Question:
Mouth-to-mouth respiration provides what percentage of oxygen to the recipient?
Mouth-to-mouth respiration provides what percentage of oxygen to the recipient?
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The rescuer's lungs have already taken some oxygen out of the 21% room air before it is blown in.
Updated On: Jun 23, 2026
- 10%
- 16%
- 21%
- 100%
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The Correct Option is B
Solution and Explanation
Step 1: Room air contains about 21% oxygen. When a rescuer inhales it, the lungs extract a portion, so the air the rescuer exhales is oxygen-depleted.
Step 2: Exhaled (expired) air delivered during mouth-to-mouth ventilation carries roughly 16% oxygen, along with about 4% carbon dioxide. Each breath gives about 0.8 to 1.2 liters of this exhaled air, which is enough to sustain life during resuscitation.
Why not the others: 21% is the oxygen of fresh room air, as delivered by an Ambu bag using room air, not by a rescuer's breath. 100% is supplemental oxygen from a cylinder. 10% is too low to support oxygenation.
Ref: Standard resuscitation physiology; AHA CPR guidance.
Step 2: Exhaled (expired) air delivered during mouth-to-mouth ventilation carries roughly 16% oxygen, along with about 4% carbon dioxide. Each breath gives about 0.8 to 1.2 liters of this exhaled air, which is enough to sustain life during resuscitation.
Why not the others: 21% is the oxygen of fresh room air, as delivered by an Ambu bag using room air, not by a rescuer's breath. 100% is supplemental oxygen from a cylinder. 10% is too low to support oxygenation.
Ref: Standard resuscitation physiology; AHA CPR guidance.
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