Pulmonary gas embolism

Pulmonary gas emboli are a specific type of pulmonary emboli. 

Clinical presentation

Presentation can vary dependantdepending on the degreevolume of airgas emboli wherewhereby patients with small amountamounts of airgas can be asymptomatic. Commonly reported clinical manifestations include sudden dyspnoea, chest pain, hypotension and/or convulsions ⁴.

Pathology

Aetiology

They can arise from both iatrogenic and non-iatrogenic causes. 

Iatrogenic causes

Venous gas embolism is a well-known complication of thoracic trauma, surgery, and a variety of diagnostic and therapeutic procedures. Small quantities of airgas have been reported in the central veins in up to 23% of patients during contrast material administration for CT scans ³. 

Non-iatrogenic causes

Non-iatrogenic gas embolism can sometimes occurs in SCUBA divers as a result of gas bubble formation in the blood, which occurs due to rapid reduction in the ambient pressure during a diver's ascent.

Radiographic features

Plain radiograph

Chest radiographs are usually normal unless there is a massive load of emboli. In the event of a large volume of airgas emboli, there may be areas of hyperlucency overlying the heart shadow, main pulmonary artery, or hepatic veins. Features of focal pulmonary oligaemia, pulmonary oedema, or enlargement of the central pulmonary arteries or superior vena cava may be seen. 

CT

May show some of the above plain film features in greater detail, as well as allow direct visualisation of gas in the systemic veins, right sided cardiac chambers or main pulmonary arteries.

Treatment and prognosis

The risk of death is affected by both the amount of gas and the speed of introduction; the minimum lethal volume and injection rate in humans are thought to be around 300-500 mL and 100 mL/sec, respectively ⁴. Treatment is to position the patient in a left lateral decubitus or TrelendenburgTrendelenburg position, with the aim to prevent the airgas passing from leaving the right heart into the pulmonary arteries. 100% supplemental oxygen can also be used to decrease the size of the bubblebubbles by reducing its their nitrogen content. 

Complications

• pulmonary oedema due to airgas embolism
• cardiovascular dysfunction and failure: can occur from obstruction of the right ventricular pulmonary outflow tract or obstruction of the pulmonary arterioles by a mixture of gas bubbles and fibrin clots formed in the heart ³
• cerebral airgas embolism: which in turn may result in cerebral oedema or ischaemic stroke

See also

• cerebral airgas embolism