Intravenous cannulation, putting a drip in or “starting an IV” (American) is a commonly performed invasive procedure. Whilst it can seem daunting at first, it’s actually a very straightforward procedure. However, if done poorly, it can lead to serious infection, loss of limb or death – so don’t pay it off.
When should we cannulate?
There are many indications for cannulation, and this is not going to be an exhaustive list. But consider the following reasons for cannulation:
- Patient requires IV medication (analgesia, anti-emetic)
- Patient requires IV fluid
- Patient has a condition you anticipate will deteriorate to the point of needing IV medication or fluid (such as deteriorating haemorrhagic shock)
- Patient has need for specialist imaging which requires IV access (typically a stroke patient will receive a CT brain with IV contrast)
- The patient has an illness which would benefit from urgent pathology at hospital, but doesn’t otherwise need an IV (such as a COPD patient on CPAP, who would benefit from an urgent venous blood gas on arrival at hospital)
When shouldn’t we cannulate?
- Where patient isn’t likely to require IV medications (eg. pain adequately controlled with oral/IN medication)
- Dehydrated patients able to tolerate oral fluids, where water is freely available
- Patients not expected to deteriorate but want to insert an IV “just in case”
What should we consider when cannulating?
Site and gauge
As listed above, there are many reasons for cannulation – but not all cannulas are created equal. Two considerations are the site (ie. target vein) and gauge (size) utilized.
We should all know that flow through a tube is not linear (Poiseuille’s law). As the tube doubles in size, the flow rate increases 16 times… for on road paramedics that means the larger cannulas flow significantly faster than smaller ones. Hence if you want to get a large volume of fluid into a patient quickly, a larger cannula is going to achieve that.
Cannulas are sized according to the Birmingham Wire Gauge system, often shortened to ‘gauge’. This is a system where a wire was progressively trimmed, starting as a large size (0 gauge) and ending at the smallest, a 30 gauge. In terms of cannulas we typically use a 16g as the largest cannula (with highest flow rate) and progress to a 24g cannula (quite small and slow, suitable for babies).
Next let’s talk about vein selection. My general advice, especially when you’re starting out, is aim for the vein you can see the most. Your mentors will have their eye tuned in and see veins you cannot – this is fine. You’ll be relying more on sight than on feel.
Once you are more comfortable and competent, now we can start making better choices. Most paramedic services will permit cannulation of the arm from the cubital fossa (inside of elbow) down to the hand.
General teaching says we should always start distally (at the hand) and work our way up. A few reasons for that are:
- If we miss, we can try higher up without having to pass medications through a compromised vein
- Further for serious infection to travel
- Generally easier for healthcare workers to access
However downsides of the hand include:
- Anecdotally more painful for patients. The hand does have more nerve endings
- Easily dislodged
- Smaller veins means slower flow rate
- Not suitable for infusions such as 10% Dextrose or Adrenaline due to risk of extravasation and tissue necrosis
The reverse tends to be true for higher/more proximal veins in the cubital fossa (front of elbow)
- Generally larger, deeper veins
- Located close to nerves, tendons and arteries
- Annoying for the patient, and bending their arm may occlude the cannula
- Suitable for irritating substances such as IV contrast
- Capable of infusing large amounts of fluid quicker than the hand (such as resuscitation with blood products)
Reason for cannulation
Large volume fluid resuscitation (traumatic arrest, severe burns) – need to be a large bore (16-18g) cannula in a proximal vein
Stroke patients/anyone needing a contrast CT scan – need to be a large bore (18-20g) cannula in a proximal vein. Must have a reflux valve attached
Adenosine – a specific circumstance because of adenosine’s 8 second half-life, it needs to reach the heart quickly. Needs a large bore (18-20g) in a proximal vein. Flushed with at least 20mL N Saline.
10% Dextrose / Adrenaline / other necrotising drugs – need to be a large bore (16-18g) cannula in a proximal vein, which is flushing well
Small fluid boluses / analgesia / anti-emetics – can be any vein, any size cannula. Generally attempt the hand to minimize risk of complications
What type of cannulas are available?
Most services will have multiple brands of cannula available. This helps when there are supply disruptions, but means you need to be comfortable using several different devices. Although the insertion technique is generally the same, knowing the nuanced differences will improve the likelihood of success.
How long is the cannula? Some safety cannulas have quite long barrels, which make them harder to handle for people with smaller hands
Does the cannula have a single use valve to prevent blood loss from the cannula? Whilst they’re great for preventing mess, some brands mean that flashback is not seen in the cannula itself (Autoguard 16g and 18g for example)
Is the cannula single beveled or multi-beveled? Single bevels are good for a higher approach angle, the multi-bevel is suitable for a lower angle.
