The Bag-Valve-Mask (BVM) device is a manual ventilator used in emergency medical situations to deliver oxygen and air to a patient who is not breathing adequately or at all. Since the device relies on the rescuer’s manual action, the volume of air delivered with each squeeze can vary significantly, which makes precision highly important. Delivering the correct volume of air is fundamental to effective resuscitation. Providing too little air leads to inadequate oxygenation, while providing too much can cause direct patient harm. The goal is to achieve a precise balance to maintain life while preventing secondary injury.
The Physiological Goal of Ventilation
Modern resuscitation science emphasizes “lung-protective ventilation,” a significant shift from older methods that often prioritized large, forceful breaths. The primary physiological goal is to deliver just enough air to ensure adequate gas exchange: the movement of oxygen into the bloodstream and carbon dioxide out. This approach aims to support the lungs without subjecting them to unnecessary stress or excessive pressure.
The specific volume of air moved in and out of the lungs with each breath is called the tidal volume. In an emergency, the focus is on matching this tidal volume to the patient’s needs to maintain oxygen saturation without overstretching the delicate lung tissue. Excessive pressure from large volumes can cause lung injury, so the current philosophy centers on minimizing pressure while maximizing oxygen delivery.
Specific Volume Guidelines for Adults and Children
For adult patients, the recommended technical target for tidal volume is between 500 and 600 milliliters (mL) per breath. This volume corresponds to approximately 6 to 7 mL of air for every kilogram of the patient’s ideal body weight, not their actual weight. Using ideal body weight helps prevent over-inflation in larger individuals whose lung size may not correlate with their overall weight. The standard adult BVM device holds a much larger volume, often up to 1,500 mL, meaning a full squeeze delivers far too much air and must be avoided.
Since rescuers cannot accurately measure milliliters in an emergency, the most practical guidance is the visual cue of a slight, visible chest rise. The air volume delivered should only be enough to make the chest gently rise, indicating the lungs have received sufficient air for oxygen exchange. If the chest does not rise, the volume is insufficient; if the chest rises forcefully or rapidly, the volume is excessive. This visual indicator is the primary check for adequate volume delivery.
Pediatric patients require much smaller, weight-based volumes due to their smaller lung capacity and more delicate anatomy. Infants under one year may require 4 to 6 mL per kilogram, and older children between 6 to 8 mL per kilogram. As with adults, the practical application focuses on providing only enough air to achieve a gentle, visible rise of the chest. Using a pediatric-sized BVM helps a rescuer avoid inadvertently delivering an adult-sized breath to a child.
Proper Delivery Technique and Ventilation Rate
Achieving the correct volume is dependent on the technique used to deliver the breath. The first action is securing a proper mask seal against the patient’s face, often using the two-handed E-C clamp technique to prevent air from leaking out. A good seal ensures that the air being squeezed from the bag actually reaches the patient’s lungs.
The actual squeeze of the bag should be slow and controlled, not a rapid, forceful compression. It is recommended to deliver the breath over approximately one second to allow the air to flow smoothly into the lungs. A rapid squeeze can generate high peak inspiratory pressures, which contributes to the risk of lung injury.
Equally important is the ventilation rate, or the frequency of breaths. For an adult patient, the standard recommendation is to deliver one breath every 5 to 6 seconds, which translates to a rate of 10 to 12 breaths per minute. Delivering breaths too quickly is a common error that can be counterproductive. Maintaining this slow, consistent pace allows sufficient time for the lungs to exhale the previous breath and prevents a buildup of pressure within the chest cavity.
Risks Associated with Incorrect Air Volume Delivery
The consequences of deviating from the correct volume and rate are significant and can undermine resuscitation efforts. Delivering too much air, known as over-ventilation, is a frequent and dangerous error in manual ventilation. Excess volume creates high pressure inside the chest, which can lead to barotrauma, a physical injury to the lungs such as a pneumothorax, where the lung collapses.
Over-ventilation also increases the pressure within the chest cavity, which compresses the large blood vessels returning blood to the heart. This effect reduces the amount of blood the heart can pump out, thereby decreasing blood flow to the brain and other vital organs. Furthermore, excessive volume or rapid delivery can force air into the stomach, causing gastric inflation, which increases the risk of the patient vomiting and aspirating stomach contents into the lungs.
Conversely, delivering an inadequate volume, or under-ventilation, results in hypoxia, which is a dangerous lack of oxygen in the patient’s blood. If the chest rise is not visible or is barely perceptible, the lungs are not receiving enough air to sustain life. Both over- and under-ventilation are serious concerns that highlight why the visual cue of a gentle chest rise is the most important practical guide during BVM use.