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HIGHLIGHTED TOPIC
The Physiology and Pathophysiology of the Hyperbaric and Diving Environments

Short oxygen prebreathe periods reduce or prevent severe decompression sickness in a 70-kg swine saturation model

¹Undersea Medicine Department, Naval Medical Research Center, Silver Spring, Maryland; ²Uniformed Services University of the Health Sciences, Bethesda, Maryland; and ³Navy Experimental Diving Unit, Panama City, Florida

Submitted 26 August 2008 ; accepted in final form 27 January 2009

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 "prebreathing" (OPB) can accelerate decompression in a DISSUB scenario. In-70 kg swine saturated at 2.82 atm absolute (ATA), 1 h of OPB eliminated death and reduced severe DCS. We hypothesized that even shorter periods (<1 h) of OPB before 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 >95% O₂ for 45 min (OPB₄₅), 15 min (OPB₁₅), or 5 min (OPB₀₅) of OPB, or no OPB (control). The chamber was then decompressed without stops (0.91 ATA/min). 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 with 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.

disabled submarine; nonrecompressive therapy; preoxygenation; prebreathe