An inexpensive venepuncture arm simulator
I coordinate the acute block for second year medical students at Flinders University. One of the sessions is venepuncture. In previous years, this session was conducted by an external provider who brought all materials including plastic ‘arms’ for practice learning the procedure before taking blood from their peers.
At very late notice in 2011, (Wed before the planned session on the following Mon) this external provider informed me that they would not be able to do this training. We were faced with the prospect of either cancelling this important session or finding an alternate.
Thus out of necessity was born this invention – an inexpensive, easily constructed venepuncture arm that can accommodate numerous punctures.
All artificial arms used for venous access leak. Some more than others. Reasonably thick walled latex tubing seals best. but is difficult to find. Silicone tubing has largely replaced latex. Due to the very tight timeframe for initial construction of these arms, locally available materials were chosen.
There are basically three parts to these arms, a core, the vessels and the skin.
The core is made from pool noodles. These are readily available, inexpensive and waterproof. I used solid core material 67mm dia and approx 1460mm in length $4.95 ea. This was divided into four lengths of approx 365mm each.
Several materials were evaluated for veins. Some very nice silicone tubing was sourced from FMC anaesthetics, but only small quantities were available at short notice. Clarke Rubber had ‘windshield washer’ tubing made out of some sort of rubber at $3.95 per meter and exercise tubing which was very similar to the nice silicone tubing but cost $7.50 per meter. The harder pvc tubing and oxygen tubing were trialed but rejected as unsuitable. Aquarium airline is available in silicone of an appropriate diameter. The bonus of this tubing is that it is readily available in large quantities and is $1.50 per meter.
Several materials were also evaluated for use as skins. Elastic exercise band (0.4mm thick) is very stretchy but is also very expensive at $11.76 per meter and only comes in 148 mm widths. A beige colored vinyl was trialed. It comes in 1.37m widths at a cost of $25.96/meter. This was a leading contender but the fabric liner tended to wick the blood from the punctured veins resulting in a higher leak rate and saturated skin. While the colour, texture and stiffness of the vinyl was ideal, it was deemed unsuitable due to the liner and wicking of fluid. Two materials were used for the first construction run. Black pond liner and blue pool liner were both used successfully. The black ponder liner is 2m wide x 0.5mm thick and costs $22.96 per meter while the blue pool liner is slightly narrower at 1.3m x 0.5mm thick and costs $25 per meter. The pool liner has a textured surface on one side which is nice but tends to trap the blood coloring and leave stains.
All prices as of 1 Sept 2011
As previously stated, the core of the device is a section of pool noodle. 300mm length was considered adequate but the bulk material divided evenly into four lengths of 365mm or 5 lengths of 292mm. It was decided to use the longer lengths to allow placement of the tourniquet on the model. During the first session, students placed the tourniquet on their partner while practicing on the arm models. The shorter length could easily be used to save some material and fit slightly better on the blue waterproof sheets during use.
The noodles are grooved to hold the veins in place and at a more suitable height. Four vein grooves are marked and cut into the sides of the material. Equal spacing is achieved by marking a + on the end of the noodle and then drawing lines along the length aligned with the points of the +.
A sharp knife is used to cut shallow v-shaped grooves in the surface of the noodle. These grooves stop about 20mm from the end and are approx 5mm deep and 5mm wide. This was all done by eye and is not that critical. The cut material is removed by pinching the strip off at either end.
A 5mm diameter hole is drilled in the end of each groove at approx a 45 degree angle, exiting in the end of the noodle. This was most easily accomplished by hand using a running drill rather than placing the stationary drill in the groove.
The skin material was wrapped around the noodle with approx a 15mm overlap. There were actually two sizes of noodle purchased. A very small difference in diameter resulted in a significant change in circumference. The smaller noodle used a skin width of 230mm while the larger one used 240mm width.
3mm holes were punched approx 10mm from the edge of the skin material. These were laced together using 370mm long cable ties. The number and placement of these holes was again done by eye and is not critical.
The arm models are assembled in several steps.
First, 2x 1 meter lengths of tubing are cut for each model. These are threaded through the holes in the end of the core and along the grooves, crossing over at one end.
Next the skin is lubricated with a small squirt of soapy water and slid onto the core.
Finally, one end of one of the tubes is connected to a bag of artifical blood which is allowed to flow through the tubing to purge the air. The other end is folded over and held with a small binder clip. Both tubes could be used if desired. We chose to use one at a time and save the other for a future session.
Total cost is as follows:
- 1/4 pool noodle = $1.24
- 2m aquarium tubing = $3
- Cable tie = $0.14
- Skin = $2.87
- TOTAL = ~$7.25/arm + misc tools (knife, hole punch), blood, blood bags & Y connector
These arm models are designed to allow practice of the process of venepuncture, not necessarily the feel of sticking a needle into a vein.
These sessions are attended by approximately 24 students at a time so we constructed 12 arm models. These are connected in pairs to 6 bags of artificial blood. A blue waterproof sheet is placed under each arm model to catch the inevitable drips.
There were some leaks but not significantly more than commercial models.
After the session, the artifical blood was drained out of the tubes. Then the skin was removed and the core and inside of the skin rinsed with clean water