HBOT for Decompression Sickness

Recognizing Decompression Illness, Providing Immediate Oxygen, and Delivering Definitive Recompression Therapy

Decompression sickness, commonly abbreviated as DCS, occurs when dissolved inert gas forms bubbles within blood or tissue after a reduction in ambient pressure. It is most often associated with compressed-gas diving, but it can also occur in compressed-air workers, aviators, astronauts, and people exposed to other substantial pressure changes.

Hyperbaric oxygen therapy, or HBOT, is the definitive treatment for clinically significant diving-related DCS. Recompression reduces bubble volume, while oxygen accelerates inert-gas elimination and supports tissues affected by impaired circulation, inflammation, and edema.

Treatment should begin as early as practical, but a delay does not automatically eliminate the potential value of HBOT. Suspected cases require immediate oxygen, medical evaluation, consultation with a diving-medicine specialist, and coordinated transport to a suitable recompression facility. (Divers Alert Network)

How Decompression Sickness Develops

While a diver breathes compressed gas at depth, the increased ambient pressure causes more inert gas, usually nitrogen, to dissolve in blood and tissue. The quantity absorbed depends on depth, time, breathing-gas composition, blood flow, and tissue characteristics.

During ascent, ambient pressure decreases and the dissolved inert gas must move from tissue into the blood, reach the lungs, and be exhaled. If pressure falls faster than the gas can be eliminated, tissues become supersaturated and bubbles may form.

These bubbles can cause injury through several interacting mechanisms:

• Mechanical disruption of tissue
• Obstruction of venous or microvascular blood flow
• Endothelial injury
• Platelet and leukocyte activation
• Inflammatory signaling
• Increased vascular permeability
• Local edema
• Secondary tissue hypoxia

The result is not simply a collection of gas bubbles. DCS becomes a vascular and inflammatory disorder in which tissue injury may continue even after bubble volume begins to decline. (PubMed)

Decompression Sickness and Arterial Gas Embolism

Decompression illness, or DCI, is an umbrella term that includes both decompression sickness and arterial gas embolism.

DCS generally results from inert-gas bubbles forming within tissues or the venous circulation after decompression. Arterial gas embolism, or AGE, usually occurs when gas enters the arterial circulation, often following pulmonary barotrauma during ascent. AGE commonly produces abrupt stroke-like manifestations, while DCS may affect the spinal cord, brain, inner ear, joints, skin, lymphatic system, or cardiopulmonary circulation.

The two conditions may overlap clinically, and the initial response is similar: stabilize the patient, provide the highest practical concentration of oxygen, contact emergency and diving-medicine resources, and arrange recompression when indicated. (German Journal of Sports Medicine)

A diver who develops sudden unconsciousness, seizure, confusion, focal weakness, visual disturbance, or severe dizziness during ascent or within minutes of surfacing should be treated as having a serious decompression-related emergency. The precise distinction between DCS and AGE should not delay oxygen or evacuation.

DCS Can Occur After an Apparently Acceptable Dive

A history of exceeding a dive computer or decompression table strengthens suspicion, but DCS can occur after a dive that appeared to remain within accepted limits.

Dive computers and tables estimate risk across populations. They cannot account perfectly for individual susceptibility, physiologic stress, equipment differences, or every feature of the dive.

Factors that may increase risk include:

• Greater depth or bottom time
• Rapid ascent
• Missed decompression stops
• Repetitive or multiday diving
• Cold exposure
• Heavy exertion
• Dehydration
• Recent illness
• Reduced physical fitness
• Post-dive altitude exposure
• Individual cardiovascular or pulmonary factors

A normal dive-computer record therefore does not exclude DCS when the clinical presentation is convincing. Diagnosis depends on the dive history, timing, symptoms, examination, and exclusion of important alternative conditions. (Divers Alert Network)

Musculoskeletal and Cutaneous Manifestations

Musculoskeletal pain is one of the most familiar presentations. The pain may involve a shoulder, elbow, hip, knee, or another joint. It is often described as deep, poorly localized, and unrelated to movement or a specific mechanical injury.

