Venturi face masks

High-flow Venturi oxygen masks yield a precise fraction of inspired oxygen by use of a Venturi valve. The size of the valve aperture ensures that specific proportions of oxygen and entrained air are mixed to obtain a fixed oxygen concentration in quantities that exceed the full ventilatory requirement. By contrast, low-flow oxygen masks do not provide the entire ventilatory requirement because air is drawn in through the loosely fitting mask in an uncontrolled fashion to supplement the oxygen flow rate. The fraction of oxygen can, therefore, be more accurately titrated using a Venturi system (eg, 24%, 28%, 35%) than with altered flow when using low-flow simple masks (eg, 2 L, 3 L, 4 L).