An air embolism occurs when air bubbles enter the bloodstream, creating a blockage that can disrupt normal blood flow and lead to serious health issues. The amount of air that constitutes a danger is complex, as severity depends on various factors beyond just volume. This article explores air embolisms and the circumstances that make them dangerous.
Understanding Air Embolisms
Air can enter the bloodstream through various means, often during medical procedures, traumatic injuries, or diving incidents. During medical procedures like IV insertions, central line care, or surgery, air can be drawn into the circulatory system if a blood vessel is open and pressure conditions allow. Significant trauma exposing large veins can also allow air to enter. In diving, rapid ascent while holding one’s breath can cause lung tissue to rupture, allowing air bubbles to enter the bloodstream.
Once air enters the bloodstream, it travels through the circulatory system. If the air enters a vein (venous air embolism), it typically moves towards the right side of the heart and then into the pulmonary arteries. Large air bubbles can obstruct blood flow in the lungs, leading to increased pressure in the pulmonary system. If air enters an artery (arterial gas embolism), it can directly block blood flow to vital organs like the brain or heart, causing immediate and severe complications.
The Critical Threshold
Determining a universally “dangerous” amount of air for an air embolism is not straightforward, as several factors influence the outcome. The volume of air is a primary consideration, with small amounts often being absorbed without symptoms, especially in the venous system. However, human case reports suggest that injecting more than 100 mL of air into the venous system can be fatal. Some sources estimate a lethal dose in adults to be between 200 and 300 mL, or approximately 3 to 5 mL per kilogram of body weight, although fatalities have been reported with as little as 50 mL in the venous system. In the arterial system, much smaller volumes are hazardous; as little as 2 mL of air in the cerebral circulation can be fatal, and 0.5 mL in a coronary artery can cause cardiac arrest.
The rate at which air enters the bloodstream significantly impacts severity, with rapid entry being more dangerous than slow entry because it overwhelms the body’s ability to absorb the gas. The location where the air enters and its eventual destination also play a role. Venous air embolisms are generally considered less serious than arterial ones because the lungs can often filter out smaller bubbles. However, if a venous air embolism is large enough or if a person has a heart defect like a patent foramen ovale (PFO), air can cross from the right side of the heart to the left, becoming an arterial embolism and traveling to the brain or other organs. Approximately 20-30% of the population has a PFO, increasing vulnerability.
A patient’s overall health also influences the impact of an air embolism. Individuals with underlying heart conditions or lung diseases may be more susceptible to severe outcomes. The patient’s position during a medical procedure can also affect risk; for example, surgeries performed with the patient in a seated position can increase the risk due to pressure differences.
Recognizing and Responding to an Air Embolism
Recognizing the signs of an air embolism is important for prompt intervention. Symptoms can vary widely depending on where the air travels in the body. Common signs include sudden shortness of breath, chest pain, and a rapid drop in blood pressure. Neurological symptoms such as dizziness, confusion, vision changes, or paralysis can occur if the air reaches the brain. A distinctive sign, particularly in venous air embolisms, can be a “mill-wheel murmur,” a splashing or churning sound heard over the heart with a stethoscope.
If an air embolism is suspected, immediate medical attention is necessary. The first priority is to contact emergency services. While waiting for professional help, positioning the patient can be beneficial.
For a suspected venous air embolism, placing the patient in the left lateral decubitus position (lying on the left side) with the head lowered can help trap air in the right ventricle. For an arterial air embolism, a supine (flat on the back) position is generally advised. Administering 100% high-flow oxygen can also help reduce the size of the air bubbles. It is important not to attempt to treat the embolism yourself, as specialized medical procedures like hyperbaric oxygen therapy are often required.
Preventing Air Embolisms
Preventing air embolisms involves careful adherence to safety protocols, especially in situations where air entry into the bloodstream is a possibility. In medical settings, trained professionals follow strict guidelines during procedures such as IV insertions, central line placements, and surgeries. This includes removing air from syringes and IV tubing before administration and securing all connections. During central venous catheter insertion or removal, patients may be positioned supine with their head lowered, and can be asked to hold their breath or perform a Valsalva maneuver to increase central venous pressure and reduce the risk of air entry.
For divers, proper technique and awareness are important to preventing air embolisms. Avoiding rapid ascents while holding one’s breath is an important rule, as this can lead to lung overexpansion and subsequent air entry into the bloodstream. Divers should ascend slowly, perform safety stops, and breathe normally throughout the ascent to allow gases to off-gas safely. Utilizing dive computers or tables helps maintain safe ascent rates and appropriate surface intervals between dives.