Table 1

Differential diagnosis of free gas

Tracti	Origin
Airway	Drugs (eg, cocaine) Pneumothorax asthma/COPD idiopathic iatrogenic (eg, mechanical ventilation) trauma Retropharyngeal abscess Trauma of the upper respiratory tract
Gastrointestinal	Abscess Appendicitis Bacterial peritonitis Diverticulitis Foreign bodies (Incarcerated) hernia abdominal wall hernia hiatus hernia Iatrogenic drugs (eg, NSAIDs) endoscopy paracentesis peritoneal dialysis postradiation surgery Inflammatory bowel disease Ischaemic bowel Malignancy primary metastatic Necrotising enterocolitis Peptic ulcer disease Reflux esophagitis Trauma Volvulus after prior abdominal surgery congenital
Soft tissue	Gas from other tracti airway gastrointestinal Infectious fasciitis necroticans toxic shock syndrome Iatrogenic Trauma
Vascular	Diving Iatrogenic

COPD, chronic obstructive pulmonary disease; NSAIDs, non-steroidal anti-inflammatory drugs.