The Saga of the Home Made Lumbar Puncture Task Trainer
Thanks for all the re-tweets about this model and all of the requests for instructions on how to make it.
This trainer was made for the ED Procedures Junior Doctors/Paramedics Course:
And yes, it was a saga. Possibly better suited to a multi-chapter book than a blog post. But several people asked me for the instructions, so for those who dare, read on:
1 x plastic anatomy skeleton (about $180 on eBay, I had an old damaged in laying around)
Screws (40mm or thereabouts)
1kg Silicone: e.g. Pinkysil (This is a Shore 20A hardness silicone)
(i.e. at least 500ml Part A and 500ml Part B)
Plastic takeaway containers
Heat shrink tubing
Rubber tubing cut into 4-5cm lengths (alternatively you can use IV bungs)
IV fluid giving set
IV fluid (e.g. saline 500ml or 1000ml)
Permanent marker pen/texta
Electric drill (various sized drill & screwdriver bits)
Hacksaw, angle-grinder or Dremel (with small angle-grinder bit)
Plastic cups/small buckets
Wooden spatulas/tongue depressors
Non-stick moulding spray (e.g. J-Wax)
Hot glue gun
Ceramic hair-straighteners (e.g. GHD brand)
I have no idea.
To go out and buy all of these items individually will cost hundreds of dollars and you’d be better off buying a commercial LP trainer. I happened to have most of it in my shed or at the ETM office.
And I have a LOT of tools.
All up I spent at least 30+ hours on this project over the course of 2 weeks.
If you have some tools already and like to tinker, you may be able to knock one of these up in your shed in less time now that there’s a plan! I was making it as I went and there was a lot of trial and error.
Regardless you may get some tips and ideas on how to use the various items & techniques in this project for other task trainers you make.
So grab a cup of tea and a biscuit, this takes a while…
STAGE 1 – THE SPINE
Deconstruct your plastic skeleton and pull off the pelvis, the L1 to L5 vertebrae and the L1-2 to L5-S1 rubber inter-vertebral disks.
If there’s a metal rod running through the centre of the vertebral bodies into the sacrum, keep it attached to the sacrum/pelvis and cut it off an inch or so above L1 (using hacksaw, angle grinder or Dremel)
Tip: Label all vertebrae and disks with permanent marker pen as you remove them!
They’ll fit together better when you re-build if you get the sequence/orientation right!
Remove any rubber/plastic spinal cord or nerves & discard.
If you removed/disconnected the metal rod, put it back into the sacrum, as you’ll use this to slide the disks/bones back on.
You will now thread the vertebrae back onto the metal rod in correct order one by one, screwing each one to the vertebrae below as you go.
Start with the L5-S1 disk on top of sacrum and and then put the L5 vertebrae on top.
Then drill a hole from the superior surface of L5 body, off to one side, down through the disk, into the sacrum.
Then place a long screw into this hole and drill it in all the way until it’s in the sacrum.
So the L5 vertebrae and L5-S1 disk are now firmly secured to the sacrum.
Now repeat this at each level, but place the screw on alternating sides of the vertebral bodies as you ascend.
You should end up with L1 to L5 vertebrae and all disks firmly attached to the pelvis.
This piece will from now on be referred to as “the spine”.
STAGE 2: THE PELVIS
It’s useful to leave at least one iliac wing on to use as a landmark.
I removed the left one as I always do my laterally positioned LP’s with the patient’s head to my left, and use the right iliac crest as my landmark, so that’s what I did for this model – it just unscrews from the sacrum.
If you can figure out a way to fix your spine to a mount with both iliac wings still attached, go for it!
STAGE 3: “SKIN & SOFT TISSUE”
I wanted a skin/tissue layer that could withstand multiple needle punctures without needing replacement which would also still give a realistic feel for palpation of spinous processes and needle resistance and wouldn’t get wet/soggy if the “CSF” leaked onto it.
I thought about using 2cm thick foam and some 3mm foam fake skin over the top but it was too soft/spongy, wouldn’t fit nicely over the spinous processes and didn’t handle getting wet very well (from “CSF” leak) and would need frequent replacement.
So having fooled around quite a bit with silicone moulds in the past, I figured this was the perfect material, although making the mould was the hardest part of the project. If you want to try it, here’s how I did it:
Tip: If you want the best advice and range of products for silicone mould making (in Australia), just go to a Barnes shop. They literally have everything you need, and the staff are very knowledgeable.
If you want to learn about moulding before you try it, check out their YouTube channel.
Tip: If you are unfamiliar with moulding silicone, you are likely to f**k this step up several times before you get it right. That’s OK. Take your time and don’t be disheartened if your first attempt doesn’t succeed. You’ll learn something with each attempt.
Tip: Drink beer while doing this step to take the edge off your inevitable frustration.
Remove both iliac crests before starting this step. (You can put the right one back on when it’s done).
Lay “the spine” supine (spinous-processes-down), in a baking tray.
Ensure the spinous processes are raised off the base of the tray the distance you want them below the skin surface (ideally a few mm to 1cm).
