Interrupted oxygen pre-breathing and decompression outcomes in swine

Background: Rescue from a disabled submarine may result in substantial risk for severe decompression sickness (DCS) among survivors. Oxygen prebreathe (OPB) before rapid decompression has been shown to signifi cantly reduce risk or delay onset for severe DCS in animals. However, the duration of this benefi t remains unknown and might even be lost if a delay between the prebreathe period to initiation of recompression therapy allows for nitrogen reaccumulation. Methods: We hypothesized that the benefi t of OPB would be lost following subsequent periods of air interruption in a 70-kg swine saturation model. Following OPB of 45 or 60 min with varying periods (30, 45, 60 min) of air interruption, 61 swine exposed to 2.7 ATA for 22 h were rapidly decompressed. Swine without OPB served as negative controls and swine treated with 45 min of OPB without air interruption served as positive controls. Results: Comparing experimental groups for Type II DCS incidence showed OPB 120/60 being the only experimental group (11%) statistically different than the negative control group OPB 0 (80%). Log rank tests comparing Type II DCS free survival only showed statistically signifi cant differences for OPB 45/60 compared to positive control group OPB 45, while, more importantly, demonstrating a signifi cant difference for OPB 120/60 compared to that approximated for OPB 45, indicating a signifi cant reversal of the air interruption effects with longer OPB on Type II DCS disease free survival. Discussion: Based on these fi ndings we concluded that the protective effects of OPB against severe DCS are reduced with increasing periods of air interruption.