OVERVIEW

What is decompression sickness?

Decompression sickness, also known as diver's disease, caisson disease, or the bends.

As the name suggests, it occurs when a diver ascends from a high-pressure underwater environment to the surface's atmospheric pressure. Due to the decrease in external pressure, excess gas accumulated in the body cannot be released in time, forming bubbles in the blood and tissues, leading to discomfort.

Main symptoms include rashes, joint pain, muscle pain, chest pain, limb numbness, paralysis, etc. Severe cases can be fatal.

The primary treatments are oxygen therapy and hyperbaric oxygen therapy, with most patients responding well.

Is decompression sickness common?

With more people learning and trying recreational scuba diving (SCUBA, using self-contained underwater breathing apparatus), cases of decompression sickness have increased.

However, for the general recreational diving population, the incidence is relatively low—about 4–6 cases per 10,000 people. Occupational divers have a higher incidence.

What are the types of decompression sickness?

Decompression sickness is classified into Type I and Type II.

• Type I: Mild, mainly affecting the musculoskeletal system, skin, and lymphatic system. Common symptoms include muscle pain, localized joint pain (especially in elbows and knees), rashes, itching, and swollen lymph nodes. This type is less severe and usually not life-threatening.
• Type II: Severe, primarily involving the nervous, respiratory, and circulatory systems. Symptoms include numbness, paralysis, seizures, confusion, difficulty breathing, etc. This type is serious and may cause permanent damage or death.

SYMPTOMS

What are the common manifestations of decompression sickness?

Decompression sickness occurs when oxygen and nitrogen not promptly expelled from a diver's body form bubbles in the blood and tissues.

Since bubbles can travel with the blood to any part of the body, the clinical symptoms of decompression sickness can involve multiple systems and vary widely.

Among patients with decompression sickness, about 75% develop symptoms within 1 hour of surfacing, and approximately 90% experience symptoms within 12 hours. Only a few patients exhibit symptoms 24 hours after surfacing.

Symptoms often appear gradually, taking some time to peak. Initial symptoms may include discomfort, fatigue, loss of appetite, headache, and mental confusion. Depending on whether it is mild (Type I) or severe (Type II), different manifestations may occur, as detailed below.

What are the symptoms of mild decompression sickness?

Type I decompression sickness is the milder form, primarily affecting the musculoskeletal system, skin, and lymphatic system, also known as musculoskeletal decompression sickness.

The hallmark symptom is pain, often felt in joints and muscles, with the elbows and knees being the most commonly affected. Initially, the pain may be mild or intermittent but gradually worsens, typically described as "deep." Movement may exacerbate the pain.

If the skin or lymphatic system is involved, symptoms like itching, skin mottling, rashes, swollen lymph nodes, or localized edema may occur. Itching is relatively common, usually affecting the upper torso and often resolving on its own within half an hour. Other symptoms are rare.

Note that while these symptoms are not life-threatening, they may signal more severe conditions, requiring close monitoring.

What are the symptoms of severe decompression sickness?

Type II decompression sickness is the more severe form, potentially causing permanent damage or death, primarily affecting the nervous system and lungs.

Since nitrogen dissolves easily in fat, and the brain and spinal cord are rich in fat, the nervous system is particularly vulnerable.

About 60% of decompression sickness patients experience neurological symptoms, ranging from nonspecific issues like headaches and fatigue to spinal cord damage, such as sensory loss, numbness, tingling, difficulty urinating, or incontinence. Mild weakness or tingling can progress to irreversible paralysis within hours.

Patients with brain involvement may exhibit memory loss, unsteady gait, slurred speech, blindness, seizures, confusion, coma, or even death.

In about 5% of cases, bubbles may block part of the pulmonary circulation, causing chest pain, coughing, wheezing, difficulty breathing, and a sense of suffocation. Though rare, this can lead to acute circulatory failure, shock, and death.

What serious consequences can decompression sickness cause?

Severe decompression sickness may result in irreversible neurological damage, leading to paralysis, blindness, coma, or death. It can also affect the respiratory and circulatory systems, causing acute circulatory failure, cardiogenic shock, and death.

