Surgical emphysema (subcutaneous trapped air) is a complication of chest drain insertion, or sometimes of the pneumothorax itself.
Surgical emphysema can form because of poor technique during drain insertion or because of displacement of the drain such that a side hole near the end of the drain lies within the subcutaneous tissues.
Surgical emphysema has the clinical characteristic of feeling like 'rice crispies' or 'bubble wrap' on palpation.