Acute Decompression Illness
(“The Bends”)
Decompression illness occurs as a result of excessive gas bubble formation in tissues. These bubbles may form when ascent to the surface is done rapidly. As an illustration, it is like putting a wet Alka Seltzer tablet in the middle of your muscle tissue and allowing it to dissolve. As the gas bubbles formed they could cause pain and/or damage.
During a dive nitrogen or other common gases present in breathable air accumulate in body tissues, because the pressure under the sea is much greater than at the surface. The increased pressure at depth effectively “pushes” nitrogen or other inert gases into tissues. When you ascend to the surface slowly, gases are able to escape your tissues slowly and not form painful or damaging bubbles. The deeper and longer you dive, the more gas forms in your tissues. If you ascend rapidly nitrogen and other gases accumulate in your tissues in high concentrations and often form bubbles. If this happens tissue damage or pain may occur. The symptoms that occur from the bubbles lead to what is called acute decompression illness (DCI). If ascent is very rapid the bubbles often damage the lungs, leading to shortness of breath, coughing up blood, or chest pain. DCI from rapid ascent can lead to widespread bubble formation in the brain and spinal chord. Stupor, coma, and death may ensue. If ascent is slower and staged, yet still fast enough to result in bubble formation, a multitude of other symptoms may predominate (see below). Divers with DCI are placed in decompression chambers with high oxygen content for treatment. Chambers reapply gaseous pressure to your entire body. This keeps the gases in your tissues from escaping rapidly. The pressure is then slowly released, allowing the gas to escape your body in a controlled manner until it is safe to breathe air at normal surface pressures.
Factors that increase your risk of developing DCI
Missed or incomplete decompression: Most dives require staged ascents guided by established decompression tables. If the tables are not followed, bubbles may form.
Flying or altitude after diving: High altitudes (low atmospheric pressures) may result in existing bubble expansion or the formation of new bubbles. If you must fly shortly after a dive the cabin must be pressurized. We recommend that you wait at least a day. After deep or multiday dives wait 36 hours before you fly. For the same reasons, don’t hike a mountain after diving without a standard wait period. If you notice minor precursor signs of the bends, such as the feeling of pins and needles in an extremity or generalized fatigue or malaise, wait until you are feeling normal before you take on a high altitude.
Dehydration: Water loss leads to a lower blood volume. Thus, when you are dehydrated less blood is filtered through the lungs. This decreases the transport of gases to your lungs and hence your ability to exhale the gases from your body. This leads to more gases that are stuck in your tissues.
Alcohol: Causes dehydration.
Rapid ascents: Causes bubble formation in the tissues and blood. The recommended rate of safe ascent is 33 ft/min (A. Kayle, Safe Diving, 1994).
Exposure to heat: Promotes bubble formation (like boiling water). Avoid hot showers, Jacuzzis, or saunas after a dive.
Limb injury: Injury to an extremity produces swelling and circulatory compromise. This may impede gas release from injured tissues and lead to decompression illness in the injured limb (“limb decompression illness”).
Exercise: Increases body heat and thus bubble formation if done five hours before or six hours after a dive. Interestingly, vigorous exercise done 24 hours before a dive markedly decreases your risk of developing bubbles and DCI. The cause for this phenomenon is under investigation.
Obesity: Gases are stored more efficiently in fat, making obese persons capable of storing more nitrogen, etc. This may lead to excessive bubble formation.
Poor physical fitness: Divers should be in excellent physical shape. Oxygen and nitrogen carrying capacity is relatively compromised by poor physical fitness.
Caffeine: Causes dehydration.
How to recognize acute decompression illness
The symptoms of acute decompression illness depend on the body parts that are affected by trapped gas bubbles. If bubbles form in your knee you will have knee pain. If they form in a blood vessel to your heart you may have the symptoms of a heart attack, e.g., chest pain or shortness of breath. If they form in the brain slurred speech, altered mental status, visual disturbances, or limb weakness may occur. The process is also a dynamic one so it may be hard to pinpoint. Bubbles may form in one part of the body and later move somewhere else causing symptoms that may change in severity and location. If you feel or notice any physical abnormality that cannot be easily explained we recommend that you inform your dive master or captain and seek an evaluation from a dive physician before serious damage has occurred.
Acute decompression illness typically occurs on ascent or within 30 minutes of resurfacing. Within six hours 90 percent of cases have occurred. Within 12 hours 99 percent. Most cases affect the skin and joints (60 percent) and of the more serious cases, many manifest with central nervous system dysfunction.
According to statistics compiled at the Institute of Underwater and Hyperbaric Medicine (IUHM) from November 1996 and December 2002 the graph represents the symptoms of DCI and their incidence within a population of 150 divers treated for DCI.
Illnesses or problems that might mimic decompression illnesses include hyperventilation, a panic attack, a drug side effect or a stroke. An injury that occurred during diving, e.g., shoulder sprain from lifting a heavy tank, may be difficult to differentiate from DCI. Headache may be from an undiagnosed brain tumor. Never assume that a symptom is diving-related. Have a medical doctor evaluate all physical complaints or conditions.
| COMMON SYMPTOMS | ASSOCIATED WITH | ACUTE DEPRESSION |
| joint pain | general weakness | shortness of breath |
| irritability | confusion | cough |
| visual loss | excessive fatigue | imbalance |
| loss of hearing | skin rashes | loss of bowel function |
| abdominal pain | ringing in the ears | dizziness |
| chest pain | unconsciousness | urinary retention |
| memory loss | orange peel skin | impaired thinking or numbness |
| headache | itching |
Basic principles of decompression illness treatment
The most important principle of treatment is prevention. Follow your dive tables and do not ascend rapidly. Follow the advice listed above and avoid factors that increase bubble formation. Drink plenty of non-alcoholic, decaffeinated fluids.
If you do suspect that a diver is suffering from acute decompression illness follow these guidelines:
- Inform a dive physician
- Keep the diver calm, quiet, and lying flat at all times. Prop the diver’s head up 15°. If unconscious turn the diver on his or her left side.
- Administer 100 percent oxygen (if available).
- Encourage oral fluid intake if the diver is sufficiently conscious.
- Administer CPR if necessary.
- Administer an IV and start fluid resuscitation (if available).
- Transport to the decompression chamber or dive medicine facility.
