Flow Problems
Air entrainment masks, although considered high flow systems, are not always able to guarantee the total flow with oxygen percentages above 35% in patients with high inspiratory flow demands. The problem with air entrainment systems is that as the FiO2 is increased, the air to oxygen ratio decreases. For example, for 30% the ratio is 7 parts air to 1 part oxygen. For 40% the ratio decreases to 3 to 1. Since the jets in venturi masks generally limit oxygen flow at 12 to 15 liters per minute the total flow decreases as the ratio decreases. At an oxygen flow rate of 12 liters per minute and a 30% FiO2 setting, the total flow would be 108 L/min. At a 40% FiO2 setting, the total flow would decrease to 48 L/min. As a rule of thumb, 60 L/min is considered the minimum flow rate to qualify as a high flow device.
Read more about this topic: Venturi Mask
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