pneumomediastinum

see also:

• pathophysiology of mechanical ventilation
• asthma
• oesophageal rupture - Boerhaave syndrome
• J Thorac Dis. 2015 Feb; 7(Suppl 1): S44–S49. Pneumomediastinum

• pneumomediastinum is air within the mediastinum which is usually readily visible on a plain CXR and it may arise from either:
  • air leaks through small alveolar ruptures to the surrounding bronchovascular sheath as with spontaneous pneumomediastinum (SPM) which is generally benign and self-resolving
  • air leaking from oesophageal rupture - Boerhaave syndrome which is a life threatening pathology
  • air tracking down from upper airway air leak
• sometimes, air leaks into the pericardial space causing pneumopericardium
• pneumothorax may occur
• extremely rarely (and usually only with mechanical ventilation) a massive pneumomediastinum may develop which can cause tension pneumomediastinum and/or tension pneumopericardium

• spontaneous pneumomediastinum in neonates, children and adolescents
  • usually in tall, thin males as with spontaneous pneumothorax
  • usually there is an inciting event such as:
    • asthma
    • Valsalva-like manouvre (eg. during sports, coughing, choking, vomiting, child birth, etc)
    • inhalation of helium gas in party balloons
    • dental extractions
    • barotrauma / scuba diving
    • inhalation of illicit drugs
  • generally self-resolves with 2 weeks (usually within 6 days on CXR) without complication as the air is slowly resorbed
  • 5% are recurrent but usually benign

• oesophageal rupture
  • usually follows severe vomiting and results in painful swallowing, hypotension +/- pleural effusion
  • classic Meckler's triad of oesophageal rupture includes vomiting, lower chest pain, and cervical subcutaneous emphysema following overindulgence in food or alcohol.
    • unfortunately, vomiting, lower chest pain, and cervical subcutaneous emphysema also occur with spontaneous pneumomediastinum
  • early contained oesophageal perforations may be subclinical and hard to recognize, especially in those who are immonocompromised, on steroids or on antibiotics already
  • one should have a low index of suspicion if pneumomediastinum occurs in the context of severe vomiting or an episode of haematemesis

• chest pain usually radiating to neck or back
• SOB
• some may also have cough, neck pains, pain on swallowing or difficulty swallowing, or change to voice
• subcutaneous emphysema is common, especially noted in the neck or precordium
• some have a positive Hamman's sign - crunching precordial sound with each heart beat
• blood tests are usually unhelpful - elevated CRP, etc may occur but these are often raised due to underlying condition
• CXR is usually diagnostic - if there is none seen on CXR it is unlikely to be significant
• CT is not usually needed unless there is concern for Ix of underlying problems
• if there is concerm for oesophageal rupture then emergent gastrograffin contrast study of oesophagus and CT chest should be considered

• distended neck veins suggest tension pneumomediastinum
• unilateral decreased breath sounds suggest either:
  • pneumothorax
  • inhaled FB
  • pneumonia
• if septic or febrile - consider oesophageal rupture or underlying cause such as pneumonia

• emergent resuscitation
• IV access, fluids
• bloods
• CXR
• early referral to thoracic surgery
• broad spectrum cover IV antibiotics if rupture is very likely or patient is septic
• consider CT chest and gastrograffin contrast study of oesophagus
  • if confirmed, will need ICU admission
  • if no evidence of rupture but still suspicion for rupture then consider:
    • there is no need for intravenous antibiotics in patients with negative swallow studies or those who are unlikely to have rupture as this will only mask an occult rupture
    • overnight admission for observation
    • initially nil orally
    • repeat FBE, CRP next day and if remains normal with WCC less than 11,000, then re-introduction of normal diet
    • NB. slow diet advancement and holding up discharge until chest x-ray resolution of pneumomediastinum prolongs hospitalization with no difference in long term outcome

• exclude complications (and treat these on their own merit) and the much more serious oesophageal rupture
• analgesia
• rest
• avoid Valsava like manouvres
• treat underlying conditions such as asthma
• it is probably safe to travel by air after 2wks post-radiographic resolution