A pocket mask, sometimes called a pocket face mask or CPR mask, is a device used to safely deliver rescue breaths during a cardiac arrest or respiratory arrest.
The pocket mask is a small device that can be carried by a rescuer. Air is administered to the patient when the rescuer exhales through a one-way filter valve which is designed to protect a rescuer from a casualty’s potentially infectious bodily substances, such as vomit or even blood if the casualty has suffered facial injuries.
Most masks also have a built-in oxygen intake tube, allowing for administration of oxygen. Without being hooked up to an external oxygen line, exhaled air from the provider can still provide sufficient oxygen to live. Inhaled air contains about 21% oxygen and exhaled air contains about 16%. So there is ample oxygen in a rescuers exhaled breath to keep the casualty supplied with oxygen.