Peripheral IV Cannulation — OSCESup
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Procedure April 2026

Peripheral IV Cannulation

Patient Mrs Sarah Okafor
Age / Sex 68F
Setting Medical Admissions
Year Group Y2 / Y3
Duration 10 minutes

Clinical Scenario

Candidate Briefing

Mrs Sarah Okafor is a 68-year-old woman admitted via the Emergency Department with a 3-day history of right-sided loin pain, dysuria, frequency and fever. She has a background of type 2 diabetes and osteoarthritis. Her only regular medication is metformin 1g BD. She has no known drug allergies.

Investigations confirm a diagnosis of acute pyelonephritis. The admitting team has prescribed co-amoxiclav 1.2 g IV TDS, and IV access is required.

Temp 38.8 °C
HR 104 bpm
BP 118/74 mmHg
RR 18 /min
SpO₂ 97% (air)
NEWS2 4

Please site a peripheral IV cannula in Mrs Okafor. A simulated arm is provided. The examiner will observe and ask questions throughout.

Equipment Checklist

Non-sterile glovesCorrect size
TourniquetSingle-use or decontaminated
18G (green) cannulaAppropriate for IV antibiotics
Alcohol wipe70% isopropyl · Allow 30 sec to dry
Transparent semi-occlusive dressinge.g. Tegaderm / IV3000
Extension set / Luer-lock cap
10 ml syringe + 10 ml 0.9% NaCl flushTo confirm patency before use
Gauze / cotton wool
Sharps binWithin reach before starting
Cannula labelDate · Time · Gauge · Operator initials

Cannula Sizes

Colour Gauge Flow Rate Common Indications
Orange 14G ~270 ml/min Major haemorrhage, rapid volume resuscitation
Grey 16G ~180 ml/min Blood transfusion, large volume fluid resuscitation
Green ✓ 18G ~90 ml/min IV antibiotics, standard fluids, most adult admissions — correct choice here
Pink 20G ~60 ml/min CT contrast, slower infusions, fragile veins
Blue 22G ~36 ml/min Paediatrics, elderly/fragile veins, slow infusions only
Yellow 24G ~20 ml/min Neonates, very fragile veins

Mark Scheme

Competency Marks Awarded
Introduction & Consent
Introduces self (name and role); confirms patient name and date of birth against wristband 1
Explains the procedure and the reason for it in lay terms; obtains verbal consent
e.g. "I need to put a small plastic tube into a vein in your arm so we can give you the antibiotics directly into your bloodstream"
 1
Asks about previous cannulation difficulties, latex allergy; checks for IV drug use, AV fistula or lymphoedema before selecting arm 1
Preparation
Selects correct gauge (18G green); gathers all equipment before approaching; places sharps bin within reach 1
Performs hand hygiene (6-step technique) and applies non-sterile gloves 1
Site Selection
Applies tourniquet 5–10 cm above planned site; encourages venous filling (fist, dependent arm) 1
Selects appropriate site — antecubital fossa or dorsum of hand; avoids areas of infection, bruising, valves or bifurcations
Dorsum of hand is acceptable but more painful — acknowledge this to the patient
 1
Cleans skin with alcohol wipe using outward motion; allows minimum 30 seconds to dry fully 1
Does NOT re-palpate the site after cleaning 1
Cannulation Technique
Warns patient ("sharp scratch"); anchors skin below site; inserts bevel-up at 15–30° and advances until flashback seen in hub 1
Advances cannula and needle a further 2–3 mm together to ensure cannula tip is in lumen; then slides cannula fully into vein while withdrawing needle 2
Releases tourniquet; occludes vein proximally with index finger before fully withdrawing stylet 1
Disposes of stylet directly into sharps bin without re-sheathing
Automatic fail if stylet is re-sheathed or placed on a surface
 2
Post-Insertion
Attaches extension set; flushes with 10 ml 0.9% NaCl; observes for swelling (infiltration) or resistance (blockage) during flush 2
Secures cannula with transparent dressing, ensuring insertion site is visible through dressing 1
Labels cannula with date, time, gauge and operator initials 1
Removes gloves, performs hand hygiene; documents in notes (date, time, site, gauge, indication, operator) 1
Thanks patient; advises them to report pain, swelling or redness around the cannula site 1
Total 20 marks

Examiner Questions

Why did you choose an 18G (green) cannula for this patient?
An 18G cannula provides a flow rate of approximately 90 ml/min — adequate for IV antibiotic infusions in an adult. A larger cannula (16G/14G) is reserved for blood transfusion or rapid volume resuscitation. A smaller cannula (20G/22G) would be appropriate only for elderly patients with fragile veins, but risks being too slow for repeated antibiotic boluses.
What are the signs of phlebitis, and how do you grade it?
Use the Visual Infusion Phlebitis (VIP) score:
  • 0 — No signs
  • 1 — Slight pain or redness near insertion site
  • 2 — Pain, redness and/or swelling
  • 3 — Pain, redness, swelling and palpable venous cord
  • 4 — Pain along vein, redness, swelling, cord >3 cm, purulent discharge
  • 5 — All of the above plus pyrexia — thrombophlebitis, systemic infection
Score ≥2 requires cannula removal and re-siting. Score ≥3 may require antibiotic treatment.
How often should peripheral cannulae be reviewed and replaced?
Per NICE and local trust guidance, cannulae should be reviewed at each shift and replaced every 72–96 hours, or sooner if there are any signs of phlebitis, infiltration, or the cannula is no longer needed. The insertion date and time label you apply allows nursing staff to track this. Cannulae should be removed as soon as they are no longer clinically indicated.
You notice Mrs Okafor has an AV fistula in her right arm. What do you do?
Never cannulate the arm with an AV fistula — this risks thrombosis, infection and permanent fistula damage. You must use the contralateral (left) arm. If both arms are compromised, escalate to a senior. Also avoid blood pressure cuffs, blood draws and tight clothing on a fistula arm.
You get flashback but when you flush there is swelling around the site. What has happened and what do you do?
This is infiltration — the cannula tip has either not advanced far enough into the vein or has penetrated the posterior wall, causing IV fluid to extravasate into subcutaneous tissue. Stop the flush immediately. Remove the cannula and apply gentle pressure. Inspect the site. Re-site in a different location, ideally in the opposite arm. If the drug was vesicant (e.g. amiodarone, certain chemotherapy agents), follow your trust's extravasation protocol and document carefully.

Safety Points

Fail Re-sheathing the stylet is the most common automatic fail. Once removed from the cannula, the stylet goes directly and immediately into the sharps bin — no exceptions.
Fail Cannulating an arm with an AV fistula is a serious patient safety error. Always inspect both arms and ask the patient about fistulae before selecting a site.
Key Point The most common technical error is not advancing the cannula/needle unit far enough after flashback. If you pull back the needle before the cannula tip is fully in the lumen, you will withdraw the cannula from the vein. Advance 2–3 mm after flashback before sliding the cannula off the needle.
Key Point Occlude the vein proximally with your finger before removing the stylet. Failing to do this results in blood back-flow, contaminating the field and alarming the patient.
Top Tip Always flush before declaring a cannula successful. A cannula that gives flashback but fails to flush (or causes swelling) is not usable — better to find this out now than when the nurse tries to give the first drug dose.