Pulmonary gas embolism

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Pulmonary gas emboli are a specific type of pulmonary emboli.

Clinical presentation

Presentation can vary depending on the volume of gas emboli whereby patients with small amounts of gas can be asymptomatic. Commonly reported clinical manifestations include sudden dyspnea, chest pain, hypotension and/or convulsions .

Pathology

Etiology

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

Iatrogenic

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

Non-iatrogenic

Non-iatrogenic gas embolism 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 gas emboli, there may be areas of hyperlucency overlying the heart shadow, main pulmonary artery, or hepatic veins. Features of focal pulmonary oligemia, pulmonary edema, 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 visualization 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 . Treatment is to position the patient in a left lateral decubitus or Trendelenburg position, with the aim to prevent the gas passing from the right heart into the pulmonary arteries. 100% supplemental oxygen can also be used to decrease the size of the bubbles by reducing their nitrogen content.

Complications
  • pulmonary edema due to gas 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
  • cerebral gas embolism: which in turn may result in cerebral edema or ischemic stroke

See also