The Bag-Valve-Mask (BVM), often called a manual resuscitator, is a handheld device used to provide positive pressure ventilation to individuals who cannot breathe adequately on their own. This device is used in emergency and critical care settings. “Tidal volume” refers to the amount of air delivered into the lungs with a single squeeze of the bag. Delivering the correct tidal volume determines the effectiveness and safety of the ventilation. The goal is to ensure sufficient oxygenation and carbon dioxide removal without causing lung injury or interfering with circulation.
Understanding the Goal of Manual Ventilation
The primary purpose of manual ventilation is to support gas exchange by supplying oxygen to the blood and removing carbon dioxide. This is achieved by forcing a specific volume of air into the lungs. Delivering an excessive volume of air or squeezing the bag too forcefully can undermine the resuscitation effort.
One major danger is barotrauma, a lung injury caused by over-pressurization or over-stretching of lung tissue. Excessive pressure can damage the alveoli, the tiny air sacs where gas exchange occurs, or lead to conditions like pneumothorax (a collapsed lung). This risk is elevated when rescuers mistakenly believe that more air equals better outcomes.
Another risk is gastric inflation, where air is forced into the stomach instead of the lungs. This occurs when the BVM pressure overcomes the lower esophageal sphincter, causing air to enter the digestive tract. A distended stomach can lead to vomiting and aspiration, introducing foreign material into the lungs.
Gastric inflation also pushes the diaphragm upward, reducing the space available for the lungs to expand and making subsequent ventilations less effective. Current guidelines emphasize using the minimal volume necessary to achieve sufficient oxygenation, rather than completely filling the lungs. This prioritizes a controlled rate and volume to minimize harmful pressure increases within the chest cavity and abdomen.
Recommended Tidal Volume for Adult Patients
The standard recommendation for BVM tidal volume in adult patients is based on ideal body weight, ranging from 5 to 7 milliliters of air per kilogram (mL/kg). This translates to approximately 500 to 600 milliliters for an average-sized adult. The standard adult BVM contains between 1,500 and 2,000 milliliters of air when fully inflated, meaning a full squeeze delivers far too much volume.
Since BVM devices are non-metered, the technique for achieving the correct volume is to squeeze the bag only partially. Rescuers should aim to compress about one-third to one-half of the adult bag to deliver the target 500 to 600 mL. This partial compression mitigates the risk of over-ventilation.
The primary visual cue for sufficient tidal volume is “visible chest rise.” The breath should be delivered over approximately one second, and the rescuer should observe a gentle, noticeable rise of the chest, similar to a normal breath. If the chest rises too dramatically, the volume is likely excessive and should be reduced on the next breath.
The recommended ventilation rate for adults in cardiac arrest is 10 breaths per minute, or one breath every 6 seconds, without interrupting chest compressions. For adults who have a pulse but are not breathing adequately, the rate is around one breath every 5 to 6 seconds. Maintaining this slow, controlled rate is crucial, as hyperventilation reduces blood flow to the heart and brain.
Adjusting Ventilation for Infants and Children
Ventilation for pediatric patients requires modification due to their smaller size and vulnerability to pressure injury. Tidal volume must be scaled down based on weight: 6 to 8 mL/kg for children and 4 to 6 mL/kg for infants. These lower volumes protect against barotrauma and gastric inflation in smaller airways.
A dedicated pediatric or infant BVM should always be used, as these bags have a smaller total volume than adult versions, making controlled delivery easier. The technique involves using minimal pressure, often described as a gentle “puff,” just enough to cause a slight, visible chest rise. The goal is to avoid forceful squeezing, which can easily exceed safe pressure limits.
Ventilation rates for children and infants are faster than for adults due to their higher metabolic rates. Rescue breaths should be delivered at a rate of 20 to 30 breaths per minute, or one breath every 2 to 3 seconds. This faster rate helps meet their increased oxygen demand.
Proper mask sizing is important for children. The mask must fit snugly over the mouth and nose to create an effective seal without covering the eyes or extending past the chin. An ill-fitting mask allows air to leak out, resulting in ineffective ventilation or requiring excessive pressure to compensate.