All About Decompression Sickness

Causes, Types and Symptoms

Navy Diver 2nd Class Josh King, assigned to Commander, Task Group (CTG) 56.1, cleans the inside of a transportable recompression chamber system (TRCS) as part of regular maintenance. The TRCS simulates surface decompression for the treatment of decompression sickness and pressure tests for prospective divers.
A Navy Diver inside a portable decompression chamber, used for treating the bends. U.S. Navy photo by Mass Communication Specialist 3rd Class Wyatt Huggett/Flickr/CC BY 2.0

Also known as "the bends" and Caisson Disease, decompression sickness affects divers or other people (such as miners) exposed to rapid changes in air pressure. In recent years, the medical term decompression illness has gained more traction—the term is technically more precise than decompression sickness, but it relates to the same condition.

DCS, as it is commonly known, is caused by a build-up of nitrogen gas in the bloodstream.

When we breathe at sea level, approximately 79 percent of the air we're breathing is nitrogen. As we descend in water, the pressure around our bodies increases at the rate of one unit of atmosphere for every 33 feet of depth, causing nitrogen to be forced from the bloodstream and into adjacent tissues. This process is not actually harmful and it's quite possible for the body to continue to absorb nitrogen until it reaches a point called saturation, which is the point at which the pressure in the tissues equals the surrounding pressure.

Decompression Safety

The problem arises when the nitrogen in the tissue needs to be released. To remove the nitrogen slowly from the body—a process called off-gassing—a diver must ascend at a slow, controlled rate and carry out decompression stops if necessary; this hovering in the water allows the nitrogen to slowly seep out of the body tissues and return to the bloodstream, where it's released from the body through the lungs.

If a diver ascends too fast, the residual nitrogen in the tissues expands too quickly and forms gas bubbles. These bubbles must normally be on the arterial side of the circulatory system to be harmful—they are usually harmless on the venous side.

Type I Decompression Sickness

Type I decompression sickness is the least serious form of DCS.

It normally involves only pain in the body and is not immediately life threatening. However, the symptoms of Type I decompression sickness may be warning signs of more serious problems.

Cutaneous Decompression SicknessThis condition arises when the nitrogen bubbles come out of solution in skin capillaries. This normally results in a red rash, often on the shoulders and chest.

Joint and Limb Pain Decompression Sickness: This type is characterized by aching in the joints. It is not known exactly what causes the pain as bubbles in the joint would not have this effect. The common theory is that it is caused by the bubbles aggravating bone marrow, tendon and joints. The pain can be in one place or it can move around the joint. It is unusual for bisymmetric symptoms to occur.

Type II Decompression Sickness

Type II decompression sickness is the most serious and can be immediately life-threatening. The main effect is on the nervous system.

Neurological Decompression Sickness: When nitrogen bubbles affect the nervous system they can cause problems throughout the body. This type of DCS normally shows as tingling, numbness, respiratory problems and unconsciousness. Symptoms can spread quickly and if left untreated can lead to paralysis or even death.

Pulmonary Decompression Sickness: This is a rare form of Decompression Sickness that occurs when bubbles form in lung capillaries. Although the majority of the time the bubbles dissolve naturally through the lungs; however, it is possible for them to interrupt blood flow to the lungs, which can lead to serious and life-threatening respiratory and heart problems.

Cerebral Decompression Sickness: It is possible for bubbles that make their way into the arterial blood stream to move to the brain and to cause an arterial gas embolism. This is extremely dangerous and can be identified by symptoms such as blurred vision, headaches, confusion and unconsciousness.

Other Forms of Decompression Sickness

Extreme tiredness is very common in cases of DCS and can sometimes be the only symptom of decompression sickness present.

It is also possible for decompression sickness to occur in the inner ear. This problem is caused by bubbles forming in the cochlea's perilymph during decompression. The result can be hearing loss, dizziness, ringing of the ears and vertigo.

