Decompression illness (DCI), also known as “the bends” or caisson disease, is a illness that occurs when bubbles form in your body’s tissues because of an excessive quantity of inert gas (nitrogen or helium) due to inadequate decompression following the exposure to increased pressure. During a dive, your body’s tissues absorb nitrogen or helium from your breathing gas in proportion to the surrounding pressure. As long as you remain at pressure (depth), the inert gas does not present any problems. If the pressure is reduced too quickly, from a rapid ascent for example, the inert gas can come out of solution and form bubbles in your body’s tissues and bloodstream. Once bubbles are formed they may or may not produce symptoms based on their eventual growth. When symptoms occur, they relate to the area in the body where the bubble is located.
DCI can occur as a result of violating no decompression limits and not properly decompressing during your ascent, ascending too rapidly on a no decompression dive, pushing dive tables to their limits, skipping or shortening decompression stops during a staged decompression dive, or pushing the limits on tables or dive computers when making repetitive dives. But, DCI can also occur even when you follow all of the recommended guidelines and safety factors.
Every dive you make is a decompression dive, whether it’s to 30 feet (9 m) on a reef or to 200 feet (61 m) on a deep wreck. When you breath compressed gas, no matter at what depth, your body absorbs a certain amount of inert gas. This inert gas must be off gassed eventually. Some of this inert gas is off gassed during your slow ascent, some at your safety stop, and if you’re doing a decompression dive, some is off gassed at each of your stop depths. When you surface after your dive, there is still a residual amount of inert gas in your body’s tissues. If you properly performed your ascent, safety stop, and decompression stops (if required), hopefully no bubbles formed and the amount of residual inert gas is small enough that it doesn’t cause DCI. It’s important to realize that all ascents even from moderate depths are a part of a decompression profile. As mentioned, DCS is a very random thing, meaning that even if you ascended following all of the guidelines, DCS could still occur.
If DCI does occur, it is sometimes mild and not an immediate threat. In some cases, DCI can cause serious injury, which requires quick treatment so that there is a better chance of full recovery. Bubbles forming in or near joints are typically the cause of the classical “bends” joint pain. If a large amount of bubbles occurred, serious reactions can take place in your spinal cord or brain. Numbness, paralysis, and other higher brain function disorders can occur. If the amount of bubbles is great enough, the bubbles can enter the venous bloodstream causing congestive symptoms in the lungs, which can cause circulatory shock.