The fraction of O2 in inspired air in mouth-to-mouth respiration is
**Core Concept**
Mouth-to-mouth respiration, also known as rescue breathing, is a technique used to provide oxygen to a person who is not breathing or is breathing inadequately. The fraction of oxygen in inspired air is critical in determining the effectiveness of this technique.
**Why the Correct Answer is Right**
In mouth-to-mouth respiration, the rescuer blows air into the victim's mouth, and the air is then inhaled by the victim. The fraction of oxygen in the air is approximately 21%, which is the same as the fraction of oxygen in room air. The primary goal of mouth-to-mouth respiration is to provide a higher concentration of oxygen to the victim, which is achieved by increasing the tidal volume and respiratory rate of the rescuer. This technique is often used in conjunction with chest compressions to provide cardiopulmonary resuscitation (CPR).
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because mouth-to-mouth respiration does not involve the use of a mask or a bag-valve-mask (BVM) device, which can deliver a higher fraction of oxygen.
**Option B:** This option is incorrect because the fraction of oxygen in inspired air in mouth-to-mouth respiration is not significantly different from room air.
**Option C:** This option is incorrect because the fraction of oxygen in inspired air in mouth-to-mouth respiration is not typically increased by using a specialized mask or device.
**Option D:** This option is incorrect because mouth-to-mouth respiration does not involve the use of a nasal cannula or other oxygen delivery devices that can provide a higher fraction of oxygen.
**Clinical Pearl / High-Yield Fact**
It is essential to remember that mouth-to-mouth respiration should only be performed by trained individuals, and the American Heart Association recommends using a bag-valve-mask (BVM) device to provide rescue breathing in most situations.
**Correct Answer: C. 21%**