Introduction
Peripheral venous cannulation — the insertion of a short plastic cannula into a peripheral vein — is one of the most common clinical procedures performed in hospital medicine. It provides IV access for the administration of fluids, medications, blood products, and for blood sampling. Competency in this skill is essential for all junior doctors from day one.
Equipment Required
Before approaching the patient, gather all equipment. Preparation is the key to a smooth procedure.
- Peripheral IV cannula (appropriate gauge — see below)
- Tourniquet
- Non-sterile gloves
- Alcohol skin prep wipe (2% chlorhexidine in 70% alcohol — or 70% isopropyl alcohol)
- Sterile gauze or cotton wool balls
- Adhesive dressing (transparent film dressing, e.g. Tegaderm or IV3000)
- Tape
- Blood tubes and/or pre-flushed syringe (if blood sampling is planned)
- Saline flush (10 mL 0.9% sodium chloride)
- Sharps bin positioned nearby before you start
- Bandage or splint (if cannulating at the antecubital fossa or a joint)
Cannula Size Selection
| Gauge (G) | Colour | Flow Rate | Common Use |
|---|---|---|---|
| 14G | Orange | 343 mL/min | Major trauma, massive haemorrhage |
| 16G | Grey | 236 mL/min | Rapid fluid resuscitation, blood transfusion |
| 18G | Green | 96 mL/min | Routine IV fluids, CT contrast |
| 20G | Pink | 60 mL/min | Routine IV medications, elderly patients |
| 22G | Blue | 36 mL/min | Paediatrics, fragile veins, outpatients |
| 24G | Yellow | 13 mL/min | Neonates, very small veins |
Step-by-Step Technique
The following photographs illustrate the key stages of peripheral cannulation, from equipment preparation to securing the line.
Step 1 — Gather Equipment
Assemble all equipment before approaching the patient. Having everything prepared in advance prevents interruptions during the procedure and reduces the risk of contamination.
Step 2 — Wash Hands and Apply Gloves
Perform a formal 6-step hand wash or use alcohol gel before applying non-sterile gloves. Gloves protect both you and the patient from cross-contamination.
Step 3 — Apply Tourniquet and Select a Vein
Apply the tourniquet approximately 10 cm above the intended insertion site, firm enough to obstruct venous flow but not arterial flow. Ask the patient to clench and release their fist repeatedly to distend the veins. Allow 30–60 seconds for the veins to fill.
Preferred vein sites (in order of preference):
- Dorsum of hand — metacarpal veins
- Forearm — cephalic and basilic veins
- Antecubital fossa — median cubital vein (large and reliable but restricts arm movement; avoid if possible for long-term access)
- Cephalic vein at the wrist (be careful near the radial nerve branch)
Choose a straight, visible, and palpable vein. Avoid areas over joints if the cannula needs to stay in for more than a few hours. Do not use a vein distal to a previous unsuccessful attempt or infiltration site.
Step 4 — Clean the Skin
Clean the skin with an alcohol prep wipe (2% chlorhexidine in 70% isopropyl alcohol). Use a single wipe in one direction, or use a circular motion from inside outwards. Allow to dry completely for a minimum of 30 seconds — this is essential for the antiseptic to be effective and also improves cannula adhesive dressing sticking. Do not re-palpate the vein after cleaning.
Step 5 — Insert the Cannula
Hold the cannula with your dominant hand between your thumb and index finger. Anchor the skin distally with your non-dominant hand to prevent the vein from rolling. Insert the cannula at 15–30 degrees (shallower for dorsal hand veins, slightly steeper for larger forearm veins). Advance with a smooth, steady motion until you see a flashback of blood in the chamber (the transparent hub of the needle). This confirms you are within the vein.
Step 6 — Advance the Cannula and Withdraw the Stylet
Once you see the initial flashback, lower the angle of the entire device to almost parallel with the skin, then advance the entire device 2–3 mm further to ensure the tip of the plastic cannula (not just the needle) is within the vein lumen. Then, hold the needle (stylet) stationary and advance only the plastic cannula hub fully into the vein with your non-dominant hand. Simultaneously withdraw the needle with your dominant hand in a controlled manner.
