How To Use Nitrous Oxide
With both types of apparatus, the gas mixture is only delivered when the machine detects that someone is attempting to take a breath in. (It does this by opening a valve when a negative pressure is applied to the breathing tube.) For this to occur, an airtight seal must exist and so the mask (or mouthpiece) must be applied firmly to the face (Figure 6.4), otherwise the machine switches off automatically. This not only reduces wastage and pollution but prevents everyone else in the room from becoming 'under the influence' as well! When the machine is being used properly, you will hear the valve clicking on and off with each breath. It is not necessary to take the mask or mouthpiece away from your face every time you breathe out because another valve, situated close to the mask, allows the expired breath to pass easily into the atmosphere. This valve makes a quiet hissing sound and confirms that you are using the machine properly.
The speed of entry into the lungs and bloodstream depends on how deeply you breathe: slow deep breaths are better than rapid shallow ones. Remember that there is some time lag before the concentration starts to build up sufficiently in the brain to have an effect . So it is important to start breathing from the machine as soon as you feel the contraction coming on. Don't wait until it hurts, or the gas will not have time to help you at all. Once the contraction starts to feel easier again, then you can take the mask away from your face until you begin to feel the next one coming on.
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