Tech note #003

On my third Friday session working at Mt. Meru I completed work on repairing the raise/lower mechanism on an operating table, working with another EWH-SI student, David.

David and I demonstrating the repaired operating bed
David and I demonstrating the repaired operating bed

Recap: When I began a faulty hydraulic jack meant the bed could not be adjusted up and down. Previously we had removed the jack and sourced new hydraulic fluid to replace the congealed old stuff clogging up the works. Previous post here. My partner on the project, David, has also written about it here.

The reservoir of fluid on the operating bed is not sealed and spills when no upright, which made it difficult to test the jack before refitting it. The new fluid was not as viscous as what we took out, so we were concerned it might leak around the piston seals, causing the bed to slowly descend rather than hold its position. We reasoned if the seals could hold air, they could hold the fluid, so we jury-rigged an apparatus to test for air leaks.

After a deep clean, we pumped air into the large cylinder and applied a load on the piston, simulating the weight of the bed. We used a water fire extinguisher as it was the densest thing we could find.

The rig for leak testing of the hydraulic jack
The rig for leak testing of the hydraulic jack

With the load applied, we were then able to estimate the leak rate of air around the seals from how much the piston lowered in a given time.

The jack slowly descending during the leak test
The jack slowly descending during the leak test

We lost about 10mm of height over half an hour, which we reasoned was acceptable, since the fluid leak rate would be orders of magnitude smaller than this.We refitted the jack, which was a job in itself, and refilled the fluid reservoir. It worked, though initially only sort of.

David and I after reinstalling the jack into the operating bed
David and I after reinstalling the jack into the operating bed

We found there was a sweet spot the foot lever had to be within for the bed to descend smoothly. There was an adjustment bolt for this, and we fiddled with it until the mechanism was in the sweet spot when the foot lever was on the ground. We fitted some washers to ensure the bolt stayed put.

The adjustment bolt, used to ensure the sweet spot is level with the ground
The adjustment bolt, used to ensure the sweet spot is level with the ground

This might seem like a minor fix, but this operating bed is the crown jewel of the surgery department. It’s in use almost every day, and the broken mechanism was having a big impact on the standard of care. The surgeons were having to either operate up around their chests or hunched over. A four hour operation in those conditions is a real strain: the doctors were very happy to have it working again, and I even got my first sterile high five.

Elbow bump [reconstruction]
Elbow bump [reconstruction]

3 comments

  1. Love the idea that the bed might slowly, slowly descend during an operation…very Roald Dahl. Well done you guys! Elbow bump is the new high five!

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