Decompression Sickness and Hyperbaric Oxygen: Symptoms, Treatment and Prevention

What is decompression sickness?

When a diver breathes compressed gas underwater, the surrounding pressure rises with depth. Nitrogen or another inert gas dissolves progressively into blood and tissues according to pressure, exposure time, tissue blood flow and the breathing mixture. During ascent the ambient pressure falls, and the body must carry that dissolved gas back to the lungs for elimination. If decompression is too rapid or the inert-gas load is excessive for the individual circumstances, clinically important bubbles may form in tissues and blood.

These bubbles do more than mechanically block circulation. They can injure the vascular lining, trigger inflammation, impair microcirculation and reduce oxygen delivery. Symptoms can therefore arise in joints, skin, spinal cord, brain, inner ear or lungs. DCS should not be reduced to the stereotype of “the bends” or joint pain.

The broader term decompression illness (DCI) includes decompression sickness and arterial gas embolism (AGE). AGE commonly follows pulmonary barotrauma when gas enters the arterial circulation and can produce abrupt stroke-like symptoms, seizure or loss of consciousness near the time of surfacing. The mechanisms differ, but initial priorities are similar: stabilize airway, breathing and circulation; deliver high-concentration oxygen; activate emergency services; and obtain diving-medicine advice.

Who is at greater risk?

No table or computer creates a perfect boundary between safe and unsafe exposure. Deeper and longer dives, rapid ascent, omitted required stops, short surface intervals, repetitive or multiday diving, cold exposure and heavy work at depth are recognized contributors. Altitude diving and flying or travelling to elevation too soon after a dive add further decompression stress.

Dehydration, alcohol, inadequate sleep, illness, obesity, heavy exercise soon after surfacing and certain cardiopulmonary conditions may add risk, although the strength of evidence differs. The practical lesson is to avoid stacking preventable stressors. A diver who is sleep-deprived, hungover and dehydrated, then conducts repetitive deep dives in cold current before carrying heavy equipment and rushing to a flight has accumulated risk that could have been reduced.

A patent foramen ovale (PFO) may be relevant in selected divers with recurrent or particular patterns of DCS. It does not mean that every diver needs routine screening or that every person with a PFO must stop diving. Testing and management should be individualized with clinicians familiar with diving and cardiovascular medicine.

What are the symptoms, and when do they begin?

Symptoms may begin underwater, immediately after surfacing or later. Most occur in the first several hours, but delayed onset is possible, particularly when subsequent altitude exposure adds decompression stress. Mild, transient or atypical symptoms cannot safely exclude DCS.

• Musculoskeletal: deep, persistent and poorly localized pain around a shoulder, elbow, hip, knee or other area.
• Skin: itching, swelling, rash, peau d’orange change or irregular red-purple mottling.
• Neurologic: tingling, numbness, altered sensation, weakness, slowed thinking, poor coordination, abnormal gait, or urinary retention or incontinence.
• Inner ear: vertigo, tinnitus, hearing loss, nausea, vomiting or inability to walk straight. Inner-ear DCS and inner-ear barotrauma require expert differentiation.
• General: unusual fatigue, headache, malaise or a sense that something is distinctly wrong.
• Cardiopulmonary: cough, chest pain, rapid breathing, shortness of breath, or frothy or blood-stained sputum—features of severe illness.

DCS is primarily a clinical diagnosis. No routine blood test, X-ray or CT scan can reliably rule it out on its own. Clinicians integrate the dive profile, gases, ascent and stops, repetitive exposures, symptom timing and a detailed neurologic, ear, lung and circulatory examination. Tests may identify barotrauma or another emergency, but oxygen and consultation should not be delayed merely to complete every investigation.

What should be done immediately?

1. Stop diving. Do not return underwater to “complete” decompression. In-water recompression adds drowning, hypothermia, oxygen-toxicity and monitoring risks.
2. Provide the highest available oxygen concentration. A trained responder should use an appropriate mask and flow. Improvement on oxygen is welcome but does not prove the injury has resolved.
3. Contact local emergency medical services first. A severely ill diver should be stabilized at the nearest capable medical facility before transfer to a chamber. Do not undertake an unplanned long private drive.
4. Keep the diver resting and avoid further pressure reduction. Use a comfortable supine or recovery position as clinically appropriate. Avoid walking, exertion, altitude and commercial flight.
5. Give reasonable oral nonalcoholic fluids only if fully alert. Do not force fluids when consciousness, swallowing or vomiting is a concern.
6. Preserve details. Save the dive computer and record depth, time, ascent, stops, gases, earlier dives, symptom onset and oxygen administration.

