Intravenous cannulation
PLAB 2 & PRES 3 · practical skills · medium · 8 minutes
Candidate brief
You are an FY2 doctor on a medical ward. Mr Brian Doyle, 63, was admitted yesterday with cellulitis of the left leg and is prescribed intravenous antibiotics. His previous cannula tissued this morning and has been removed. The nurse has asked you to site a new cannula so that his next dose can be given. Please insert an intravenous cannula. Verbalise each step as you perform it, and explain to the patient what you are doing and why.
What examiners look for
Chlorhexidine must dry. The antisepsis happens during the drying time — wiping it on and immediately puncturing through wet antiseptic both stings and sterilises nothing. The pause is part of the procedure. Never re-insert the stylet. Once the needle has been withdrawn part-way, pushing it back in can shear the tip off the plastic cannula and embolise a fragment into the vein. If a cannula will not advance, it comes out and you start again with a fresh device. Patency is proven, not assumed. "Flashback seen" is not the end of the station: the flush that runs freely without pain, swelling or resistance is the evidence the cannula is in the vein and safe to give antibiotics through. Site selection is a clinical decision. Forearm veins splint naturally and last longer for ongoing therapy; the antecubital fossa bends with every elbow movement and tissued cannulas are the usual result. The hand is a reasonable first choice in some patients, but listen to the patient who tells you where his good vein is — he has been cannulated before. The two-attempt rule protects everyone. It protects the patient's veins, the patient's trust, and the candidate: examiners are explicitly watching for the candidate who keeps stabbing. Stopping and escalating is scored as senior behaviour, not failure. Documentation is part of the device. An undated cannula with no record of who sited it or when cannot be reviewed, scored (VIP/phlebitis) or removed on time — and peripheral cannulas left undocumented are a genuine source of bacteraemia. Allergy questions in practical stations must include the unglamorous ones: chlorhexidine, latex, and the dressing itself — as this patient demonstrates, the dressing allergy was the one that would actually have harmed him.
Guideline references
- https://geekymedics.com/how-to-perform-cannulation-osce-guide/
- https://www.nice.org.uk/guidance/cg139
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