what is decompression sickness

When deciding to become a scuba diver and explore the underwater world, the most important rule you will learn is to “continue breathing, and never, ever hold your breath.” Holding your breath while on a dive can cause a diver’s lungs to expand, putting them at risk for lung overexpansion injuries.

Scuba diving students also learn how to set up dive gear, how to clear water from their mask while on a dive, and to maintain their buoyancy in the water. These are just a few of the many skills learned by divers to be safe in the water.

Another important concept you will learn about in your diving course is decompression sickness and how to avoid it while scuba diving. Decompression sickness (DCS) is caused when nitrogen bubbles form in the bloodstream and tissues of the body. These nitrogen bubbles occur when a diver ascends from deep water towards the surface too quickly.

A diver with decompression sickness usually notices the symptoms almost immediately following a dive. Decompression sickness can cause unconsciousness or even death.

the bends

You do not have to be a scientist to understand what causes decompression sickness. So, let’s talk about gas law and how it relates to decompression sickness. You can also learn more about the science of breathing underwater in the video below.

In 1803, William Henry, an English physician, and chemist proposed what is now called Henry’s law. Henry’s law states that “at a constant temperature, the amount of a given gas dissolved in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid.” The air we breathe every day contains roughly 79% nitrogen and 21% oxygen, so does the compressed air in a standard diving tank. As a scuba diver, Henry’s law tells us that when the depth of your dive increases, so does the pressure, causing the amount of nitrogen being dissolved into a diver’s bloodstream to increase.

If safety precautions are not taken by a diver to maintain a slow controlled ascent, including a safety stop, the risk of decompression sickness increases. The depth and time of a dive also affect the amount of nitrogen absorbed into your body tissues and bloodstream, so it is crucial to plan each dive accordingly.

Dive tables and standards have been developed over the years to help divers plan their dives safely to prevent decompression sickness. Using the dive tables, a diver can plan repetitive dives that include safety stops, no-decompression limits, and surface intervals. The dive tables create boundaries based on gas law and the time needed to allow the nitrogen to escape from the body safely. Many divers now use dive computers in place of dive tables. The Professional Association of Dive Instructors (PADI) recommends that each diver has their own dive computer. PADI also suggests and that when diving with a buddy, to follow the most conservative computer’s limits.

Even if divers follow the dive tables or a dive computer, that does not guarantee decompression sickness will be avoided. Factors such as diving in cold water, in strong currents, overexertion, or lack of fluid can also put divers at risk for decompression sickness. Physical fitness, age, sex, and percentage of body fat should also be considered.

To help prevent the bends in scuba diving, always perform slow and controlled ascents, never exceed your no-decompression limits (NDL), do not drink alcohol before diving, stay hydrated, and avoid flying or driving to higher elevations within 24 hours of a dive.

Why is decompression sickness called the bends? DCS is known as “the bends” because of the associated joint pain. Joint pain is the most common symptom of decompression sickness. Decompression sickness occurs when nitrogen forms bubbles in the blood, coming up too fast from a dive puts divers at risk for the bends.

Contrary to some belief, decompression sickness can be called “the bends” not “the benz” in scuba diving. Some other names given to types of decompression sickness are the “staggers” for nervous system-related symptoms and “the chokes” when divers experience breathing-related symptoms with DCS.

The bends in scuba diving can affect almost any area of the body or any organ. Symptoms of decompression sickness usually occur within one hour and up to twenty-four hours after a dive; sometimes even longer in severe cases.

Symptoms of the bends include the following:

  • Joint and muscle pain
  • Confusion and unusual behavior
  • Coughing up blood
  • Difficulty urinating
  • Dizziness or vertigo
  • Fatigue
  • Headache
  • Loss of hearing or ringing in ears
  • Memory loss
  • Nausea
  • Rashes
  • Sensitive, painful, or itchy skin
  • Shortness of breath
  • Swelling
  • Tingling, numbness, and paralysis
  • Unconsciousness
  • Uncontrollable shaking
  • Visual disturbances
  • Vomiting
  • Weakness

Decompression sickness is usually divided into two categories. According to the Divers Alert Network, “Type 1 DCS is usually characterized by musculoskeletal pain and mild cutaneous, or skin, symptoms,” and “Type 2 symptoms are considered more serious. They typically fall into three categories: neurological, inner ear, and cardiopulmonary.”

Itching skin and mild rashes are a typical Type 1 symptom. Swelling and localized pain in the tissues surrounding lymph nodes, such as the groin, armpits or behind the ears, is another Type 1 symptom; but is less common.

In Type 2 DCS, neurological symptoms generally include numbness, muscle weakness, confusion, difficulty walking, paresthesia, or a tingling sensation. Ringing in the ears, known as “tinnitus,” as well as hearing loss, vertigo, vomiting, and impaired balance are also common. These symptoms are related to the inner ear. Dry cough, chest pain, and breathing difficulty are Type 2 cardiopulmonary symptoms.

In extreme cases of decompression sickness, nitrogen bubbles in the brain can form; or in the spinal cord or nervous system column. If any of these symptoms are noticed during or after a dive, it is essential to react quickly. If still on the dive, end the dive immediately but safely. After the dive, remain calm, contact local emergency services, and administer 100% oxygen and fluids as soon as possible.

