Decompression Sickness: Symptoms and What to Do

Decompression sickness, commonly called the bends, is the diving-specific medical condition every recreational diver should understand and very few experience. It happens when nitrogen absorbed into a diver's tissues during a dive comes out of solution as bubbles during ascent, lodges in joints, soft tissue or the central nervous system, and produces symptoms ranging from mild joint pain to life-threatening neurological damage. Modern dive computer use and adherence to no-decompression limits have reduced the incidence dramatically, but the condition remains one of the most serious dive emergencies, and recognition matters because, as DAN (the Divers Alert Network) puts it, the sooner treatment begins, the better the chance of a full recovery.

This article is for recognition and first response only. It is not medical advice. Any suspected case of decompression sickness requires immediate professional medical assessment and access to hyperbaric treatment. In an emergency in Australia, call Triple Zero (000) first, then the DAN emergency hotline on 1800 088 200.

What it is

When a diver breathes compressed air at depth, the increased pressure forces additional nitrogen into the body's tissues at a rate that depends on depth and time underwater. On ascent, the pressure drops and that excess nitrogen has to come back out through the lungs. If ascent is slow enough and the no-decompression limits are observed, the nitrogen usually leaves the tissues gradually and harmlessly, although DAN notes that bubbles can form even when accepted limits are followed. If the ascent is too fast, the dive too long, or the depth profile too aggressive, the nitrogen comes out of solution as bubbles inside the body before it can reach the lungs to be exhaled. Those bubbles are decompression sickness.

Decompression sickness is divided into two clinical types. Type 1 (joint bends, skin bends) is the milder form: bubbles in the soft tissues and joints producing pain, rash and fatigue. Type 2 is the serious form: bubbles in the central nervous system, spinal cord or lungs, producing neurological symptoms, paralysis and respiratory distress. Type 2 cases are medical emergencies. DAN says a diver with severe symptoms must be stabilised at the nearest medical facility before being transported to a chamber, and untreated cases can be fatal or permanently disabling.

Symptoms

DAN says symptoms usually appear between 15 minutes and 12 hours after surfacing. In severe cases they can start before the diver reaches the surface or immediately afterwards, and a delayed onset is rare but possible, especially if the diver flies after diving.

The most common Type 1 symptoms are joint pain, particularly in the shoulders, elbows and knees, often described as a deep aching that worsens with movement. The pain appears without recent trauma to explain it. Skin symptoms include itching, mottled rashes (cutis marmorata) and unusual fatigue disproportionate to the dive profile.

Type 2 symptoms are neurological and require immediate response. They include numbness or tingling in the limbs, weakness or paralysis, difficulty walking, vertigo, blurred vision, confusion, slurred speech, chest pain, or shortness of breath. Any combination of these symptoms after a dive must be treated as a Type 2 case until medical assessment proves otherwise.

A recognisable but easily missed pattern is the diver who feels generally unwell after a dive, dismisses it as fatigue or dehydration, and finds the symptoms worsening over the following hours. Time matters: DAN says delays in seeking treatment raise the risk of lasting symptoms, and after a delay of 24 hours or more treatment may be less effective. Even after a delay, see a dive medicine specialist, who can judge whether treatment will still help.

What causes it

The clinical causes are well-documented:

- Ascent rate exceeding the recommended 9 metres per minute (or 18 metres per minute for older training) - Skipped or shortened safety stops at 5 metres for 3 minutes - Profiles that exceed the no-decompression limits for the depth and time - Repetitive dives without adequate surface interval - Multi-day, multi-dive trips that allow nitrogen to accumulate across days - Flying, or driving up over mountains, too soon after diving (see the waiting times under Prevention below) - Dehydration, fatigue and poor general fitness, all of which slow nitrogen elimination - Cold water and heavy work underwater, both of which alter circulation and tissue saturation - Patent foramen ovale (a small hole between the heart's atria, present in about 25% of the population), which allows nitrogen bubbles to bypass the lungs and enter arterial circulation

The most common cause in recreational diving is a combination of two or three of the above on the same dive. A dive that violates the no-decompression limit by a few minutes, in a diver who is dehydrated and fatigued from a long travel day, with a slightly fast ascent, produces a much higher risk than any single factor alone.