How does the safety device deploy? Do you need to extend it completely or push a button? Some may be suited to smaller hands
Insertion technique
I strongly recommend to all my graduates that you look at cannulation videos on YouTube, in particular you should look up the brand of cannulas you have available and watch videos produced by the manufacturer!
Firstly – identify patients who need cannulation and explain to patient. Gain consent.
Prepare your equipment. This may be a pre-packaged bundle, or you get each component separately. You can also ask your partner to set you up!
- IV cannula (with backup if you’re feeling unlucky)
- Chlorhexidine/alcohol swab
- Venous tourniquet
- Adhesive dressing (such as Tegaderm or Opsite)
- Reflux valve or 3-way extension
- Gauze (in case you miss – although some superstitious people say you will miss if you get gauze out!)
- Normal Saline flush (10mL)
- Sharps container
- Date label
- Hand sanitizer
- Clean gloves
Hot Tip – make sure you can reach all these items without letting go of the cannula!
Prepare the patient and environment for insertion. This means selecting a site and cleaning it (use water or wipes if there is visible dirt/contamination). Ensure you have good access to the limb – this will usually be achieved by placing a towel on your knee and resting the patient’s hand on it. Adjust lighting where necessary, remembering that excessive light may make the vein harder to spot.
Pro tip: if the patient has hairy arms, use a disposable razor to gently remove excessive hair. This will improve visibility of the vein, make your dressing stick better and avoid the patient receiving a free wax when it’s removed!
Apply the venous tourniquet to the limb, allowing enough distance above the vein for you to work (usually 10cm will suffice). Avoid restricting arterial blood flow. Observe the limb for suitable veins, favouring those that are straight, immobile (don’t roll away) and visible.
Tips to make veins more visible:
- Ask the patient to clench their fist
- Hang the limb over the edge of the bed, letting gravity cause venous pooling
- Tap the vein with your finger (no need for aggressive slapping)
- Apply a warm compress
Clean the area with an appropriate alcohol/chlorhexidine solution (or iodine if the patient is allergic to chlorhexidine). Ideally clean a 5cm x 5cm area around the insertion site for 10 seconds using slight friction. If patient condition permits, repeat this with a second alcohol wipe.
Once cleaned, don’t re-palpate the site. This is an aseptic procedure
Hold the cannula with the needle facing away from you (obvio), and bevel (pointy bit) facing up. Grip it in such a way that you can see the flash chamber, reach the push-off tab and fully advance the catheter with one hand.
Foxy’s Tip: try picking up the cannula with your thumb and middle finger, which allows you to easily see the flash chamber and feed off the catheter with your index finger.
Anchor the vein using your opposite hand, applying gentle traction to prevent the vein moving away. For the hand I generally hold the patient’s hand, for forearm/cubital fossa I hold underneath their arm.
Holding the cannula at an angle less than 45 degrees, advance the needle into the skin, towards the vein. Steeper angle is necessary for deeper veins (which are harder to see but easy to feel) and shallower angle is suitable for superficial veins. I generally use a 30 degree angle.
Once you see the first blood appear in the cannula (“flashback”) – pause, take a breath. You’re in the vein but not quite done
Next, advance the entire cannula 2mm – this ensures that both the needle and catheter are in the vein
Practice point: note I’m referring to the different parts here. Cannula refers to the whole unit, catheter refers to the plastic sheath that remains in the vein, and needle is the needle!
From here, feed the catheter off into the vein, whilst keeping the needle still. Advance the catheter until it is flush with the skin. Release the tourniquet and retract your sharp to deploy the safety mechanism (this will vary slightly depending on the type of cannula). Discard it appropriately.
Apply the reflux valve or 3-way extension. Secure with a tape strip or similar and flush to assess for patency. Doing this prior to securing with your dressing allows for adjustment if needed.
Secure with the dressing of your choice, apply a date label and tidy up. Job done!
A note on inadvertent arterial cannulation
Occurring in 0.5-1% of cannulations, inadvertent arterial cannulation describes the accidental insertion of the catheter into an artery, instead of the vein. It presents risks to distal limb perfusion and can cause haematomas. Arterial drug administration can cause tissue necrosis.
Inadvertent arterial cannulation can be identified by:
- Excessive, pulsatile back flow of bright red blood
- Immediate bruising
- Intense pain distal to insertion site (particularly after medication administration)
- Neurovascular compromise distal to the insertion site
Any suspected arterial cannulation must not be utilised. It should be removed, with firm pressure applied to prevent bleeding. This information should be handed over for further management at hospital.
Bottom Line
Obtaining IV access is a core skill for operational paramedics – many of our interventions rely on it. Whilst daunting for junior paramedics, it is very achievable. Practice often, in realistic situations. Ask your mentor for tips. See the vein, aim for it and succeed! You can do it!!
