Embolism refers to any large moving mass (cloth, gas, fat, bacterial deposit etc.) or defect in the blood stream that finally stick in some blood vessel. If that "moving mass" in the blood is gas that is called air (gas) embolism. Most of the small air embolisms stick in the lungs but here the air is expelled without causing pulmonary embolism. Gas bubble, if large, sticks in the right ventricle without reaching the lungs and can cause fatal gas embolism. If gas enter the arteries it can cause infarct in the affected organs.
Pulmonary embolism a usually due to blood cloth that sticks in the main lung arteries or in their branches. Small bubbles can't cause pulmonary embolism but small blood clothes can. Big bubble can cause heart shock in a similar way like when blood cloth sticks in the main pulmonary arteries.
If large amount of gas enters into the central line it can cause embolism in the right ventricle of the heart not in the lungs. Symptoms, in such case, would be immediate.