Additionally, decompression sickness can damage bone tissue, leading to long-term complications like dysbaric osteonecrosis or aseptic bone necrosis, which may cause chronic pain and severe disability. However, these are more common in professional divers and rarely occur in recreational divers.

CAUSES

What is the cause of decompression sickness?

To understand the cause of decompression sickness, we first need to review some basic physics:

• First, the main components of air are nitrogen and oxygen;
• Second, "Henry's Law," which states that at a constant temperature, the amount of gas dissolved in a liquid is proportional to the partial pressure of the gas.

In other words, because air is compressed in high-pressure underwater environments, divers breathing at depth inhale more gas molecules than they would on the surface. While the oxygen is typically consumed by the body, excess nitrogen molecules accumulate in the blood and tissues.

When a diver ascends, the external pressure decreases, and the total gas tension in the tissues may exceed the ambient pressure. If the nitrogen is not eliminated in time, bubbles can form in the blood and tissues.

Depending on the size and location of these bubbles, they can cause various symptoms, including rashes, joint pain, muscle pain, chest pain, limb numbness, and even paralysis.

Who is more prone to decompression sickness?

Decompression sickness can occur in anyone, but individuals with organic heart diseases—especially right-to-left shunts (such as patent foramen ovale, atrial/ventricular septal defects, patent ductus arteriosus, or partially corrected tetralogy of Fallot)—are at higher risk. Inexperienced divers, fatigued divers, obese individuals, and the elderly are also more susceptible.

Additionally, studies suggest that men may have a higher risk of decompression sickness than women. However, this difference may be related to specific diving behaviors—such as men tending to dive deeper, ascend faster, or perform multiple dives per day—rather than gender itself.

DIAGNOSIS

How is decompression sickness diagnosed?

The diagnosis of decompression sickness is primarily clinical, based on medical history and physical examination: A patient with a history of diving and typical decompression sickness-related symptoms can be diagnosed.

During the visit, doctors may use CT, MRI, echocardiography, or other related methods to assist in confirmation or differential diagnosis.

What tests are needed for decompression sickness?

As mentioned earlier, the diagnosis of decompression sickness mainly relies on medical history and clinical manifestations, and auxiliary tests are not mandatory. Some tests, such as CT or MRI, may sometimes reveal abnormalities in the brain or spinal cord or help differentiate other neurological disorders, but they are not entirely reliable.

Before CT or MRI results are available, hyperbaric oxygen therapy can often be initiated unless the diagnosis is unclear or the diver's condition is stable.

Additionally, for some long-term complications, such as dysbaric osteonecrosis, X-ray plain film examination is required.

TREATMENT

Which department should I visit for decompression sickness?

General Internal Medicine or Respiratory Medicine.

Can decompression sickness heal on its own?

For mild cases with symptoms like fatigue, rash, or itching, most patients may recover with adequate rest and avoiding further diving. However, close monitoring is still necessary to watch for potential worsening.

It is still recommended that such patients receive 100% oxygen therapy via a sealed mask to relieve symptoms, shorten the course, and prevent progression.

For severe cases involving neurological symptoms (e.g., sensory abnormalities, paralysis, seizures, confusion) or respiratory distress, immediate hospital treatment with hyperbaric oxygen therapy (HBOT) is essential to avoid serious consequences.

How is decompression sickness treated?

Hyperbaric oxygen therapy (HBOT) is the primary treatment. Patients typically undergo 2–5 hours in a single- or multi-person chamber to reduce bubble size, accelerate absorption, and allow excess gas to safely exit the body, restoring normal blood flow and oxygen supply to affected tissues.

Prognosis is closely tied to the timing of HBOT—delays increase the risk of permanent damage.

Note that symptoms may rebound within the first 24 hours, and some patients experience neurological deterioration post-treatment. Thus, even mild or transient pain or neurological symptoms warrant HBOT.

Patients with residual injuries may require repeated, intermittent HBOT over several days for maximal improvement.

