Air Embolism: What It Is, Why It Is an Emergency, and How It Is Treated

Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: September 2026

TL;DR

An air embolism happens when an air or gas bubble enters a vein or artery and blocks blood flow or triggers dangerous inflammation. Most cases occur as a rare complication of medical procedures — catheter placement, surgery, hemodialysis — while divers can develop one after surfacing too quickly. Symptoms such as chest pain, sudden drop in blood pressure, confusion, or paralysis require immediate emergency care. Treatment begins with 100% oxygen and sometimes hyperbaric oxygen therapy.

Quick Answer

An air embolism is a rare but life-threatening condition in which an air bubble enters a blood vessel and blocks circulation or injures tissue [1]. It most often occurs as a complication of medical procedures such as central venous catheter placement, surgery, or hemodialysis; in divers, it follows rapid ascent that tears the lungs' air sacs [1] [2]. Symptoms — chest pain, sudden low blood pressure, irregular heartbeat, confusion, or sudden paralysis — are always an emergency. Treatment starts immediately with high-flow oxygen and, for serious arterial cases, hyperbaric oxygen therapy; small venous bubbles are usually absorbed by the body harmlessly [1] [4].

What Exactly Is an Air Embolism?

An air embolism — also called a gas embolism — is a bubble of air or gas that enters a vein or artery and travels through the bloodstream [1]. The bubble can block blood flow the way a clot does, cutting off oxygen to the heart, brain, or other organs. Even when a bubble does not fully block a vessel, it triggers inflammation in the blood vessel wall that can damage surrounding tissue [1].

Air embolisms are rare overall. Most occur as a complication of medical procedures — surgeries, catheter placements, and vascular interventions. Deep-sea divers can develop them when they surface too quickly, because falling pressure lets expanding gas damage the lungs' air sacs [1].

There are two main types, and the distinction matters greatly for severity [1]:

Type	What Happens	Severity
Venous gas embolism (VGE)	Air enters a vein and travels toward the heart and lungs	More common than arterial; still rare. Most small venous bubbles cause no symptoms and are absorbed by the body [1]
Arterial gas embolism (AGE)	Air enters an artery or reaches the arteries, often affecting the brain or heart	Rare, but life-threatening. Even small bubbles can cause stroke or cardiac arrest [1]

The route matters. Venous bubbles usually pass through the heart and get trapped in the lungs, where the body can filter them out through breathing [1]. Arterial bubbles travel with the blood flow to the brain, heart, and other organs — which is why arterial embolisms are the dangerous form [2].

Why Are All Air Embolism Symptoms an Emergency?

Every air embolism symptom is treated as an emergency because a moving bubble can block blood flow to a vital organ within seconds, and because the bubble itself provokes inflammation that damages blood vessels [1]. The recognized emergency symptoms include [1]:

• Irregular heartbeat

• Sudden drop in blood pressure

• Rapid, shallow breathing

• Chest pain

• Coughing up blood

• Headache

• Confusion or dizziness

• Vision changes

• Paralysis in one area of the body

• Loss of consciousness

Because the bubble keeps moving, a patient can appear stable one moment and deteriorate quickly the next. That is why emergency guidance for any suspected air embolism is the same: call emergency services immediately. Do not wait to see whether symptoms improve [1].

How Big an Air Bubble Is Actually Dangerous?

Not all air entering the bloodstream is dangerous. Small venous bubbles are common during many procedures and are usually harmless — the body filters them out through the lungs and breathes them out [1] [3]. Danger begins when bubbles become large enough to obstruct circulation.

The published lethal-volume estimates put the threshold in concrete terms [2]:

Measure	Estimate
Lethal air volume	3–5 mL of air per kg of body weight [2]
Estimated fatal dose	300–500 mL of gas introduced at 100 mL per second [2]
For a 70 kg (154 lb) adult	Roughly 210–350 mL of air [2]
Small venous bubbles	Common, usually absorbed without symptoms [1]

Context helps. A standard 10 mL syringe holds far less than a lethal volume, which is one reason central venous catheterization — where larger amounts of air can theoretically enter — is managed with specific precautions. And some gases dissolve far faster than others: carbon dioxide and nitrous oxide bubble sizes shrink quickly, while room-air nitrogen persists longer, which affects both risk and treatment urgency [1].

What Causes an Air Embolism?

