Mouth-to-mask ventilation without supplemental oxygen delivers approximately what percent FiO2?

• A. 16%
• B. 21%
• C. 28%
• D. 40%

Answer: (A)

The amount of oxygen you deliver with mouth-to-mask ventilation without giving any extra oxygen is limited by mixing with surrounding air and the patient’s exhaled breath. Because you’re not creating a tight seal or supplying oxygen, the inspired gas is largely room air plus dilution from exhaled air, resulting in an FiO2 around 16%.

If you want a higher FiO2, you’d need to attach supplemental oxygen with a device like a bag-valve mask or a pocket mask that has an oxygen source or reservoir. The other numbers aren’t reached without that oxygen supply: 21% is room air and would require minimal dilution, while 28% or 40% would require delivering oxygen-enriched gas with a proper oxygen source.