PPRuNe Forums - View Single Post - BA Flight LHR - GLA Returned due to both pilots becoming lightheaded and dizzy
Old 9th Jan 2012, 11:43
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Bartlett1
 
Join Date: Aug 2008
Location: Birminham
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I'm a doctor (surgeon), not a pilot but a reasonably regular passenger. I agree with Skittles' post with regard to the description of the ambu-bag and why it would not be advisable to use it without training. However, I must take issue with the constant reference to rebreathe bags. In most cases, bags attached to masks have nothing to do with rebreathing. They are reservoir bags. When you take a breath in the peak flow rate is around 40-60 l/min, significantly higher than the maximum 15 l/min flow of oxygen supplied by most systems in hospital (not sure what's available on aircraft). Therefore air is entrained from the surroundings thus diluting the inhaled oxygen concentration. A mask without a reservoir bag will deliver a maximum of around 50% oxygen with a flow rate of 15 l/min. The purpose of the reservoir bag is to fill with oxygen in between breaths. During peak inspiration, oxygen will come straight from the supply as well as from the reservoir bag, increasing the inspired oxygen concentration to around 80% max. The only way to deliver 100% oxygen is with a closed anaesthetic circuit.
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