[yakkwak]

Originally Posted by pstinard

It can also happen from excessive air pressure during mechanical ventilation (maybe this was done during surgery to keep the puppy breathing?):

"Medical procedures, such as the insertion of a central venous catheter into one of the chest veins or the taking of biopsy samples from lung tissue, may lead to pneumothorax. The administration of positive pressure ventilation, either mechanical ventilation or non-invasive ventilation, can result in barotrauma (pressure-related injury) leading to a pneumothorax." (from Wikipedia article on pneumothorax)

Yes, a pneumothorax can happen this way during surgery (even to humans - believe me, I know first hand).