Decompression illness (DCI) describes the dysbaric injuries (such as AGE) and decompression sickness (DCS). Because scientists consider the two diseases to result from separate causes, they are described here separately. However, from a clinical and practical standpoint, distinguishing between them in the field may be impossible and unnecessary, since the initial treatment is the same for both. DCI can occur even in divers who have carefully followed the standard decompression tables and the principles of “safe” diving. Serious permanent injury or death may result from AGE or DCS.

Arterial gas embolism

Gas entering the arterial blood through ruptured pulmonary vessels can distribute bubbles into the body tissues, including the heart and brain, where they can disrupt circulation or damage vessel walls. The presentation of AGE ranges from minimal neurologic findings to dramatic symptoms requiring urgent and aggressive treatment.

In general, a clinician should suspect AGE in any scuba diver who surfaces unconscious or loses consciousness within 10 minutes after surfacing. Initiate basic life support, including administration of the highest fraction of oxygen. Since relapses can and do occur, evacuate rapidly to a hyperbaric oxygen treatment facility even if the diver appears to have recovered fully.

Decompression sickness

Breathing air under pressure causes excess inert gas (usually nitrogen) to dissolve in and saturate body tissues. The amount of gas dissolved is proportional to—and increases with—the total depth and time a diver is below the surface. As the diver ascends, the excess dissolved gas must be cleared through respiration. Depending on the amount of gas dissolved and the rate of ascent, some can supersaturate tissues, where it separates from solution to form bubbles, interfering with blood flow and tissue oxygenation.

Decompression sickness (DCS) is a condition in which gases dissolved in the blood or in other body tissues are no longer dissolved following a reduction in pressure on the body. This condition affects underwater divers who surface from a deep dive too quickly, and it can affect pilots flying at high altitudes in planes with unpressurized cabins. Divers often call this condition “the bends,” a reference to joint pain that is a symptom of DCS.

In all cases, DCS is brought about by a reduction in barometric pressure. At high altitude, barometric pressure is much less than on Earth’s surface because pressure is produced by the weight of the column of air above the body pressing down on the body. The very great pressures on divers in deep water are likewise from the weight of a column of water pressing down on the body. For divers, DCS occurs at normal barometric pressure (at sea level), but it is brought on by the relatively rapid decrease of pressure as divers rise from the high pressure conditions of deep water to the now low, by comparison, pressure at sea level. Not surprisingly, diving in deep mountain lakes, where barometric pressure at the surface of the lake is less than that at sea level is more likely to result in DCS than diving in water at sea level.

In DCS, gases dissolved in the blood (primarily nitrogen) come rapidly out of solution, forming bubbles in the blood and in other body tissues. This occurs because when pressure of a gas over a liquid is decreased, the amount of gas that can remain dissolved in the liquid also is decreased. It is air pressure that keeps your normal blood gases dissolved in the blood. When pressure is reduced, less gas remains dissolved. You have seen this in effect when you open a carbonated drink. Removing the seal of the bottle reduces the pressure of the gas over the liquid. This in turn causes bubbles as dissolved gases (in this case, carbon dioxide) come out of solution in the liquid.

The most common symptoms of DCS are pain in the joints, with headache and disturbances of vision occurring in 10 percent to 15 percent of cases. Left untreated, very severe DCS can result in death. Immediate treatment is with pure oxygen. The affected person is then moved into a hyperbaric chamber. A hyperbaric chamber is a reinforced, closed chamber that is pressurized to greater than atmospheric pressure. It treats DCS by repressurizing the body so that pressure can then be removed much more gradually. Because the hyperbaric chamber introduces oxygen to the body at high pressure, it increases the concentration of oxygen in the blood. This has the effect of replacing some of the nitrogen in the blood with oxygen, which is easier to tolerate out of solution.

The dynamic pressure of body fluids is also important to human survival. For example, blood pressure, which is the pressure exerted by blood as it flows within blood vessels, must be great enough to enable blood to reach all body tissues, and yet low enough to ensure that the delicate blood vessels can withstand the friction and force of the pulsating flow of pressurized blood.

Arterial gas embolism

• Chest pain or bloody sputum
• Loss of consciousness
• Personality change, difficulty thinking, or confusion
• Muscular weakness
• Paralysis
• Numbness or paresthesias
• Dizziness
• Ataxia
• Blurred vision
• Convulsions

Decompression sickness

• Coughing spasms or shortness of breath
• Collapse or unconsciousness
• Personality changes
• Weakness
• Paralysis
• Numbness or tingling
• Dizziness
• Staggering, loss of coordination, or tremors
• Mottling or marbling of skin
• Loss of bowel or bladder function
• Itching
• Joint aches or pain
• Unusual fatigue

The risk of developing decompression sickness increases when divers go to increased altitude too soon after a dive. The cabin pressure of commercial aircraft may be the equivalent of 6,000–8,000 ft (1,829–2,438 m). Thus, divers should wait before flying at an altitude >2,000 ft (610 m) for:

• ≥12 hours after surfacing from a single no-decompression dive
• ≥18 hours after multiple dives or multiple days of diving
• 24–48 hours after a dive that required decompression stops

These recommended preflight surface intervals reduce, but do not eliminate, risk of DCS. Longer surface intervals further reduce this risk.

