Pulmonary gas embolism
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Pulmonary gas emboli are a specific type of pulmonary emboli that, while rare, should be kept in mind especially with the use of automatic injectors and interventional procedures. The seriousness of the problem will depend on both the amount and rate of injected air in the circulatory system.
The presentation can vary depending on the volume of gas emboli. Small volumes of gas are often asymptomatic. A moderate volume may result in headaches, chest pain and gasping and/or cough. Larger volumes can impede the blood flow into the pulmonary circulation causing an "air-block" resulting in hypotension and neurologic symptoms (e.g. seizure) 4.
Small amounts of air are eliminated from the circulation by molecular diffusion of gases across the arterial-alveolar basement membranes 6. A larger amount can impede the blood flow into the pulmonary circulation, and this "air-block" results in circulatory and neurologic consequences 6.
Occasionally, air may pass from venous to arterial circulation with subsequent neurologic manifestations development as in persistent patent foramen ovale and/or right-to-left shunts.
They can arise from both iatrogenic and non-iatrogenic causes 3,7.
Venous gas embolism is a well-known complication of:
- intravenous devices, e.g. central venous catheters, Swan-Ganz catheters, cardiac pacemaker, drug infusions
- trauma, e.g. penetrating injuries
- surgery including accidental air injections
- wound irrigations with excessive hydrogen peroxide
- positive pressure ventilation
- imaging-related, e.g. contrast injection, angiography, needle biopsy
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
- pulmonary diseases, e.g. asthma, COPD
- reported following oral intercourse 8
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.
May show some of the above plain radiograph features in greater detail, as well as allow direct visualization of gas in the systemic veins (usually seen along the injection trajectory e.g. subclavian, innominate, and SVC) versus the positive contrast, 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.
Training and periodic orientation of staff dealing with automatic injectors in the radiology suite to avoid intra-vascular inadvertent air injection and recognize the manifestations of air embolism as early as possible is a must to avoid this serious complication
- Durant's maneuver: position the patient in a left lateral decubitus in Trendelenburg position (head down), 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
- 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 3
- cerebral gas embolism: which in turn may result in cerebral edema or ischemic stroke
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