Pulmonary Barotrauma & AGE

What this is about

Pulmonary barotrauma (PBT) is a lung injury, and arterial gas embolism (AGE) is its most dangerous consequence. Together they are one of the few diving emergencies measured in minutes, not hours. The good news is that the single most effective prevention is the first rule every diver is ever taught.

How a held breath tears a lung

Boyle's law is the whole mechanism: as pressure drops on the way up, the gas in your lungs expands. From 10 m to the surface, the pressure roughly halves, so that gas tries to double in volume. Your chest cannot expand that much, so if your airway is shut, the lung tissue tears instead of stretching.

The cruel part is that the expansion is not spread evenly up the water column. It is worst in the shallows. Going from 30 m to 20 m, the gas grows about a third. Going from 10 m to the surface, it doubles, and from 5 m up it is still expanding fast. The last few metres, exactly where new divers relax and pop up, are the most dangerous part of the whole ascent. A held-breath ascent from the deep end of a 4 to 5 m pool has caused fatal embolism; "shallow" is not "safe."

It takes surprisingly little overpressure to do this: on the order of 80 mmHg across the lung wall (Germonpré et al 2008), which a breath held through an ascent of barely a metre or two can produce if the lungs are already full. The valve that traps the air is usually the glottis (the valve at the top of your windpipe) clamping shut, in a breath-hold or a panic.

Pre-existing lung problems (cysts, blebs, or asthma that traps air) lower the threshold further. But published case series consistently document PBT in divers with completely normal lungs and normal chest X-rays (van Hulst & van Ooij 2024; Germonpré et al 2008; Acott 2002). A healthy lung is not immune: when a full breath is held through a real pressure change, the physics tears it regardless.

When the alveoli (the lungs' tiny air sacs) rupture, gas escapes into the surrounding structures:

• Pneumothorax: gas in the chest cavity, which can collapse the lung.
• Mediastinal emphysema: gas tracking into the centre of the chest.
• Subcutaneous emphysema: gas migrating to under the skin of the neck and chest.

These range from clinically minor to immediately fatal.

How arterial gas embolism happens

If the rupture is next to a pulmonary vein, gas is carried straight into the arterial blood leaving the lungs. From there it goes to the left side of the heart and out into the body's arteries, where bubbles can block the vessels feeding the brain, heart, or spinal cord.

That is arterial gas embolism (AGE), and it is fast. Symptoms appear within minutes of surfacing, long before any decompression-sickness mechanism could be active. The picture is stroke-like: sudden loss of consciousness, seizures, one-sided weakness or speech trouble, visual loss, profound confusion. If the bubbles reach the heart's own arteries, they can cause a dangerous rhythm or arrest. The window between injury and permanent damage is measured in minutes.

Who is at risk

• Any diver ascending while breath-holding, even from shallow water.
• Divers who stop breathing under stress or when low on gas, then bolt for the surface.
• Divers with air-trapping lung conditions (asthma, cysts, blebs), declared or not.
• Dry-suit or harness setups that restrict the chest from expanding on ascent.
• Out-of-air emergencies with rapid, buoyant ascents.

Recognising it

Pulmonary barotrauma can show as sharp chest pain during or just after ascent, coughing up frothy or blood-streaked sputum, breathlessness, or a crackling feeling (crepitus) under the skin of the neck and chest.

Arterial gas embolism typically appears within minutes of surfacing: sudden loss of consciousness or altered awareness, seizure, one-sided weakness, slurred speech, visual disturbance, or cardiovascular collapse.

The tell that points to AGE rather than DCS is the timing and the history: stroke-like signs within minutes of surfacing, after a breath-hold or panic ascent, with no need for heavy decompression exposure.

Things that mimic it

A few conditions cause stroke-like symptoms after a dive, and telling them apart matters even though the first-line treatment (oxygen, then recompression) overlaps:

• Neurological DCS usually comes on 30 minutes to a couple of hours after a dive with real gas loading (deep or repetitive), not within seconds of a breath-hold ascent.
• Inner-ear injuries can be either decompression sickness or barotrauma, and they need different treatment. Inner-ear DCS comes mostly as vertigo and nausea after deeper dives and needs urgent hyperbaric oxygen; inner-ear barotrauma comes mostly as hearing loss and ringing from a pressure imbalance on descent and may need surgery instead, with hyperbaric oxygen not the primary fix (Lindfors et al 2021). Misclassifying one as the other delays the right care.
• Cervical arterial dissection (a tear in a neck artery) is uncommon but real: a review of 19 reported cases in divers found contributing factors including the blood-pressure swings of immersion combined with pre-existing hypertension (Pollock et al 2024). It can mimic DCS or AGE and needs vascular imaging to find.

The practical rule from the DAN differential-diagnosis work: decompression illness is a clinical call with no confirmatory test, so do not let imaging delay recompression, but keep these mimics in mind when symptoms do not fit or do not respond.

Prevention

The single most effective measure is an open airway on every ascent: breathe continuously, never hold your breath, and keep the ascent slow (no faster than 9 to 10 m/min). On any uncontrolled or emergency ascent, the priority is simple: keep exhaling. Pre-dive screening helps the minority of divers with hidden lung disease, but no screening removes the risk of a breath-hold ascent, which is why the rule applies to everyone.

Emergency response

1. Get the diver out of the water and lay them flat on their back, level. (The old head-down position is no longer recommended and can worsen brain swelling.)
2. Give 100% oxygen continuously via a tight-fitting non-rebreather mask.
3. Do not give aspirin if AGE is suspected (bleeding risk).
4. Call a diving emergency line and local emergency services at the same time.
5. Evacuate to the nearest recompression chamber. Recompression on US Navy Treatment Table 6 is standard for AGE.
6. Do not delay evacuation to "see if it improves." AGE can briefly seem to recover, then deteriorate.

Time to recompression is the main thing that decides the neurological outcome.

References

• Germonpré P, Balestra C, Vanmaele P (2008). Pulmonary barotrauma. Diving and Hyperbaric Medicine.
• Acott CJ (2002). Pulmonary barotrauma case series. South Pacific Underwater Medicine Society Journal.
• van Hulst RA, van Ooij PJAM (2024). Pulmonary barotrauma in diving. Diving and Hyperbaric Medicine.
• Lindfors OH, Räisänen-Sokolowski AK, Hirvonen TP, Sinkkonen ST (2021). Inner ear barotrauma and inner ear decompression sickness: a systematic review on differential diagnostics. Diving and Hyperbaric Medicine 51(4):328–337. doi:10.28920/dhm51.4.328-337
• Pollock NW, Lippmann J, Pearn J, Hayman J (2024). Arterial dissection in scuba divers. Diving and Hyperbaric Medicine 54(3):188–195. doi:10.28920/dhm54.3.188-195
• Denoble PJ, Marroni A (eds) (2019). Differential Diagnosis of Decompression Illness Workshop Proceedings. DAN/UHMS.

Related reading

• Decompression Sickness

• Predisposing Factors for DCS

• Thermal Stress in Diving

• Immune Suppression and Diving

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