The Bends (Decompression Sickness)

What Is the Bends (From Diving)?

The bends, or decompression sickness, occurs when nitrogen bubbles expand in the bloodstream and tissues when a scuba diver surfaces too fast.
The bends, or decompression sickness, occurs when a scuba diver surfaces too fast.
  • The bends, also known as decompression sickness (DCS) or Caisson disease, occurs in scuba divers or high altitude or aerospace events when dissolved gases (mainly nitrogen) come out of solution in bubbles and can affect just about any body area including joints, lung, heart, skin and brain.
  • Decompression sickness (DCS) is caused by the formation of bubbles of gas that occur with changes in pressure during scuba diving. It is also experienced in commercial divers who breathe heliox (a special mixture of oxygen and helium), and astronauts and aviators who experience rapid changes in pressure from sea level. Scuba diving will be the focus of this article, as it is the most common activity that may result in the bends.
  • Scuba diving is a sport and hobby that continues to increase in popularity each year. There are several organizations that certify individuals to become recreational divers, two of which are PADI (The Professional Association of Diving Instructors) and NAUI (The National Association of Underwater Instructors).
  • Data collected by Divers Alert Network (DAN) and presented in 2010 revealed 41 cases of DCS out of 137,451 dive profiles collected. It is important to know that even divers who follow decompression schedules and tables may still experience DCS.

What Causes the Bends?

Nitrogen or any gas from a diver's air tank increases in pressure as a diver descends. For every 33 feet in ocean water, the pressure due to nitrogen goes up another 11.6 pounds per square inch. As the pressure due to nitrogen increases, more nitrogen dissolves into the tissues. The longer a diver remains at depth, the more nitrogen dissolves. Unlike the oxygen in the air tank a diver uses to swim underwater, the nitrogen gas is not utilized by the body and builds up over time in body tissues. The underlying cause of symptoms throughout the body is due mainly to nitrogen bubbles being released when the diver returns to sea level and blocking blood flow and disrupting blood vessels and nerves by stretching or tearing them. They may also cause emboli, blood coagulation and the release of vasoactive compounds.

A clear example to illustrate this bubble formation process is that of a bottle of carbonated soda. A bottle of carbonated soda is filled with gas (carbon dioxide), which cannot be seen because it is dissolved in solution under pressure. When the bottle is opened, the pressure is released and the gas leaves the solution in the form of bubbles. A diver returning to the surface is similar to opening the bottle of soda. As a diver swims to the surface, the pressure decreases. The nitrogen, which has dissolved in tissues, wants again to leave, because the body can hold only a certain amount based on that nitrogen pressure.

  • If a diver surfaces too fast, the excess nitrogen will come out rapidly as gas bubbles. Depending on which organs are involved, these bubbles produce the symptoms of decompression sickness.
  • The risk of decompression illness is directly related to the depth of the dive, the amount of time under pressure, and the rate of ascent. Dive tables, such as the U.S. Navy Dive Tables, provide general guidelines as to what depths and dive times are less risky for the development of decompression sickness.

Symptoms of the Bends

The nervous and musculoskeletal system are most often affected. If divers are going to develop symptoms, they will show within 48 hours in all cases. Most have symptoms within 6 hours, while some develop them within the first hour of surfacing from a dive.

DCS is often categorized into two types. Type I indicating mild symptoms and Type II with neurologic and other serious symptoms.

Symptoms of the bends include the following:

Musculoskeletal Symptoms (most common symptoms)

  • Pain in and around major joints with the shoulder and elbows being the most commonly affected in divers, but any joint can be involved due to nitrogen being released into the joints and muscles.


  • Extreme tiredness that is out of proportion to the activity just performed.


  • Rashes that are red or marbled may occur. They can be very itchy also.
  • It is rare to have skin findings with DCS.

Itching (also known as "the creeps")

  • Seen more commonly during decompression in hyperbaric chamber workers (see media photos)
  • Very itchy reaction on the skin that is exposed to pressures of the dive (i.e. not covered up by a wet suit)
  • This is due to gas from the chamber dissolving into the skin and forming bubbles under the skin.
  • The creeps do not occur in divers.

The Chokes (pulmonary or lung decompression sickness)

  • Rare but if it occurs can be very serious
  • A burning pain in the chest that is usually worse with breathing in (inspiration).
  • Other symptoms include cough, difficulty breathing, and cyanosis (blue lips and skin).
  • Divers with the chokes can progress to shock rapidly.

Neurologic Decompression Sickness (these symptoms may be the only DCS signs)

  • The most common area affected in divers is the spinal cord.
  • Symptoms classically include low back pain, "heaviness" of the legs, paralysis and/or numbness of the legs, and even loss of control of the sphincter (or valve) that controls urine and stool resulting in incontinence.
  • Other symptoms may include fatigue, weak or numb upper extremities, chest or abdominal pains.
  • DCS involving the brain can present with dizziness, confusion, decreased awareness, loss of consciousness, loss or limited vision and even difficulty with balance and/or walking.

Lymph nodes (glands)

The lymph glands can be swollen and painful.


