Gastric distension is bloating of the stomach when air is pumped into it. This may be done when someone is performing cardiopulmonary resuscitation and blowing air into the mouth of someone who is not breathing spontaneously. The primary reason this occurs is too much air is delivered during rescue breathing.
It may also occur when more advanced medical procedures are performed by emergency or hospital personnel, and air leaks past the opening of the lungs and into the stomach. However this problem can be prevented by inserting a gastric tube and suctioning the air and other stomach contents.
Gastric distension is potentially dangerous since it can cause the contents of the stomach to come up the esophagus (gullet) and spill back down into the lungs. This can cause drowning, by filling the lungs with fluid, if there has been enough material in the stomach. With lesser material, gastric distension can cause stomach acids to damage the lungs and create a condition known as "aspiration pneumonia". The other problem this causes is that the expanded stomach will push against the lungs decreasing the amount of air that can be placed into the lungs.
CPR standards issued by the American Heart Association suggest that people suffering gastric distension be turned on their sides and the stomach be compressed gently to push out the air bloating the stomach. By turning the individual on their side into what is known as the recovery position, the stomach contents will often continue past the opening of the lungs and drain out the mouth, thus sparing the victim lung damage or the internal drowning which can be caused by large volumes of stomach material getting into the lungs.