Which device is most appropriate for delivering high concentrations of oxygen to a spontaneously breathing patient who is conscious and not in need of assisted ventilation?

• A. Bag-mask device
• B. Nasal cannula
• C. Mouth-to-mouth
• D. Nonrebreathing mask

Answer: (D)

Delivering a very high inspired oxygen concentration to a conscious, spontaneously breathing patient is best achieved with a nonrebreathing mask. Its design includes a reservoir bag and one-way valves that prevent exhaled air from entering the bag, so during each inhale the patient draws nearly pure oxygen from the reservoir. When you provide a high flow (roughly 10–15 L/min) and achieve a good seal, FiO2 can reach about 90% or more, which is why this device is preferred in situations needing high oxygen delivery without assisting ventilation.

Nasal cannulas deliver oxygen comfortably but only up to about 44% FiO2 at typical flow rates, which is insufficient when a high concentration is required. A bag-mask device is used for patients who need assisted ventilation, not someone who is breathing adequately on their own. Mouth-to-mouth is unreliable for delivering high and consistent oxygen concentrations and carries hygiene concerns.