Decompression Sickness (DCS), often called “the bends,” is a medical condition resulting from a rapid reduction in surrounding pressure. This pressure change causes gases dissolved in body tissues to come out of solution and form bubbles. These gas bubbles can lodge in various parts of the body, leading to a wide range of symptoms. While most commonly associated with scuba diving, DCS also affects aviators, astronauts, and workers in compressed air environments.
The Physics of Gas Absorption and Bubble Formation
Decompression sickness is caused by Henry’s Law: the amount of gas dissolved in a liquid is proportional to the partial pressure of that gas over the liquid. Under high pressure, such as when diving, the inert gas component, primarily nitrogen, is forced into the body’s tissues and bloodstream. The deeper and longer a person remains under pressure, the greater the concentration of nitrogen that dissolves, loading the tissues until equilibrium is reached. This absorbed gas presents no problem while the pressure remains high.
The issue arises when ambient pressure is reduced too quickly, such as during a rapid ascent. As pressure drops, the solubility of dissolved nitrogen decreases sharply. If the gas cannot be eliminated through exhalation, it comes out of solution and forms microscopic bubbles, a process known as nucleation.
These bubbles obstruct blood flow and irritate nerve tissues. Bubble formation is similar to opening a carbonated drink, where rapid pressure release causes dissolved gas to fizz out. The severity of DCS depends on the volume and location of these gas bubbles.
Identifying the Clinical Manifestations
Symptoms of DCS are highly variable, depending on where the bubbles lodge. Clinicians classify manifestations into two categories: Type I and Type II DCS. Type I DCS is the milder form, primarily involving the musculoskeletal system, skin, and lymphatic system.
The most common symptom of Type I DCS is joint pain, often felt as a deep ache in the elbows and shoulders, giving the condition its nickname, “the bends.” Other manifestations include skin mottling, a blotchy rash, localized swelling, and itching. This type of DCS is generally not immediately life-threatening.
Type II DCS is the more serious form, involving the central nervous system, inner ear, and pulmonary system. Neurological symptoms range from numbness, tingling, and weakness to paralysis and loss of bladder control. Inner ear involvement can cause severe vertigo, dizziness, and hearing loss.
A rare manifestation is pulmonary DCS, sometimes called “the chokes,” involving shortness of breath, chest pain, and a persistent cough. The presence of any neurological or cardiopulmonary symptom necessitates immediate medical intervention. Symptoms can appear minutes to hours after surfacing, with earlier onset often indicating a more severe case.
Emergency Response and Recompression Therapy
If DCS is suspected, the immediate priority is to administer 100% oxygen via a tight-fitting mask. High-flow oxygen rapidly increases the gradient for nitrogen to leave the tissues and can alleviate initial symptoms. The patient should be kept warm, lying down, and transported without delay to a facility equipped with a hyperbaric chamber.
The definitive medical treatment for DCS is Hyperbaric Oxygen Therapy (HBOT), also known as recompression therapy. This procedure involves placing the patient in a chamber where pressure is increased to simulate depth. The increased ambient pressure physically shrinks the nitrogen bubbles, reducing their obstructive effects and forcing the gas back into a dissolved state.
Simultaneously, the patient breathes 100% oxygen, which significantly increases the partial pressure of oxygen in the blood. This high oxygen concentration accelerates the rate at which dissolved nitrogen is eliminated through respiration. Timely treatment with HBOT is crucial, as a delay significantly reduces the chance of a full recovery and increases the risk of long-term residual symptoms.
Strategies for Prevention
The most effective approach to preventing DCS is adherence to strict protocols during every dive. Proper dive planning involves using dive computers or decompression tables to calculate maximum bottom times and safe ascent profiles. These tools use mathematical models to predict the rate of inert gas absorption and elimination, helping to keep nitrogen levels within safe limits.
A controlled ascent rate, typically not exceeding 30 feet (9 meters) per minute, is fundamental for off-gassing nitrogen slowly. Mandatory safety stops involve a three- to five-minute pause at about 15 feet (5 meters) near the end of a dive. This brief stop provides additional time for nitrogen to diffuse out of tissues before reaching the surface.
Divers can also reduce their susceptibility by managing specific risk factors. Dehydration increases the risk of DCS, making adequate fluid intake before and after diving important. Other factors, such as obesity, excessive exertion at depth, and flying too soon after diving, can also increase the likelihood of developing symptoms.