The two classic scenarios are medical procedures and diving, though trauma can also be responsible [1]:

• Medical procedures (the majority of cases). Central venous catheterization — including PICC lines and implanted ports — is a leading cause, along with arterial catheterization, lung biopsy, removal of fluid from the chest, cesarean section and other gynecological procedures, cardiopulmonary bypass surgery, head and neck or brain surgery, hemodialysis, contrast dye injection, and mechanical ventilation [1].

• Diving. Rapid ascent causes expanding gas to rupture the lungs' air sacs, and the freed gas enters the arterial circulation [1] [3].

• Trauma. Blunt or penetrating chest injury can introduce air into the circulation [1].

One large 25-year review of 67 air embolism cases at a single center found that 94% occurred in-hospital and 77.8% happened during an operation or invasive procedure, with vascular access procedures (33% of cases), central vascular access, and open neurosurgery among the most common single triggers [4].

Cause Setting	Examples	Notes
Vascular access	Central venous catheter placement/removal, PICC lines, ports	Leading procedural cause; incidence during CVC placement reported from 0.03%–2% [4] [5]
Major surgery	Cardiopulmonary bypass, head/neck/brain surgery (especially seated position), C-section	Seated position raises risk because the surgical site sits above the heart [1] [4]
Cardiac procedures	Cardiac catheterization, bypass	Significant intracoronary air embolism ~0.2% overall [2]
Dialysis and ventilation	Hemodialysis circuits, mechanical ventilation	Air can enter through circuit disconnections [1]
Diving	Rapid ascent, breath-holding during ascent	Can occur in as little as six feet of water [3]
Trauma	Blunt or penetrating chest injury	Rare [1]

Why Does Position and Heart Anatomy Matter?

Two anatomical factors determine how dangerous a venous bubble becomes. First, body position: surgeries performed with the head elevated — such as some brain and head-and-neck operations — create a pressure difference between the surgical site (above the heart) and the heart itself, which can draw air into open veins [1]. Second, heart anatomy: roughly one in four people has a patent foramen ovale (PFO), a small flap-like opening between the heart's two upper chambers [1].

A venous bubble that reaches the right side of the heart can cross through a PFO (or an atrial septal defect or ventricular septal defect) into the left side of the heart and out into the arteries — a route called a paradoxical embolism. In one case series, a PFO was identified in 77% of suspected paradoxical cases [4]. This is why a "venous" air embolism can still end up causing a stroke [1] [2].

What Happens if an Air Embolism Goes Untreated?

Untreated or under-treated air embolisms can be fatal, and even survivors can carry lasting injury [1]. Documented complications include cardiac arrest, heart failure, heart muscle damage (myocardial ischemia), stroke, and temporary or permanent neurological problems affecting vision, movement, or causing seizures [1].

The outcomes data from the largest published case reviews are sobering but also hopeful when treatment arrives quickly [4]:

Outcome Measure	Finding
Mortality (single-center, 67 cases, 25 years)	21% [4]
Mortality when immediate cardiac arrest occurred	53.8% vs 13.5% without arrest [4]
Timing of deaths	69% of deaths occurred within 48 hours [4]
Patients with no lasting effects	63% [4]
Patients who received hyperbaric oxygen therapy	21% [4]
Full recovery after hyperbaric oxygen (441 cases, 2013 review)	78% (346 of 441) [6]

The pattern is clear: when a patient arrests immediately, mortality roughly quadruples, and most deaths come within two days. Rapid recognition and treatment are the decisive factors [4].

How Is an Air Embolism Diagnosed?

In practice, most air embolisms are diagnosed in the moment — the patient is already in a hospital, often on the operating table or undergoing a procedure, when symptoms appear [1] [4]. Providers respond to the symptom picture and vital-sign changes: sudden drops in blood pressure, oxygen levels, or end-tidal CO2 on the monitor can signal air in the circulation [1] [4].

Diagnostic Step	What It Involves
Rapid symptom assessment	Sudden chest pain, low blood pressure, irregular heartbeat, neurological signs during or after a procedure [1]
Continuous monitoring	Oxygen saturation, blood pressure, ECG, end-tidal CO2 — often how the embolism is first detected [1] [4]
Imaging during high-risk procedures	Used selectively in high-risk surgeries to detect air in real time [1]
Echocardiography	Can visualize bubbles in the heart chambers [2]
CT or MRI of the brain	Assesses stroke-like damage in arterial cases [2]
PFO screening	Bubble-contrast echocardiogram when a paradoxical route is suspected [4]

It is worth noting that many small venous air embolisms never cause symptoms and never come to medical attention at all, which is one reason published incidence figures are likely underestimates [4].

