Decompression Illness (DCI) is a medical condition resulting from a rapid reduction in the ambient pressure surrounding the body, most commonly seen in scuba divers, but also in aviators and compressed-air workers. DCI is an umbrella term that encompasses two distinct conditions: Decompression Sickness (DCS) and Arterial Gas Embolism (AGE). Both are caused by the formation and expansion of gas bubbles within the body’s tissues and bloodstream when pressure is reduced too quickly.
The Physics of Bubble Formation
The underlying mechanism of DCI is explained by Henry’s Law, which states that the amount of gas dissolved in a liquid is directly proportional to the partial pressure of that gas above the liquid. When a diver descends, the surrounding water pressure increases, causing the partial pressure of inert gases—primarily nitrogen—to rise. This elevated pressure forces more nitrogen to dissolve into the blood and subsequently into the body’s tissues.
The tissues become saturated with this dissolved inert gas during the dive. During a controlled ascent, the pressure decreases slowly, allowing the excess nitrogen to leave the tissues, enter the bloodstream, and be expelled through the lungs. However, if the ascent is too rapid, the reduction in ambient pressure occurs faster than the body can eliminate the gas.
This rapid depressurization creates a state of supersaturation, where the gas remains dissolved at a concentration higher than the surrounding pressure can maintain. Consequently, the dissolved gas comes out of solution and forms microscopic bubbles within the tissues and circulation. These bubbles cause injury by physical damage or by blocking blood flow to various organs.
Recognizing the Signs and Symptoms
The presentation of DCI is highly varied, depending on where the gas bubbles form and lodge within the body. Decompression Sickness (DCS) is classified into two main types based on severity. Type I DCS is considered milder and typically involves musculoskeletal and cutaneous symptoms. The most common manifestation is deep, aching joint pain, often referred to as “the bends,” which typically affects the shoulders and elbows. Other Type I symptoms include skin mottling, a rash known as cutis marmorata, and localized swelling.
Type II DCS is the more serious form, involving neurological, respiratory, or circulatory systems. Neurological symptoms can be diverse, ranging from numbness, tingling, and muscle weakness to paralysis, confusion, and loss of bladder control. A rare but dangerous presentation is pulmonary DCS, known as “the chokes,” characterized by a burning pain beneath the sternum, coughing, and shortness of breath.
Arterial Gas Embolism (AGE) has a distinct mechanism, typically resulting from a lung over-expansion injury caused by breath-holding during a rapid ascent. This ruptures lung tissue, allowing air bubbles to enter the arterial circulation directly. AGE symptoms are usually immediate and severe, often mimicking a stroke, presenting with sudden loss of consciousness, visual blurring, or focal neurological deficits.
Emergency Management and Definitive Treatment
Immediate first aid is paramount in managing a suspected case of DCI, as prompt intervention significantly improves the chances of a full recovery. Lay the patient flat and ensure basic life support measures are initiated if necessary. Crucially, 100% oxygen must be administered continuously using a non-rebreather mask.
Breathing pure oxygen helps to create a steeper diffusion gradient, increasing the rate at which inert gas bubbles shrink and are eliminated from the body. Even if symptoms resolve with oxygen, the patient requires urgent transportation to a specialized medical facility. The definitive treatment for DCI is hyperbaric oxygen therapy, also known as recompression.
This treatment involves placing the patient in a hyperbaric chamber and pressurizing the environment beyond normal atmospheric pressure. This physical recompression shrinks the gas bubbles, reducing their destructive effect. The patient then breathes 100% oxygen at this elevated pressure, maximizing the elimination of inert gas and improving oxygen delivery to damaged tissues.
Addressing Acronym Ambiguity
While DCI is a well-known acronym for Decompression Illness within diving and hyperbaric medicine, it has other meanings in the broader medical field. DCI can stand for Ductal Carcinoma In Situ, a non-invasive form of breast cancer. It can also refer to Delayed Cerebral Ischemia, a complication that occurs after a subarachnoid hemorrhage. Context is important when interpreting the abbreviation DCI.