(DCS) refers to symptoms caused by blocked blood supply, damage from direct mechanical effects, or later biochemical actions from suspected bubbles evolving from inert gas dissolved in blood or tissues when atmospheric pressure decreases too rapidly. DCS can occur after scuba diving, ascent with flying, or hypobaric or hyperbaric exposure.
DCS can be broken down into the following 3 types:
Hyperbaric oxygen therapy (HBOT) is used to diminish the size of the bubbles, not simply through pressure, but also by using an oxygen gradient. According to Boyle's law, the volume of the bubble becomes smaller as pressure increases. With a change in 1.8 ATA, this is only about 30%. The bubble causing DCS is thought to be composed of nitrogen. When a tissue compartment is at equilibrium and then ascends to a decreased atmospheric pressure, nitrogen seeps out of blood, tissue, or both, causing a bubble. During HBOT, the patient breathes 100% oxygen, creating oxygen-rich, nitrogen-poor blood. This creates a gradient of nitrogen between the blood and the bubble, causing nitrogen to efflux from the bubble into the bloodstream, which, in effect, makes the bubble smaller.
The treatment of choice is recompression. Although treatment as soon as possible has the greatest success, recompression is still the definitive treatment, and no exclusionary time from symptom onset has been established. DCS Type I can be treated using the US Navy Treatment Table 5: 60 fsw for two 20-min periods, with a slow decompression to 30 fsw for another 20 minutes. For DCS types I, II, and III, the US Navy Treatment Table 6 is a recommended treatment protocol. Patients are placed at 60 fsw (2.8 ATA) for at least three 20-min intervals and then are slowly decompressed to 30 fsw. They remain there for at least another 2.5 hours. The time a patient is kept at 60 or 30 fsw can be extended depending on the patient's symptom response to therapy.