During the EVA they breathe 100% oxygen in their spacesuits, which operate at 4.3 psi (0.30 bar), although research has examined the possibility of using 100% O2 at 9.5 psi (0.66 bar) in the suits to lessen the pressure reduction, and hence the risk of DCS. Treatment
Recompression on air was shown to be an effective treatment for minor DCS symptoms by Keays in 1909. Evidence of the effectiveness of recompression therapy utilizing oxygen was first shown by Yarbrough and Behnke, and has since become the standard of care for treatment of DCS. Recompression is normally carried out in a recompression chamber. At a dive site, a riskier alternative is in-water recompression.Oxygen first aid has been used as an emergency treatment for diving injuries for years. Particularly if given within the first four hours of surfacing, it increases the success of recompression therapy as well as decreasing the number of recompression treatments required. Most fully closed-circuit diving rebreathers can deliver sustained high concentrations of oxygen-rich breathing gas and could be used as a means of supplying oxygen if dedicated equipment is not available.It is beneficial to give fluids, as this helps reduce dehydration. It is no longer recommended to administer aspirin, unless advised to do so by medical personnel, as analgesics may mask symptoms. People should be made comfortable and placed in the supine position (horizontal), or the recovery position if vomiting occurs.
diving before travelling to altitude – DCS can occur without flying if the person moves to a high-altitude location on land immediately after diving, for example, scuba divers in Eritrea who drive from the coast to the Asmara plateau at 2,400 m (7,900 ft) increase their risk of DCS. diving at altitude – diving in water whose surface pressure is significantly below sea level pressure — for example, Lake Titicaca is at 3,800 m (12,500 ft). Versions of decompression tables for altitudes exceeding 300 m (980 ft), or dive computers with high-altitude settings or surface pressure sensors may be used to reduce this risk. Individual
The following individual factors have been identified as possibly contributing to increased risk of DCS:

dehydration – Studies by Walder concluded that decompression sickness could be reduced in aviators when the serum surface tension was raised by drinking isotonic saline, and the high surface tension of water is generally regarded as helpful in controlling bubble size. Maintaining proper hydration is recommended. There is no convincing evidence that overhydration has any benefits, and it is implicated in immersion pulmonary oedema. patent foramen ovale – a hole between the atrial chambers of the heart in the fetus is normally closed by a flap with the first breaths at birth. In about 20% of adults the flap does not completely seal, however, allowing blood through the hole when coughing or during activities that raise chest pressure.