If you’ve already read the DFTB article about difficult intravenous cannulation and wish to improve your ultrasound-guided peripheral IV cannulation skills further, here are some more practical tips. We’ve picked these tricks up from our mentors, many failed attempts, and from placing IVs with ultrasound as often as possible.
We firmly believe that if you master putting in peripheral cannulas by ultrasound, your success rates with midlines, arterial lines, and central venous cannulas will skyrocket; simply because, believe it or not, peripheral cannulation tends to be more challenging. If you’re learning this skill, always remember to take the time to prepare, remove self-planted mines, and mentally rehearse what you’re going to do.
TIP 1: Know your gadgetry
Whichever machine you use, either handheld or a big one, know them well. Starting on a vascular preset always helps in having a better resolution to see the vessel and needle. In addition, some machines have a needle profiling function, which is good when learning the skill. Another function that may be useful is the ‘centerline’ in most devices, which shows you what area the middle of the probe corresponds to by showing a solid line on the screen.
Always use a linear probe for vascular access. If you have a hockey stick probe, it gives the advantage of a smaller footprint, which is particularly useful in babies. But any linear probe with a frequency of 11-15 Hz should be suitable. Always align the probe marker with the same side on the screen.
Any appropriately-sized cannula can be used, but it will be good to know how your needle appears on the screen. Larger cannulae appear brighter than small ones. Some cannulae with special, extra-reflective coating are commercially available, but they are not a must-use. Also, make sure you check the length of the cannula, especially if you are aiming for a deeper vein (more about choosing the right vein later)
TIP 2: Setting up the field
This is the most important step, and we can’t stress enough the importance of planning and preparation before poking the skin. The picture below shows the things which you should pay attention to. Always make yourself comfortable and have everything by your side before you start. Align yourself with the patient and US machine, with the right probe marker orientation. Adjust the screen to get the right depth and gain (not so much gain that the vessel remains black and the needle tip is sufficiently bright to see) and adjust the probe to get the aimed vein (more of this in the next section) in the middle of the screen.
- Bed and patient optimised
- Get comfy, sit down
- Line everything up – US machine in the direct view
- US probe marker (on the same side as the blue dot in the screen’s top Right corner)
- Equipment right next to the field
Tip 3: Choosing the best target
Always have a tourniquet applied proximally so the vein is distended while waiting for your cannula.
Depth of the vein
It’s a no-brainer that the bigger the vein and more superficial, the easier it is to cannulate. But that’s not always the case. We should always aim for a vein less than 1 cm deep to have the cannula at a reasonable angle from the skin surface. Also, for a deeper vein, you may struggle to change the angle of the cannula – your insertion angle will have been more vertical to access the vessel. Still, it will need to become more horizontal as you advance the catheter once in the vessel.
Neighbours to the vein
You might have heard of the neurovascular bundle as a family, and they (vein, artery, and nerve) tend to run together. Know the anatomy of the nerves in the arm, so we don’t go through them (a common mistake is aiming for a vein in the antecubital fossa, where the median nerve is).
As a rule of thumb, arteries always have a venous partner, but a vein can run without a partner vein (if you see one vessel only, more often, it is the vein). One method to differentiate between vein and artery is by compressing the vessel – rather than compressibility (peripheral arteries may be compressible, especially in shock states), we prefer looking for pulsatility (by closely looking at the vessel wall for the pulsatile movements, which indicates an artery). A common cause of non-compressible veins is blood clots from previous cannulas or cannulation attempts.
The course of the vein
This is another crucial thing to look at before selecting the vein. You should choose a vein that is longer than your cannula length. You should know the path well so that when you move the probe during cannulation, you can follow the course of the vein (tip to keep the probe in correct alignment to the course of the vein: when you move the probe up and down along the path of the vein, the vein should remain in the same position and should not move sideways on the screen.
TIP 4: Getting it inside – all the way
Now that you are sitting comfy, with everything you need in the right place, and you have the right cannula and know the right vein, with the vein in the middle of the screen, this should be straightforward. Next, we will highlight tips for out-of-plane vein cannulation. For a real in-depth description of the technique, you can click here.
Finding the needle tip
Before poking the needle into the skin, it is a good idea to know where you are entering by putting some pressure without actually puncturing it and seeing the movement on the screen.
Once you are sure your needle is on top of the vein, puncture the skin and wait. If the child wiggles or moves, this time gives you a better chance of not going wayward. Then move the probe and find the needle. Always move one hand at a time, either probe or needle. If you lose the needle on the screen, stop and move your probe to find it again before moving the needle.
The angle of insertion
There’s no particular angle to remember, but we should be able to see the needle on the screen, and having the needle around 30-45 degrees gives you the best chance of that.
Track the needle tip all the way through
Once you see the needle under the skin, move the probe a tiny bit to lose the needle tip on the screen, and then only move the needle to get the needle in the screen. We can call this ‘walking the needle’ under US guidance, which is one of the crucial skills to master. (Remember: US beam is a cross-sectional image in one plane, and the shaft can appear as a dot too! The only way to differentiate that from the tip is by moving the probe and making it disappear from the screen). The following sequential picture shows how the needle tip is walked with USG.
Don’t look for flash in the cannula hub; instead, follow the lead on the USG screen (“Your game is on the screen”). Once you are in the vein (dot inside the vein, and by moving the probe dot disappears rather than moving deeper to the vein), flatten the cannula and repeat until the whole cannula is placed in the vein under direct US vision.
TIP 5: Secure it
Now that the cannula is in the vein, you can remove the needle and pat yourself on the back. But we have all been there where the child pulls it out in the next few minutes. This needs luxurious dressing to secure.
Wipe the gel off the skin with dry gauze and use a second round of alcohol wipes to clear any blood in the field. Once dry, use transparent dressing +/- steristrips to secure it. If the child’s skin is sweaty, an adhesive material to get the dressing to stick is a good option.
Now it’s time to celebrate!
As with every skill, US-guided peripheral venous access can be mastered with practice. To succeed, the key steps are knowing your equipment, getting yourself comfy with everything in place, aiming at the right vein, and walking the needle into the vein. Now it’s time for you to put this into practice.