An air embolism, or more accurately, a gas embolism, occurs when one or more gas bubbles enter a vein or artery. This can block the passage of blood, and it can be life-threatening.
Depending on where the blockage occurs, symptoms and severity vary. Air embolism is one of the leading causes of death in the diving community.1
Air embolism can be caused by a number of factors – most commonly diving – but certain medical procedures can also cause gas bubbles in the blood. The exact prevalence of air embolisms is not known; more minor cases may go untreated and can be without symptoms.
This article will look at the causes, symptoms and diagnosis of air embolism. It will also include ways to avoid the condition when diving.
An embolism, in general, refers to anything untoward that has become trapped within the vascular system.
An air embolism, specifically, is a bubble, or bubbles, of gas trapped within the blood vessels. The bubbles will, at some point, cut off the blood supply to a particular area of the body.
Air embolism can easily cause significant and permanent damage to the central nervous system and as such must be treated as an emergency.
A venous embolism is not as serious as an arterial embolism, which is itself not as serious as a cerebral embolism. However, all of the above have the potential to cause severe damage to organs and systems if left unchecked.2
Some medical procedures can cause small amounts of air to enter the venous system; via an intravenous drip, for instance. In general, these are stopped at the lungs and do little or no harm. In rare cases, they can reach the heart and disrupt its workings.
Arterial gas embolisms are much more serious. The embolism might potentially prevent oxygenated blood from reaching the target organ and cause ischemia (an inadequate blood supply to an organ); if the heart is affected it can produce a heart attack.
If an arterial gas embolism reaches the brain, it is referred to as a cerebral embolism and can cause a stroke.
An injection of 2-3 ml of air into the cerebral circulation can be fatal. Just 0.5-1 ml of air in the pulmonary vein can cause a cardiac arrest.3
As mentioned, some medical procedures can allow small amounts of air to enter the body; this can be serious, but it happens rarely. The vast majority of air embolism cases involve diving.
In fact, air embolism is the most common cause of death among divers.
There are two ways in which an air embolism can form in response to a dive; both occur during the ascent but via two different processes:
- Decompression sickness: also known as “the bends,” an embolism can occur when a diver surfaces too rapidly. As a diver descends, their body, along with the gas they are breathing (oxygen and nitrogen) is under increasing pressure. The diver constantly uses the oxygen, but the nitrogen pools in the diver’s tissues.
If the diver returns to the surface too swiftly, the nitrogen is not given the chance to be reabsorbed into the blood and will leave the tissue as bubbles of gas.
A good analogy to help understand this process involves a bottle of carbonated soda. When the bottle is sealed, the carbon dioxide cannot be seen because it is under pressure. However, if the pressure is quickly released by opening the cap, the carbon dioxide forms into readily visible bubbles.
If the cap is slowly released in stages, the bubbles will not form.
- Pulmonary barotrauma: if a diver holds their breath during a rapid ascent, trauma can be caused to the lining of the lungs. As the pressure decreases during the ascent, the volume of the air in the lungs increases. If the breath is held voluntarily, the small air sacs of the lungs (alveoli) can rupture. These tears can allow gas to pass into the blood.
Other causes of air embolism can be iatrogenic (caused by a medical intervention). These can include:
- Intravenous drip: most commonly via disconnected central venous catheterization
- Hemodialysis: treatment for kidney failure
- Laparoscopic insufflations: otherwise known as keyhole surgery, air is sometimes pumped into the space between the organs and the skin to clear a passage for the surgeon to work
- Open heart surgery
- Lung biopsy: removal of a section of lung for examination
- Radiologic procedures: specifically where the injection of dye is necessary
- Childbirth: particularly cesarean section
- Endoscopic retrograde cholangiopancreatography (ERCP): a procedure designed to examine the pancreatic and bile ducts, ERCP involves injecting a dye into the region via an endoscope.4
No accurate figures are known for the prevalence of air embolisms due to surgical procedures. Some estimate that vascular air embolism occurs in anything from 10-80% of neurosurgeries and 57% of orthopedic surgeries.5
For air to move from the atmosphere to the blood system, the pressure gradient has to be such that air entering the site is favored. In general, the pressure in blood vessels is greater than the surrounding atmospheric pressure. Therefore, a normal wound will not allow for gas to enter.
