you are doing a clinical on the medical-surgical floor of a local hospital when mr. b arrives from the emergency room. mr. b is a 32-year-old who was thrown off his bicycle in an accident; he has three fractured ribs and a punctured lung. in the er, they inserted a chest tube to drain air and fluid out of his pleural cavity, allowing his lungs to re-expand. he had one dose of demerol 3 hours ago for pain and a second dose just before transfer, according to the telephone report from the er nurse. how does removing air from the chest allow the lungs to expand? to begin, let's review the pleural cavity and what it is.