Introduction
Ultrasound-guided venous access has become a core skill for both emergency medicine providers, and nursing staff, to help facilitate difficult access. While clinical experience is critical to learning this technique, phantoms are also a necessary component, specifically with regards to developing both fine-motor skills and spatial orientation. In this post, we provide a step-by-step guide to creating a high-quality, affordable, phantom that can be used for educational purposes at large conferences or for small group training sessions.
1. The Set Up
The Mold: water, metamucil, gelatin, citric acid, blue food coloring
The Veins: animal balloons, red food coloring
The Container: supply case ( 5.08 x 5.25 x 1.9 )
The Tools: sharpie, scissors, syringe, sharp knife or razor blade, large whisk (not shown)
2. Create your Container
We chose the above container because it only requires 500 ml of gelatin mixture, it is plastic (which allows us to cut into it), and it has a lid which allows for easy transport and keeps the phantom fresh.
What you will be doing is creating small slits in the sides of the container to allow for the vessels to "float" and avoid having to pour gelatin in two steps which is both time consuming and messy.
2a. Measure out vessel depth and location
I like to place the vessels 1.5 cm below the surface of the gelatin mold. Using the thick plastic line near the opening of the box, measure 1.5 cm down from here. Measure 4 cm from each side of the box and connect everything with lines. The areas that cross will be where your vessels will go. Repeat this process on opposite side.
2b. Puncture four small slits in container
Now it's time to make small cuts in the plastic container which will allow the vessels to "float." I sit by the stove when doing this and turn on vent above to prevent significant inhalation of burning plastic fumes. Hold the tip of sharp knife or razor knife directly in flame until it turns red. Then quickly push knife into plastic at each line intersection, making approximately a 7-8 mm slit. You may have to re-heat knife between punctures.
Your container is now ready to be used, onto creation of your vessels.
2. Create your Vessels
The red food coloring adds an extra element to your phantom by making the "flash" in the angio-catheter chamber visible.
Fill your syringe with colored water and inject into balloon until it is plump. Next, make sure to get all the air out of the balloon that may have become trapped by holding the balloon vertical, allowing the air to rise to the top, and then tying this off. Continue to tie off the ends of the balloon and trim down with scissors until the vessel is just longer than the width of your container.
Make sure to leave around 1 cm of balloon on each side of your knots as you will need this to pull the vessels through the slits in the container.
3. Cannulate your Container
Take each balloon vessel and thread the ends through the slits in your container. Note as shown in the image that the knot will get caught up on the slit. I use the end of my scissors to pry open the slit slightly, allowing the knot to be pulled through with a little bit of force.
Once the knot is through, pull the balloon vessel out about 1 cm. This will allow the container to "auto-seal." so you do not have to worry about leaking when pouring in the gelatin mold.
This is the hardest step in constructing your phantom so do not be dissuaded if it takes you a few tries.
4. Make your Gelatin Mold
Now it's time to make your gelatin mold. Here are the amounts required for a 500 ml gelatin mold. You can multiply these amounts as needed if making multiple models at a time:
Water: 500 ml
Gelatin: 40 grams (~3.5 Tbsp)
Metamucil: 20 grams (~1.75 Tbsp)
Citric Acid: 1 Tbsp
Blue Food Coloring: 1 tsp
4a. Combine ingredients
Heat up the water in a large pot until it just begins to boil. At this point turn down heat so that water stays warm but is not bubbling. Too much heat will cause the mixture to froth and overflow.
Now add your ingredients, I do the gelatin first as this is the most difficult. It is critical to whisk the water the entire time while adding the gelatin slowly. If you dump the gelatin in all at once, it will form large clumps and ruin your phantom. I would also follow this same technique when adding the other ingredients.
Once all ingredients have been well combined and your mixture has thickened you are ready to pour your gelatin mold into your container.
4b. Pour the mold
Pour gelatin mold into your container, up to the thick plastic line. Allow the mold to cool for 10-15 minutes, then close lid and place in the fridge overnight to set.
The next day your mold will be ready to use!
5. Use your Mold
The mold is probably good for ~ 50-100 IV insertion attempts and can be used at multiple training sessions, though I probably would not keep it for more than 2 weeks. Here are a few other tips:
- The gelatin mold should be chilled until just prior to use to keep it firm; clean surface with water after use, pat completely dry, and store back in fridge to increase longevity.
- To optimize movement of probe along the surface of gelatin mold, be sure to apply a generous quantity to the surface.
- If you notice the balloons appear flat after multiple cannulations, you can refill by directly accessing them through the gelatin under ultrasound guidance and injecting slowly until they appear plump again (do not over pressurize or you may damage the phantom or cause a leak).
Questions?
Leave a comment or email us at ucsdultrasound@gmail.com
