A bag valve mask, often referred to by the most common brand of the device, Ambu Bag(TM) is a breathing assistance device used in emergency situations, often where a respirator is not available. They are standard equipment in ambulances and crash carts. It takes the place of mouth-to-mouth resuscitation which poses a risk to both the patient and medical personnel of cross-infection. They first came into common use in 1956. They come in a number of different sizes from infant to adult. They can either be disposable or reusable.
The "mask" is often interchangeable for use on the mouth, on a tracheal tube, or even on an intubation tube. The bag is roughly the size and shape of an American football. When squeezed, air flows only through a valve leading to the mask, providing positive pressure to the lungs. When released, the valve to the mask closes, and another opens allowing air to flow into the bag to reinflate it as the bag regains its shape. The fill valve usually opens to the air, but an oxygen tube can also be attached to increase the partial pressure of oxygen.