Pulmonary oedema due to air embolism is one for the uncommon causes of non-cardiogenic pulmonary oedema. It usually occurs as an iatrogenic complication of an invasive procedure. Rarely, it may also be associated with open or closed chest trauma.
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Pathology
Air may enter into the low-pressure venous system when a pressure gradient favours such access. This occurs most frequently during neurosurgical procedures 2,3 performed with the patient in the sitting position and during manipulation or placement of central venous lines.
Mechanical obstruction of the pulmonary microvasculature from embolised air bubbles can occur due to the relatively low absorption coefficient of air. These then create turbulent flow, which favours platelet aggregation, fibrin formation, and vasoconstriction, and increasing the pressure exerted on the vessel wall.
Non-mechanical factors such as the liberation of oxygen radicals from neutrophils may also contribute to the disruption of the capillary endothelium. Macromolecules, proteins, and blood cells may then enter the interstitial and alveolar spaces.
This then creates a variable pathologic picture that ranges from mild interstitial oedema to haemorrhagic airspace consolidation.
Radiographic features
Plain radiograph
May be difficult to differentiate from other causes of non-cardiogenic pulmonary oedema. Chest radiography may initially demonstrate an interstitial oedema pattern followed by bilateral, peripheral alveolar areas of increased opacity with a basal predilection 1. There is no associated cardiomegaly, and the radiographic changes often rapidly disappear in patients who survive the acute event.
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