three minutes. This can be avoided by ensuring that there is no palpable pulsatile vessel prior to inserting a cannula.
  • A Haematoma Has Formed

  • The vein has likely blown. Remove the needle and apply pressure to the area.

Removing the Cannula

Wash your hands and don gloves.
Remove the dressing and any tape surrounding the cannula.
Remove the cannula in a steady, fluid motion.
Apply pressure to the area using sterile gauze, then place a small dressing (such as a cotton ball) to the area with tape.


  • Cannula Blockage

  • A blocked cannula may occur due to clotting in the cannula or line, or due to kinking of the cannula or line. This should be suspected when the infusion is not able to run and the machine is displaying a high pressure area, or if the patient is in pain.
Check for kinks, and then remove the cannula if it is not flushing.
  • Bruising

  • Haematomas may occur due to blood leaking from the vein into surrounding tissue, either around a cannula or after a cannula has fallen fully out. 
Haematoma formation can be prevented by inserting the cannula properly, and by placing pressure onto the site when a cannula is removed.
To assess for bruising, look for a red/purple discolouration of a cannula, which may be associated with swelling and tenderness.
Bruising should be treated by applying a pressure bandage to the area. If the cannula is no longer in the vein or ongoing bleeding occurs then the cannula should be removed.
  • Cannula Extravasation

  • Extravasation of infused fluids may occur if a cannula falls out of a vein, or if there is leakage around the cannula. This should be suspected if there is swelling around the site, pain, tightness or coolness due to accumulation of fluid.
If extravasation is suspected, stop the infusion and remove the cannula. The limb should be elevated to assist in drainage of fluid. Consider whether the medication is vesicant, or likely to cause significant irritation of the soft tissues; further supportive management may be required in this case.
  • Line-Related Infections

  • Line-related infections vary from small localised reactions to life-threatening staphylococcal bacteraemia. 
In order to prevent infection, ensure that proper aseptic technique is used and don't insert a cannula through infected tissue. Cannulas should be reviewed regularly for signs of infection, and not left in for too long.
Signs of infection include erythema, swelling, warmth, tenderness and pus surrounding a current or previous cannula site. More severe infection is suggested by fevers and other constitutional symptoms.
If infection is suspected, remove the cannula and observe the site. If clinically indicated, the patient may require treatment for cellulitis or bacteraemia.
  • Thrombophlebitis

  • Thrombosis may occur with any cannula - particularly if it is left in too long, if the area is infected. Irritant medications such as potassium infusions can cause painful phlebitis without thrombosis.
Suspect thrombosis or thrombophlebitis if there is erythema, oedema, pain or swelling surrounding a cannula site. In some cases there may be erythema and swelling along the course of the vein.
If thrombophlebitis is suspected, any infusions should be stopped and the cannula should be removed. The area should be monitored.
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