Bag-mask ventilation (BMV) helps individuals breathe by delivering air into their lungs. Despite its effectiveness, BMV can lead to gastric inflation, where air enters the stomach and hinders ventilation.
What is Gastric Inflation?
Gastric inflation occurs when air intended for the lungs inadvertently enters the stomach. This happens because the airway (trachea) and esophagus (food pipe) are anatomically close. During positive pressure ventilation, if esophageal pressure exceeds the lower esophageal sphincter’s opening pressure, air can be forced into the stomach instead of the lungs. The stomach’s inflation can increase pressure within the abdominal cavity.
How Gastric Inflation Impairs Bag-Mask Ventilation
Gastric inflation significantly reduces the effectiveness of bag-mask ventilation through several mechanisms, directly impacting a patient’s ability to receive adequate oxygen. A distended stomach pushes upward against the diaphragm, the primary muscle for breathing, limiting its downward movement. This compression restricts the space available for the lungs to fully expand, making it difficult to deliver sufficient air into the patient’s lungs and hindering proper oxygenation and carbon dioxide removal.
Air in the stomach increases the risk of regurgitation, where stomach contents are forced back up the esophagus and into the airway. This can lead to aspiration, meaning stomach fluids enter the lungs, potentially causing aspiration pneumonia or blocking the airway entirely. This can worsen a patient’s respiratory condition.
A severely distended stomach can also compromise blood flow back to the heart. The increased pressure within the abdomen can compress major blood vessels, such as the vena cava, reducing the amount of blood returning to the heart. This diminished venous return can lead to a decrease in the heart’s output, affecting overall circulation and the delivery of oxygenated blood to the body’s tissues.
Gastric inflation makes the physical act of ventilating the patient much more challenging for the rescuer. The increased pressure in the abdomen can make the bag-mask device harder to squeeze effectively, and it becomes more difficult to achieve visible chest rise, indicating that air is reaching the lungs. This creates a cycle where ineffective ventilation leads to more gastric inflation, further impairing efforts.
Causes of Gastric Inflation
Several factors can contribute to air entering the stomach during bag-mask ventilation, often stemming from improper technique or patient-specific conditions. One common cause is the use of excessive ventilation pressure, volume, or a rapid rate of breath delivery. When breaths are delivered too forcefully or too quickly, especially if the airway is not completely open, air is more likely to bypass the lungs and enter the esophagus, flowing into the stomach.
A poor mask seal is another significant contributor to gastric inflation. If air leaks around the mask instead of entering the patient’s airway, rescuers may instinctively apply higher pressure to compensate. This increased pressure, rather than directing air into the lungs, can more easily force it into the stomach.
Improper head or airway positioning also plays a role. If the patient’s head is not positioned correctly, such as in a “sniffing position” or with a head-tilt/chin-lift, the airway may be partially obstructed. In such cases, air will preferentially enter the esophagus, which presents less resistance than a kinked or poorly aligned trachea. Any pre-existing airway obstruction, such as the tongue falling back, foreign bodies, or swelling in the upper airway, can also redirect air into the stomach. Additionally, certain patient factors, like a relaxed esophageal sphincter tone in unconscious individuals, the absence of teeth, obesity, or advanced age, can increase the likelihood of gastric inflation.
Preventing Gastric Inflation
Preventing gastric inflation during bag-mask ventilation involves careful attention to technique and continuous patient monitoring. Proper airway positioning is fundamental; this often involves using a head-tilt/chin-lift maneuver or a jaw-thrust maneuver to open the airway and align the oral, pharyngeal, and laryngeal axes. For patients without a suspected neck injury, the “sniffing position” (head extended, neck flexed) is ideal for optimizing airway patency.
Achieving an effective mask seal is equally important to ensure that air goes into the lungs and not around the mask or into the stomach. This typically involves using a two-handed “C-E” grip, where one hand forms a “C” around the mask for a tight seal while the other fingers form an “E” to lift the jaw into the mask. Selecting the correct mask size and leaving dentures in place, if possible, can also help create a better seal.
Delivering breaths using minimal effective pressure and a slow ventilation rate is crucial. This means applying just enough pressure to achieve visible chest rise, typically delivering each breath over approximately one second. Rapid or overly forceful breaths increase the likelihood of air being forced into the stomach.
Observing for visible chest rise with each breath is a direct indicator that air is successfully entering the lungs, rather than the stomach. Recognizing early signs of gastric inflation, such as abdominal distension or increased resistance when squeezing the bag, allows for prompt adjustments to ventilation technique.