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In patients with difficult venous access, intravenous (IV) cannulation can be challenging and may require multiple attempts. Ultrasound is a valuable tool in improving the success rate of IV cannulation, providing visualisation of the veins and guidance for correct needle insertion. While ultrasound-guided cannulation requires practice and training, it is a safe and effective procedure when performed correctly.1
This guide provides a step-by-step approach to performing ultrasound-guided cannulation, which should be read in conjunction with our IV cannulation and basics of ultrasound articles.
Indications
Indications for ultrasound IV access may include:
- Difficult vein visualisation and palpation: often due to large body habitus or oedema
- To minimise further patient discomfort: if many previous unsuccessful attempts have occurred
- Extreme dehydration: veins will be smaller, hence more difficult to locate
- Large number of previous cannulations: common in IV drug users or chemotherapy patients with scarred veins
Ultrasound code of conduct
- POCUS is rarely used to rule out pathology
- POCUS should be used in accordance with local hospital guidelines, which often requires credentialing or accreditation
- Ensure patient consent, privacy and comfort throughout
- Document/capture your findings
- Seek help if you are unsure of any findings
- Ultrasound is a radiation-free method of imaging, so the risks to the patient are minimal
- Always use POCUS as part of a wider clinical examination
Upper limb venous anatomy
Typically, when performing IV cannulation, it is safer to use superficial veins. When using ultrasound, this changes slightly, as the ideal veins are the:
1. Cephalic vein in the forearm
2. Basilic vein in the forearm
3. Median cubital vein in the antecubital fossa
The cephalic and basilic veins in the upper arm can be used. However, as these tend to be used by specialist vascular access teams to insert peripherally inserted central cannulae (PICCs), these are best avoided unless in an absolute emergency.
Deeper veins can be located closer to adjacent nerves and articles, so meticulous needle guidance is paramount.
Gather equipment
Gather the appropriate equipment:
- Clean procedure tray
- Gloves
- Disposable apron
- Tourniquet
- Cannula (size appropriate to the indication for cannulation)
- Sterile dressing pack (to provide a sterile field)
- Cannula dressing
- Luer lock cannula cap or extension set
- Gauze swabs
- 10 mL 0.9% sodium chloride
- 10 mL syringe
- Alcohol swab (2% chlorhexidine gluconate in 70% isopropyl)
- 10 mL syringe with 0.9% sodium chloride
- 5 mL 1% lidocaine*
- 5 mL syringe*
- Blunt drawing up needle*
- 25G needle*
- Sterile ultrasound probe cover
- Sterile ultrasound gel sachets
- Universal disinfectant wipes
- Ultrasound machine (with a linear probe)
- Sharps container
* required if administering local anaesthetic
Sterile ultrasound gel
Using sterile ultrasound gel (from a sealed sterile packet as opposed to an opened bottle) during ultrasound-guided cannulation is essential to maintaining aseptic technique and reducing the risk of introducing infection, especially when placing intravenous lines or performing procedures that breach the skin barrier.
Preparing the ultrasound machine
1. Turn the ultrasound machine on.
2. Select the appropriate preset; ‘vein’ or ‘vascular access’ are commonly used, but this varies by machine.
3. Select the linear probe and ensure it is connected to the machine.
4. Disinfect the linear probe with a universal disinfectant wipe.
5. Optimise the depth and gain.
6. Position the ultrasound machine on the opposite side of the patient to the arm you are cannulating, with the equipment nearby and accessible.
Introduction
Wash your hands using alcohol gel. If your hands are visibly soiled, wash them with soap and water.
Don PPE if appropriate.
Introduce yourself to the patient including your name and role.
Confirm the patient’s name and date of birth.
Briefly explain what the procedure will involve using patient-friendly language.
Example explanation
“I’d like to use an ultrasound machine to help find the best vein to insert a cannula. A cannula is a small plastic tube inserted into your vein using a needle, allowing us to administer fluids and medication directly into your bloodstream. You may feel some pushing or discomfort when the needle is inserted, but most people find this easily tolerable.”
Gain consent to proceed with the ultrasound-guided cannulation.
Check if the patient has any allergies (e.g. latex or ultrasound gel)
Adequately expose the patient’s arms for the procedure.
If possible, position the patient supine at 45º so that they are comfortable, resting their extended arm on a flat surface or pillow.
Ask if the patient has any pain before beginning.
