How does a nonrebreather mask prevent exhaled air from mixing with inhaled air?

A nonrebreather mask effectively prevents exhaled air from mixing with inhaled air primarily because of a specific valve mechanism. The valve closes during expiration, which creates a one-way system that allows only fresh oxygen to be inhaled while preventing stale air from being re-breathed. This design ensures that the patient receives a higher concentration of oxygen from the reservoir bag without contamination from their own exhaled carbon dioxide.

The ability to deliver high concentrations of oxygen makes nonrebreather masks suitable for patients requiring emergency treatment or those with severe respiratory distress. The integrity of the mask's design — particularly the proper functioning of the valves — is crucial to achieving its intended purpose in oxygen therapy.