Gas Embolism

Abstract

The use of gas injection for contrast in clinical diagnostic roentgenology is increasing. The danger of venous or arterial gas embolism is always inherent in such diagnostic procedures as well as in therapeutic procedures in which entry of air into the circulation may occur. Deliberate introduction of air or oxygen by the presacral route into the mediastinum is now being widely advocated for diagnostic purposes. Pneumoperitoneum and pneumothorax have long been employed in diagnostic roentgenology; insufflation of the urinary bladder and many of the larger joints has also been performed. Angiocardiography involves a potential hazard because of possible accidental venous air embolism. The accidental occurrence of air embolism is well known in other clinical situations, particularly in surgical procedures involving the veins of the neck or the dural sinuses, performed with the patient in a sitting position, in uterine curettage, and during delivery of patients with placenta previa. Serious sequelae following accidental entrance of air into intravenous apparatus are rare. The greatest practical hazard probably lies in the practice of obstetrics and gynecology, since the uterine sinuses are the veins into which air may most readily enter, A number of deaths from air embolism have been reported, for example, as a result of vaginal insufflation for Trichomonas infestation either during pregnancy or in non-pregnant women near the time of menstruation (1). This problem is currently of additional interest because of the possibility of gas embolism in connection with explosive decompression at high altitudes, in aviation accidents, as for instance rupture of a sealed pressurized cabin (2, 3). Differentiation of Pulmonary (Venous) and Arterial Air Embolism: In pulmonary (venous) air embolism, the air enters one of the systemic veins and produces its effect by an air “trap” in the outflow tract of the right ventricle and main pulmonary artery and, when the patient is supine, by blockade of the small peripheral pulmonary arteries. This requires fairly large amounts of air. In arterial embolism, the air enters the pulmonary venous channels and is carried thence to the superiorly located systemic arteries. In this fashion, very small quantities of air may produce serious blockade of one or more of the coronary or cerebral vessels. The two forms of embolism present clinical pictures entirely different from each other. In venous embolism, the air in the right ventricle produces a loud, churning sound which may be audible without the stethoscope. This has been termed a “millwheel” murmur. If the patient is in such a position that an air trap develops in the right ventricle, the venous pressure rises and cyanosis ensues; the systemic blood pressure falls, the pulse becomes rapid and thready, and syncope develops as a result of cerebral ischemia.