Identifying a suitable vein
1. Inspect the patient’s arm for an appropriate site. Apply the tourniquet to enlarge the veins, but ensure it is not left on longer than 1-2 minutes or if the patient is uncomfortable.
- Pre-existing medical conditions may prevent particular limbs from being used (e.g. arterio-venous fistula, lymphoedema, broken skin).
2. Using your non-dominant hand, hold the probe transversely (and directly perpendicular to the skin), with the orientation marker aligned (tap one side of the probe window to confirm orientation).
3. Apply ultrasound gel and place the probe on the skin to obtain a short-axis view of the vasculature.
In the short axis, a vein appears as a black, circular anechoic structure, whilst in the long axis, it will appear long and tubular.
Artery vs vein
To differentiate between an artery and a vein:
- Check for pulsatility: arteries are pulsatile and veins are not
- Check for compressibility: veins will collapse with slight pressure
- Use colour Doppler: blue indicates flow away from the probe, and red towards the probe
4. Map the vein’s trajectory by sliding the probe proximally from a distal starting point, keeping the vessel central, and make note of any surrounding structures, such as arteries and nerves.
5. Make note of the approximate location of the chosen vessel, with a proposed entry site.
6. Wipe the ultrasound gel from the arm in preparation for skin cleaning.
Tips for choosing a suitable vein
Choose a vein with a greater lumen size, as a lumen greater than 2 mm has a higher chance of successful cannulation. The vein size should be correlated to the gauge of the cannula used.
Consider the dwell time of your cannula. For emergency purposes, a deep or superficial vein will suffice. For longer-term IV antibiotics, a deeper, more durable vein may be preferable to a superficial vein.
Be cautious with deep veins near any arteries; meticulous needle guidance is essential.
Preparation
Setting up the ultrasound machine for sterile use
1. Disinfect the linear probe with a universal disinfectant wipe. From this point onwards, the probe window should be treated as sterile and should not be touched.
2. Wash hands and don a pair of sterile gloves.
3. Apply sterile ultrasound gel over the window of the ultrasound probe, avoiding touching the window with the gel packaging.
4. Place a sterile probe cover over the probe and cable, securing it with a rubber band.
5. While maintaining an aseptic non-touch technique, apply a second layer of sterile gel over the probe cover, avoiding touching the probe cover with the gel packaging.
Preparing the cannula
1. Wash hands and don gloves.
2. Open the dressing pack from the corners and place the cannula, cannula dressing and other sterile items onto the field.
3. Prepare the 0.9% sodium chloride flush by drawing the saline into your syringe (if you have a pre-filled flush you can ignore this step).
4. If you are planning on using an extension set, you should attach this to the flush and prime each line.
5. Place a pillow under the arm to be cannulated to make the procedure more comfortable for the patient.
6. Place a sterile field below the patient’s arm to prevent blood spillage.
7. Apply a tourniquet to the patient’s arm, proximal to the intended cannulation point.
8. Clean the skin of the desired site with an alcohol swab for 30 seconds and then allow to dry completely for 30 seconds.
Performing ultrasound-guided cannulation
1. Remove the cannula sheath.
2. Prepare the cannula:
- Open the cannula wings if present.
- Slightly withdraw and replace the needle (this will allow it to glide easier during cannulation).
- Unscrew the cap at the back of the cannula and place upright in the tray (if the cannula is ported).
3. If the vein is deep, consider infiltrating local anaesthetic in the skin to reduce patient discomfort. 2-3 mL of 1% lidocaine solution will usually suffice.
4. Whilst holding the probe with your non-dominant hand, use the ultrasound to obtain a short axis view of the vein at the desired location (ensuring the probe is kept perpendicular to the skin).
5. Warn the patient that they will experience a sharp scratch.
6. Insert the cannula at a 30-45º angle, with the bevel facing upwards, 5 mm distal to the desired vein location, at the centre line of the probe.
7. Check the display for the needle tip; this will appear as a shining dot. If it cannot be visualised, hold the needle still, then slide the probe proximally towards the needle. Either adjust the needle or the probe, but do not move them at the same time.
The chasing method
Once the needle tip has been visualised in the short axis, we recommend using the chasing method to guide the needle into the vein:
1. Visualise the needle tip at the surface of the skin.
2. Slide the probe forward a few millimetres until the needle tip disappears, and then hold the probe in its new position.
