HFNC physiologic effect includes flushing of anatomic deadspace. Which option describes this mechanism?

HFNC physiologic effect includes flushing of anatomic deadspace. Which option describes this mechanism?

• A. Reduces airway edema
• B. Flushing of anatomic deadspace
• C. Increases mucous production
• D. Decreases airway temperature

Answer: (B)

High-flow nasal cannula works by delivering a large amount of heated, humidified gas at high flow, which continuously washes out the air in the upper airway. This excess flow clears the anatomic dead space, so the next breath brings in fresh gas instead of gas that carries CO2 from the previous breath. By reducing rebreathing of CO2, the work of breathing is decreased and ventilation becomes more efficient. In addition, the warmed, humidified gas helps mucociliary function and can provide some mild positive airway pressure, but the mechanism described here specifically refers to flushing the dead space. The other options don’t describe this effect—they relate to edema, mucus production, or a decrease in temperature, which isn’t how HFNC operates (the gas is warmed, not cooled).

High-flow nasal cannula works by delivering a large amount of heated, humidified gas at high flow, which continuously washes out the air in the upper airway. This excess flow clears the anatomic dead space, so the next breath brings in fresh gas instead of gas that carries CO2 from the previous breath. By reducing rebreathing of CO2, the work of breathing is decreased and ventilation becomes more efficient. In addition, the warmed, humidified gas helps mucociliary function and can provide some mild positive airway pressure, but the mechanism described here specifically refers to flushing the dead space. The other options don’t describe this effect—they relate to edema, mucus production, or a decrease in temperature, which isn’t how HFNC operates (the gas is warmed, not cooled).