An Ambu bag is a handheld device used to manually push air into the lungs of someone who isn’t breathing adequately on their own. Officially called a bag-valve-mask (BVM), it’s one of the most fundamental pieces of emergency medical equipment, found in nearly every ambulance, hospital crash cart, and first-aid kit in clinical settings. The name “Ambu” comes from the original brand, but it’s become a generic term the same way “Band-Aid” refers to any adhesive bandage.
How It Works
The device has three core parts: a flexible self-inflating bag, a one-way valve, and a face mask. When a rescuer squeezes the bag, air is forced through the valve and into the patient’s airway via the mask, which fits over the nose and mouth. When the rescuer releases the bag, it re-expands on its own, drawing in fresh air for the next squeeze. The one-way valve prevents exhaled air from flowing back into the bag, so each breath delivers clean air.
This process is called positive pressure ventilation. Instead of the lungs pulling air in through normal breathing muscles, the Ambu bag pushes air in from the outside. It essentially does the work of breathing for someone whose body can’t do it.
Where the Name Comes From
In 1954, a shortage of oxygen deliveries to Danish hospitals prompted an engineer named Holger Hesse to invent the first self-inflating resuscitator. The name stood for “Air Mask Bag Unit.” After modifications, Hesse’s company, Testa Laboratory, began manufacturing the device in 1956 under the name “Ambu Bag.” The invention was a major step forward because earlier resuscitation bags needed an external gas source to inflate. The self-inflating design meant it could work anywhere, with or without a connected oxygen supply.
When It’s Used
An Ambu bag is used whenever someone needs help breathing but isn’t yet connected to a mechanical ventilator. The most common scenarios include cardiac arrest, respiratory failure, drug overdose causing breathing to stop, near-drowning, and severe allergic reactions that compromise the airway. Emergency responders also use it to deliver breaths during CPR between chest compressions.
It’s also a bridge device. In hospitals, medical teams often use an Ambu bag to ventilate a patient while preparing to insert a breathing tube or connect a ventilator. If a ventilator malfunctions or a patient needs to be transported between rooms, the Ambu bag provides immediate backup ventilation with no power source required.
Sizes for Different Patients
Ambu bags come in three standard sizes based on the volume of air the bag holds:
- 250 mL: designed for newborns and very small neonates
- 500 mL: used for neonates through infants
- 1,500 mL: covers infants through adults
The size matters because delivering too much air to a small patient can damage the lungs, while too little air won’t ventilate an adult effectively. The face masks also come in multiple sizes to ensure a proper seal against the face, which is critical for getting air into the lungs rather than leaking out around the edges.
Oxygen Delivery With and Without a Tank
On its own, an Ambu bag delivers room air, which contains about 21% oxygen. That’s enough to sustain life in many emergencies. But when connected to a supplemental oxygen source, the device can deliver much higher concentrations.
Most Ambu bags have a port to attach an oxygen reservoir bag on the back end. When oxygen flows into this reservoir at around 15 liters per minute, the patient receives close to the maximum possible oxygen concentration with each squeeze. Without the reservoir, even with oxygen connected, some room air gets mixed in during the bag’s re-expansion, diluting the oxygen. The reservoir solves this by storing pure oxygen between breaths so the bag refills from the reservoir rather than from the surrounding air. If the oxygen flow can’t keep up with rapid squeezing, a valve opens automatically to pull in room air so the bag still inflates.
The C-E Grip Technique
Holding the mask properly against the face is often the hardest part of using an Ambu bag. The standard method is called the C-E grip. The rescuer places their thumb and index finger in a “C” shape around the top of the mask, pressing it down against the face. The remaining three fingers form an “E” shape under the patient’s jawbone, pulling the jaw upward. This does two things at once: it seals the mask and lifts the jaw to open the airway.
During cardiac arrest, the recommended pace is 8 to 10 breaths per minute, which works out to one breath roughly every 6 to 7 seconds. Squeezing too fast or too hard is a common mistake and creates real problems.
Risks of Improper Use
The biggest complication with Ambu bag ventilation is air going into the stomach instead of the lungs. This is called gastric insufflation, and it happens when too much pressure, volume, or speed forces air past the esophagus. Once the stomach fills with air, it pushes the diaphragm upward, which compresses the lungs and makes ventilation even harder. This creates a cycle: as the lungs become harder to inflate, even more pressure is needed, which sends even more air into the stomach.
Gastric distension also raises the risk of vomiting. If stomach contents travel up and enter the lungs, it can cause a serious complication called aspiration, which damages lung tissue and makes the situation significantly worse. Research published in Resuscitation found that even moderate stomach inflation from bag-valve-mask ventilation negatively affects CPR outcomes and post-resuscitation care. One case report documented a pediatric cardiac arrest where severe gastric distension caused enough breathing compromise to potentially contribute to the patient’s death.
These risks are why training emphasizes slow, steady squeezes rather than forceful ones. Delivering just enough air to see the chest rise visibly, without overinflating, is the goal.
Single-Use vs. Reusable Models
Ambu bags come in both disposable and reusable versions. Single-use models are designed for one patient only and are discarded afterward. They’re typically made of less durable materials that can’t withstand sterilization. Reusable models are built from heat-tolerant silicone or similar materials and can be disassembled, cleaned, and autoclaved (steam-sterilized) between patients.
The CDC’s guidance on single-use devices is clear: if a device doesn’t include reprocessing instructions, it should be treated as disposable regardless of labeling. In practice, many emergency services and hospitals stock disposable Ambu bags because they eliminate the risk of cross-contamination between patients and are always ready to use straight from the packaging. Reusable versions are more common in operating rooms and intensive care units, where sterilization protocols are well established.