Can you die from the bends? The answer is yes. Decompression sickness is a serious condition that can lead to death if not treated properly. If a diver presents symptoms that could be related to decompression sickness, have the diver evaluated by a medical professional. It is better to be safe than sorry. Depending on the part of the world you are diving in, there may be a specific medical practice or physician that specializes in diving medicine, hyperbaric oxygen therapy, or treatment for the bends.

After taking a diver from the water who is showing symptoms of the bends, make sure they are placed in a comfortable position; and keep them dry and warm. When decompression sickness is suspected, the diver should initially be given 100% oxygen and fluids.

Emergency services should be contacted immediately. Depending on the severity of the diver’s condition, they may need to be put in a hyperbaric chamber. Transporting a diver with suspected DCS should be done carefully. The diver should be transported in a horizontal position, lying on their back. If air transport is necessary, find a time frame in the air that can transport the diver below 1,000 feet or that can be pressurized to sea level pressure. Always use high-flow oxygen during transport if it is available.

After reaching a medical facility, the diver should first be treated for breathing problems or shock and evaluated to determine if hyperbaric oxygen therapy is necessary.

Depending on the severity of the decompression sickness, the symptoms may clear up immediately after receiving oxygen but can reoccur later. Soreness in the affected area usually dissipates after a few hours following treatment. Monitoring the diver after treatment may be necessary and follow up evaluations should be scheduled accordingly.

why is decompression sickness called the bends

How long should you wait to dive after DCS? The answer varies depending on the organization you ask and the severity of the decompression sickness. For professional divers, the U.S. Navy recommends waiting thirty days after the DCS is wholly resolved with treatment. If it is pain-only DCS, the time may be shorter. Because professional divers are expected to be in top physical condition compared to some recreational divers, the time should be doubled before recreational divers re-enter the water to dive. All divers should dive more conservative profiles after receiving treatment for the bends and should be evaluated by a professional dive doctor before diving again.

A hyperbaric chamber, or recompression facility, is used for recompression for divers with decompression sickness or the bends. Traditional hyperbaric chambers are made of a rigid material and can be run at absolute pressures around six bars, or more in special cases. These chambers are typically operated by professional diving organizations (i.e., Divers Alert Network is also known as DAN), hospitals, or the Navy. Recompression facilities can range from semi-portable units, one-patient vessels, to large rooms with the ability to treat more than one diver at a time.

decompression sickness

During the recompression process, the chamber is pressurized to help increase the ambient pressure surrounding the diver. This process shrinks the nitrogen gas bubbles in their bloodstream and body tissues, reversing the effects of DCS. During the treatment, the pressure is gradually reduced to normal atmospheric pressure.

Depending on the severity of the case, the more aggressive the treatment will be. A recompression treatment can last up to twelve hours or even more. Some facilities use helium in the place of ambient air to decrease the time needed in the hyperbaric chamber.

the bends sickness

Other Considerations

Maintaining a slow ascent rate is vital to preventing decompression sickness. Depending on the organization you ask, the ascent rate varies. The National Oceanic Atmospheric Administration (NOAA) and the U.S. Navy use a rate of thirty feet per minute. Recreational dive training agencies range from thirty to sixty feet per minute.

There has been a great deal of discussion as it relates to the bends and marine animals. Unlike humans, aquatic animals are not usually affected by decompression sickness; this is due to their lung structure. Recent studies have shown that when putting a deceased seal and dolphin in a pressurized hyperbaric chamber, two pulmonary regions are created. One part was compressed, and the other was filled with air. Researchers suggest that the compressed pulmonary region still allows blood flow, but will limit the nitrogen bubbles from building up in the tissues and bloodstream.

This difference between humans and marine mammals explains why marine mammals like dolphins, seals, and whales do not get the bends as frequently as humans.

Human-made sound, like Naval sonar testing, has been known to cause stress in whales and increased risk for decompression sickness. In recent years, mass beachings have been reported and are believed to be caused by these sonar testing events. It has been suggested that the mammals in these events were suffering from decompression sickness-like symptoms.

Because freedivers do not breathe compressed air underwater, they are not at risk for the bends. Freedivers take a breath of air at the surface before descending and return to the surface with that same breath of air. They are at more risk for shallow water blackouts caused by holding a single breath for long periods; or drowning. Freedivers are affected by the pressure in other spaces like their ears and sinuses, so they do need to equalize just as scuba divers do when they descend.

decompression sickness symptoms

As always, we create our content with you, fellow divers, in mind. So, how’d we do? Did you find this informative? Did it help you make a decision? Did we miss anything? We’d love to hear from you below. Thanks for reading and we hope your next dive is a great one!

Heather Wyatt

Heather is a product expert, a degreed communications and business professional, and an adventurous, entrepreneurial travel writing enthusiast originally from Raleigh, North Carolina. Heather is a PADI-certified Master Scuba Diver Trainer (MSDT) and holds a Silver Advanced Open Water Instructor certification from SSI, having logged more than 300 training classes over the last four years. Heather is a certified Travel Specialist and also holds a Day Captain's license qualifying her to skipper a boat up to 72 feet. She has extensive experience in specialty dive training, navigation, and booking travel accommodations. Her interests include writing, social media marketing, and serving her Virtual Assistant and Travel Clients from around the globe.

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