A bag valve mask (also known as a BVM or Ambu bag, which is a brand name) is a hand-held device used to provide ventilation to a victim who is not breathing. The device is self fills with air, although it may be connected to an oxygen system.
Use of the BVM to ventilate a victim is frequently called “bagging.” Bagging is regularly necessary when the victim’s breathing is insufficient or has ceased completely. The BVM is used in order to manually provide mechanical ventilation in preference to mouth-to-mouth resuscitation (either direct or through an adjunct such as a pocket mask).
The BVM consists of a flexible air chamber, about the size of an American football, attached to a face mask via a shutter valve. When the air chamber or “bag” is squeezed, the device forces air into the victim’s lungs; when the bag is released, it self-inflates, drawing in ambient air or oxygen supplied from a tank. A bag valve mask can be used without being attached to an oxygen tank to provide air to the victim, but supplemental oxygen is recommended since it increases the amount of oxygen reaching the victim. Some devices also have a reservoir which can fill with oxygen while the patient is exhaling (a process which happens passively), in order to increase the amount of oxygen that can be delivered to the victim by about twofold. A BVM should have a valve which prevents the victim from rebreathing exhaled air and which can connect to tubing to allow oxygen to be provided through the mask.
Bag valve masks come in different sizes to fit infants, children, and adults. Some types of the device are disposable, while others are designed to be cleaned, disinfected, and reused.
The BVM directs the gas inside it via a one-way valve when compressed by a rescuer; the gas is then delivered through a mask and into the victim’s airway and into the lungs. In order to be effective, a BVM must deliver between 700 and 1000 milliliters of air to the victim’s lungs, but if oxygen is provided through the tubing and if the victim’s chest rises with each inhalation (indicating that adequate amounts of air are reaching the lungs), 400 to 600 ml may still be adequate. Squeezing the bag once every 5 seconds for an adult or once every 3 seconds for an infant or child provides an adequate respiratory rate (12 respirations per minute in an adult and 20 per minute in a child or infant).
Professional rescuers are taught to ensure that the mask portion of the BVM is properly sealed around the patient’s face (that is, to ensure proper “mask seal”); otherwise, air escapes from the mask and is not pushed into the lungs. In order to maintain this seal, some protocols use a method of ventilation involving two rescuers: one rescuer to hold the mask to the patient’s face with both hands and ensure a mask seal, while the other squeezes the bag. However, to make better use of available rescuers, the BVM can be operated by a single rescuer who holds the mask to the victim’s face with one hand (using a C-grip), and squeezes the bag with the other.
When using a BVM, as with other methods of ventilation, there is a risk of overinflating the lungs. This can lead to pressure damage to the lungs themselves, and can also cause air to enter the stomach, causing gastric distention which can make it more difficult to inflate the lungs and which can cause the victim to vomit. This can be avoided by care on behalf of the rescuer. Alternatively, some models of BVM are fitted with a valve which prevents overinflation, by blocking the outlet pipe when a certain pressure is reached, though they should all be able to be bypassed in a situation where more pressure is needed, such as in anaphylaxis.
In the case of a victim who vomits or has other secretions in the airway, these techniques will not be enough. Suitably trained first aiders may use suction to clean out the airway, although this may not always be possible. A unconscious victim who is vomiting or has copious secretions in the mouth should be turned into the semi-prone position when there is no suction equipment available, as this allows (to a certain extent) the drainage of fluids out of the mouth instead of down the trachea.