3. Advance the cannula forward towards the target until the needle tip is visualised again. Repeat this process until the needle tip is above the blood vessel wall.
4. Continue this process to carefully and slowly advance the needle into the centre of the vein. The vein may ‘tent’ as the needle tip makes contact.
5. Observe for a flashback of blood into the cannula chamber, which confirms that the needle has punctured the vein.
6. Continue to chase and advance the needle a further 2-4 mm into the vessel, to ensure the entire bevel is within the vein. This will usually involve reducing the angle of approach of the cannula.
7. Correct placement can be confirmed with a long-axis view of the vein.
Securing the cannula
1. Partially withdraw the introducer needle, ensuring the needle end is within the plastic tubing of the cannula (you should observe blood entering the plastic tubing of the cannula as you do this).
2. Carefully advance the cannula into the vein as you simultaneously withdraw the introducer needle until the cannula is fully inserted and the needle is almost removed.
3. Release the tourniquet.
4. Safely place the ultrasound probe down whilst keeping one hand on the cannula.
5. Place some sterile gauze directly underneath the cannula hub.
6. Apply pressure to the proximal vein close to the tip of the cannula to reduce bleeding.
7. Gently pull the introducer needle backwards whilst holding the cannula in position until it is completely removed.
8. Connect a Luer lock cap or primed extension set to the cannula hub.
9. Dispose of the introducer needle immediately into a sharps container.
10. Apply adhesive strips to secure the cannula wings to the skin. Do not obscure the insertion site with the strips, as this needs to remain visible to allow early identification of phlebitis.
Flushing the cannula
1. Inject the 0.9% sodium chloride into the cannula using the flush you prepared earlier:
- The flush should be easy to administer with minimal resistance.
- Observe for signs of swelling around the site or pain during administration and stop if this occurs.
2. Close the cannula port (if ported).
3. Secure the cannula with a dressing if the cannula flush was successful.
You can also confirm this with the ultrasound machine by placing your probe on a vein, proximal to the point of cannulation; flushing the cannula should be associated with mild distension of the vein and ‘bubbles’ seen within the lumen.
To complete the procedure
Explain to the patient that the procedure is now complete and that they should seek review if the cannulation site becomes painful or inflamed.
Thank the patient for their time.
Remove the sterile probe cover and disinfect the probe.
Dispose of your PPE and other clinical waste into an appropriate clinical waste bin.
Wash your hands.
Ensure the probe is stored away correctly, and the machine is switched off with all wires stored safely.
Document the details of the procedure on a cannulation chart or in the patient’s notes including:
- The patient’s details: full name, date of birth and unique identification number
- The date and time that cannulation was performed
- The indication for cannulation
- The type of cannula used (e.g. 20 gauge)
- The site of cannulation (e.g. dorsum of the left hand)
- That ultrasound-guided cannulation was used
- That aseptic non-touch technique, sterile ultrasound gel and a sterile probe cover were used
- The date on which the cannula should be removed or replaced
- Your name, grade and contact details
Top tips
Helpful tips to assist you with ultrasound-guided cannulation include:
- Secure the probe cover tightly to ensure there are no air bubbles which could distort the image
- Focus on the screen instead of your hands to guide the cannula accurately
- Stabilise the probe by resting your little finger on the patient’s skin to prevent unnecessary probe sliding
- If you lose sight of the needle tip, slide the probe back towards the needle and adjust positioning
- Use gentle probe pressure throughout to prevent vein collapse whilst scanning and improve visibility
Reviewer
Dr Segun Olusanya
Consultant in Intensive Care Medicine
Editor
Dr Jamie Scriven
References
- Tada M, Yamada N, Matsumoto T, et al. Ultrasound guidance versus landmark method for peripheral venous cannulation in adults. Cochramne Database of Systematic Reviews. 2022. Available from: [LINK].
- OpenStax College. License: [CC BY 3.0]
- Nakayama Y, Takeshita J, Nakajima Y, et al. Ultrasound-guided peripheral vascular catheterization in pediatric patients: a narrative review. Critical Care. 2020. Adapted by Geeky Medics. License: [CC BY 4.0].
UltraLearn
The UltraLearn Project is a student-led, clinician-supervised initiative whereby students across UK medical schools gain confidence and interest in the basics of POCUS. Find out how you can join the community @ultralearnpocus on Instagram, X and LinkedIn.
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