A venous gas embolism is defined by an abnormal collection of gas which forms a bubble in the systemic venous circulation. This bubble can act as an embolus affecting blood flow.
A venous gas embolism is usually caused by medical interventions which expose the venous circulation to outside air/gas. Examples of procedures and situations which have caused venous gas embolism include central venous catheter insertion/removal, CT injector, hemodialysis, penetrating chest injuries, lung biopsy, cardiovascular surgery, neurosurgery, angioplasty, arthroscopy, laparoscopic procedures, hysteroscopy, among many others. The common factor in these procedures is the possibility of the introduction of air/gas into the venous circulation. Additionally, deep sea diving can result in nitrogen gas coalescing in the venous system as the diver ascends. When ascending, the pressure decreases and the nitrogen which was dissolved in the blood at a much higher temperature begins to form bubbles and is no longer kept in solution with the blood. The nitrogen boils out of the venous system in particular as this is a lower pressure system. The nitrogen gas will then form bubbles and coalesce into emboli. This is prevented by slowly ascending and ensuring the diver has adequate breathes as they ascend to wash out excess nitrogen via exhalation.
Due to an increase of invasive medical procedures, the incidence of gas embolism has been steadily increasing. Additionally, the use of end-tidal carbon dioxide and doppler monitoring has lead to an increase in gas embolus detection. The actual incidence is unknown however because most venous gas emboli are largely subclinical and do not result in any obvious symptoms in patients. Neurosurgical procedures have the highest risk of a venous gas embolus due to the patient being upright, the position of the brain relative to the heart, and the brain's noncompressed venous system.
The severity of venous gas embolism is dependent upon the rate of gas introduced into circulation as well as the volume of gas. Rapid gas entry and larger volumes of gas both increase the size of the venous gas embolism and increase the severity of symptoms. Assuming no right to left shunting is occurring, the venous gas embolus will lodge in the pulmonary artery in the lungs. This can cause pulmonary artery hypertension and subsequent right heart strain. Occasionally, the gas embolus can pass through the pulmonary artery and make it's way to the left heart and into systemic arterial circulation, possibly causing far more severe sequelae such as stroke. This can also happen with right-to-left shunts such as a fistulous tract or a patent foramen ovale which allows the embolus to travel to systemic arterial circulation thus bypassing the lungs. This is called an arterial gas embolus or paradoxical embolism.
A history of recent surgical procedures or trauma increases the suspicion for venous gas embolism. It can be difficult to diagnose at times due to the similarity to various other causes for the patient's symptoms. Clinical manifestations of venous gas embolism include the following: Right heart strain on EKG, tachyarrhythmias, hypotension, dyspnea, chest pain and coughing. If the patient is being monitored, you may see a decrease in end-tidal CO2 and hypercapnia. Increased pulmonary artery pressure may also be seen if invasive monitoring is established. If severe hypotension due to pulmonary artery hypertension and right heart strain is present, an altered mental status may also be seen. Arterial gas emboli will not be discussed here but can lead to stroke and myocardial infarction among other sequelae.
The diagnosis of venous gas embolism is largely clinical and requires high suspicion. Sudden symptoms after or during an invasive procedure such as loss of consciousness or hemodynamic instability are highly suggestive of gas embolism. The temporal relationship between symptoms and invasive procedures is the biggest clue in making the diagnosis. Various monitors used during surgery which may already be in place can be helpful in making the diagnosis of venous gas embolism or arterial gas embolism. Transesophageal echocardiography may visualize a gas bubble in the heart and is the most sensitive diagnostic test for venous gas emboli. Precordial Doppler monitoring is the most sensitive noninvasive test routinely used. As noted previously, end-tidal carbon dioxide and nitrogen monitoring are useful in detecting venous gas emboli that have lodged into the pulmonary vasculature. Additionally, a drop in tidal volume is more specific for venous gas embolism than many other tests.
Treatment of venous gas embolism is largely supportive. The first intervention should be to discontinue any gasses such as nitrous oxide which may be flowing into the patient. One hundred percent O2 supplementation may be used to correct hypoxia/hypoxemia as well as decrease the size of the bubble due to a diffusion gradient allowing nitrogen to leave the gas embolus. For severe venous gas embolism causing hemodynamic instability, cardiac massage may be beneficial. Cardiac massage would move air out of the pulmonary outflow vasculature and into the smaller vessels thus improving blood flow. If a catheter is already in place such as a subclavian vein catheter, it is possible to advance the catheter into the heart and "suck out" the gas emboli. Positioning in the left lateral decubitus may be beneficial during this procedure so as to trap the emboli in the right heart for easier removal. However, there is no data supporting the emergent placement of an intravenous catheter for venous gas embolism management if one is not already in place.
Inotropic agents such as dobutamine and ephedrine may be used if the right heart function is compromised. This will increase preload to the left heart resulting in improved cardiac output.
While hyperbaric oxygen therapy is commonly used in arterial gas embolism, its use in venous gas embolism is not routine. Most patients with small venous gas embolisms have few, if any, symptoms and do not require treatment. Generally, with smaller venous gas embolisms, the embolus will eventually reach the lungs, become trapped, and diminish in size as the patient breathes. In cases of severe hemodynamic instability, hyperbaric oxygen therapy may be considered, but there is no data clearly demonstrating benefit.
Trendelenburg position has been advocated in the past, but when studied, has been shown to be ineffective and potentially harmful.