Which oxygen delivery method is typically used for severe hypoxemia or when a high FiO2 is required?

• A. Nasal cannula
• B. Nonrebreather mask
• C. Bag-valve-mask
• D. Simple face mask

Answer: (B)

When someone is severely hypoxemic, delivering a high and reliable amount of oxygen is essential. The nonrebreather mask uses a reservoir bag and two one-way valves that minimize dilution with exhaled air and room air, so the patient inhales a much higher fraction of oxygen with each breath. With proper fit and flow, it commonly achieves a high FiO2—much greater than a nasal cannula or a simple face mask—while the patient breathes spontaneously. That makes it the go-to choice for urgent, high-oxygen needs.

A nasal cannula provides only modest increases in oxygen concentration, typically up to about 40% with high flow. A simple face mask offers more than a nasal cannula but still less than a nonrebreather, often around 40–60% FiO2 and subject to dilution. A bag-valve-mask can deliver very high FiO2, even near 100%, but it is used for manual ventilation and requires more training and effort; it’s chosen when there’s a need to actively assist ventilation rather than simply supply oxygen.