Venous air embolism is a well-known complication during head and neck surgery. Also it commonly occurs during IV injection of contrast for radiographic studies and may occur during central venous catheterization. Large-volume venous air embolism may lead to cardiovascular collapse or to paradoxical arterial emboli with resulting central nervous system injury. The newer generation computerized tomography (CT) scanners with multi-slice, rapid acquisition capability are identifying small-volume air embolism more commonly. Thus, the pulmonlogist will be consulted more fequently to evaluate patients for the significance of this compication.
A 54 year-old man with myasthenia gravis, had a CT of the thorax with contrast, as an outpatient, for the evaluation of thymoma. Interpretation of the CT scan, after he had left the radiology department, showed evidence of air in the brachiocephalic vein, superior vena cava, right atrium, and right ventricle. The amount of air was estimated to be 4 to 6 milliliters(ml). The patient was contacted at home, had no symptoms, was asked to return, and on examination had normal vital signs and a normal neurological and cardiac examination. Oxygen saturation via pulse oximeter was 100 % on room air.
Iatrogenic air embolism requires that two conditions be present. These are a direct communication between the air and the vasculature, and a pressure difference favoring air entry rather than bleeding. Recent studies show the incidence of small and moderate size air embolism (diameter <20 mm) in patients undergoing CT scan of the thorax with contrast is as high as 24%, using early generation scanners. Large volume venous embolism is less common, is usually reported in case reports, and has not been systematically studied. Symptoms of air embolism depend on the amount of air injected and the rate of injection.The fatal dose in humans is unknown, but in animals injection of 300 to 500 ml of air at rate of 100 ml/sec can cause cardiac arrest. Mild air embolism may be asymptomatic, but major air embolism can lead to loss of consciousness, chest pain, shortness of breath, or cerebrovascular accident. Examination may reveal cyanosis, tachypnea, hypotension, or the classic mill-wheel heart murmur, which is a splashing sound due to the presence of gas in the cardiac chambers and great vessels. Lung exam may reveal wheezing or crackles. Exhaled end-tidal carbon dioxide may be reduced. Arterial blood gases may show hypoxemia and the electrocardiogram may show sinus tachycardia, sinus bradycardia, or conduction abnormalities. Paradoxical embolization of air may occur through a patent foramen ovale or through the pulmonary microcirculation. Doppler ultrasonography and transesophageal echocardiography are both sensitive in detecting intra-cardiac air.The potential for developing venous air embolism is reduced by preventive methods, such as proper positioning of the patient during insertion of central lines, and insuring that the IV tubing is free from air bubbles. Once venous air embolism occurs, the patient should immediately be placed in the left lateral decubitus position and in Trendelenburg (Durant’s position), which helps move the air bubble to the right atrium or into the right ventricle away from outflow tract, and administer 100% Oxygen to enhance the diffusion of nitrogen into the blood. Comatose or somnolent patients should be intubated. Immediate aspiration through a central venous catheter, already in place, may be attempted.
Although our patient’s experience with venous air embolus was inconsequential, it served to point out that air embolism is a frequent and usually mild event, that the newer generation of computered tomography equipment is likely to recognized incidental air embolism associated with contrast injection more frequent than before, and that early recognition and intervention is necessary when air embolism is severe and life threatening.
Sameh Aziz, None.