You may need to prop one end up with some more plasticine to get it to the right height.
NB: If the spinous processes are touching the base of the tray, they’ll end up protruding through the silicone which will look silly and won’t give a realistic feel when you go to use it.
Cut up the plastic takeaway containers into rectangular pieces and use these and the moulding plasticine and to build a walled box around the spine. You may need to tape 2 pieces together for the longer walls (I used packing tape to do this).
NB: You need to ensure that at the distal, dorsal end of the spine (or proximal sacrum, or wherever you build the distal “wall”) the plasticine fills any gaps and that the plasticine is firmly stuck to the baking tray so the silicone doesn’t leak out.
NB: The walls need to be at least 1-2cm higher than the level of the transverse processes
Take a lot of time to ensure that your plasticine “fence” has no gaps in it – the liquid silicone will leak out of any small gap.
Spray the whole thing liberally with J-Wax spray (this stops the silicone sticking to the tray/spine)
Measure your walled off area to get a rough idea of the volume of silicone you’ll need (length x width x height = cubic cm = approx volume in ml)
From memory mine was about 700ml
Tip: to avoid wasting silicone, only measure the height up to about the level of the transverse processes as this is how high you’ll fill the mould.
Tip: You will probably need to mix your silicone in 2 batches as hand mixing 700-odd ml of silicone is quite hard, so have 2 containers ready so you can mix & pour 2 batches in quick succession.
Tip: Use the electronic scales to measure your portions!
Trying to use any sort of containers with volume markers on them will fail, as some will stick to one container, or you’ll accidentally pour too much in. If you get the ratio slightly wrong it won’t set, and you’ll have gooey, un-set silicone all over your spine/tray and you will cry.
Just use scales.
Mix the silicone in the ratio described on the product information for your type of silicone, most are equal measures of Part A and Part B (but be sure to check as some aren’t!)
Let stand for 1-2 mins, tapping the container gently on the bench to get any air bubbles out. It should look like this (no swirls).
Gently pour the silicone into the mould, starting down the sides. Avoid pouring it directly onto the spine. Slowly fill the mould until the silicone is near the level of the transverse processes.
Then look inside and fill slowly, slowly, slowly until it’s a few mm below the posterior/dorsal wall of the spinal canal.
Tip: You must avoid over-filling and getting silicone in to the spinal canal or overlapping the back of the neural arch. If this happens you won’t be able to remove the silicone block once it sets!
Allow silicone to set.
Once set firm, lift gently out of tray, remove the plastic walls and plasticine and pull the silicone block gently off the spine.
If you got it right, it should come off and slide back on over the spinous processes and fit nice and snug.
Tip: Silicone sets quicker in a warmer environment, and there’s some “fast-set” stuff out there, so do a small test batch to see how long it takes to set (can firm up in 10-20mins on a warm night, or may take overnight if it’s really cold). If you’re in a cold place, you can put the baking tray over a central heating vent to get it to set quicker. DO NOT PUT IT IN THE OVEN!
STAGE 4: MOUNTING:
You can now mount the spine however you like.
It needs to be on a sturdy base as people will be pushing quite hard on the model to find their landmarks.
I used a large flat bit of particle board as the base, and a thick piece of treated pine as the mounting board (held together with a bunch of 50mm screws)
I then screwed one iliac crest into the top of the pine mounting board and drilled a couple of holes through the back of the mounting board at the L1 body level, fed some wire through around the L1 body and out the back, and twisted them together to hold it in place which worked quite well.
Spine – tick
Skin/soft tissue – tick
Mount – tick
Now all we need is a spinal column full of CSF. Easy, right?
Stand up, stretch, go and get a another cup of tea and another biscuit…
There’s still a while to go in this saga…
STAGE 4 – THE SPINAL CANAL/FAUX CSF CONTAINER
I spent hours fooling around with different types of rubber/plastic tubing, straws and other useless ways to get a sealable tube filled with water, free from air/bubbles, that would also push CSF out of the needle hub when it was punctured. I just couldn’t figure it out.
I then spoke to the amazing Taryn Gollop from the BUCERC sim centre, and she suggested this stuff called “heat shrink” tubing, available at Bunnings.
So I went to Bunnings and found this:
I was about to pay $28 for a pack of short pieces of heat shrink, of which only about 4 looked the correct diameter, and the rest would go in the bin, when a nice old Bunnings bloke (we’ll call him “O.B.B.” – Old Bunnings Bloke) comes up and asks if I need some help.
Conversation as follows:
OBB: Hi there, can I help you?
Me: Yeah, I need some heat shrink
OBB: Well we have that packet you’re looking at, and around the corner here there’s another packet with smaller bits in it which is quite good for smaller jobs.
Me: Listen, I’ll come clean, I’m not using it for wrapping electrical cables…
OBB: Oh, really? What are you using it for?
Me: Ok, see the thing is, I’m a doctor…
Me: And I run medical education courses, and we make trainers that mimc human body parts.
