The Bag-Valve-Mask (BVM) device, often called an Ambu bag, is a self-inflating manual resuscitator used to provide artificial ventilation in emergency situations. This handheld apparatus delivers positive pressure ventilation to a patient who is not breathing or whose breathing is inadequate. The BVM is standard equipment in both pre-hospital and in-hospital settings, such as ambulances and crash carts. Its primary function is to support oxygenation and ventilation until a more advanced airway can be secured or until the patient recovers spontaneous breathing.
Components and Pre-Use Assembly
The BVM system consists of three main parts: the self-inflating bag, the non-rebreathing patient valve, and the face mask. The bag is compressed by the rescuer to deliver the breath and automatically reinflates, drawing in ambient air or supplemental oxygen. A one-way valve ensures that the delivered air goes to the patient and that the patient’s exhaled air is vented away, preventing rebreathing of carbon dioxide.
The opposite end of the bag contains an oxygen inlet port to which an oxygen source and a reservoir bag should be attached before use. Attaching a reservoir bag and flowing oxygen at a high rate, typically 10 to 15 liters per minute, allows the device to deliver an oxygen concentration close to 100%. Proper pre-use assembly requires confirming that all connections are secure and that the mask size is appropriate, covering the patient’s nose and mouth without extending over the chin or eyes. It is also important to test the device by briefly squeezing the bag to ensure it inflates, deflates, and that the patient valve is functioning without leaks.
Proper Single-Rescuer Ventilation Technique
Effective ventilation begins with positioning the patient’s head to open the airway. For patients without suspected neck or spinal injury, the head-tilt/chin-lift maneuver is performed to move the tongue away from the back of the throat. If a spinal injury is possible, a jaw-thrust maneuver should be used instead, gently lifting the angles of the lower jaw forward without extending the neck.
The most difficult step for a single rescuer is achieving and maintaining a tight seal between the mask and the patient’s face. The one-handed technique requires the rescuer to use their non-dominant hand to form a “C-E” grip. The thumb and index finger form the “C” shape over the mask dome to press it onto the face, while the remaining three fingers form an “E” shape under the bony part of the jaw.
This “E” portion lifts the jaw upward into the mask, simultaneously helping to maintain the open airway and securing the seal. The rescuer then uses their dominant hand to compress the bag. The squeeze should be delivered slowly and steadily over approximately one second, providing just enough volume to cause a visible rise of the chest.
For an adult patient who is not breathing but has a pulse, ventilations should be delivered at a rate of one breath every five to six seconds (10 to 12 breaths per minute). This controlled rate and volume help avoid complications associated with hyperventilation. Allowing the chest to fall completely and the bag to fully re-inflate between breaths prevents air trapping and elevated pressure within the chest cavity.
Troubleshooting and Advanced Considerations
If the chest does not rise with the initial breath delivery, the first steps involve reassessing and repositioning the patient’s airway and adjusting the mask seal. Ineffective ventilation is commonly caused by a poor seal or an obstructed airway, which may require more aggressive head repositioning or the insertion of an airway adjunct (oropharyngeal or nasopharyngeal). If the airway remains obstructed, the rescuer should check for foreign material and ensure the mask is not pressing down on the soft tissue under the chin, which can block the airway.
A significant risk of BVM ventilation is gastric inflation, where air is forced into the stomach instead of the lungs. This complication is usually caused by delivering breaths too forcefully, too quickly, or with excessive volume. To prevent this, the rescuer must limit the bag squeeze to the minimal volume necessary to produce a visible chest rise, avoiding rapid or vigorous compression.
In situations where the single-rescuer technique proves ineffective or during prolonged resuscitation, a two-person BVM technique is preferred. This approach allows one rescuer to focus entirely on maintaining a two-handed mask seal and airway position. The second rescuer is dedicated solely to squeezing the bag and monitoring the patient’s response. The two-person technique, sometimes using a “thenar eminence” or “two thumbs down” grip, significantly improves the quality of the mask seal and reduces air leaks.