Bag-mask ventilation (BMV) is a manual procedure that provides positive pressure breaths to a patient who is unable to breathe effectively on their own. Used commonly in emergency medicine, BMV delivers oxygen to the lungs through a face mask connected to a self-inflating bag. While effective for immediate life support, BMV carries a significant risk of a complication known as gastric inflation, where air is inadvertently forced into the stomach instead of the lungs. Air accumulation in the stomach causes swelling, which can lead to regurgitation and aspiration of stomach contents into the lungs. Understanding the causes of gastric inflation ensures safer and more effective ventilation.
Excessive Air Pressure and Ventilation Rate
The primary cause of gastric inflation is the mechanical difference between the pressure needed to inflate the lungs and the pressure needed to open the esophagus. The lower esophageal sphincter (LES) is a muscular ring that normally prevents air from entering the stomach, but it opens when ventilation pressure exceeds a threshold, typically around 20 cm of water (H2O) in adults.
This threshold is often surpassed when the operator squeezes the bag too forcefully. Delivering breaths too quickly or with excessive volume significantly increases the peak inspiratory pressure within the airway, easily surpassing the 20 cm H2O threshold. Rapid ventilation rates, such as exceeding the recommended 10 to 12 breaths per minute for an adult, reduce the time available for exhalation and increase the overall pressure and volume delivered over time.
Operator technique, specifically the force and speed of bag compression, is a major determinant of gastric inflation risk. The average adult bag-mask device can deliver up to 1600 milliliters of air, yet the lungs typically only require a volume of 500 to 600 milliliters per breath. Squeezing the entire bag, or squeezing it rapidly, forces high-pressure, high-volume air toward the lungs, increasing the likelihood that the path of least resistance becomes the esophagus instead of the trachea.
Patient Conditions Increasing Susceptibility
Certain physiological and anatomical factors inherent to the patient can make them more susceptible to gastric inflation, even when the ventilation technique is appropriate. Any form of airway obstruction requires the operator to apply greater pressure to achieve chest rise, which often inadvertently exceeds the esophageal opening pressure. Common obstructions include the patient’s tongue falling back against the throat, excessive secretions, or the presence of a foreign body.
Poor patient positioning is a frequent cause of airway obstruction, such as when the head or neck is improperly flexed or extended. This misalignment increases airway resistance, forcing the clinician to use more force to move air past the obstruction and into the lungs. A poor mask seal, which allows air to leak out around the mask, also contributes indirectly to gastric inflation, as the operator often compensates for this leak by squeezing the bag harder and faster.
Conditions that naturally weaken the tone of the lower esophageal sphincter (LES) also lower the pressure threshold at which air enters the stomach. For example, certain medications, existing disease states, and conditions like pregnancy can reduce the LES tone, making the patient more vulnerable to air entry into the stomach. Additionally, individuals with significant facial trauma or anatomical differences may be difficult to seal, leading to higher-force ventilation attempts and increased risk of gastric air accumulation.
Techniques for Minimizing Risk
Mitigating the risk of gastric inflation involves practical, evidence-based changes to ventilation technique and patient management. The most effective strategy is to deliver breaths gently, using only enough volume to observe a slight chest rise. This low-pressure, low-volume approach ensures that the inspiratory pressure remains well below the 20 cm H2O threshold that opens the esophagus.
Proper positioning of the patient’s head and neck is essential for establishing a clear airway. Utilizing the “sniffing position”—where the neck is flexed and the head is extended—helps align the airway axes and reduces obstruction, lowering the pressure needed for successful ventilation. If the airway remains difficult, the immediate use of airway adjuncts, such as an oropharyngeal or nasopharyngeal airway, can physically move the tongue and soft tissues out of the way.
Achieving and maintaining an effective mask seal is another important step to prevent air leakage and the compensatory use of excessive force. The two-handed technique, where one rescuer focuses on securing the seal while the other compresses the bag, is preferred over the one-handed method for creating a reliable, leak-free connection. Applying gentle pressure to the cricoid cartilage (Sellick’s maneuver) has been used to compress the esophagus and potentially prevent air entry, although its routine effectiveness is a matter of ongoing discussion.