Hyperbaric Oxygen Therapy for Decompression Sickness (The Bends)
What to do if you suspect the bends, how hyperbaric oxygen recompression treats decompression sickness, what US Navy Table 6 involves and where to get help.
This content is for informational purposes only and does not constitute medical advice. Always consult a healthcare professional. Read full disclaimer
Decompression sickness (DCS, "the bends") is treated with recompression: the diver breathes close to 100% oxygen in a medical hyperbaric chamber, commonly following US Navy Treatment Table 6 at 2.8 atmospheres absolute (ATA). First aid is surface oxygen at the highest concentration available, given straight away, and any diver who becomes unwell after diving should be discussed with a diving medicine physician as soon as possible. Hyperbaric oxygen is the standard treatment for both DCS and arterial gas embolism in European and US guidance.
If you suspect decompression sickness or gas embolism
- Stop diving. Do not go back underwater to try to relieve symptoms. In-water recompression is only an option for trained, equipped teams following a recognised protocol.
- Give oxygen as close to 100% as possible, as soon as possible, and keep it going. Keep the diver lying flat, or in the recovery position if unconscious.
- Call local emergency services (for example 911, 112 or 999) or get the diver to the nearest hospital if the situation is life-threatening.
- Then call DAN's 24/7 emergency hotline: +1-919-684-9111. DAN Europe's international hotline is +39 06 4211 5685, and within Australia DAN Asia-Pacific uses 1800 088 200. If you reach a hospital, tell staff the person was diving and ask them to consult DAN.
- Do not fly or travel to altitude unless a diving physician has approved it.
- Offer water or an isotonic drink only if the diver is fully conscious, and keep them warm but not overheated.
Symptoms that improve on oxygen can return once the oxygen stops, so the diver still needs a medical assessment.
What Is Decompression Sickness?
When you breathe compressed gas underwater, your tissues absorb extra inert gas, mainly nitrogen. If the surrounding pressure falls faster than that gas can leave, the gas pressure in the tissues exceeds the pressure around you and bubbles form in tissues or blood. The Undersea and Hyperbaric Medical Society (UHMS) describes how those bubbles can damage tissue directly, block blood flow and trigger clotting and inflammation.
DCS is usually linked to diving, but it can also follow a rapid trip to altitude. It does not only happen to careless divers. The US Navy Diving Manual notes that DCS can occur in divers who stayed well within no-decompression limits or carefully followed their tables.
What Is Arterial Gas Embolism?
Doctors group DCS and arterial gas embolism (AGE) together as decompression illness (DCI). In AGE, gas bubbles enter the arteries and can block blood flow to the brain or heart. In divers this usually follows lung over-expansion during ascent. UHMS notes that lung injury and gas embolism from breath-holding can happen after an ascent of as little as one metre, so it can occur even in a swimming pool.
AGE tends to start suddenly, often within minutes of surfacing. The US Navy's rule is that any diver who has breathed compressed gas and surfaces unconscious, loses consciousness or has obvious neurological symptoms within 10 minutes of surfacing must be treated as having AGE.
What Are the Symptoms of the Bends?
The US Navy splits DCS into two types, because treatment can differ.
| Type | Typical symptoms |
|---|---|
| Type I (pain-only, skin, lymphatic) | A deep, dull ache in or around joints, most often the shoulder, elbow, wrist, hand, knee or ankle. Itching or faint rash. Painful, swollen lymph nodes. |
| Type II (serious) | Numbness, tingling, weakness, paralysis, confusion or personality change, bladder problems. Inner-ear DCS ("staggers"): ringing ears, hearing loss, vertigo, nausea. Lung involvement ("chokes"): chest pain on breathing in, cough, fast breathing, collapse. |
Two details catch people out. Pain in the chest, abdomen or hips, and a blotchy, marbled skin rash (cutis marmorata), are treated as Type II because they can signal spinal cord or more serious involvement. And early Type II symptoms are easy to dismiss as tiredness. The Navy manual warns that "initial denial of DCS is common."
When do symptoms start? In a US Navy database of several thousand air dives, 42% of DCS cases began within 1 hour of surfacing, 60% within 3 hours, 83% within 8 hours and 98% within 24 hours. Divers Alert Network (DAN) gives a typical window of 15 minutes to 12 hours.
How Does Hyperbaric Oxygen Treat Decompression Sickness?