Symptoms

Decompression sickness can manifest itself in many different ways and has many different symptoms, but the most common symptoms are:

  • Extreme fatigue
  • Joint and limb pain
  • Tingling
  • Numbness
  • Red rash on skin
  • Respiratory problems
  • Heart problems
  • Dizziness
  • Blurred vision
  • Headaches
  • Confusion
  • Unconsciousness
  • Ringing of the ears
  • Vertigo
  • Stomach sickness

Risk Factors

Every diver has a different level of risk of Decompression Sickness. Many risk factors are still not fully understood, but there are a few basic factors that doctors agree increase the chance of developing Decompression Sickness:

  • Body Fat: The theory is that nitrogen absorbs more easily into fat, so an overweight diver is at a greater risk of decompression sickness.
  • Exercise: Interestingly, exercise has both a positive and negative effect. Exercise at least 12 hours before a dive seems to produce proteins that protect the body and decrease the risk of decompression sickness. On the other hand, exercise less than 12 hours before a dive can raise the number of gas micronuclei on which bubbles form, and this increases the risk of decompression sickness. Exercise immediately after a dive increases the risk of bubbles forming as blood pressure is increased and bubbles can more easily be transferred from the venous to the arterial side of the circulatory system.
  • Gender: Theoretically women should have a higher risk of Decompression Sickness due to the fact that women typically have a higher body fat percentage. However, this has not been proven in studies and it's possible that gender does not affect the chances of suffering from decompression sickness.
  • Age: Generally, older people are at an increased risk of decompression sickness. This is due to less efficient circulatory and respiratory systems.
  • Fitness: Fitness definitely decreases the risk of decompression sickness. A fitter body is able to tolerate more physical stress, including decompression sickness.
  • Dehydration: Dehydration causes less blood to be available for gas exchange which makes it more difficult for the body to off-gas, increasing the risk of decompression sickness.
  • Injury and Illness: Injury and illness can affect normal circulation, increasing the risk of decompression sickness.
  • Alcohol: Consuming alcohol before or after a dive accelerates circulation which helps tissues to load with gas. Alcohol also dilates capillaries which can increase the rate of nitrogen released.
  • Carbon Dioxide: Improper breathing can lead to elevated levels of carbon dioxide, which interferes with the bodies ability to transport gas. This will lead to an increased chance of decompression sickness.
  • Cold: It is generally believed by doctors that diving in cold water increases the risk of decompression sickness. This is due to the body working harder to keep warm as it becomes colder. Meaning that when the body is warmer it is able to absorb gas normally but as it becomes cold it has difficult offing the gas.
  • Altitude and Flying After Diving: When ascending on land or in a plane, the atmospheric pressure changes, and this increases the chances of decompression sickness. It is best not to ascend above 300 meters (1000 feet) or fly after diving. Consult the current flying after diving guidelines to know when it is safe to fly.
  • Patent Foramen Ovale (PFO) - Hole in the Heart: As a fetus, a baby doesn't breathe and needs a way for blood to bypass the lungs until it is born. The body achieves this by having a small opening in the middle of the heart that allows blood to bypass the lungs. Normally, this hole would close within a year of birth, but in approximately 20-34 of people this does not happen, leaving a permanent opening in the heart. Usually, a flap grows over the opening and there is no effect. However, in some cases the flap allows blood to pass through the opening. This means that bubbles are more easily able to pass from the venous to the arterial side of the circulatory system, greatly increasing the risk of decompression sickness. It has been found that a large proportion of divers who suffered from decompression sickness had a PFO.
  • Reverse Profiles: The jury is still out on reverse profiling, or making a deeper dive after a shallower dive. Theoretically it should increase the risk of decompression sickness, but this has not been proven scientifically. It would still be better to err on the side of caution.

Prevention

As there are many risk factors, there are also many methods of prevention. Here's a basic checklist that will help you lower your risk of suffering from Decompression Sickness:

  • Always ascend slowly and safely from every dive
  • Don't push your limits and do all required decompression stops
  • Keep physically fit and within a healthy weight range
  • Don't exercise within 12 hours of diving
  • Don't ascend to altitude or fly immediately after diving
  • Breathe normally throughout the dive, don't exert yourself or skip breathe
  • Make sure you're adequately hydrated before every dive
  • Don't drink alcohol before or after diving and never dive when hungover
  • Get checked out by a doctor to find out if you have a PFO
  • Avoid reverse profiling—just in case

Treatment

Minor cases of DCS may be treated by medical professionals with oxygen; in time, the excess nitrogen in the body will naturally off-gas. More serious situations, including rapid uncontrolled ascents from significant depth, usually require re-pressurization in a hyperbaric oxygen chamber.

Immediate on the scene treatment consists of oxygen therapy and basic first aid. This should be followed as quickly as possible by recompression treatment in a recompression chamber. When treating decompression sickness, the delay in beginning recompression treatment can be the biggest single cause of residual effects.