Skin and lymphatic findings may include:

• Itching
• Mottled or marbled discoloration
• Localized swelling
• Firm edema
• Tender lymph nodes
• A sense of skin crawling or abnormal sensation

Cutis marmorata, a mottled or marbled skin pattern, should not automatically be considered a minor manifestation. It may be associated with more significant systemic involvement and warrants specialist assessment.

Pain or skin symptoms that improve after surface oxygen may still recur. Symptom improvement should be documented, but it should not be used by itself to cancel medical evaluation or recompression planning. (PubMed)

Neurologic Decompression Sickness

Neurologic DCS is a serious form of decompression illness and commonly affects the spinal cord. Symptoms may begin subtly and then progress.

Possible findings include:

• Numbness or tingling
• Limb weakness
• Difficulty walking
• Abnormal coordination
• Loss of balance
• Back, abdominal, or girdle-like pain
• Altered sensation
• Bowel or bladder dysfunction
• Confusion
• Changes in consciousness
• Paralysis

A diver may report vague fatigue, heaviness, clumsiness, or a sensation that a limb does not feel normal before an obvious deficit becomes apparent. A careful neurologic examination is therefore more useful than asking only whether the diver has pain.

Diving-related spinal cord injury can leave persistent weakness, sensory impairment, bladder dysfunction, sexual dysfunction, and reduced mobility. Early oxygen and recompression provide the best opportunity to limit residual injury. (PubMed Central (PMC))

Inner-Ear Decompression Sickness

Inner-ear DCS may cause:

• Severe vertigo
• Nausea and vomiting
• Imbalance
• Nystagmus
• Tinnitus
• Hearing loss

These findings can resemble inner-ear barotrauma. The distinction matters because forceful attempts to equalize pressure may worsen some barotrauma injuries, while delayed recompression may worsen DCS.

The clinical assessment should consider the dive profile, gas mixture, timing of symptoms, difficulty equalizing during the dive, hearing changes, neurologic findings, and evidence of middle-ear injury. Consultation with a diving-medicine physician and, when available, an otolaryngologist familiar with diving injuries is appropriate.

First responders should provide oxygen and avoid encouraging additional ear-clearing maneuvers while the diagnosis remains uncertain. (Divers Alert Network)

Cardiopulmonary Decompression Sickness

Severe venous bubble loads can interfere with pulmonary circulation and produce cardiopulmonary DCS, historically called “the chokes.”

Potential findings include:

• Cough
• Chest pain
• Shortness of breath
• Rapid breathing
• Cyanosis
• Hypoxemia
• Hypotension
• Pulmonary edema
• Cardiovascular collapse

This is a life-threatening presentation requiring simultaneous resuscitation and urgent recompression planning. Airway management, oxygenation, hemodynamic support, and evaluation for alternative emergencies such as pneumothorax, aspiration, immersion pulmonary edema, or acute cardiac disease may take priority during initial stabilization. (PubMed Central (PMC))

Fluid therapy should be individualized. Many divers are relatively volume depleted, but aggressive administration may worsen pulmonary edema in cardiopulmonary DCS. Management should be directed by clinicians experienced in critical care and diving medicine.

DCS Is Primarily a Clinical Diagnosis

There is no blood test, imaging study, or dive-computer calculation that reliably confirms or excludes DCS.

The diagnosis is based on:

• Exposure to reduced ambient pressure
• The dive or pressure profile
• The timing of symptom onset
• The nature and distribution of symptoms
• Neurologic and cardiopulmonary examination
• Response to oxygen or recompression
• Consideration of alternative diagnoses

Laboratory testing and imaging are used primarily to evaluate severity, identify complications, and exclude other conditions.

Potential alternatives include:

• Stroke
• Seizure
• Hypoglycemia
• Musculoskeletal injury
• Inner-ear barotrauma
• Pneumothorax
• Immersion pulmonary edema
• Contaminated breathing gas
• Oxygen toxicity
• Marine envenomation
• Trauma
• Drug or alcohol effects

Normal imaging should not delay HBOT when a qualified clinician believes DCS is likely. Many bubble-related and microvascular injuries will not be visible on routine CT or MRI. (Divers Alert Network)

Recording the Dive and Neurologic History

A detailed history should be collected while emergency care continues. Useful information includes:

• Maximum depth
• Bottom time
• Breathing gases
• Ascent rate
• Safety and decompression stops
• Missed stops
• Repetitive dives
• Surface intervals
• Previous days of diving
• Dive-computer data
• Exertion, cold, or equipment problems
• Time of symptom onset
• Symptom progression
• Oxygen delivery and response

A focused neurologic examination should document mental status, speech, vision, strength, sensation, coordination, gait, and balance. The examination should be repeated because findings may evolve during transport.

