Cardiopulmonary Resuscitation (CPR) is a life-saving sequence of chest compressions and rescue breaths performed when a person’s heart has stopped beating. It aims to circulate blood and oxygen until professional medical help arrives. A frequent complication during rescue breaths is gastric inflation (GI), where air is inadvertently forced into the stomach instead of the lungs. This complication significantly hinders resuscitation effectiveness and introduces further risk to the patient. Understanding the anatomical reasons and technical errors that lead to gastric inflation is paramount for anyone involved in emergency life support.
The Anatomical Pathway of Misdirected Air
The primary issue during rescue breathing lies in the shared pathway between the respiratory and digestive systems in the upper throat. Both the trachea, which leads to the lungs, and the esophagus, which leads to the stomach, originate near the back of the mouth. When a person is unconscious, muscle tone is lost, and the airway can become partially obstructed, despite protection from the epiglottis.
The esophagus is a soft, collapsible tube offering far less resistance to airflow than the lungs. At the base of the esophagus, the lower esophageal sphincter (LES) usually maintains a tight seal to prevent stomach contents from refluxing. During cardiac arrest, however, the tone of the LES decreases rapidly and severely, often dropping significantly within minutes of circulatory collapse.
Air is diverted into the stomach whenever the pressure applied during the rescue breath exceeds the weakened resistance of the LES. While a healthy LES pressure might be around 20 cm H2O, during cardiac arrest, this pressure can drop to almost zero, making the stomach an easy path for air entry. This anatomical vulnerability means that excessive force or volume during ventilation will preferentially push air past the compromised sphincter, inflating the stomach instead of the lungs.
Rescuer Technique Errors as Primary Causes
The mechanical actions of the rescuer are the most direct cause of the excessive pressures that overcome the weakened esophageal seal. Three main technique errors contribute to gastric inflation: delivering excessive air volume, blowing air too quickly, and failing to secure the airway position.
Delivering Excessive Air Volume
Delivering an excessive volume of air, or “over-ventilation,” dramatically increases pressure within the airway, directly increasing the likelihood of air being forced down the esophagus. For adults, the recommended tidal volume during CPR is approximately 500 to 600 mL, which is just enough to make the chest visibly rise. Using larger volumes, such as 1.0 L sometimes seen in older training models, significantly increases the risk of air entry into the stomach.
High Flow Rate
The speed at which the air is delivered, or the flow rate, is another factor that generates high peak pressures. Rapid breaths shorter than one second require a much higher peak mouth pressure, sometimes up to 25 cm H2O, to achieve the necessary lung volume. This high pressure spikes well above the resistance offered by the flaccid LES, pushing air into the stomach. Delivering a breath over approximately one second allows for a lower, more controlled pressure profile, which minimizes the chance of gastric inflation.
Improper Airway Positioning
Improper positioning of the patient’s head and neck also makes gastric inflation more likely, even when using moderate pressure and volume. The head-tilt/chin-lift maneuver is designed to open the upper airway by lifting the tongue away from the back of the throat. Failure to adequately perform this maneuver leaves the trachea partially obstructed, which increases the resistance to air entering the lungs. With a blocked airway, air pressure builds up rapidly, and the path of least resistance becomes the esophagus, diverting air to the stomach.
Immediate Dangers of Gastric Inflation
Preventing gastric inflation is a priority because the resulting air accumulation in the stomach introduces several immediate, life-threatening complications that counteract the goals of CPR.
Regurgitation and Aspiration
One significant danger is the increased risk of regurgitation and subsequent aspiration. Air inflating the stomach increases abdominal pressure, which can force gastric contents past the already compromised LES and into the throat. If stomach contents are inhaled, or aspirated, into the lungs, this leads to a severe secondary injury called aspiration pneumonia. Aspiration introduces acidic fluid and particulate matter into the delicate lung tissue, complicating oxygenation efforts.
Impaired Lung Function
The inflated stomach also physically pushes upward on the diaphragm. This reduces the space available for the lungs to expand, decreasing the overall compliance of the chest cavity. The reduced lung volume makes subsequent rescue breaths less effective, severely limiting the amount of oxygen delivered to the patient’s blood.
Compromised Circulation
Severe gastric distension can also compromise the heart’s function by exerting pressure on major blood vessels within the abdomen. Specifically, it can compress the inferior vena cava, the large vein that returns deoxygenated blood from the lower body to the heart. This compression reduces the amount of blood returning to the heart, which decreases the heart’s output and lessens the effectiveness of chest compressions.