Prevention

The standard prevention practices, all of which reduce risk substantially:

1. Use a dive computer and respect its limits. Modern computers track nitrogen loading dynamically and adjust as the dive profile changes. 2. Ascend slowly, no faster than 9 metres per minute (most computers warn at this rate). 3. Always do a safety stop: 3 to 5 minutes at 5 metres on every dive. 4. Stay well hydrated before and after diving. DAN lists dehydration among the factors that may increase the risk, although it says the evidence is not conclusive. 5. Avoid alcohol within 12 hours of diving. 6. Wait before flying. DAN's minimum surface intervals before a flight are 12 hours after a single no-decompression dive, 18 hours after multiple dives in a day or several days of diving, and substantially longer than 18 hours after any dive that needed decompression stops. Queensland's code of practice for dive operators is stricter, advising 24 hours or more after multiple dives in a day, several consecutive days of diving or any decompression dive. These are minimums: DAN says a longer wait lowers the risk further. 7. Manage repetitive dives carefully: deepest dive first, longer surface intervals, and conservative computer profiles when planning multiple dives across consecutive days. 8. Maintain general fitness. Cardiovascular health correlates with safer nitrogen elimination. 9. If you have a known patent foramen ovale or a history of unexplained DCS, consider conservative profiles and discuss with a diving medicine specialist.

What to do if you suspect DCS

The response chain is straightforward and time-critical:

Immediately: Stop diving and get the diver out of the water. Do not attempt in-water recompression: DAN's general rule is that first aid is given at the surface. Position the diver as DAN advises: a diver who is awake can lie on one side with the head supported or recline comfortably, a diver who is unresponsive but breathing goes in the recovery position, and a diver who is not breathing goes flat on their back for CPR. If there is an oxygen kit and someone trained to use it, give oxygen at the highest concentration the equipment allows, as close to 100 per cent as possible. DAN calls oxygen the primary first aid for decompression sickness, and Queensland's code of practice expects dive operators to have an oxygen system and a person trained in oxygen first aid at the dive site. Keep the oxygen going until a doctor says to stop, even if the symptoms fade, because they can return once it stops. Get the diver to professional medical assessment as fast as possible.

Call Triple Zero (000), then DAN: Call 000 first, ask for an ambulance and say exactly where you are. Then call the Divers Alert Network (DAN), which operates 24-hour emergency hotlines for diving medical emergencies. In Australia, DAN's diving emergency hotline is 1800 088 200 (toll free within Australia), or +1 919 684 9111 from overseas (DAN World: Contact Us). The Australian number is the Divers Emergency Service hotline, run from the Royal Adelaide Hospital's Hyperbaric Medicine Unit, which says it is available to all divers and puts callers through to a hyperbaric doctor within minutes. Tell the operator it is a dive emergency. DAN's medical staff may give advice straight away or call back after making arrangements, which can take 30 minutes or longer, so stay by the phone.

Hyperbaric treatment: The definitive treatment for DCS is hyperbaric oxygen therapy in a recompression chamber. You do not choose the chamber: call 000, then DAN, and they will direct you. Do not drive to a hyperbaric unit on your own. DAN says chambers are generally not equipped to receive patients directly, that patients must be assessed in an emergency department first, and that not every diving injury is decompression sickness. The Royal Adelaide Hospital's unit says emergency cases should go to its emergency department by ambulance.

These public hospital units say on their own pages that they treat divers:

- Sydney: Prince of Wales Hospital, Randwick, which treats diving injuries for patients across NSW and the ACT. A hyperbaric doctor is on call after hours. - Melbourne: The Alfred, Victoria's statewide hyperbaric service. A hyperbaric doctor is on call for urgent cases out of hours. - Brisbane: Royal Brisbane and Women's Hospital Hyperbaric Medicine Service, with a 24-hour on-call service supporting Queensland's recreational and commercial dive industries. - Townsville: Townsville University Hospital Hyperbaric Medicine Unit, a 24/7 emergency service. It is the only public hyperbaric unit in Queensland outside Brisbane, so there is no public unit in Cairns. - Adelaide: Royal Adelaide Hospital Hyperbaric Medicine Unit, on call for emergency treatment 24 hours a day, 7 days a week. - Perth: Fiona Stanley Hospital Hyperbaric Medicine Unit, the state referral service for diving and hyperbaric medicine, on call 24 hours a day, seven days a week. - Hobart: Royal Hobart Hospital Department of Diving and Hyperbaric Medicine. For a diver, Tasmania's health department says to call 000 and say "diving emergency" to start its diver emergency protocol.