Me: And I’m looking for some thin-walled of tubing that I can use to mimc the spinal canal, so we can fill it with water and stick needles in it to replicated a lumbar puncture…
OBB: (Unfazed, stroking chin), OK, so you’ll need something a bit longer then…?
OBB: (Still unfazed, walks around corner, motions me to follow…): You’ll need this stuff then!
Points to large selection of individual 1 metre pieces of heat shrink, in various diameters, that are only a few dollars each.
OBB then proceeds to grill me about diameter of the spinal canal, and spends next 5 minutes with a tape measure, checking the exact diameter of each piece, ensuring that once filled with “CSF” it’ll confirm to the correct shape and giving me tips on how to get it to seal/shrink.
Thank you OBB!!
I walk out with a few bits of different diameter. One says “12/6″but measures 20mm in diameter (yellow/green) the other says “10/5″ and measures 17mm in diameter.
STAGE 4 – CONTINUED:
So this is the easy bit right?
Fill heat shrink with water, seal both ends, insert into canal, and hey presto?
1st: You need a tool that will apply heat to heat shrink but not burn it…
I tried the edge of my soldering iron, which did work, but took ages, and gave off some strong fumes.
And it was going to be of NO use once it was filled with water – too messy/fidgety.
I also thought about the heat gun I had (like an industrial hair dryer used for paint stripping), but there’s no way you can focus the heat to the small area required.
After a few failed experiments, I was about to give up, then remembered a few years ago I gave my wife a pair of GHD Ceramic Hair Straighteners for Christmas.
Thankfully she agreed to let me use them if I put some wax paper between the straightener and the heat shrink (in case it melted), and Bingo! It worked.
The green/yellow is just crimped/heated/sealed, the white is sealed, folded over once, and heat sealed again. Both provided a watertight seal.
So I then made a few water-filled segments, sealed both ends, and tried to LP them. Whilst you got an initial flow of CSF, it stopped quite quickly as you couldn’t seal it with much pressure in it.
I then tried sealing it full of water and then folding the ends over a few times to maximise the pressure and re-applying the hair straighteners to the folded over ends, with mixed results. In general it wouldn’t stick/stay folded over with more than 1 extra fold.
Also this didn’t really work in the spinal canal as the folded up end made it hard to slide it in the canal, and the CSF flow still didn’t really last long enough.
So I decided I wanted a CSF container connected to a giving set to provide a continuous flow of CSF.
But how the heck do you connect a luer lock on a giving set to heat shrink tubing with a rapidly interchangeable connection?
This is how:
I initially tried an IV bung, which kind of worked, but I only had 2, and needed at least 8 or so for the course (which was in < 24 hours) and had no access to more bungs! Scrapped that idea.
I also had various bits of rubber tubing laying around (from trying to make vein/artery models previously), and found that the RED exercise tubing from Clark Rubber fits snugly onto the distal tip of an IV giving set.
Cut heat shrink into strips that are a few cm longer than the length of canal you want it to fill (i.e. it will need to go from around L5, out the top of the canal 2-3cm beyond L1. About 18cm or thereabouts.
Apply hair-straighteners to distal 1cm of one end and shrink/seal it firmly shut (you can use wax paper over it in case it melts/sticks to hair straighteners, but I eventually ditched the wax paper, and had no sticking to the ceramic surface).
At the other (non-sealed) end: insert 4-5cm length of red tubing 1-2cm into heat shrink, (or IV bung), and gradually work the hair straighteners around it, (ensuring not to burn your fingers).
The heat shrink will eventually circumferentially shrink snugly down around the tubing.
Get your hot glue gun, and run a generous rim of hot glue around where the red tubing/IV bung exits the heat shrink to make it a watertight seal.
You are now ready to do an LP!
STAGE 5: THE LP
Take your faux CSF container and submerge it in water (e.g. in the sink), and let it fill, pushing on it to get most of the air out.
NB: It doesn’t need to be completely free of air. just mostly full of water.
Hold it vertically to avoid spillage and attach a primed giving set to the red tubing. Then slide it into the spinal canal, with the tubing protruding from L1. Then, open the flow regulator on the giving set and pump a small amount of extra fluid into the CSF container – you’ll see the heat shrink expand a bit and fill the canal.
Pass LP needle through silicone “skin”/soft tissue.
You might feel a slight loss of resistance as you enter the small gap between the silicone and the CSF container, but when you pierce the wall of the heat-shrink CSF container, there is a definite palpable “pop”.
Remove the stylet and you’ll have a continuos flow of CSF.
When finished, simply remove the LP needle, remove the CSF container, disconnect it from the giving set, and attach the next, almost-fully-filled CSF container, slide it into the canal, and open the flow regulator.
Total changeover time between participants takes about a minute.
(I pre-filled all of the CSF containers we were going to use with water and just stood them upright in a glass!)
You can also repair the small needle hole in the heat shrink tubing with super glue and re-use them!
So there you go, that’s the saga of the home-made LP trainer.
Here’s the original photo that sparked all the interest.
Thanks for all the great tweets, re-tweets and requests for instructions, I hope you’re inspired to make some task trainers of your own now!
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