Step 7 — Occlude the Vein and Remove the Tourniquet
Apply gentle pressure over the vein above the cannula tip (approximately 1–2 cm proximal to the cannula hub) using your non-dominant finger to prevent bleeding when the needle is fully withdrawn. Release the tourniquet before completing the needle withdrawal.
Step 8 — Dispose of the Sharps Immediately
Discard the needle directly into the sharps bin immediately after withdrawal. Never re-sheathe the needle. The sharps bin must have been positioned within reach before you started the procedure. Do not pass sharp objects between practitioners.
Step 9 — Confirm Patency and Flush
If blood sampling is required, take blood now using a syringe connected to the cannula hub. Then attach the saline-primed port cap or extension set and flush with 5–10 mL of 0.9% normal saline. The flush should flow in smoothly with no pain, swelling, or resistance. Resistance or swelling suggests the cannula tip is not in the vein (extravasation).
Step 10 — Secure the Cannula
Apply a transparent, sterile film dressing over the cannula insertion site. The dressing should allow you to inspect the site daily without removing it. Ensure the cannula hub is secured with tape to prevent accidental dislodgement. If the cannula is over a joint, consider splinting the limb to prevent flexion-related dislodgement.
Step 11 — Label and Document
Label the dressing with the date and time of insertion, cannula gauge, and your initials. Document the cannula insertion in the patient's notes. Per NICE guidelines and RCN guidance, peripheral cannulae should be reviewed and re-sited every 72–96 hours (or sooner if signs of phlebitis or infection develop). Remove cannulae that are no longer clinically necessary.
Common Vein Sites — Anatomy Summary
- Cephalic vein: Runs on the radial (lateral/thumb) side of the forearm and arm; large, visible, and relatively stable; good access at the wrist and forearm
- Basilic vein: Runs on the ulnar (medial/little finger) side of the forearm; larger than the cephalic but less accessible; lies close to the medial cutaneous nerve of the forearm — warn the patient of potential paraesthesia
- Median cubital vein: Crosses the antecubital fossa connecting the cephalic and basilic veins; the most reliable and easiest target but restricts elbow movement
- Dorsal metacarpal veins: Good for short-term access; uncomfortable but accessible in most patients
- External jugular vein: Emergency access only; requires patient to lie flat with neck slightly extended; only if peripheral access fails
Complications
- Haematoma: Blood extravasation into surrounding tissue; most common complication; occurs if the vein is transfixed during insertion or if pressure is inadequate after removal. Management: remove cannula, apply firm pressure for 5 minutes, elevate the limb.
- Extravasation: IV fluid or medication leaks into surrounding tissue instead of entering the vein. Can cause tissue necrosis with certain drugs (e.g. chemotherapy agents, vancomycin, phenytoin). Recognition: swelling, pain, coolness at the site, reduced or absent blood flashback. Action: stop infusion immediately, remove cannula, elevate limb, follow local extravasation protocol.
- Phlebitis: Inflammation of the vein — may be mechanical (from movement of the cannula against the vein wall), chemical (from the infused solution), or infective. Signs: redness, warmth, tenderness, and induration along the vein. Scored using the VIP (Visual Infusion Phlebitis) scale. Management: remove cannula, apply warm compress, re-site in a different vein.
- Arterial puncture: If bright red, pulsatile blood is seen in the syringe or flashback chamber, remove the cannula immediately and apply firm pressure for at least 5–10 minutes. Do not inject drugs or fluids via an arterial cannula.
- Infection and bacteraemia: Rare but serious; prevented by strict aseptic technique and regular review and re-siting of cannulae.
- Nerve injury: Rare; caused by direct needle injury to an adjacent nerve. Warn patient of this rare risk; take care at the wrist (radial nerve branch) and antecubital fossa (medial and lateral cutaneous nerves).
- Air embolism: Extremely rare with peripheral cannulae; prevented by ensuring all giving sets and ports are flushed with saline before connection.
Frequently Asked Questions
What should I do if I cannot get a flashback?
If you advance the cannula without seeing a flashback, you may have missed the vein or gone through the posterior wall (transfixed the vein). Do not blindly probe or advance further. Withdraw the needle slightly while gently aspirating with a syringe — sometimes a flashback will appear if the needle tip is still partially in the vein lumen. If there is still no flashback, withdraw fully, apply pressure, and select a different site. After two failed attempts on the same patient, consider asking a colleague with more experience to attempt, or consider an alternative plan (ultrasound-guided access, PICC line, or central access).