HBOT remains beneficial within 48 hours post-dive, so patients should be transported to a facility regardless of distance. If air transport is needed, use a plane with a cabin pressure of 1 atm to avoid worsening symptoms. Provide pure oxygen via a sealed mask and oral/IV fluids during transit.

Does decompression sickness require hospitalization?

Mild cases usually do not require hospitalization. Symptoms often resolve with oxygen therapy, rest, and avoiding further diving, or a single HBOT session if available.

Severe cases, however, typically need multiple HBOT sessions and hospitalization due to complications like neurological or cardiopulmonary symptoms.

Can decompression sickness be completely cured?

Timing of treatment and severity of injury are key prognostic factors.

• Overall prognosis is good. Mild cases often fully recover with prompt treatment.

• About 75% of severe cases achieve complete recovery with timely HBOT, while ~16% may have residual symptoms for up to 3 months. Rarely, permanent neurological damage (e.g., partial paralysis) or death occurs, often due to delayed treatment or irreversible injury.

• Professional divers may develop chronic, hard-to-treat decompression sickness, leading to long-term complications like bone necrosis, persistent pain, or disability—rarely seen in recreational divers.

DIET & LIFESTYLE

What should patients with decompression sickness pay attention to in their diet?

There are no special dietary restrictions for patients with decompression sickness. They should focus on eating more fruits and vegetables, maintaining a balanced diet with both meat and vegetables, using less salt and high-sodium seasonings during cooking, avoiding pickled foods, and refraining from alcohol as much as possible.

What should patients with decompression sickness pay attention to in daily life?

Even if patients with decompression sickness experience only mild symptoms, they must take them seriously:

• Rest and stay warm, hydrate to avoid dehydration, and receive oxygen therapy if possible.
• Lying on the left side or in a slightly head-down, feet-up supine position may help.
• Avoid diving again, flying, or traveling to high-altitude areas.
• If symptoms worsen, seek medical attention immediately. Hospitalization may be necessary—do not ignore the serious consequences of the condition.

Does decompression sickness affect fertility?

Decompression sickness itself does not affect fertility. However, pregnant women are advised against diving because abnormal maternal thermoregulation and changes in blood flow during pregnancy can increase the risk of decompression sickness in the fetus. Additionally, due to the lack of effective pulmonary capillary filtration, the fetus faces higher risks of deformities and arterial gas embolisms.

Can patients with decompression sickness fly, engage in strenuous exercise, or travel to high-altitude areas?

Patients with decompression sickness should avoid these activities until fully recovered, as they may worsen the condition and lead to irreversible damage or even death.

For those who have dived but show no symptoms of decompression sickness, it is recommended to stay on the ground for at least 12 hours before flying or traveling to high-altitude areas to avoid triggering the condition. For multiple dives or those involving decompression stops, the waiting period should be extended to at least 48 hours.

PREVENTION

Can decompression sickness be prevented? How to prevent it?

Yes, it can be prevented.

• Beginners should seek guidance from professional institutions or instructors and obtain proper certification before diving.
• Control diving depth and duration based on personal conditions, and limit the total amount of gas inhaled during diving to prevent decompression sickness.
• Use a portable dive computer or refer to authoritative guidelines (e.g., the U.S. Navy Diving Manual) to plan decompression stops during ascent, which usually helps avoid significant bubble formation and reduces harm.
• In addition to following dive computers or manuals during ascent, performing a safety stop at about 4–5 meters underwater for a few minutes may also help prevent decompression sickness.
• Even if no symptoms appear after diving, wait at least 12 hours before flying or traveling to high-altitude areas. If multiple dives occur within a few days, extend this period to over 48 hours.
• If mild symptoms of decompression sickness occur, avoid diving again for at least 2 weeks after full recovery.
• People at high risk of decompression sickness (e.g., those with structural heart conditions like PFO or atrial/ventricular septal defects, obesity, advanced age, or pregnancy) should avoid diving.
• Avoid dehydration, fatigue, cold-water diving, and strenuous exercise after diving.