Recreational divers should dive conservatively and well within the no-decompression limits of their dive tables or computers. Risk factors for DCI are primarily dive depth, dive time, and rate of ascent. Additional factors such as repetitive dives, strenuous exercise, overhead situations (such as caves or wrecks), dives to depths >60 ft. (18 m), altitude exposure soon after a dive, difficult diving conditions (for example, decreased visibility, currents, wave action) and certain physiologic variables also increase risk. Caution divers to stay well hydrated and rested and dive within the limits of their training. Diving is a skill that requires training and certification and should be done with a companion (or buddy).

Definitive treatment of DCI begins with early recognition of symptoms, followed by recompression with hyperbaric oxygen. Any unusual symptoms occurring soon after a dive should be suspect and properly evaluated. Breathing a high concentration (100%) of supplemental oxygen is recommended. Surface-level oxygen given for first aid may relieve the signs and symptoms of DCI and should be administered as soon as possible.

Because of either incidental causes, immersion, or DCI itself, which can cause capillary leakage, divers are often dehydrated. Administration of isotonic glucose-free intravenous fluid is recommended in most cases. Oral rehydration fluids may also be helpful, provided they can be administered safely (for example, if the diver is conscious and can maintain his or her airway).

The definitive treatment of DCI is recompression and oxygen administration in a hyperbaric chamber. It is worth noting that stable or remitting symptoms of mild DCI (such as limb pain, constitutional symptoms, some cutaneous sensory changes, or rash) in divers reporting from remote locations without a hyperbaric facility may not require recompression. Such conditions involve reasonable decision making with a qualified dive medicine physician and should take into account the prevailing circumstances, complicated logistics, the hazardous nature of evacuation, and the likelihood of disadvantaging the patient by failing to recompress.

Divers Alert Network (DAN) maintains 24-hour emergency consultation and evacuation assistance at 919-684-9111 (collect calls are accepted). DAN can help with the medical management of injured divers, deciding if recompression is needed, providing the location of the closest recompression facility, and arranging patient transport. Divers and health care providers can also contact DAN for routine, nonemergency consultation by telephone at 919-684-2948, extension 6222, or by accessing the DAN website (www.diversalertnetwork.org).

Travelers who plan to scuba dive may want to ascertain whether recompression facilities are available at their destination before embarking on their trip.

Underwater construction and tunnel operations use compressed air to stabilize soil and keep out water. In these conditions, workers are at risk of decompression sickness (DCS).

DCS can be treated or prevented using a decompression chamber guided by decompression tables. The tables direct the time and pressure intervals needed to ensure workers are brought back to surface pressure safely.

What is Decompression Sickness (DCS)?

DCS, also called the "bends," occurs when not enough pressure is released from the body following exposure to increased pressure. DCS is more commonly noted among scuba divers, but also occurs among those working in conditions that use compressed air, like tunnel construction.

Moving too quickly from an area of high pressure to low pressure can produce nitrogen gas bubbles in the body. If outside pressure is released too quickly, the gas is released in the body. Just like uncorking a bottle of soda, there is a sudden expansion of bubbles or "fizzing." Nitrogen bubbles in the blood or tissues can obstruct blood flow or cause pressure effects. This can be very painful and sometimes fatal.

Symptoms of DCS may include:

• joint pain
• areas of bone destruction (termed dysbaric osteonecrosis)
• skin disorders, such as cutis marmorata, which causes a pink marbling of the skin
• spinal cord and brain disorders, such as stroke, paralysis, paresthesias, bladder dysfunction, etc.
• cardiopulmonary disorders, such as shortness of breath
• arterial gas embolism (gas bubbles in the arteries that block blood flow)

How is DCS prevented?

A decompression chamber is used to gradually bring workers back to normal surface pressures. Decompression tables detail the time and pressures needed to do this safely. The pressure changes and time intervals defined in the tables are chosen based on the worker's exposure pressure and work shift length.

The first decompression tables were developed by Haldane for the British Admiralty in 1908. Other tables have since been developed. In 1971, the Washington State Decompression Tables became the federal code enforced by the Occupational Safety and Health Administration (OSHA).