First Aid Oxygen Treatment for Decompression Illness in the Goat After Simulated Submarine Escape.

BACKGROUND: Personnel responding to a distressed submarine incident require information on likely casualty levels and the severity and progression of decompression illness (DCI). Recompression may not be immediately available. First aid oxygen (FAo2) can be administered; however, there is no direct evidence of its efficacy in this scenario. METHODS: Trials were conducted between 2004 and 2006. Goats exposed to raised pressure for 24 h ('saturation') were either returned directly to atmospheric pressure (Phase A, N = 40) or exposed to simulated submarine escape at a depth of 656 ft (200 m; assumed seawater density = 1019.72 kg · m(-3); Phase B, N = 39). The pressure during saturation was selected to provoke 50% DCI. Cases of DCI were randomly assigned to receive FAo2or air. RESULTS: DCI cases were: limb pain in 39 subjects, neurological in 6, respiratory in 4, and pulmonary barotrauma in 1 subject. In Phase A, 5/12 subjects in the FAo2group and 0/11 in the air control group achieved permanent resolution of DCI. In Phase B, 6/8 subjects in the FAo2group and 5/8 in the air control group achieved permanent resolution. In both Phases, levels of venous gas bubbles reduced sooner with FAo2. Of three cases of neurological DCI receiving FAo2, two showed permanent resolution. In total, four cases of respiratory DCI occurred; none of these resolved, with three being treated with FAo2and one in the air control. DISCUSSION: Oxygen can be an effective first aid measure for DCI following submarine escape. However, it should not be used as a replacement for recompression therapy.

Oxygen and carbogen breathing following simulated submarine escape.

Escape from a disabled submarine exposes escapers to a high risk of decompression sickness (DCS). The initial bubble load is thought to emanate from the fast tissues; it is this load that should be lowered to reduce risk of serious neurological DCS. The breathing of oxygen or carbogen (5% CO2, 95% O2) post-surfacing was investigated with regard to its ability to reduce the initial bubble load in comparison to air breathing. Thirty-two goats were subject to a dry simulated submarine escape profile to and from 240 meters (2.5 MPa). On surfacing, they breathed air (control), oxygen or carbogen for 30 minutes. Regular Doppler audio bubble grading was carried out, using the Kisman Masurel (KM) scale. One suspected case of DCS was noted. No oxygen toxicity or arterial gas embolism occurred. No significant difference was found between the groups in terms of the median peak KM grade or the period before the KM grade dropped below III. Time to disappearance of bubbles was significantly different between groups; oxygen showed faster bubble resolution than carbogen and air. This reduction in time to bubble resolution may be beneficial in reducing decompression stress, but probably does not affect the risk of fast-tissue DCS.