The US Navy lists three goals of recompression:
- Shrink the bubbles. By Boyle's law, a gas volume falls as pressure rises. At 2.8 ATA a bubble takes up just over a third of the volume it had at the surface, which relieves local pressure and helps restart blood flow.
- Give the bubbles time to dissolve. Pressure alone does not make bubbles disappear.
- Raise the oxygen content of the blood to support injured tissue.
Breathing near-pure oxygen adds a second effect. The diver stops inhaling nitrogen, so the gradient that drives nitrogen out of bubbles and tissues becomes much steeper. UHMS summarises the rationale as an immediate reduction in bubble volume, a larger diffusion gradient for inert gas, oxygen for starved tissue and less swelling in the central nervous system.
How strong is the evidence? Recompression has never been tested against no treatment in a randomised trial, and ethics make such a trial unlikely. A Cochrane review describes recompression as the universally accepted standard treatment while noting the absence of trial evidence. The European Committee for Hyperbaric Medicine (ECHM) consensus uses DCI and gas embolism as examples where withholding hyperbaric oxygen to run a trial would breach accepted standards of care, and gives both its strongest (Type 1) recommendation. You can read how DCS fits among other accepted uses in our guide to hyperbaric oxygen therapy indications.
What Happens During US Navy Treatment Table 6?
The ECHM recommends US Navy Treatment Table 6, or an equivalent helium-oxygen table, as the first treatment for DCI. DAN describes it as a session at 2.8 ATA, the pressure found at 60 feet (18 metres) of seawater, lasting just under five hours. The standard table in the US Navy Diving Manual runs like this:
| Stage | Depth equivalent | What happens |
|---|---|---|
| Compression | 0 to 60 feet (18 m) | Pressure rises at 20 feet per minute. Oxygen timing starts on arrival. |
| Deep stage | 60 feet (2.8 ATA) | Three 20-minute oxygen periods, each followed by 5 minutes of air. |
| Slow ascent | 60 to 30 feet | 30 minutes. |
| Shallow stage | 30 feet (9 m) | Two 60-minute oxygen periods, each with a 15-minute air break. |
| Final ascent | 30 feet to surface | 30 minutes. |
The total is 285 minutes (4 hours 45 minutes), not counting the descent. The air breaks lower the risk of oxygen toxicity. If symptoms have not fully resolved, the table can be extended by up to two extra periods at 60 feet, up to two extra periods at 30 feet, or both. In the Navy protocol a qualified attendant stays inside the chamber throughout, and the table must never be shortened except on a diving medical officer's instruction.
Some divers need more than one session. The Navy manual advises continuing follow-up treatments while residual symptoms keep improving, and generally stopping when there is no further sustained improvement after two consecutive treatments. After treatment, divers are observed for 2 hours after pain-only symptoms and 6 hours after serious symptoms.
Does a Delay in Treatment Matter?
Yes, especially for serious cases. The Navy manual states that treatment becomes less effective as the time between symptom onset and recompression increases.
A 2018 expert review on pre-hospital management of DCI, initiated by DAN and written by specialists from Australasia, the US and Europe, adds nuance:
- The best outcomes, especially with severe symptoms, are likely with immediate recompression.
- In serious presentations there is limited evidence that delays longer than six hours lead to slower or less complete recovery.
- For genuinely mild DCI (limb pain, tiredness, some skin sensory changes, rash or lymphatic swelling that is stable or improving, with significant neurological problems excluded by a diving medicine physician), a delay is unlikely to worsen long-term outcome, and some of these divers can be managed without recompression.
The key phrase is "excluded by a diving medicine physician." Deciding a case is mild is not a call for the diver or the dive boat to make alone.
Late treatment is still worthwhile. For gas embolism, the ECHM notes that treatment within six hours is associated with better outcomes, but substantial improvement has been seen even after 24 hours or more. A 2011 review in The Lancet concludes that treatment is effective in most cases, although serious cases can leave lasting deficits, even after several recompressions.
Can You Fly After Diving or After DCS?
If you feel well: DAN's flying-after-diving guidelines recommend a surface interval of at least 12 hours after a single no-decompression dive, at least 18 hours after multiple dives per day or several days of diving, and substantially longer than 18 hours after dives that required decompression stops. These intervals reduce the risk but do not remove it.
If you have symptoms: do not get on a flight to get home and "see a doctor there." Altitude lowers the pressure around you and can make bubbles grow. The 2018 expert review advises that air evacuation should use an aircraft pressurised to one atmosphere or flying at low altitude. Some divers with mild symptoms may be cleared to fly on a commercial airliner after at least 24 hours at the surface, but only on a diving physician's advice.