How Is an Air Embolism Treated?

Treatment is immediate and proceeds while the exact picture is still being confirmed. The first move is to call for emergency help — for in-hospital cases, that means activating the team within seconds [1].

The core treatment steps are [1]:

• 100% high-flow oxygen, delivered through a nasal cannula or face mask, or inside a hyperbaric chamber. High-concentration oxygen shrinks the nitrogen bubble and restores tissue oxygenation [1].

• Specific body positioning to help move the bubble away from the heart's outflow tract (protocols differ by suspected type and are performed by the care team) [1].

• Maintaining the airway, blood pressure, and breathing with whatever lifesaving measures the situation requires — including CPR if the heart stops [1].

• Care for complications, such as stroke treatment or heart-support medications [1].

For serious arterial cases — the diving-related type and major procedural accidents — hyperbaric oxygen therapy is the definitive treatment: the patient breathes 100% oxygen at high pressure inside a specialized chamber, which physically compresses the bubble and forces oxygen into starved tissue. In one large review of 441 hyperbaric-treated cases, 78% recovered fully [6].

Small venous embolisms often need no specific treatment at all. The body typically absorbs them — the bubbles reach the lungs, get trapped in the lung's fine filter network, and are eliminated through breathing [1].

What Determines the Outlook?

Prognosis depends on several interacting factors rather than any single one [1]:

Factor	Why It Matters
Bubble size	Larger bubbles cause more obstruction [1]
Type of gas	Room air persists; CO2 and nitrous oxide dissolve faster [1]
Body position at the event	Affects where the bubble travels [1]
Body system affected	Heart and brain involvement carry the highest risk [1]
Speed of treatment	Rapid oxygen and hyperbaric therapy are the strongest survival factors [1] [6]

The aggregated data point to a workable summary: in one large modern case series, 63% of patients had no lasting effects and overall mortality was 21%, with the worst outcomes concentrated in patients who suffered immediate cardiac arrest [4]. In diving cases treated promptly with hyperbaric oxygen, full recovery is the norm rather than the exception [6].

How Can You Reduce the Risk?

For patients, the practical guidance focuses on trusting clinical protocols and knowing when to speak up [1] [2] [3]:

• Know that your care team already has precautions. Central line placement, dialysis circuits, and operating rooms follow strict anti-air protocols; serious air embolisms are rare precisely because these systems work [4].

• Ask questions about high-risk procedures. If you are having surgery in a seated position, brain surgery, or prolonged hemodialysis, ask your team what safeguards are in place [1].

• As a diver, ascend slowly and never hold your breath. Air embolism can occur in as little as six feet of water and does not depend on long, deep dives — a single breath-holding ascent is enough [3].

• Get certified and dive within your training. The recreational scuba fatality rate is steady at roughly 2 per 100,000 dives, and most deaths cluster around recognized diving errors [3].

• Know the warning signs after a dive. Confusion, paralysis, chest pain, or loss of consciousness within minutes of surfacing is a 911-level emergency — mention the dive to responders, since hyperbaric treatment is time-sensitive [1] [3].

Key Takeaways and What to Do Next

An air embolism is rare, but it is one of the emergencies where minutes determine outcomes. If you are in or near a medical facility and someone develops chest pain, sudden low blood pressure, irregular heartbeat, confusion, or paralysis during or shortly after a procedure, treat it as an emergency and make sure the team knows to act on it immediately. If you dive, protect yourself with the fundamentals — slow ascent, never hold your breath, dive within your training — and if symptoms appear after surfacing, get to emergency care and state clearly that you have been diving, because hyperbaric oxygen therapy is the definitive treatment and it works best when started early.

Whether you are a patient facing a high-risk procedure or a diver heading out this season, take one action today: know the ten warning signs and know that fast, specific treatment — 100% oxygen and hyperbaric therapy — is what saves lives. Talk to your care team or dive operator about what is already in place, and make sure the people around you know how to respond.

Frequently Asked Questions

1. What is an air embolism? An air embolism is a bubble of air or gas that enters a vein or artery and blocks blood flow or injures tissue by triggering inflammation. It is rare overall but life-threatening when bubbles reach the heart or brain.

