What is venous air embolism?
Venous air embolism is when air enters the blood circulating back to the heart. It is not a common condition but has serious and severe consequences – it may even lead to death. Most cases of venous air embolism arises with medical procedures, hence the term ‘iatrogenic’. It can also arise in divers where it is known as decompression sickness or the ‘bends’. The air bubble travels to the right side of the heart and may eventually block one of the vessels leading to the lungs.
Venous Air Embolism Incidence
The incidence of venous air embolism is difficult to estimate as the condition causes cardiovascular or neurological symptoms and is therefore not always identified. It also depends on the cause and the volume of air that enters the circulation. It has been estimated that an air embolism arises in about 1 in 800 cases of central venous catheter insertion and removal. The incidence is much higher when it arises as a complication of neurosurgical procedures and severe lung trauma occurring in as many as 80% and 14% of cases respectively.
Venous Air Embolism Pathphysiology
Blood vessels are contained hollow tubes that carry blood throughout the body. It does not directly communicate with the environment. Even when with superficial bleeding air usually does not enter the circulation in substantial amounts, if at all. Small gas bubbles that may arise in the circulation are easily absorbed and do not produce any symptoms. In order for an air embolism to occur, the following two conditions need to exist :
- Point of entry for air into the bloodstream.
- Sufficient pressure to allow the air to enter the bloodstream.
These two conditions are more likely to exist in intravenous (IV) catheterization and similar procedures that forces fluid, and accidentally air, into the bloodstream.
Venous Air Embolism Location
Air can enter the body through any blood vessel. A venous air emoblism is a bubble of air in the veins which returns oxygen-deficient blood to the right side of the heart. The site at which the air enters the system is dependent on the cause. The more significant factor in terms of location is that the closer the point of entry to the right side of the heart, the lower the quantity of air that is needed to cause serious and even life threatening complications.
Venous Air Embolism Quantity
As previously mentioned, small quantities of air in the circulation may be absorbed and will not cause any symptoms. It is also less likely to cause serious complications if it is distant from the right side of the heart and blood vessels of the brain.
It is known that if as little as 20mL (milliliters) of air into the vein can cause complications. Even smaller volumes of air can cause complications depending on where it gains entry into the venous circulation. About 2 to 3mL of air can be dangerous in the circulation of the brain. As little as 0.5mL can cause complications if it enters into the coronary arteries.
Venous Air Embolism Causes
A venous air embolism is more likely to arise in patients undergoing neurosurgical (brain and spinal cord) and otolaryngological (ear, nose and throat) procedures. However, it can occur with any head and neck and upper chest surgery. Procedures that are done in the sitting position hold the greatest risk for a venous air embolism.
Obstetric and gynecological procedures
A cesarean section (C-section) and laparoscopic gynecological procedures also hold a risk of venous air embolism occurring as a complication. Although there is a high risk, it is not a common occurrence. Venous air embolism in these instances may also be fatal often during the procedure.
Apart from surgery, there are several other situations in hospital where a venous air embolism may arise. This includes during :
- central venous catheterization
- peripheral venous lines
- lumbar puncture
It is more likely to occur with unskilled insertion and removal of the needle, faulty sealing valves, breakage or detachment of the catheter and failure of the soft tissue to close after removal of the needle.
Sometimes air is blown into a body cavity for the purpose of distending an organ and inserting a surgical or diagnostic piece of equipment. This is seen with endoscopes inserted into the joint (arthroscopy), abdomen (laparoscopy), uterus (hysteroscopy) or bladder (cystocopy). This is known as air insufflation.
Sometime air can be mistakenly injected the blood vessels during an intravenous injection of contrast dyes for various diagnostic imaging techniques. It is more likely to happen with catheterization than the use of a syringe and needle.
Mechanical positive pressure ventilation can also cause air to enter the bloodstream through the lungs. However, the lung tissue has to be damaged for this to occur.
Venous Air Embolism Symptoms
An air embolism can be asymptomatic if it is a small volume of air and enters the bloodstream a distance away from the heart and head. Symptoms arise as a result of the the air bubble causing an obstruction in a vessel thereby blocking the flow of blood. The heart also has to work harder and faster. The symptoms are therefore a consequence of these effects.
The symptoms that may be seen include :
- Difficulty breathing
- Dizziness or lightheadedness
- Chest pain
- Occasional gasping
In addition, there are various signs showing disruption in the heart activity, breathing, brain and nerves, eyes and skin. However, these clinical signs, as is the case with the symptoms mentioned above, are not specific for venous air embolism.
Venous Air Embolism Diagnosis
The symptoms and clinical signs alone are insufficient for a diagnosis because a venous air embolism appears similar to so many other conditions which are more common. Blood tests may show abnormalities in the oxygen and carbon dioxide levels as well as the pH but here as well, none of these features are specific for a venous air embolism.
Imaging studies are the best diagnostic investigations to confirm the presence of air bubbles in the venous circulation. These tests include :
- Transesophageal echocardiography (TEE)
- Doppler ultrasound
- Chest x-ray
- Computed tomography (CT) scan
- Magnetic resonance imaging (MRI)
Venous Air Embolism Treatment
Supportive measures should be instituted as soon as possible. This includes :
- Lying in the left lateral decubitus position (lying on the left side). This is done to prevent the air bubbles from entering the right side of the heart.
- Administer 100% oxygen to increase blood oxygenation. This may also help reduce the size of the air bubble.
- Fluid resuscitation to increase blood volume and possibly force the return of blood should the air bubble cause an obstruction.
- Administration of drugs known as vasopressors.
- Mechanical ventilation if necessary.
Removing the air bubble
Although the supportive measures above stabilizes the patient and prevents life-threatening complications, it can also help to remove the air bubbles. More decisive measures for treating an air embolism includes :
- Aspiration from the right atrium in a bid to directly remove the air bubble.
- Hyperbaric oxygen therapy to compress air bubbles as well as the benefits of oxygen therapy as a supportive measure.
- Cardiopulmonary resuscitation (CPR) may break large air bubbles.