Arterial Gas Embolism (AGE)

A life-threatening injury in which gas from an overexpanded lung enters the arteries and blocks blood flow, often striking within minutes of surfacing.

An arterial gas embolism happens when gas bubbles enter the arterial bloodstream and lodge in small vessels, cutting off blood flow downstream. In diving, the usual source is lung overexpansion: a diver holds their breath or ascends with a blocked airway, expanding air ruptures alveoli, and gas is forced into the pulmonary veins, through the heart, and out into the arteries. Bubbles reaching the brain cause the most dramatic form, cerebral AGE, which behaves like a sudden stroke.

The signature of AGE is speed. Symptoms typically appear within minutes of surfacing, often before the diver is even back on the boat: sudden unconsciousness, paralysis or weakness on one side, seizures, confusion, vision loss, or bloody froth at the mouth. Any diver who surfaces and rapidly loses consciousness should be treated as an AGE until proven otherwise. First aid is basic life support and 100 percent oxygen, with an immediate call to DAN to arrange transport to a hyperbaric chamber, since recompression is the definitive treatment and every minute counts.

Prevention is the first rule of scuba: never hold your breath, and ascend slowly with a normal, open airway. Even a shallow pool ascent from 1 to 2 m can cause AGE, depth is not required. Divers with lung conditions that trap air, like some forms of asthma or prior spontaneous pneumothorax, need a dive medical evaluation before training for exactly this reason.