Quote from SRNAbasketcase
I have a couple of questions about gas flow rates:
1. What are the typical flow rates for oxygen, nitrous and air in the anesthesia machine?
2. When and why would you use air instead of oxygen?
3. How much oxygen do you need to run with nitrous?
Thank you very much,
1. Depends on what you are trying to do. If you are trying to get some agent on quickly or get it down quickly, high flow rates will help you do that. Low flow rates will help you preserve existing gas that's in, or slowly bring on new agent. Lower rates will also cause you to use less agent (for example, 6% Des when you are running flow rates of 10L will use up a lot more des than if you are running it with flow rates of 2L). This translates into less cost for the department and for the patient. I usually run my flows at 1L of air and 0.7L of O2, or 1L N2O and 0.7L O2, unless its sevo. Running low flow will also keep the patient warm.
2. In most cases, I would not use air instead of oxygen. I use air a lot of times instead of nitrous. I can think of only once that I ran someone on air and nothing else - it was a radical retro prostatectomy, with periaortic lymph node dissections in a patient with a history of testicular cancer. The patient had been on bleomycin, and bleo can cause pulmonary fibrosis if you expose lungs to high FI02. That case I ran on 2L of air the whole time, no problems. You can also run your patient on air if you lose wall pressure - of course, switch to your O2 tank first, but when that runs out, bag 'em on room air.
I guess you would want to also use low FI02s with laser procedures to prevent airway fire (in ENT). I haven't done my ENT rotation yet, so maybe someone who has more experience with laser tumor destructions in the airway can shed some light.
3. When you run oxygen with nitrious, the bare minimum you need to give is the same as atmospheric air: 21%. Anything less will give you a hypoxic mixture. All machines made now have built in safety mechanisms to prevent the anesthetist from delivering a hypoxic mixture, but you still need to know how to calculate the FI02 in case those safety devices fail.