Decompression illness (DCI) is a general term used to describe two potentially serious diving-related conditions:
Both result from gases coming out of solution inside the body due to pressure changes, but they have different mechanisms and symptoms. DCI is the term often used in emergency medicine and dive safety training to capture both conditions under one umbrella.
Don’t worry about whether it’s DCS or AGE—the initial treatment is exactly the same. Do it immediately. Worry about the diagnosis later.
This is the same approach whether they have joint pain, tingling, paralysis, or collapse at the surface. Early oxygen and fast transport are your best chance to prevent lasting injury.
DCS occurs when inert gas (mostly nitrogen) absorbed into tissues under pressure forms bubbles during or after ascent. These bubbles can cause local tissue damage, inflammation, and interference with blood flow.
AGE is caused by gas bubbles entering the arterial bloodstream, typically due to lung overexpansion injuries during ascent. It is considered a more acute and immediately life-threatening form of DCI.
Note: AGE can occur even in shallow water if a diver surfaces too quickly while holding their breath.
A patent foramen ovale (PFO) is a small hole between the right and left atria of the heart. In about 25 percent of adults, it never fully closes after birth.
Under normal conditions, venous gas bubbles are filtered out by the lungs. But with a PFO, bubbles can bypass the lungs and enter arterial circulation directly, increasing the risk of neurological DCS or stroke-like symptoms.
DCI is rare but serious. It can affect any diver, not just technical divers or those pushing the limits. Understanding the differences between DCS and AGE, and knowing how a PFO can complicate risk, makes you a more informed, safer diver.
You can follow every dive table, computer, and safety stop perfectly—and still get hit. These are called undeserved hits, and while they are uncommon, they do happen. Factors like hydration, exertion, temperature, microbubbles, or undiagnosed medical conditions (like a PFO) may contribute.
That’s why it matters who you dive with and how prepared you are:
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