Knowledge · Procedural Skills

Cannulation: Aseptic Insertion, Flushing and Setting Up an Infusion

By Dr Richard Miller, MBChB FRCS with the MRCS Part B Questions Team · Reviewed 15 September 2026

In brief

Cannulation is marked on aseptic non-touch technique and safety: decontaminate the skin with chlorhexidine gluconate in 70% alcohol, advance the cannula rather than the needle, flush with sterile sodium chloride, and remove the device as soon as it is no longer needed.

Cannulation is marked on aseptic technique and on what you do after the cannula is in. NICE CG139 requires skin decontamination with chlorhexidine gluconate in 70% alcohol before a peripheral vascular access device is inserted, an aseptic technique throughout, a sterile transparent dressing, and removal of the device as soon as it is no longer needed.

Key takeaways

NICE CG139 recommendation 1.4.3.1 is to decontaminate the insertion site with chlorhexidine gluconate in 70% alcohol before insertion.
An aseptic technique must be used for device care and whenever the system is accessed; CG139 names aseptic non-touch technique as an example.
Cover the site with a sterile transparent semipermeable membrane dressing, which CG139 says can stay for the life of the cannula if it stays intact.
CG139 prefers sterile 0.9% sodium chloride to flush and lock catheter lumens.
NICE quality standard QS61 asks for the device to be removed as soon as it is no longer needed.

What is the examiner marking at the cannulation station?

The Intercollegiate blueprint runs two procedural stations and marks them differently. A procedural skills station with a patient carries 8 marks for clinical and technical skill and 4 each for clinical knowledge, communication and professionalism. A technical procedural station, performed on a model rather than a person, carries 12 for skill and 8 for knowledge, with no communication or professionalism marks available.

Prepare for the version with a patient, because it is the harder of the two: the same technique has to be delivered while consenting, explaining and keeping the patient comfortable, and those marks are gone if you work in silence.

The examiner is marking asepsis, sharps handling and a working, secured, flushed cannula. Choosing an appropriate site and gauge for the indication is part of the mark.

Narrate the steps a model cannot demonstrate, such as checking the patient's identity and allergies.

What are the indications, and how do you choose a site?

Cannulation is indicated for intravenous fluids, drugs, blood products and contrast, and for access in an unwell patient who may deteriorate.

Choose a straight, palpable vein, usually in the forearm, and avoid the antecubital fossa for an infusion that must run
Avoid an arm with a fistula, lymphoedema or previous axillary clearance, and avoid infected or damaged skin
Match the gauge to the purpose: a larger gauge for resuscitation or blood, a smaller one for routine drugs
Avoid the dominant hand and a joint where flexion will occlude the device

Explain the purpose, the procedure and what it feels like, then take verbal consent. Royal College of Surgeons of England, describing the Montgomery ruling, notes that clinicians must take reasonable steps to ensure patients are aware of risks material to them.

Mention pain, bruising, failed attempts, phlebitis and infection, and check the patient understands before proceeding.

What equipment do you need?

Clean tray, tourniquet, chlorhexidine gluconate in 70% alcohol applicator, gauze
Cannula of the chosen gauge, plus a spare, and a needle-free extension or cap
10 mL sterile 0.9% sodium chloride flush in a syringe
Sterile transparent semipermeable membrane dressing and a sharps container at the point of use
Gloves and apron, and eye protection if splashing is likely

What are the steps, in order?

Wash your hands, confirm the patient's identity and allergies, and gain verbal consent
Prepare the equipment on a clean tray and check that the cannula and flush are in date
Apply the tourniquet, select a vein, then perform hand hygiene and put on gloves and apron
Decontaminate the skin with chlorhexidine gluconate in 70% alcohol and allow it to dry fully, and do not re-palpate the cleaned site
Anchor the vein with your non-dominant hand and insert the cannula bevel up at a shallow angle
Watch for flashback, then lower the angle, advance a few millimetres, and advance the cannula off the needle into the vein while keeping the needle still
Release the tourniquet before you withdraw the needle, occlude the vein proximally, then remove and immediately discard the needle into the sharps container
Attach the cap or extension, apply the sterile transparent dressing and date it
Flush with sterile 0.9% sodium chloride, watching for swelling, resistance or pain that would indicate extravasation
Dispose of waste, wash your hands, and document the site, gauge, date and any difficulty

How do you keep cannulation aseptic and safe?