However, in the head or neck region, the pressure is less than the atmospheric pressure; injuries at these sites can cause air embolisms. For this reason, operations on the head and neck are more likely to cause iatrogenic air embolisms.
Signs and symptoms of air embolism can include the following6:
- Pain in the joints or muscles
- Irregular heart rhythms
- Blurring of vision
- Itchy skin
- Bloody frothing from the mouth
- Low blood pressure and dizziness
- Difficulty catching breath
- Chest pain
- Extreme fatigue
- Loss of coordination
- Visual or auditory hallucinations
- Nausea or vomiting
- Cyanosis (faint blue coloration of the skin)
- Paralysis or weakness of the extremities, or one or more limbs
- Loss of consciousness.
If a scuba diver is seen to develop these symptoms within 10-20 minutes of a dive, they should lie horizontally, receive 100% oxygen and be taken to a hospital – preferably one with a recompression chamber.
The most clinically important factor in diagnosing an air embolism is the patient’s history. The symptoms themselves could be a manifestation of a number of disorders; however, a recent diving expedition or surgical procedure might point to an air embolism.
The surgical procedures that hold the biggest risk of air embolism are craniotomy performed with the patient in the sitting position, cesarean section, hip replacement and cardiac surgery with cardiopulmonary bypass.
If an air embolism is a possibility or a risk, the following procedures might be carried out during or after surgery:4
- Chest X-Ray: gas bubbles can sometimes show up on X-rays
- Stethoscope: to the trained ear, a “millwheel” murmur can sometimes be detected
- Change in gases: if the patient is under anesthetic and still being monitored, the anesthesiologist may be able to detect a decrease in the amount of carbon dioxide released at the end of an expiration
- Doppler ultrasonography: this non-invasive procedure estimates blood flow through the vessels by bouncing high-frequency sound waves off circulating red blood cells. This procedure is often used during operations with a high risk of air embolism
- Transesophageal echocardiography: this method uses sound to produce a highly detailed image of the heart and the vessels that lead to it.
If the air embolism has been caused by diving, the only choice is immediate recompression treatment in a hyperbaric chamber. The diver will lie vertically and breathe a mixture of gases at high pressure.
This will restore normal blood flow and reduce the size of the embolism. The pressure forces the nitrogen to be reabsorbed into the blood stream.
The treatment will take a number of hours as the pressure is slowly decreased in the chamber, mimicking a slow diving ascent. Depending on the severity of the condition, the treatment may continue for several days.
Other treatments for air embolism
If the air embolism is iatrogenic in nature or due to trauma and a large bubble of air is trapped in the heart, the patient may be placed in certain positions to help prevent further damage:
- Trendelenburg position: lying on their back with their pelvis above their head
- Left lateral decubitus: lying on the left side in an effort to trap the air next to the right ventricular apex; this prevents or minimizes the obstruction of the pulmonary artery.
The patient will also receive a high oxygen percentage gas mix. This accelerates the reduction in bubble size and helps reverse the ischemia. Recompression can be helpful whether the air embolism is iatrogenic or due to diving.
Diving is the most common cause of air embolisms. The following list can help prevent their occurrence:
- Limit the duration and depth of dives
- Always surface slowly and use safety stops to allow gases to be safely and naturally reabsorbed
- Never dive with a cold or a cough
- Show extra caution if diving in particularly cold water7
- Avoid alcohol consumption before and after diving
- No vigorous activity before, during or after a dive
- Remain on the surface for adequate time between dives
- Keep hydrated before diving
- Leave at least 24 hours before going to a higher altitude, e.g. mountain climbing or a flight.