How does hyperbaric oxygen treat DCS?

Decompression sickness is a recognized indication for hyperbaric oxygen therapy. The diver is recompressed in a treatment chamber while breathing high-concentration oxygen. Increased ambient pressure reduces bubble volume. Oxygen creates a strong gradient for inert-gas elimination, raises dissolved oxygen in plasma, supports hypoxic tissue and helps counter bubble-related inflammation and edema.

The treatment table, pressure, oxygen periods and need for additional sessions depend on neurologic findings, severity, response and the treating team. Some divers improve substantially after one session; severe, neurologic or inner-ear disease may require repeated therapy and rehabilitation. A delay does not automatically make treatment futile, so a diver should still seek assessment rather than deciding that the opportunity has passed.

Common treatment issues include difficulty equalizing the ears or sinuses, temporary visual change, fatigue and claustrophobia. Less common but important risks include oxygen-induced seizure and pulmonary barotrauma. An untreated pneumothorax is a major concern. Safe care therefore requires medical assessment, controlled pressure changes, monitoring and emergency capability—not simply sitting in a chamber and breathing oxygen.

How can divers reduce the risk of decompression sickness?

No strategy guarantees zero risk. Prevention works best when the diver maintains a conservative margin and avoids combining multiple stressors.

Before diving

• Obtain appropriate training for the planned environment, depth, gas and decompression obligation.
• Do not dive with fever, chest symptoms, impaired ear equalization, severe fatigue, hangover or significant acute illness.
• Seek diving-medical assessment for important heart or lung disease, previous DCS, pneumothorax, neurologic disease, pregnancy or medications that may impair awareness or performance.
• Plan depth, bottom time, gas, ascent, reserves and contingencies. Treat computer limits as boundaries, not targets.
• Confirm that emergency oxygen, a suitable delivery system, adequate supply, communication and an emergency plan are available.
• Arrive normally hydrated and well rested; avoid alcohol. Excessive forced water intake is unnecessary and can itself be harmful.

During the dive

• Follow the selected table or computer for depth, time, ascent rate and all required stops.
• Ascend slowly and under control, including the shallowest portion. Perform safety stops according to training and the dive plan.
• Avoid saw-tooth profiles, chasing no-decompression limits and unplanned extensions.
• Allow adequate surface intervals and greater margins during repetitive or multiday diving. Deeper dives are generally planned earlier.
• Minimize unnecessary heavy exertion at depth. Cold, current and task loading require additional conservatism.
• Nitrox does not replace training. Analyze the cylinder, set the computer correctly and remain within maximum operating depth and oxygen-exposure limits.

After the dive

• Avoid immediate strenuous exercise, heavy lifting, excessive heat exposure and heavy alcohol use. Rehydrate normally and remain observant.
• Account for all dives and residual inert-gas load, not only the final dive of the day.
• Do not massage pain, hide it with alcohol or medication, or redive to “test” symptoms.
• Allow an adequate interval before flying, crossing high mountain roads or visiting altitude.
• Use buddy observation. Affected divers may mislabel unusual fatigue, slowed responses or poor gait as ordinary seasickness.

How long should a diver wait before flying?

Aircraft cabin pressure is lower than sea-level pressure and therefore adds decompression stress. Widely used DAN consensus guidance suggests at least 12 hours after a single no-decompression dive, at least 18 hours after multiple dives in one day or multiple days of diving, and substantially longer than 18 hours after dives requiring decompression stops. A training agency, computer or individual medical situation may justify a more conservative interval.

These intervals apply only to divers without symptoms. A diver with possible DCS should not board a commercial flight to reach a chamber. Medical evacuation altitude and cabin pressure must be planned by the treating and retrieval teams.

When can someone return to diving after treatment?

There is no universal waiting period. Decisions depend on whether the event was DCS or AGE, the affected organ system, severity, complete versus incomplete recovery, modifiable causes and whether cardiac, pulmonary, neurologic, hearing or balance evaluation is needed. Premature return may worsen residual injury or place the diver far from care during a recurrence.

Follow-up with a hyperbaric or diving-medicine physician is essential. Spinal, cerebral, neurologic or inner-ear cases often require detailed functional reassessment. Resolution of symptoms alone does not confer immediate fitness to dive; the return plan should be individualized.

Author: Dr. Marco Ha

Pediatric surgery, trauma surgery, hyperbaric and diving medicine. Written and medically reviewed July 29, 2026.