Ambu bag: A bag used to give rescue breaths for victims of cardiac arrest, used along with a face mask (bag and mask ventilation). It is an integral part of any emergency kit.
“Ambu” stands for Artificial Manual Breathing Unit. Holger Hesse and Henning Ruben introduced the concept of bag-valve-mask (BVM) 1953. There is a unidirectional valve at the patient end of the BVM. When the rescuer initially attaches the bag with the mask over the face and nostril of the victim who has stopped breathing. The rescuer then squeezes the bag and air enters the lungs of the victim. The self inflating bag fills up on releasing the squeezing effort. The unidirectional valve prevents sucking in of expired air when the bag inflates.
Maximum lung airway pressure of 70 cm of water is possible on squeezing the bag forcefully. Injury to the lungs by the use of excessive pressure can be prevented by having a safety valve mechanism which opens when the pressure goes above 40 cm. This mechanism is useful in case of small infants. The valve mechanism can also be manually overridden in case of dire need to give higher pressures in some cases.
Both disposable (single use) and reusable types of Ambu bags are available in market. Disposable ones do away with the potential risk of transmission of infection from patient to patient, of course, with an increase in the average cost.