Decompression sickness (the bends)

How it develops

Under higher pressure, gases such as nitrogen dissolve into blood and tissues. If pressure falls gradually, the gas is eliminated safely by exhalation. Rapid ascent or sudden decompression causes dissolved gas to form bubbles. Bubbles in the vascular system can reduce blood flow to organs and tissues, while bubbles in tissues can impair the oxygen delivery and disrupt cellular function. Physical effects include mechanical injury, obstruction, and biochemical inflammatory cascades.

Signs and classification

Symptoms vary with the size, number and location of bubbles. Clinicians commonly group DCS into two categories:

• Type I — localized pain in joints or muscles, skin changes such as itching or mottling.
• Type II — more serious involvement such as neurological deficits (weakness, numbness, confusion), inner-ear problems, or cardiopulmonary compromise.

Treatment and immediate actions

Suspected DCS is a medical emergency. First aid typically includes administering high-concentration oxygen, keeping the patient supine and hydrated, and avoiding further physical exertion. Definitive care is recompression therapy in a hyperbaric chamber, which reduces bubble size and helps redissolve gases while providing oxygen to tissues. Early treatment improves outcomes.

Prevention, risk factors and historical context

Prevention relies on controlled decompression: slow ascent, planned decompression stops, and following dive tables or dive-computer guidance. Risk factors include depth and duration of exposure, rapid ascent, strenuous exercise after exposure, cold, and individual susceptibility. The condition was first recognized in workers and divers exposed to changing pressures; historically it was called caisson disease among 19th-century construction workers and later described in divers.

Distinctions and notable points

DCS is related to but distinct from arterial gas embolism, which results from pulmonary barotrauma. Both may coexist and require urgent evaluation. Recreational and professional divers, aviators, and workers in pressurized environments should be familiar with symptoms and prevention. For authoritative guidance, consult professional dive medicine resources or local emergency services.

Further reading and resources: pressure physiology, circulatory effects, oxygenation and therapy, mechanical damage from bubbles.