Air embolism
Gas bubbles blocking blood vessels cause serious medical emergencies.
An air embolism, or gas embolism, happens when one or more gas bubbles block a blood vessel. This blockage can be introduced into the bloodstream during surgery, from a lung over-expansion injury, or during decompression, among other causes. In plants, air embolisms can also occur in the xylem of vascular plants, particularly those under water stress.
For divers, arterial gas embolisms can result from lung over-expansion injuries. When gas enters the venous system of the lungs due to pulmonary barotrauma, it is not trapped in the alveolar capillaries and instead circulates through the systemic arteries, posing a high risk of embolism. Inert gas bubbles from decompression typically form on the venous side of the systemic circulation, where inert gas concentrations are highest. These bubbles are usually trapped in the lung capillaries and eliminated without symptoms. However, if they are shunted to the systemic circulation through a patent foramen ovale, they can travel to the brain and cause an embolic stroke, to the coronary capillaries and cause myocardial ischaemia, or to other tissues, where consequences are generally less severe. First aid involves administering the highest possible concentration of oxygen, treating for shock, and transporting the patient to a hospital for definitive treatment with therapeutic recompression and hyperbaric oxygen therapy.
**Signs and symptoms**
In surgery, symptoms include abnormally low blood pressure and shortness of breath.
In divers, symptoms of arterial gas embolism include loss of consciousness, cessation of breathing, vertigo, convulsions, tremors, loss of coordination, loss of control of bodily functions, numbness, paralysis, extreme fatigue, weakness in the extremities, areas of abnormal sensation, visual or hearing abnormalities, personality changes, cognitive impairment, nausea or vomiting, and bloody sputum. Symptoms of other lung overexpansion consequences, such as pneumothorax, subcutaneous or mediastinal emphysema, may also be present.
**Causes**
Interventional radiological, cardiac, and neurosurgical procedures can predispose someone to air embolism. The increasing use of pump injectors for contrast delivery and percutaneous intervention to the lungs also raises the risk.
Gas embolism is a diving disorder that occurs in two distinct ways. First, pulmonary barotrauma: air bubbles enter the bloodstrea
- field
- Medicine, Diving Medicine
- known_for
- Blood vessel blockage by gas bubbles; cause of decompression illness and surgical complications
- lethal_dose
- 300-500 mL of gas at 100 mL/s; 2 mL in cerebral circulation can be fatal
Lore & Background
Air embolism can occur whenever a blood vessel is open and a pressure gradient favors entry of gas. In veins above the heart, such as in the head and neck, venous pressure may be less than atmospheric, allowing air entry. This is why surgeons tilt the head of the bed down when inserting or removing a central venous catheter from the jugular or subclavian veins. When air enters the veins, it travels to the right side of the heart and then to the lungs, potentially causing vessel constriction and raising right heart pressure. In the 20% to 30% of the population with a patent foramen ovale, the gas bubble can travel to the left side of the heart and on to the brain or coronary arteries, causing the most serious symptoms.
Reader's Guide
Air embolism is significant as a potentially fatal complication in diving, surgery, and certain medical procedures. For divers, arterial gas embolism can result from lung over-expansion injuries during ascent, leading to loss of consciousness, paralysis, or stroke. In clinical settings, interventional radiological, cardiac, and neurosurgical procedures can predispose to air embolism, as can misuse of syringes or pump injectors. The first aid treatment is administration of oxygen at the highest practicable concentration, treatment for shock, and transport to a hospital for therapeutic recompression and hyperbaric oxygen therapy. The condition highlights the importance of proper technique in catheterization and ventilator use, and the need for screening for patent foramen ovale in divers undertaking deep technical diving. Its study has advanced understanding of decompression physiology and the mechanisms of embolic stroke.
Did You Know?
- The lethal dose for humans is considered theoretically between 3 and 5 mL per kg; 300-500 mL of gas introduced at 100 mL per second would prove fatal.
- 2 mL of air in the cerebral circulation can be fatal, while 0.5 mL of air into a coronary artery can cause cardiac arrest.
- In the 20% to 30% of the population with a patent foramen ovale, gas bubbles can travel from the right to the left side of the heart and cause embolic stroke or myocardial ischaemia.
- Air embolisms can also occur in the xylem of vascular plants, especially those suffering from water stress.
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