Decompression Sickness

Severe symptoms may manifest within minutes of surfacing, but in most patients, symptoms begin gradually, sometimes with a prodrome of malaise, fatigue, anorexia, and headache. Symptoms occur within 1 hour of surfacing in about 50% of patients and by 6 hours in 90%. Rarely, symptoms can manifest 24 to 48 hours after surfacing, particularly by exposure to altitude after diving (such as air travel).

Type I decompression sickness typically causes pain in the joints (most commonly elbows and shoulders) and occasionally muscles; the pain typically does not intensify during movement and is described as “deep” and “boring.” Other manifestations include lymphedema, skin mottling, itching, and rash.

Type II decompression sickness consists of neurologic and sometimes respiratory symptoms. It typically manifests with paresis, numbness and tingling, difficulty urinating, and loss of bowel or bladder control. Headache and fatigue may be present but are nonspecific. Dizziness, tinnitus, and hearing loss may result if the inner ear is affected. Severe symptoms include seizures, slurred speech, vision loss, confusion, and coma. Death can occur.

The chokes (respiratory decompression sickness) is a rare but grave manifestation; symptoms include shortness of breath, chest pain, cough, resulting from pulmonary edema. Massive bubble embolization of the pulmonary vascular tree can result in rapid circulatory collapse and death.

Dysbaric osteonecrosis is a late manifestation of decompression sickness and often occurs without any previous symptoms. It is an insidious form of osteonecrosis Osteonecrosis (ON) Osteonecrosis is a focal infarct of bone that may be caused by specific etiologic factors or may be idiopathic. It can cause pain, limitation of motion, joint collapse, and secondary osteoarthritis... read more caused by prolonged or closely repeated exposures to increased pressure (typically in people working in compressed air and in deep commercial rather than recreational divers). Deterioration of shoulder and hip articular surfaces can cause chronic pain and disability due to secondary osteoarthritis.

Deep vein thrombosis Deep Venous Thrombosis (DVT) Deep venous thrombosis (DVT) is clotting of blood in a deep vein of an extremity (usually calf or thigh) or the pelvis. DVT is the primary cause of pulmonary embolism. DVT results from conditions... read more and pulmonary embolism Pulmonary Embolism (PE) Pulmonary embolism (PE) is the occlusion of pulmonary arteries by thrombi that originate elsewhere, typically in the large veins of the legs or pelvis. Risk factors for pulmonary embolism are... read more can complicate immobility due to decompression sickness.

Diagnosis is clinical. CT and MRI may be helpful to rule out other disorders that cause similar symptoms (eg, herniated intervertebral disk, ischemic stroke, central nervous system hemorrhage). Although these studies sometimes show brain or spinal cord abnormalities due to decompression sickness, their sensitivity for decompression sickness is low, and treatment should usually begin based on clinical suspicion.

Arterial gas embolism Arterial Gas Embolism Arterial gas embolism is a potentially catastrophic event that occurs when gas bubbles enter or form in the arterial vasculature and occlude blood flow, causing organ ischemia. Arterial gas... read more can have similar manifestations (for a comparison of features, see table ). However, immediate treatment for both is similar.

For dysbaric osteonecrosis, skeletal x-rays may show joint degeneration, which cannot be distinguished from that caused by other joint disorders; MRI is usually diagnostic.

The majority of patients recover completely.

Initially, high-flow 100% oxygen enhances nitrogen washout by widening the nitrogen pressure gradient between the lungs and the circulation, thus accelerating reabsorption of nitrogen-containing embolic bubbles.

To restore lost intravascular volume, oral resuscitation fluid (or plain water) is indicated for alert patients with mild manifestations. Isotonic, glucose-free IV fluids are indicated for those with serious manifestations.

Recompression therapy Recompression Therapy Recompression therapy is administration of 100% oxygen for up to several hours in a sealed chamber pressurized to at least 1.9 (usually 1.9 to 3.0) atmospheres, gradually lowered to atmospheric... read more is indicated for all patients except perhaps those whose symptoms are limited to itching, skin mottling, and fatigue, which may be treatable with oxygen alone; patients should be observed for deterioration (1 Treatment references Decompression sickness occurs when rapid pressure reduction (eg, during ascent from a dive, exit from a caisson or hyperbaric chamber, or ascent to altitude) causes gas previously dissolved... read more ). Patients with more severe symptoms are transported to a suitable recompression facility. Because time to treatment and severity of the injury are important determinants of outcome, transport should not be delayed for performance of nonessential procedures.

If air evacuation is required, an aircraft capable of 1 atmosphere internal pressure is preferred. In unpressurized aircraft, low altitude (< 609 m [< 2000 ft]) should ideally be maintained and oxygen given continuously. Commercial aircraft, although pressurized, typically have a cabin pressure up to an equivalent of 2438 m (8000 ft) at normal cruise altitude, which may exacerbate symptoms. Flying in commercial aircraft shortly after a dive can precipitate symptoms. The risk of altitude exposure in patients with decompression illness should be balanced against the risk of deterioration if not evacuated for definitive treatment.

When symptoms are mild (eg, normal neurologic examination and stable for 24 hours), delayed recompression or evacuation by commercial airliner is unlikely to worsen long-term outcome.

Because decompression sickness or arterial gas embolism can be complicated by deep vein thrombosis Deep Venous Thrombosis (DVT) Deep venous thrombosis (DVT) is clotting of blood in a deep vein of an extremity (usually calf or thigh) or the pelvis. DVT is the primary cause of pulmonary embolism. DVT results from conditions... read more and pulmonary thromboembolism Pulmonary Embolism (PE) Pulmonary embolism (PE) is the occlusion of pulmonary arteries by thrombi that originate elsewhere, typically in the large veins of the legs or pelvis. Risk factors for pulmonary embolism are... read more , periodic ultrasonography of the leg veins should be considered.

Significant bubble formation can usually be avoided by limiting the depth and duration of dives to a range that does not need decompression stops during ascent (called no-stop limits) or by ascending with decompression stops as specified in published guidelines (eg, the decompression table in the chapter Diagnosis and Treatment of Decompression Sickness and Arterial Gas Embolism in the U.S. Navy Diving Manual). Many divers wear a portable dive computer that continually tracks depth and time at depth and calculates a decompression schedule.

In addition to following published and computer-generated guidelines, many divers make a safety stop for a few minutes at about 4.6 m (15 ft) below the surface. However, cases can occur after appropriately identified no-stop dives, and the incidence of decompression sickness has not decreased despite widespread use of dive computers (although fewer serious cases occur).

Dives < 24 hours apart (repetitive dives) and dives performed at altitude require special techniques to determine proper decompression procedures.

The following English-language resources may be useful. Please note that THE MANUAL is not responsible for the content of these resources.