**Aseptic non-touch technique** is an approach to asepsis in which the key parts and key sites of the equipment are never touched, and CG139 names it as an example of an aseptic technique for vascular access.

Decontaminate hands before accessing or dressing the device, as CG139 requires
Decontaminate the injection port or hub with chlorhexidine gluconate in 70% alcohol before and after every access
Use a sterile gauze dressing covered by a transparent dressing only if the site is bleeding or oozing, changing the gauze every 24 hours
Inspect the site at least daily and remove the cannula when it is no longer needed, as QS61 requires

How do you set up an infusion once the cannula is in?

Check the fluid against the prescription, including the drug, additives, volume, rate and expiry, with a second checker where local policy requires it.

Prime the giving set without contaminating the end, connect it to the cannula, run the fluid at the prescribed rate, and record it on the chart. NICE CG139 notes that administration sets in continuous use generally need changing no more often than every 72 hours.

What are the complications and the common mistakes?

Failed cannulation, haematoma, arterial puncture and nerve irritation
Extravasation, which is why the flush is watched rather than just performed
Phlebitis and catheter-related bloodstream infection, the reason CG139 and QS61 emphasise asepsis and early removal
Needlestick injury, usually from recapping or from a sharps container out of reach
The classic station errors are touching the cleaned skin, advancing the needle rather than the cannula, and forgetting to flush and document

How do you finish and document?

Make the patient comfortable, clear the tray, remove gloves and wash your hands, then complete the cannula record.

Document the date, site, gauge, number of attempts and who inserted it, and hand over the plan for review and removal.

The MRCS Part B Questions bank has a cannulation station at /Sample-Questions.

Key evidence

Healthcare-associated infections: prevention and control in primary and community care (CG139), section 1.4 — National Institute for Health and Care Excellence (2017)
Infection prevention and control (QS61), quality statement 5: vascular access devices — National Institute for Health and Care Excellence (2014)
WHO guidelines on drawing blood: best practices in phlebotomy — World Health Organization (2010)

FAQ

Which antiseptic should be used before cannulation?

NICE CG139 recommendation 1.4.3.1 is to decontaminate the skin at the insertion site with chlorhexidine gluconate in 70% alcohol before inserting a peripheral vascular access device or a peripherally inserted central catheter. NICE also records the 2012 MHRA safety alert about chlorhexidine and the risk of adverse events. Let it dry fully before insertion.

What should I flush a new cannula with?

NICE CG139 states that preferably a sterile 0.9% sodium chloride injection should be used to flush and lock catheter lumens. Watch the site as you flush for swelling, pain or resistance, which suggest extravasation. Heparin locks are only for certain implanted devices when the manufacturer recommends them.

How long can a peripheral cannula dressing stay on?

NICE CG139 says the transparent semipermeable membrane dressing applied to a peripheral cannula insertion site can stay in situ for the life of the cannula, provided the dressing stays intact. If the site is bleeding or oozing, a sterile gauze dressing under a transparent dressing may be used and changed every 24 hours. Inspect the site daily.

When should a cannula be removed?

NICE quality standard QS61 asks for vascular access devices to be removed as soon as they are no longer needed, because they are a major cause of healthcare-associated infection. Review every cannula on the ward round. Document the decision to keep or remove it.

What is aseptic non-touch technique?

It is an aseptic technique built around never touching the key parts and key sites of the equipment, such as the cannula hub or the syringe tip. NICE CG139 cites it as an example of aseptic technique for vascular access device care and says an aseptic technique must be used whenever the system is accessed. Say the term in the station and then show it.

How often should giving sets be changed?

NICE CG139 states that, in general, administration sets in continuous use need not be replaced more frequently than at 72-hour intervals unless they become disconnected or a catheter-related infection is suspected or documented. Blood and lipid-containing infusions follow different local rules. Check your trust policy.

The MRCS Part B Questions Team

Written and maintained by doctors who have sat and scored well at this interview, and reviewed against the current published guideline in each case. Guidance changes — check the source before you rely on a threshold.

Last reviewed 15 September 2026

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