Pain can occur at the head, neck, or torso. Pain at these sites versus the arms or legs carries a worse prognosis.


Occasionally someone with decompression illness may have symptoms suggesting an inner ear problem, such as a spinning sensation, deafness, ringing in the ears, or vomiting. This group of symptoms is called the "staggers."

When to Seek Medical Care

Anyone reporting signs or symptoms of decompression illness that began within 48 hours of scuba diving should be seen by a doctor at an emergency care facility immediately.

The doctor will likely presume that a victim reporting symptoms within 48 hours of surfacing from a scuba dive to have decompression illness. It is important to inform the doctor of your recent diving experience and of your symptoms.

The Bends Self-Care at Home

Rescue the diver from the water and provide emergency care within the limits of your training.

  • Dry and rewarm the diver with blankets if hypothermia (drop in body temperature) develops.
  • If you have access to oxygen, a mask should be applied to deliver high-flow oxygen to the individual with symptoms.
  • You can visit the Divers Alert Network website or call them in the United States at (919) 684-9111 to determine where the nearest hyperbaric chamber is located.
  • Transport the person in a supine position (horizontal, lying on his or her back) to an emergency care facility. If a hyperbaric chamber is available, you may coordinate to transport directly to that facility for definitive care.
  • If air transport is used, attempt to find an air frame that can transport the diver below 1,000 feet or is able to be pressurized to sea level pressure. Use high-flow oxygen if it is available during transport.

Treatment for the Bends

The bends are treated in a hyperbaric recompression chamber.

The doctor will first treat immediate life threats, such as breathing problems or shock, if present.

The diver will need high-flow oxygen and IV fluids. Blood and urine will be sent for laboratory tests to assess any blood clotting problems and hydration status.

The diver will likely need to go to a hyperbaric chamber for recompression. During recompression, the chamber becomes pressurized with air and oxygen based on prearranged protocols to simulate pressure depths of 30 to 60 feet. The duration of "the dive" within the chamber varies, but can be up to 12 hours and sometimes longer. At this depth or chamber pressure, bubbles are reduced in size or reabsorbed to ensure adequate blood flow. Recompression prevents further bubble formation and provides high amounts of oxygen to the injured tissues. Further treatments depend on how the diver responds to the initial treatment.

Often the person is admitted to the hospital to monitor medical condition and to ensure that there is no recurrence of symptoms.

The Bends Follow-Up

Follow up immediately for any further signs or symptoms of decompression illness within the next 7 days. After suffering decompression sickness, individuals should not dive again until cleared by a doctor. Depending on the severity of symptoms, and if the person has suffered decompression sickness before, the doctor will likely recommend not to dive again or to avoid diving for some amount of time.

The Bends Prevention

Decompression illness or the bends and other types of barotrauma (decompression sickness) may be prevented by following guidelines for diving taught in professional diving courses.

The following actions increase risk of developing decompression illness:

  • Diving outside dive table recommendations
  • Flying within 18 hours after diving: Most experts consider it reasonably safe to fly 12 hours after the last dive if the person only dove once, dove easily within the dive tables, and no decompression stop was required. For more complicated diving, waits of 48 hours have been recommended. In general, the longer a person waits to fly after diving, the lower the risk of developing decompression sickness. Even long waits, however, do not reduce the risk all the way to zero. Data collected by DAN (Divers Alert Network) from 1987 to 1999, showed that 17% of divers in the DAN injury database had their first symptoms of DCS either during or after flying.
  • Diving in cold water
  • Obesity (nitrogen is lipid-soluble)
  • Dehydration
  • Recent alcohol intoxication
  • Vigorous exertion while diving
  • Multiple repetitive dives
  • Jogging or other heavy exercise within 6 hours of a dive

The Bends Prognosis

Prognosis or outlook of people who develop the bends varies with the following factors:

  • Prognosis is good with hyperbaric oxygen treatment.
  • Delay to hyperbaric oxygen treatment: Although reports show that divers can do well after days of symptoms, delay in definitive treatment may cause damage that is irreversible.
  • Severity of symptoms: Joint pains alone do better than focal weakness or inability to urinate.
  • Preexisting health: Young, healthy people can tolerate a greater insult to their health than an older person with other diseases.

The Bends Pictures

State-of-the-art hyperbaric oxygen chamber by HyperTec.
State-of-the-art hyperbaric oxygen chamber by HyperTec.

State-of-the-art single person chamber by HyperTec.
State-of-the-art single-person chamber by HyperTec.

Simulated dive.
Simulated dive.

symptoms of the bends, decompression sickness symptoms

Decompression Sickness Symptoms

What are the signs of the bends?

Decompression sickness symptoms generally begin within 6-48 hours after diving.

Type I (involving the muscles, skin, and lymphatics) symptoms include:

  • aching of joints (most commonly the elbow and shoulder),
  • mottling of the skin,
  • itching, and
  • rash.

Type II (involving the brain, ears, and lungs) symptoms include:

  • nausea,
  • vomiting,
  • headaches,
  • fatigue,
  • dizziness,
  • numbness and tingling, and
  • chest pain.
References Decompression Sickness.