Documentation should not delay evacuation. Its purpose is to preserve information that may otherwise be lost once the diver reaches an emergency department or hyperbaric center. (Divers Alert Network)

Immediate First Aid With 100 Percent Oxygen

The highest practical concentration of oxygen should be administered as soon as DCS is suspected.

A demand-valve system can provide a high inspired concentration to a spontaneously breathing, cooperative patient. A nonrebreather mask may be used when a demand valve is unavailable or cannot be tolerated. A patient who is not breathing adequately requires airway support and assisted ventilation with oxygen.

Surface oxygen may:

• Increase oxygen delivery to injured tissue
• Accelerate inert-gas elimination
• Reduce bubble size by replacing nitrogen within bubbles
• Improve symptoms before recompression
• Limit secondary hypoxic injury

Oxygen should generally continue during evaluation and transport, subject to available supply, airway needs, and professional direction. Symptom resolution while breathing oxygen does not prove that the injury has resolved permanently. Symptoms may recur after oxygen is discontinued. (Divers Alert Network)

Positioning, Hydration, and Supportive Care

The diver should be kept at rest and protected from unnecessary exertion. A comfortable supine position is generally appropriate unless vomiting, respiratory distress, trauma, or another clinical problem requires different positioning.

The historical practice of placing suspected gas-embolism patients in a head-down position is not recommended. It can interfere with airway management and does not reliably prevent cerebral bubble distribution.

Oral fluids may be reasonable for a fully alert patient without nausea, swallowing difficulty, or planned anesthesia. Isotonic intravenous fluids may be used when clinically appropriate, particularly if dehydration is suspected. Excessive fluid administration should be avoided in pulmonary edema, significant cardiac dysfunction, or other conditions in which fluid loading may cause harm. (German Journal of Sports Medicine)

Routine steroids, anticoagulants, antiplatelet drugs, or other adjunctive medications should not be started solely for DCS without specialist guidance. The current U.S. Navy guidance does not recommend routine steroids or antiplatelet therapy for neurologic DCS because benefit has not been established and harm may be possible.

Medical Stabilization Before Chamber Transfer

A diver with severe DCS or possible AGE should generally be stabilized at the nearest capable medical facility before transport to a chamber, particularly when airway compromise, shock, trauma, pulmonary injury, or altered consciousness is present.

This evaluation may include:

• Airway and respiratory assessment
• Electrocardiography
• Glucose measurement
• Chest imaging when pulmonary barotrauma is suspected
• Evaluation for pneumothorax
• Neurologic reassessment
• Treatment of seizures or dysrhythmias
• Management of associated trauma

An untreated tension pneumothorax requires immediate treatment and cannot safely be ignored during recompression. Transport directly to a chamber should not replace essential resuscitation that the chamber facility cannot provide. (Divers Alert Network)

Transport and Altitude Exposure

Reduced atmospheric pressure at altitude can increase bubble volume and worsen decompression-related symptoms. Transport planning should therefore minimize additional altitude exposure whenever practical.

Ground transport is often preferred when it can reach an appropriate facility without excessive delay. When air evacuation is necessary, the transport team should use the lowest practical cabin altitude or an aircraft capable of maintaining near-sea-level cabin pressure when available.

These decisions require specialist coordination. A longer ground transfer may be less appropriate than a carefully managed flight when the patient has progressive neurologic or cardiopulmonary symptoms. Oxygen should continue during transport, and the receiving chamber should be contacted before departure. (Divers Alert Network)

How HBOT Treats DCS

HBOT addresses both the gas phase and the injured tissue.

Recompression reduces bubble volume according to the relationship between pressure and gas volume. Breathing oxygen replaces nitrogen within the lungs, lowers blood nitrogen tension, and creates a gradient that favors movement of inert gas from bubbles and tissue into the circulation for elimination.

