What if the abdomen begins to swell during CPR?

Answer 1

A common problem in CPR is accidentally blowing air into the stomach instead of the lungs. If the stomach area rises when giving breaths, you likely have your airway inserted incorrectly, and tubes have gone into the esophagus instead of the trachea.

Answer 2

The most likely cause is over-breathing.

Once you've given enough breath to fill their lungs, anything further you blow in will 'overflow' down into the stomach and start to cause bloating. (Next step is that they'll probably vomit on you, so watch out!)

Answer 3

Air gets into the stomach from either blowing too hard when giving the breath or blowing too long when giving the breath.