Venturi masks

Venturi systems: The masks operate on the principle of a small restricted entry point where oxygen flows at a high rate. Air is drawn in (entrained) by shear forces around the jet. These systems typically provide an oxygen concentration of 60% or less.

High-flow nasal cannulas have largely replaced Venturi masks, so they are not commonly seen now. A Venturi mask consists of a plastic mask connected to a jet nozzle.

For patients with COPD, a Venturi mask is often chosen because it delivers a precise and consistent FiO2 (fraction of inspired oxygen). Example: FiO2 of $0.24$ is achieved with an air-to-oxygen ratio of $25:1$.

Higher Flow Oxygen Delivery Systems

• These devices provide a prescribed gas mixture (blended oxygen and air) at a flow rate that exceeds the patient's inspiratory flow demand.

• To qualify as a high-flow device (according to Egan's, page $917$):

  • The system should provide a total flow that meets or exceeds the patient's peak inspiratory flow. The average adult peak inspiratory flow is approximately $3$ times their minute volume.

  • All high-flow systems mix air and oxygen to provide a specific, stable FiO2.

• Can deliver high FiO2 up to $90\%$.

• Can provide flow rates up to $40$ L/min.

• Provides humidity.

• Generates positive end-expiratory pressure (PEEP).

• Provides carbon dioxide washout from anatomic dead space.

• Can be used with all patient populations.

• Examples of devices from different vendors include Optiflow, Vapotherm, and Aerogen.

Blenders

• Blenders combine air and oxygen from $50$ psi wall outlets (sources).

• Blending systems are used when a precise air-oxygen mixture is required, especially when air entrainment methods are insufficient.