Peripheral Intravenous (IV) Cannula Insertion Tips

Author: Dr Lee Jervis, Anaesthesia Provisional Fellow, West Australian Rotational Training Program. Currently working as an anaesthesia fellow at Mount Sinai Hospital, Toronto

Disclaimer: These tips are based on my own preferences and experiences. I would recommend using these tips a guide only.

Indications

• Administration: Medications, fluids, blood products
• Venepuncture: Blood must be drawn immediately at the point of cannula insertion (before saline flush). Using the cannula for subsequent blood draws produces inaccurate results and puts the patient at risk of cannula thrombus obstruction.

Risks

• Unsuccessful placement
• Vascular damage (e.g. venous perforation resulting in haematoma formation)
• Extravasation of fluid/medications: May cause local tissue injury/necrosis
• Pain: especially if placed into a small vein or if certain irritant medications are administered (e.g. KCl)
• Infection
• Thrombosis

Equipment:

• Gloves
• Torniquet
• Alcohol skin swab (usually chlorhexidine digluconate 2% in isopropyl alcohol 70%)
• Cannula – see ‘choosing the correct cannula gauge’
• IV bung
• IV dressing
• 10ml syringe with saline
• Sharp disposal box

Vein selection

• Pre-requisite: understanding of the venous anatomy of the upper and lower limb
• Cannulation sites:
  • 1st line:
    • Cephalic vein on lateral aspect of wrist
    • Anterior forearm
    • Dorsal venous network of hand
  • 2nd line (vascular access not possible in upper limb)
    • Antecubital fossa: If used, should be for the shortest possible duration (e.g. single infusion only) and replaced by a cannula at an alternative site if cannula required for >24hr.
    • Long saphenous vein of the legFoot: Associated with high infection risk, should be replaced ASAP
  • Not recommended
    • Joints (e.g. wrist): due to cannula obstruction, patient discomfort (esp. on joint movement), higher infection (around skin creases)
    • Arm: with an arteriovenous fistula, infection, to be operated on, previous axillary clearance

Tips for visualising the vein

• Ensure tourniquet is applied to the proximal limb
• Place limb in the dependent position (hand hanging towards the floor). Ask patient to open and close their hand to encourage venous engorgement.
• Gently tap or rub (not slap) potential veins to promote venous distension
• Consider transillumination in neonates/infants
• Ultrasound is useful for visualising veins and inserting the cannula: Aids visualisation and selection of an appropriate vein, improves cannulation success (esp. for difficult IV access), reducing complications (e.g. nerve injury)

Selecting the cannula

• Cannula gauge (number):
  • Gauge: a smaller gauge correlates to a larger internal diameter (increase maximal flow rate) and a longer cannula length.
  • Considerations:
    • Indication for cannulation
      • Large volume resuscitation (e.g. haemorrhagic shock): 2 x 14G cannulae.
      • Non-irritant medications or maintenance fluid administration: 20G is usually sufficient.
      • Paediatric patients: 24G (neonates, infants), 22G (young children).
    • Limitations in cannula size:
      • Small cannula (high gauge): More likely it is to become obstructed and require replacement.
      • Large cannula (small gauge): Ensure vein diameter and length are large enough to accommodate the cannula.
• Long-length cannulas: consider in obese patients where the distance from the skin to the vein is larger (best appreciated under ultrasound guidance). Enables a greater length of the catheter to exist within the vein, reducing the risk of the catheter inadvertently coming out of the vein (i.e. tissuing)
• Cannula design: Numerous are available – use one with which you are most familiar. Safety cannulas can improve sharp safety by either retracting or covering the needle tip after use.

Table 1. Comparison of flow rates through different cannula gauges.

Cannula gauge (G)	Internal diameter (mm)	Flow rates (ml/min)
14G	2.1mm	330
16G	1.7mm	205
18G	1.3mm	105
20G	1.1mm	60
22G	0.9mm	35
24G	0.7mm	25

Insertion tips

1. Disinfect skin: Swab insertion site with 2% chlorhexidine + 70% isopropyl alcohol, and allow to dry
2. Stabilise the skin surrounding the vein
   • Rationale: Inadequate stabilisation increases the likelihood of the cannula pushing the vein to the side, making insertion more difficult
   • Recommendation: I usually stabilise the skin distal to the insertion site whilst ensuring that I do not touch the insertion site after the disinfecting the skin
   • Stablising the vein is most difficult in elderly patients who have less robust subcutaneous connective tissue
3. Local anaesthesia (if indicated)
   • Aim: Produce a small bleb of a local anaesthetic to anaesthetise skin in preparation for inserting a larger cannula
   • Recommendation: I would recommend administering 0.5-1ml of lignocaine 1% subcutaneously, adjacent to the vein, for cannula gauges 14-18G. Need to wait at least 30 seconds to ensure good local anaesthesia
   • Indication: Although the patient experiences a small sting with administration of local anaesthetic, it makes insertion of a larger-bore cannula much more comfortable for the patient. I do not feel that local anaesthesia is required for insertion of 20-22G cannulas
4. Insertion angle
   • Recommendation: My recommended angle of insertion is ~30 degrees
   • Too deep: may perforate the back wall of the vein
   • Too shallow: bevel of the needle may inadequately pass through the skin or lay between the skin and vein
5. Advancing the catheter over the cannula:
   • Considerations:
     • Cannula diameter: The larger the cannula diameter, the longer the bevel and the further the distance between the needle tip and tip of the plastic catheter.
     • Early advancement of the catheter over the needle (e.g. at the point of blood flashback) may result in the inability to advance the catheter as it is likely to still be outside the vein (especially 16-14G cannula)
   • Recommendation: Once a flashback of blood into the cannula is achieved, flatten the angle of insertion, advance the cannula 2-3mm within the vein and then advance the catheter over the needle until the hub rests at the skin insertion site. This allows a sufficient length of the catheter to be inside the vein.

Post-insertion

1. Documentation: Document the insertion procedure and place a date of insertion sticker over the IV dressing.
2. Monitoring of the cannula site:
   • Medical team: Review daily during ward rounds to determine whether the cannula is still required (e.g. can antibiotics be stepped down to oral) and assess for signs of infection
   • Nursing staff: Assess the cannula site every shift (generally every 8 hours) or as per hospital guidelines and notify the treating team if there are signs of infection
3. Removal: Most hospital policies recommend that the cannula should be removed within 72 hours and replaced by a new cannula or a longer-term IV access device such as a peripherally inserted central catheter (PICC) line if ongoing IV access is required.