At the same time, hyperbaric oxygen:

• Increases dissolved plasma oxygen
• Supports tissue beyond partially obstructed microvessels
• Reduces edema through hyperoxic vasoconstriction
• Improves oxygenation without proportionally reducing oxygen delivery
• Supports cellular metabolism
• May reduce leukocyte-endothelial interactions and inflammatory injury

These effects explain why patients may improve rapidly during the early portion of recompression, while others continue to recover gradually after bubble reduction and tissue oxygenation have been restored. (Divers Alert Network)

Recompression Treatment Tables

Hyperbaric treatment is delivered according to a structured recompression profile rather than a routine outpatient wound-care protocol.

The U.S. Navy Treatment Table 6, or a clinically equivalent oxygen recompression protocol, is widely used for diving-related DCS. Treatment commonly begins at approximately 2.8 atmospheres absolute, equivalent to 60 feet of seawater, and includes scheduled oxygen-breathing periods separated by air breaks. The profile may be extended when significant symptoms continue to improve under pressure. (UHMS)

The selected table depends on:

• Symptom severity
• Neurologic findings
• Response at treatment pressure
• Time from symptom onset
• Previous recompression
• Pulmonary status
• Oxygen tolerance
• Chamber capability
• The diving physician’s assessment

More severe or refractory cases may require a longer table, a modified protocol, or additional treatments. Treatment-table selection should be directed by a physician experienced in diving and hyperbaric medicine.

Oxygen Toxicity During Recompression

DCS treatment tables may deliver a larger oxygen dose than many routine HBOT protocols. Scheduled air breaks help reduce uninterrupted exposure, but central nervous system or pulmonary oxygen toxicity can still occur.

Possible warning findings include:

• Visual or auditory changes
• Nausea
• Facial or limb twitching
• Irritability
• Dizziness
• Seizure
• Substernal burning
• Cough
• Pain with inspiration

If central nervous system oxygen toxicity is suspected, oxygen exposure is stopped and the patient breathes chamber air according to the treatment protocol. An active convulsion should be managed without placing objects in the mouth, and decompression should wait until the patient is relaxed and breathing normally unless another overriding emergency exists.

The possibility of oxygen toxicity does not remove the need for recompression. It requires trained chamber personnel, continuous observation, air breaks, and modification of the treatment profile when necessary.

Early Treatment Is Preferred, but Late Treatment May Still Help

The probability of complete recovery is generally greater when recompression begins early. Bubbles may become less responsive over time, and inflammatory or ischemic tissue injury may become established.

Real-world treatment is often delayed because symptoms are not recognized, the diver is in a remote location, oxygen is unavailable, or transport requires many hours. A delay of 24 hours or more may reduce treatment effectiveness, but it does not prove that HBOT will provide no benefit.

Divers with persistent or recurrent symptoms should still be discussed with a diving-medicine specialist. Meaningful improvement has been observed after delayed recompression, and the decision should be based on the patient’s current findings rather than time alone. (German Journal of Sports Medicine)

Additional HBOT for Residual Symptoms

Many patients improve substantially after one recompression treatment. Some have persistent weakness, sensory changes, vertigo, bladder dysfunction, pain, or cognitive findings.

Additional HBOT may be considered when:

• Significant symptoms remain
• Improvement occurred during the initial treatment
• Symptoms recur after initial relief
• Further improvement occurs with subsequent treatment
• Tissue remains clinically salvageable

The U.S. Navy manual allows additional recompression for residual manifestations and advises continuing while sustained improvement is occurring. Treatment may be stopped when further sessions no longer produce meaningful progress, with the decision individualized by the treating diving-medicine physician.

Repeat treatment should not become automatic. Persistent symptoms may also require imaging, neurologic evaluation, rehabilitation, urologic care, audiology, or assessment for another diagnosis.

Evidence Supporting Recompression

Recompression with oxygen is accepted as the standard treatment for DCS, although the evidence base differs from that of many common therapies.