After treatment: the US Navy manual says divers whose symptoms fully resolved should not fly for at least 72 hours, and those with residual symptoms should fly only with a diving medical officer's agreement.
Why a Wellness Soft-Shell Chamber Is Not a Treatment Option
Many wellness centres and home users have inflatable "mild" chambers. They cannot treat decompression sickness, for three reasons.
- They cannot reach treatment pressure. Table 6 starts at 2.8 ATA. A typical FDA 510(k) summary for a portable soft chamber (K072757) lists a maximum of 1.3 ATA (4 psi), air rather than oxygen, and one indication: acute altitude sickness.
- Emergency treatment needs hospital-level support. A seriously injured diver may need intravenous fluids, a ventilator and an attendant in the chamber. A 2016 survey of US hyperbaric centres found that only 43 of 361 (11.9%) had the equipment and staff to treat high-acuity patients. Many hard-shell outpatient clinics are not set up for diving emergencies either.
- Time matters. A detour to the wrong facility delays proper recompression for the cases where delay does the most harm.
For a plain explanation of the differences, see our guide to hard-shell vs soft-shell chambers.
Where Are Emergency Recompression Chambers?
Not every chamber can take a diving emergency. It needs staff who can respond at short notice and equipment to look after a sick patient under pressure, and as the US survey above shows, most centres do not have both.
That is why the safest route is local emergency services plus a call to DAN, rather than searching online for the nearest chamber. DAN runs a Recompression Chamber Network and states that in a dive emergency it can refer divers to "the closest suitable chamber."
Before a dive trip, it is worth:
- saving the DAN hotline for your region in your phone
- checking that your dive operator carries an oxygen kit with enough supply to cover a likely evacuation, as the 2018 expert review recommends for all diving
- finding out which hospital near your destination treats diving injuries
Our directory lists hyperbaric facilities in popular dive destinations such as Egypt, Thailand, the Philippines and Mexico. Many listings are outpatient or wellness centres, so contact a facility in advance to ask whether it treats diving emergencies 24 hours a day. In an actual emergency, follow the advice of emergency services and DAN.
Sources
- Vann RD, Butler FK, Mitchell SJ, Moon RE. Decompression illness. Lancet. 2011;377(9760):153-164.
- Mitchell SJ, Bennett MH, Bryson P, Butler FK, Doolette DJ, Holm JR, Kot J, Lafère P. Pre-hospital management of decompression illness: expert review of key principles and controversies. Diving and Hyperbaric Medicine. 2018;48(1):45-55.
- Bennett MH, Lehm JP, Mitchell SJ, Wasiak J. Recompression and adjunctive therapy for decompression illness. Cochrane Database of Systematic Reviews. 2012;(5):CD005277.
- Mathieu D, Marroni A, Kot J. Tenth European Consensus Conference on Hyperbaric Medicine: recommendations for accepted and non-accepted clinical indications and practice of hyperbaric oxygen treatment. Diving and Hyperbaric Medicine. 2017;47(1):24-32.
- US Navy, US Navy Diving Manual, Revision 7 Change A, Volume 5, Chapter 17: Diagnosis and Treatment of Decompression Sickness and Arterial Gas Embolism (PDF hosted by UHMS)
- Undersea and Hyperbaric Medical Society, Hyperbaric oxygen therapy indications, 15th edition: air or gas embolism and decompression sickness
- Chin W, Jacoby L, Simon O, et al. Hyperbaric programs in the United States: locations and capabilities of treating decompression sickness, arterial gas embolisms, and acute carbon monoxide poisoning: survey results. Undersea and Hyperbaric Medicine. 2016;43(1):29-43.
- Divers Alert Network, DAN Emergency Hotline
- Divers Alert Network, Chapter 4: Treating Decompression Sickness
- Divers Alert Network, Decompression Illness: what is it and what is the treatment?
- Divers Alert Network, Guidelines for Flying After Diving
- Divers Alert Network, The DAN Recompression Chamber Network
- DAN Europe, Emergency hotline; DAN World, Asia-Pacific emergency numbers
- US Food and Drug Administration, 510(k) summary K072757: portable mild hyperbaric chamber (PDF)
This article is for information only and is not medical advice. Diving injuries are emergencies: contact local emergency services and a diving medicine specialist such as DAN.