Decompression sickness (DCS), often called “the bends,” is a medical condition caused by a rapid reduction in surrounding pressure. This typically occurs in divers ascending too quickly from underwater, but it can also affect individuals in unpressurized aircraft at high altitudes or those emerging from caissons. While DCS can range from mild joint pain to more serious issues, it does have the potential to be fatal if not promptly and appropriately treated.
Understanding Decompression Sickness
Decompression sickness arises from the behavior of inert gases, primarily nitrogen, which dissolve into the body’s tissues and blood under increased pressure, such as during a dive. According to Henry’s Law, the amount of gas dissolved in a liquid is directly proportional to the partial pressure of the gas. As a diver descends, the ambient pressure increases, leading to more nitrogen dissolving in the body.
Upon ascent, the surrounding pressure decreases, and these dissolved gases begin to come out of solution. If the ascent is too rapid, the gases form bubbles within the blood and tissues. While some bubbles may be harmlessly expelled through the lungs, a rapid decrease in pressure can cause them to grow too quickly for the body to eliminate them safely. These bubbles can then cause mechanical disruption, block blood flow, and trigger inflammatory responses, leading to the various symptoms of DCS.
The Spectrum of Symptoms
The symptoms of decompression sickness can vary widely in their presentation and severity, from mild discomfort to life-threatening conditions. Mild manifestations, often categorized as Type I DCS, include localized deep pain in joints, commonly in the arms or legs, which can range from a dull ache to excruciating pain. Skin issues such as itching, mottling, or rashes, along with general fatigue, are also common initial signs.
More severe forms, known as Type II DCS, involve the nervous system, respiratory system, and circulatory system, and these are the manifestations that can lead to fatality. Neurological symptoms may include numbness, tingling, weakness, or paralysis, particularly affecting the spinal cord. Headaches, confusion, vision problems like double vision, dizziness, vertigo, and difficulty with urination or bowel control can also occur. The most severe neurological symptoms can progress to seizures, slurred speech, coma, and ultimately death. Respiratory symptoms, sometimes called “the chokes,” are rare but serious and involve shortness of breath, chest pain, and coughing due to pulmonary edema.
Factors Influencing Severity
Several factors can influence the severity and outcome of decompression sickness. The dive profile, including depth, bottom time, and ascent rate, plays a significant role; deeper and longer dives, especially with rapid ascents, increase the risk of bubble formation. For instance, a faster ascent rate, such as 18 meters per minute, causes greater decompression stress compared to 9 meters per minute.
Individual physiological factors also contribute to susceptibility. Dehydration can increase the risk of DCS, as it affects blood viscosity and circulation. Age and body composition, particularly a higher percentage of fat tissue, have been linked to increased bubble production and a greater risk of DCS. The presence of a patent foramen ovale (PFO), a small opening between the heart’s upper chambers, can allow venous gas bubbles to bypass the lungs and enter the arterial circulation, potentially leading to more severe neurological DCS.
Immediate Actions and Treatment
Immediate action is important when decompression sickness is suspected to improve outcomes and reduce the risk of fatality. The first step involves removing the affected individual from the water, if they are still submerged, and administering 100% oxygen via a non-rebreather mask. Keeping the person lying flat and still is advised to help prevent further bubble migration, especially to the brain.
The definitive medical treatment for DCS is hyperbaric oxygen therapy (HBOT), which involves recompression in a specialized chamber. This treatment works by reducing the size of the gas bubbles in the body and increasing the dissolution of gas back into the blood, allowing for its safe elimination through respiration. Rapid transportation to a hyperbaric facility is important, as prompt treatment can significantly reduce the likelihood of permanent injury and improve recovery.
Preventing Decompression Sickness
Preventing decompression sickness is the most effective way to avoid its potentially serious consequences. Adhering to dive tables or dive computer guidelines is a primary safety measure, as these tools calculate safe ascent rates and no-decompression limits based on depth and bottom time. Divers should always plan their dives and stick to the planned depths and durations, avoiding excursions that could increase nitrogen absorption.
Implementing safety stops allows for additional nitrogen off-gassing before surfacing. Maintaining proper hydration by drinking non-alcoholic, non-caffeinated fluids is also important, as dehydration can increase susceptibility to DCS. Avoiding strenuous activity immediately after diving and observing recommended no-fly times helps prevent bubbles from forming or expanding at altitude.