Greetings from Honduras, where I am serving as anesthesiologist for a Volunteer Head and Neck Surgical Team. We are at a small 26 bed charity hospital in the small town of Sula doing many different cases such as tonsillectomies and septoplasties for severe obstruction, and tympanoplasties for chronic ear perforations, among other cases.
Doing anesthesia in the developing world is always challenging, as you don´t have all of the equipment, supplies or even medications that you would normally use. Yesterday was a case in point. My anesthesia machine in Honduras gets it´s oxygen from an H cylinder. So in addition to watching all of the other monitors and dials we normally watch, you have to keep one eye on the manometer to make sure you´re is not going to run out of oxygen in the middle of the case.
All oxygen tanks contain liquid oxygen. As long as there is any liquid in the tank, the manometer will read full. Once the last drop of liquid has vaporized, and the oxygen gas in the tank starts to be used up, then the manometer reading will start to drop. And sure enough, when the tympanoplasty we were doing took longer because it turned out to be more difficult than expected, my manometer began to plummet, even though I was running low flows. Fortunately I was prepared.
Preparation Before Starting the Case
When running on an oxygen tank you always have to prepare for the possibility of running low on oxygen, so before I began the case I made sure I was ready.
- Have an extra, full oxygen tank immediately available
- Have a self-filling ambu bag
- Make sure you have the tank wrench for switching the manometer to the full tank
- Know how to switch the manometer safely
Tank Wrench needed to change the manometer on an H cylinder. The manometer in the back attaches to the screw fitting on the head of the tank, as seen on the front tank.
What To Do When Running On Empty
Before the tank runs dry:
- Tell your surgeon what is going on
- Make sure your patient is deeply anesthetized
- Have an IV agent such as propofol available in case changing the tank takes longer than expected
- Go to 100% oxygen
- Allow the ventilation bag to fill with anesthetic/oxygen mixture (don´t use the flush as this will fill the bag with oxygen alone)
- Decrease flows to around 300 ml/min and close the pop-off to maintain it as full as possible without over pressurizing
- Turn off your oxygen tank. NEVER attempt to loosen the manometer with the tank on because you will get an explosive release of pressure and risk injury from the flying manometer
- Use the pipe wrench to loosen and remove the manometer
- Attach the manometer to the new tank quickly, tighten with the wrench securely but don´t overtighten. Someday someone is going to have to take it off change it again
- Turn on the new tank
- Immediately check you patient´s breathing circuit to make sure you now have oxygen
- Check the pop-off before you increase flows to make sure that you are not going to over pressurize the circuit
If your tank were to run dry during this procedure, you would of course use the ambu bag ventilate until oxygen flow is re-established. Work with your surgeon to do this safely without putting the surgery at risk.
Avoiding the Need To Change A Tank In the Middle
When running on tanks it´s helpful to run low flows whenever possible. Once induction is complete, closing the circuit and running 500 ml flows is usually possible. And inducing and waking with 2-3 liter flows is also possible, despite the practice in the US of using ten liter flows. It may take a little longer, but ten liter flows empty your tank pretty quickly.
Also, many machines continue to run 200 ml through the circuit even when the dials are turned off. This is a safety precaution. Older machines may have leaky “plumbing”. Often it´s best to turn off the tank between cases if there will be a prolonged break.
The need to change a tank in the middle of the case can happen anywhere to anyone. But if you´re prepared, it will go smoothly and your patient will remain safe.
May The Force Be With You
