Decompression sickness (DCS), commonly known as “the bends,” is a medical condition resulting from a rapid reduction in surrounding pressure, typically after a dive. During descent, inert gases like nitrogen dissolve into the body’s tissues under high pressure. If the pressure is lowered too quickly, these dissolved gases come out of solution and form bubbles within the body. While many cases of DCS are treatable, the condition can be fatal, with severity related to the location and volume of gas bubbles formed.
The Critical Risk: When DCS Becomes Life-Threatening
DCS becomes life-threatening when gas bubbles form in or travel to vital organ systems. This severe manifestation, categorized as Type II DCS, involves the central nervous system, including the brain and spinal cord. Bubbles can damage neural tissue or block blood flow, leading to severe neurological impairment, paralysis, or death. The spinal cord is particularly vulnerable, and injury here can rapidly progress to irreversible damage.
A massive load of bubbles entering the circulatory system can precipitate shock, leading to circulatory collapse. Pulmonary DCS, often called “the chokes,” is a rare presentation where bubbles obstruct circulation in the lungs, causing severe respiratory distress and acute respiratory failure. The likelihood of a fatal outcome increases significantly with delayed treatment, deep or prolonged dives, or pre-existing conditions like a Patent Foramen Ovale (PFO). A PFO is an opening in the heart that allows bubbles to bypass the lungs and enter arterial circulation.
Understanding Bubble Formation and Symptoms
The physics behind DCS is governed by Henry’s Law, which states that the amount of gas dissolved in a liquid is proportional to the partial pressure of that gas. As a person descends, the increased pressure causes more inert gas, primarily nitrogen from the breathing mixture, to dissolve into the tissues and blood. If the ascent is too fast, the ambient pressure drops quickly, and the excess dissolved gas cannot be eliminated fast enough through the lungs, leading to bubble formation. These bubbles cause injury through mechanical obstruction, tissue compression, and triggering inflammatory responses in the body.
The milder form, Type I DCS, involves symptoms that are painful but rarely life-threatening. The classic symptom, which gives the condition its nickname, is pain in the joints of the arms and legs, commonly referred to as “the bends.” Other non-fatal symptoms include skin manifestations like a blotchy rash or mottling, along with unusual fatigue or mild swelling. These symptoms occur when bubbles form in the musculoskeletal system or the skin.
More serious symptoms arise when bubbles affect the nervous system or inner ear. Neurological Type II DCS can manifest as numbness, tingling, muscular weakness, or difficulty with urination. Inner ear involvement, known as vestibular DCS, can cause severe vertigo, dizziness, and ringing in the ears. Even in cases that are not immediately fatal, Type II symptoms signal a serious condition that requires immediate medical intervention.
Emergency Treatment: Recompression Therapy
The definitive treatment for DCS is hyperbaric oxygen therapy, which is administered in a recompression chamber. This treatment works by physically increasing the ambient pressure surrounding the patient, shrinking the gas bubbles in the body. According to Boyle’s Law, as pressure increases, the volume of a gas decreases proportionately, forcing the nitrogen bubbles back into a dissolved state in the tissues and blood.
Once the bubbles are shrunk and redissolved, the patient is treated with 100% oxygen at increased pressure. Breathing pure oxygen helps create a large gradient between the nitrogen dissolved in the tissues and the nitrogen in the lungs. This gradient accelerates the removal of the inert gas from the body, essentially flushing the nitrogen out much faster than normal breathing.
Immediate first aid for a suspected case of DCS involves administering 100% oxygen via a tight-fitting mask, even before transport to a chamber. The success of recompression therapy is highly dependent on the speed of treatment. Delays can allow the gas bubbles to cause irreversible damage to the spinal cord or brain, making the difference between a full recovery and permanent disability or death.
Mitigation: Essential Safety Protocols
Since DCS is a preventable condition, divers rely on strict adherence to established protocols to minimize risk. The primary preventative measure involves managing the rate of gas absorption and elimination through controlled ascent. This is achieved by following the limits set by dive tables or personal dive computers.
A primary preventative action is maintaining a slow ascent rate, typically not exceeding 30 feet per minute, to allow for controlled off-gassing. Required safety stops involve pausing the ascent near the surface for a few minutes, aiding in the elimination of nitrogen before surfacing. Divers must also adhere to adequate surface intervals between multiple dives to ensure sufficient time for the body to off-gas accumulated nitrogen. Avoiding flying or ascending to high altitudes too soon after a dive is crucial, as the lower cabin pressure promotes bubble formation.