Decompression Sickness (DCS)

Illness from dissolved gas forming bubbles in blood and tissue after ascent, ranging from joint pain to neurological injury; treated by recompression.

Decompression sickness is what happens when the nitrogen your body absorbed at depth comes out of solution too fast. During a dive, Henry's law drives inert gas into your tissues in proportion to depth and time. Ascend in a controlled way and that gas off-gasses harmlessly through the lungs. Ascend too fast, or skip required decompression, and the gas forms bubbles in blood and tissue, like opening a shaken soda bottle. Those bubbles block circulation, distort tissue, and trigger inflammation.

Symptoms usually appear within six hours of surfacing: deep joint pain (the classic bends), unusual fatigue, skin rashes or marbling, numbness and tingling, weakness, dizziness, or bladder problems. Neurological signs mean the spinal cord or brain is involved and are an emergency. First aid is 100 percent oxygen and fluids, then call DAN, the Divers Alert Network, whose emergency line coordinates evacuation. Definitive treatment is recompression in a hyperbaric chamber, and outcomes are best when treatment starts early, so never wait to see if it passes.

Prevention is everything your training drilled: stay well inside no-decompression limits, ascend no faster than 9 to 18 m per minute, make the 3 minute safety stop at 5 m, stay hydrated, and leave 12 to 18 hours or more before flying after diving. DCS can still occur on dives done entirely by the book, which is why detailed logbook records of depth, time, and gas are genuinely useful to the treating physician.