When should I consider ultrasound-guided cannulation?
Ultrasound-guided peripheral venous cannulation should be considered when: peripheral veins are not visible or palpable after clinical assessment; the patient has a history of difficult IV access; after two failed blind attempts; or when access is urgently needed in a critically unwell patient. Many hospitals have portable ultrasound machines available on wards and in the emergency department. Training in ultrasound-guided cannulation is now widely available and recommended for all junior doctors. When peripheral access is truly impossible, escalate to your senior for consideration of a central venous catheter or peripherally inserted central catheter (PICC).
How long can a peripheral cannula remain in situ?
Per the Royal College of Nursing (RCN) IV Therapy Standards and NICE guidance, peripheral cannulae should be reviewed every 24 hours and re-sited every 72–96 hours (3–4 days) in adults, or sooner if there are any signs of phlebitis, infection, or extravasation. In practice, a cannula should be removed as soon as it is no longer clinically necessary. In patients with very poor venous access, clinicians may decide to leave a well-functioning cannula in place for longer than 72 hours if removing and re-siting it carries significant risk — document this decision in the notes.
What is the VIP (Visual Infusion Phlebitis) score?
The VIP score is a validated tool for the early detection of infusion phlebitis. It is scored on a 0–5 scale based on clinical signs at the cannula site: 0 = no signs; 1 = slight pain or redness near site; 2 = pain, erythema, or swelling; 3 = pain, erythema, swelling, and induration along the vein; 4 = all of the above plus palpable venous cord; 5 = all of the above plus pyrexia. A score of 2 or above requires the cannula to be removed and re-sited. Many UK hospitals incorporate VIP scoring into routine nursing observations.
What are the contraindications to peripheral cannulation at a particular site?
Avoid inserting a cannula in the following situations: on the same side as a mastectomy (risk of lymphoedema); in an arteriovenous fistula arm (for dialysis patients); in a limb with an acute DVT; in areas of active infection, skin breakdown, burns, or rash; in a vein distal to an unsuccessful previous attempt or area of extravasation; across a joint that will need to flex; in the antecubital fossa if prolonged access is needed (high phlebitis rate, limits movement). Always ask the patient about their preference and any previous problems with IV access.
How do I manage a patient who is frightened of needles?
Fear of needles (needle phobia or trypanophobia) is very common and should be taken seriously — it can trigger vasovagal syncope and patient distress. Effective strategies include: explain the procedure fully and honestly; ensure the patient is lying down (to reduce the risk of fainting); apply topical anaesthetic cream (EMLA or Ametop) 30–60 minutes in advance if time allows; use the smallest effective cannula gauge; allow a companion or nurse to be present for support; use distraction techniques; consider the "tell-show-do" approach; and be calm, confident, and reassuring. If a patient refuses despite these measures, document the refusal and consider whether IV access is truly essential.
What is the correct technique for removing a peripheral cannula?
To remove a peripheral cannula: wash hands and apply gloves; stop any infusion; gently peel back the dressing; hold a sterile gauze pad over the insertion site; withdraw the cannula in one smooth movement in the direction it was inserted; apply firm pressure to the site for 2–5 minutes (longer in anticoagulated patients); inspect the cannula tip to confirm it is intact; apply a small adhesive dressing; and document the removal in the patient's notes. If the patient develops a haematoma or signs of phlebitis after removal, document and manage appropriately.
References
- Royal College of Nursing. Standards for Infusion Therapy. 5th ed. RCN, 2022. Available at: rcn.org.uk
- Scales K. Vascular access: a guide to peripheral venous cannulation. Nursing Standard. 2005;19(49):48–52.
- National Institute for Health and Care Excellence. Healthcare-associated infections: prevention and control in primary and community care. NICE Clinical Guideline CG139. NICE, 2012 (updated 2017).
- Jackson A. Infection control: a battle in vein infusion phlebitis. Nursing Times. 1998;94(4):68–71.
- Wallis MC, McGrail M, Webster J, et al. Risk factors for peripheral intravenous catheter failure: a multivariate analysis of data from a randomized controlled trial. Infect Control Hosp Epidemiol. 2014;35(1):63–68.