To the Editor:—
In their review of vascular air embolism, Mirski et al .1define the condition as the entrainment of gas into the venous or arterial vasculature, but virtually the entire review is about venous air embolism (VAE), and arterial air embolism is described solely as secondary to VAE. Although blast injury and thoracentesis are included in a comprehensive list consisting mainly of VAE causes, no explanation of etiology is given for these two conditions, and readers may be led to believe that their pathophysiology is the same as that of VAE. Two case reports that actually describe arterial air embolism are also cited among the many VAE causes, and the explanation is simply excessive ventilatory pressure.
Arterial air embolism is a far more dangerous condition, requiring little air to inflict serious damage, even fatality, and deserves a better explanation. One of the most important causes of arterial air embolism is lung trauma (occurring in 4% of major thoracic trauma2), as the following case illustrates: A 20-yr-old jockey fell off a horse in the middle of a race. The jockey was trampled by several horses and sustained severe injuries, including those involving the chest. By the time the patient arrived at the hospital, there were few signs of life. The trachea had been intubated, and assisted ventilation had already begun. A radial artery line was started during cardiopulmonary resuscitation. Copious amount of gas bubbles were aspirated from the arterial line. The jockey died from the injuries.
If the pulmonary parenchyma has been damaged, direct communication between the pulmonary vasculature and bronchial tree becomes possible. Whereas this injury may manifest in a spontaneously breathing patient as hemoptysis (pulmonary vascular pressures > airway pressure), arterial air embolism may occur when positive-pressure ventilation reverses this pressure gradient and facilitates air entry into the pulmonary veins, from whence air bubbles travel in particular to the brain and the coronary arteries, with devastating results.3Through this mechanism, arterial air embolism has been reported following external chest compression,4lung biopsy,5rapid decompression or rapid ascent from deep sea diving with a closed glottis,6and rupture of an intrapulmonary bronchogenic cyst.7Single contralateral lung ventilation and immediate thoracotomy for hilar clamping (if the injury is unilateral), avoidance of high airway pressure, and maintenance of adequate pulmonary venous pressure, where appropriate, are remedies that have been suggested.3,8,9Without understanding the underlying pathophysiology, however, one might wrongly assume that venous air has traveled to the arterial side via a cardiac defect or an overwhelmed lung vasculature,1and the above measures would make no sense (and hence would not be considered).
Some important causes of VAE are also missing from the review. In coronary artery bypass grafting, the saphenous vein grafts are sometimes harvested endoscopically using carbon dioxide insufflation. The purported advantages include reduced hematoma, pain, wound complications, hospital stay, and vein trauma.10Using transesophageal echocardiography, carbon dioxide VAE may be detected in more than 17% of patients, some of them severe and necessitating emergency cardiopulmonary bypass.10Cardiovascular collapse has also been described.11Decreasing the carbon dioxide pressure reduces the problem, and continuous transesophageal echocardiography monitoring of the inferior vena cava has been recommended.12
Venous air embolism has also been reported during hepatic resection using the Cavitron Ultrasonic Surgical Aspirator®.13,14Minimization of the duration of using the Cavitron Ultrasonic Surgical Aspirator® device (Valleylab Inc., Boulder, CO) has been suggested.14
Even in a comprehensive review, lists often cannot be totally exhaustive. Nevertheless, we thought the above causes have sufficient relevance that they should have been included.
*The Chinese University of Hong Kong, Prince of Wales Hospital, Hong Kong, People’s Republic of China. email@example.com