Randomized trials comparing recompression with no recompression are lacking. Withholding definitive treatment from a patient with neurologic, inner-ear, or cardiopulmonary DCS would create serious ethical and practical concerns. Support therefore comes from established gas physics, physiologic studies, historical experience, observational outcomes, and the frequently rapid response of symptoms during treatment. (PubMed Central (PMC))

Randomized research has compared variations in recompression and adjunctive treatment, but there is limited evidence proving that one oxygen table is superior in every presentation. This supports individualized protocol selection while preserving the central principle that symptomatic diving-related DCS should receive hyperbaric consultation and recompression whenever feasible. (PubMed)

In-Water Recompression Is Not Routine First Aid

In-water recompression involves returning a symptomatic diver underwater, usually while breathing oxygen, to increase ambient pressure before controlled ascent.

This approach carries substantial risks:

• Drowning
• Oxygen toxicity
• Hypothermia
• Vomiting or loss of consciousness underwater
• Inadequate monitoring
• Worsening weather or sea conditions
• Incomplete treatment
• Delayed evacuation

It should not be improvised by recreational divers. In-water recompression may be considered only in exceptional remote settings where chamber evacuation is not reasonably available and where trained personnel, appropriate oxygen equipment, thermal protection, communications, and a validated protocol are already in place. (Divers Alert Network)

Surface oxygen and organized evacuation remain the appropriate response for most diving operations.

Observation After Recompression

Clinical improvement at the end of a treatment does not eliminate the possibility of recurrence.

Post-treatment observation should reflect:

• Initial symptom severity
• Completeness of recovery
• Treatment table used
• Need for repeated treatment
• Distance from the chamber
• Availability of a responsible companion
• Associated medical conditions

Current U.S. Navy guidance uses longer observation for neurologic DCS and patients requiring Treatment Table 6, and it recommends that treated patients remain near recompression capability during the early post-treatment period. Patients with residual symptoms may require hospitalization or transfer to a medical facility.

Discharge instructions should identify recurrent pain, weakness, numbness, gait disturbance, vertigo, bladder problems, breathing difficulty, confusion, and loss of consciousness as reasons for immediate reassessment.

Rehabilitation After Neurologic DCS

HBOT treats the bubble-related and hypoxic components of DCS, but it cannot always reverse tissue that has already been permanently injured.

Patients with residual neurologic impairment may require:

• Physical therapy
• Occupational therapy
• Gait and balance training
• Bladder management
• Pain management
• Vestibular rehabilitation
• Audiology
• Neuropsychological assessment
• Psychological support

Rehabilitation should begin as soon as the patient is medically stable. Functional recovery may continue after the final chamber treatment, particularly when the patient receives coordinated neurologic and rehabilitation care. (Divers Alert Network)

Returning to Diving After DCS

A diver should not return to diving solely because symptoms have disappeared.

Assessment should consider:

• The severity and location of the injury
• Whether neurologic deficits completely resolved
• The number of recompression treatments required
• The cause of the incident
• Pulmonary or cardiovascular risk factors
• Possible right-to-left shunting
• The diver’s medical fitness
• The type of future diving planned

A diving-medicine physician may recommend additional evaluation after neurologic, inner-ear, recurrent, or otherwise unexplained DCS. The appropriate interval before returning varies considerably and should not be determined through a universal online schedule.

Some divers with serious residual neurologic injury, recurrent DCS, or an uncorrected predisposing condition may be advised not to return to compressed-gas diving.

A Coordinated Clinical Response

Effective treatment begins before the chamber doors close.

A practical response includes:

1. Recognize symptoms occurring after a relevant pressure exposure.
2. Stop further diving and provide the highest practical concentration of oxygen.
3. Perform basic stabilization and a focused neurologic assessment.
4. Contact emergency services and a diving-medicine resource.
5. Record the dive profile and symptom timeline.
6. Minimize unnecessary exertion and altitude exposure.
7. Stabilize serious airway, pulmonary, cardiac, or traumatic conditions.
8. Arrange early recompression at a capable hyperbaric facility.
9. Reassess after treatment and provide additional HBOT when meaningful improvement remains possible.
10. Coordinate follow-up, rehabilitation, and future diving-clearance decisions.

HBOT for decompression sickness is not simply oxygen treatment at a higher pressure. It is a structured emergency intervention that reduces bubble volume, accelerates inert-gas elimination, restores tissue oxygenation, and limits secondary vascular and inflammatory injury.

Its effectiveness depends on early recognition, immediate surface oxygen, safe transport, an appropriate recompression protocol, and continued care for any residual neurologic or functional impairment.