how does air get trapped under the skin sometimes after operations and cause surgical ephysemia

Question: how does air get trapped under the skin sometimes after operations and cause surgical ephysemia
- Keywords:
  heath,
  operation,
  skin,
  surgery,
  surgical emphysema
Asked by hannah B to Iain, Hayley on 26 Jun 2015.
- Hayley Clissold answered on 26 Jun 2015:
  
  Emphysema caused by surgery is often due to the pressure in the alveoli (in the lung) being higher than in the surrounding tissues. This causes the air to move out and may get trapped beneath the skin.

Question: how does air get trapped under the skin sometimes after operations and cause surgical ephysemia