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. 1998 Sep 19;317(7161):798–801. doi: 10.1136/bmj.317.7161.798

Figure.

Figure

High flow oxygen masks provide the entire ventilatory requirement using a venturi valve. The port size of the valve ensures the correct proportions of oxygen and entrained air are mixed to obtain a fixed oxygen concentration. Low flow oxygen masks do not provide the entire ventilatory requirement. Air is drawn in through the loose fitting mask to supplement the oxygen flow rate