Wherever you are, including the Northern Territory, 000 and DAN work out which unit the diver needs and how to get them there.

Document everything: every dive in the previous 48 hours (depths, times, surface intervals, ascent rates and the gas breathed), when the symptoms started and how they have changed, and what first aid was given, including when the oxygen started. Bring the diver's dive computer, which records the dive profiles and ascent rates. The doctors need all of this for diagnosis and treatment planning.

Insurance and DAN membership

Retrieval and treatment for a diving injury can involve ambulances, flights and several chamber treatments, so check what covers you before you need it.

- The emergency hotline is open to everyone. The Royal Adelaide Hospital says the DES hotline on 1800 088 200 is available to all divers, so you do not need to be a DAN member to call it. - DAN membership does not pay for treatment. DAN World sells membership to Australian residents. Its benefits include DAN TravelAssist emergency medical transportation, but DAN says membership alone does not cover the treatment costs of a diving accident. - DAN dive accident insurance is for diving overseas. DAN's optional Dive Accident Insurance, added on top of membership, covers treatment costs for diving accidents that happen outside Australia. Read the Product Disclosure Statement for the limits, depth conditions and exclusions. - Travel insurance often needs an add-on. Smartraveller says you may need to pay extra for scuba diving to be covered, and to check the policy's list of included and excluded activities. - For diving at home, check with your health insurer and ambulance cover provider what they would pay for.

When to seek medical advice

Any post-dive symptom that cannot be confidently explained by something else should be treated as possible DCS until ruled out. Joint pain, unusual fatigue, neurological symptoms, skin rashes or breathing problems within 24 hours of a dive all warrant medical assessment. The clinical pattern is well-recognised by emergency physicians at coastal hospitals and by hyperbaric specialists, and the cost of investigating a false alarm is much lower than the cost of missing a genuine case.

Final notes

Decompression sickness is rare in recreational diving when standard practices are followed. The Australian recreational diving community sees only a small number of cases each year given the volume of diving, and the major causes are well-documented and largely preventable. Understanding the symptoms, the causes and the response chain protects you, your buddy and the divers around you. Carry oxygen on dive trips when possible, know 000 and the DAN emergency number, check your dive insurance before you travel, and trust the standard rules: slow ascent, safety stop, hydration, conservative computer profiles, no flying inside the waiting window.

Sources

- DAN: Decompression Illness - DAN: Decompression Sickness, Chapter 4: Treating Decompression Sickness - DAN: Travelers Medical Guide, Rescuing Divers and Swimmers - DAN World, Alert Diver: PFO Concerns in Dive Injury Treatment - DAN Alert Diver: What Will the Doctor Do? (2012) - DAN: Emergency Assistance - DAN: Flying After Diving - DAN World: Contact Us (emergency hotlines) - DAN World: Membership and Dive Accident Insurance for residents of Australia - Australian Government: Triple Zero (000), when to call - WorkSafe Queensland: Recreational Diving, Recreational Technical Diving and Snorkelling Code of Practice 2024, sections 2.5, 3.6 and 6.1 (PDF, worksafe.qld.gov.au; the site blocks automated checks) - South Eastern Sydney Local Health District: Prince of Wales Hospital, Hyperbaric Medicine - Alfred Health: Hyperbaric Medicine - Royal Brisbane and Women's Hospital: Hyperbaric Medicine - Townsville Hospital and Health Service: Hyperbaric Medicine - Royal Adelaide Hospital: Hyperbaric Medicine Unit - Fiona Stanley Fremantle Hospitals Group: Hyperbaric Medicine Unit - Tasmanian Department of Health: Outpatients, Diving and Hyperbaric Medicine, and Diving (health.tas.gov.au; the site blocks automated checks) - Smartraveller: Travel insurance

Header photo: Two divers holding a decompression trapeze at the 6 m stop after a dive on 12 Mile Bank reef, south of Cape Agulhas, South Africa, by Peter Southwood, CC BY-SA 4.0, via Wikimedia Commons.