2. Is an air embolism the same as the "bends" (decompression sickness)? No, though divers can get both. Decompression sickness comes from nitrogen absorbed in body tissues during a dive. Air embolism (arterial gas embolism) comes from lung air sacs tearing during rapid ascent — it can happen in as little as six feet of water, on a very short dive.

3. Can a small syringe of air injected into a vein kill me? Most small air amounts entering a vein are harmless — the body filters them out through the lungs and breathes them out. Published estimates put the lethal dose around 3–5 mL of air per kg of body weight (roughly 210–350 mL for a 154 lb adult), far more than a small injection. Still, central venous catheters are managed with strict air precautions precisely because they are the main procedural entry route.

4. Why is every air embolism symptom an emergency? Because a moving bubble can block blood flow to the heart or brain at any moment, and bubbles also inflame blood vessel walls. Symptoms include chest pain, sudden low blood pressure, irregular heartbeat, confusion, paralysis, and loss of consciousness — call 911 immediately if these appear after a procedure or a dive.

5. How is an air embolism treated? Immediately with 100% high-flow oxygen, specific body positioning, and airway/blood-pressure support. Serious arterial cases receive hyperbaric oxygen therapy in a pressurized chamber, which shrinks the bubble and restores oxygen; in one review of 441 hyperbaric-treated cases, 78% recovered fully.

6. How common are air embolisms? They are rare. One prospective figure is 2.65 cases per 100,000 hospitalizations, and a 25-year center review found 94% of its 67 cases occurred in-hospital during operations or invasive procedures. In divers, arterial gas embolism occurs in roughly 0.4–1 per 100,000 dives.

7. Can a venous air bubble cause a stroke? Yes. About one in four people has a patent foramen ovale (PFO) — a small opening between the heart's upper chambers. A venous bubble can cross through a PFO into the arteries and travel to the brain. PFOs were found in 77% of suspected paradoxical cases in one series.

8. How long after a dive can air embolism symptoms appear? Neurological symptoms from diving-related arterial gas embolism typically appear within 10 minutes of surfacing, but delayed presentations are reported. Any neurological or chest symptom after a dive should be treated as an emergency, and responders should be told you have been diving.

References

1. Cleveland Clinic. "Air Embolism." Medically reviewed; last updated 08/07/2025. https://my.clevelandclinic.org/health/diseases/air-embolism

2. Alexander AM, Sankari A, Martin N. "Arterial Gas Embolism." StatPearls, National Institutes of Health. Last update: February 12, 2024. https://www.ncbi.nlm.nih.gov/books/NBK546599/

3. Penrice D, Cooper JS. "Diving Casualties." StatPearls, National Institutes of Health. Last update: November 28, 2022. https://www.ncbi.nlm.nih.gov/books/NBK459389/

4. McCarthy CJ, Behravesh S, Naidu SG, Oklu R. "Air Embolism: Diagnosis, Clinical Management and Outcomes." Diagnostics, 2017;7(1):5. https://pmc.ncbi.nlm.nih.gov/articles/PMC5373014/

5. Gordy S, Rowell S. "Vascular Air Embolism." International Journal of Critical Illness and Injury Science, 2013;3(1):73-76. https://pmc.ncbi.nlm.nih.gov/articles/PMC3665124/

6. Gordy S, Rowell S. "Vascular Air Embolism" (hyperbaric treatment outcomes, 441 cases). International Journal of Critical Illness and Injury Science, 2013. https://pubmed.ncbi.nlm.nih.gov/23724390/

7. Kerrigan MJ, Cooper JS. "Venous Gas Embolism." StatPearls, National Institutes of Health. Last update: October 3, 2022. https://www.ncbi.nlm.nih.gov/books/NBK482249/

8. Malik N, et al. "Air Embolism: Diagnosis and Management." Future Cardiology, 2017;13(4):365-378. https://pubmed.ncbi.nlm.nih.gov/28644058/

9. MSD Manual Consumer Version. "Arterial Gas Embolism." Revised June 2025. https://www.msdmanuals.com/home/injuries-and-poisoning/diving-and-compressed-air-injury/arterial-gas-embolism

10. Medscape eMedicine. "Central Venous Catheterization, Air Embolism Complications." https://emedicine.medscape.com/article/116716-overview

Health information, not medical advice. This article is for general education and is not a substitute for professional diagnosis or treatment. Always consult a qualified healthcare provider about your own health, and seek emergency care for urgent symptoms.