Submitted on August 6, 2008
Revised on January 22, 2009
Accepted on January 27, 2009
SHORT OXYGEN PRE-BREATHE PERIODS REDUCE OR PREVENT SEVERE DECOMPRESSION SICKNESS IN A 70 KG SWINE SATURATION MODEL
Richard T. Mahon1*, Hugh M. Dainer2, Marilisa G. Gibellato2, and Shawn E. Soutiere2
1 Uniformed Services University
2 Naval Medical Research Center
* To whom correspondence should be addressed. E-mail: Richard.mahon{at}med.navy.mil.
Disabled submarine (DISSUB) survivors are expected to achieve saturation with inert gas. However, rescue procedures may not accommodate staged decompression, raising the potential for severe decompression sickness (DCS). Alternatives to standard recompression therapy are needed. It has been demonstrated in humans that isobaric oxygen "pre-breathing" (OPB) can accelerate decompression in a DISSUB scenario. In 70 kg swine saturated at 2.82 ATA one hour of OPB eliminated death and reduced severe DCS. We hypothesized that even shorter periods (< 1 hr) of OPB prior to no-stop decompression from saturation at 2.82 ATA could reduce the incidence of DCS in a large animal model. Catheterized Yorkshire swine (68.8 ± 1.7 kg) in individual Plexiglas boxes within a large animal hyperbaric chamber were compressed to 2.82 ATA for 22 h. Following saturation and while still at depth, breathing gas was switched to either > 95% O2 for 45 min (OPB45), 15 min (OPB15), 5 min (OPB05) of OPB, or no OPB (control). The chamber was then decompressed without stops (0.91 ATA.min-1). Observers then entered the chamber and recorded signs of DCS for 2 h. All OPB periods significantly reduced the risk of developing Type II DCS. OPB45 eliminated severe DCS. Controls had a 2.5 times greater risk of developing Type II DCS than OPB05 (p=0.016). OPB45 and OPB15 significantly reduced Type I DCS compared to controls. These results support the potential of OPB as an alternative to staged decompression and that OPB could be expected to improve outcome in a DISSUB rescue scenario.
