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

Abstract

Mahon RT, Dainer HM, Gibellato MG, Soutiere SE. Short oxygen prebreathe periods reduce or prevent severe decompression sickness in a 70-kg swine saturation model. J Appl Physiol 106: 1459-1463, 2009. First published January 29, 2009 doi:10.1152/japplphysiol.91058.2008 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 (Ͻ1 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 Ϯ 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 Ͼ95% O 2 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 ϭ 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 EXPOSURE to hyperbaric air causes the human body to absorb inert gas. Levels of absorption are based on depth and duration as well tissue perfusion and gas solubility. After remaining at depth for an extended period of time the tissue beds become saturated with inert gas. When a diver's tissues become saturated with inert gas, further exposure at depth no longer increases the inert gas load (4,7,18). Decompression from saturation is generally a lengthy undertaking, with decompression from just 60 feet of sea water (fsw) requiring 14 -16 h of staged decompression (22,29).In certain situations this lengthy decompression may not be feasible. One such scenario is a disabled submarine (DISSUB). It is possible that the internal pressure of a DISSUB would increase based on partial flooding and the use of emergency air-breathing systems (25). Under such circumstances, it is likely that submariners waiting for the deployment of submarine rescue assets will achieve inert gas saturation. Lengthy decompression onboard a rescue vehicle, with their limited passenger capacity, imperils remaining survivors who are likely facing air contamination, fire, and other hazards. Lengthy d...

The autonomic effects of cardiopulmonary decompression sickness in swine using principal dynamic mode analysis

“…On the day of the hyperbaric exposure (1 day after recovery from surgery), the subjects were placed into individual custom-designed Plexiglas boxes (26 ϫ 54 ϫ 38 in.) inside a steel-hulled, 450-ft. 3 hyperbaric chamber as reported elsewhere (21). Each box allowed for an adjustable atmosphere environment in which the subjects could breathe without requiring restraints.…”

“…Hyperbaric exposure. For the nine swine in which we induced DCS, the chamber was pressurized with air to 184 kPa (60fsw) at a rate of 92 kPa/min (30 fsw/min) and remained at depth for 15 h. It is our experience from our previous studies, following saturation diving at 184 kPa, 80% of animals experienced symptoms of DCS (21). For the remaining six control swine, the chamber was pressurized with air to 15 kPa (5 fsw) and remained at depth for 15 h. The control depth of 15 kPa was chosen to recreate all experimental conditions yet pose an extremely low risk of DCS.…”

Oxygen Breathing Accelerates Decompression from Saturation at 40 msw in 70-kg Swine

“…We have previously demonstrated that " dropout decompression " (direct ascent to the surface from 22-h saturation at 18 msw) in a 15-swine cohort (mean weight 69.5 kg) resulted in 86.6% Type I cutis, 40% cardiopulmonary DCS, and 73.3% neurologic DCS ( 11 ). The anticipated occurrence of DCS in a dropout from 40 msw was anticipated to equal or exceed these rates.…”

“…On the day of the hyperbaric exposure, the subjects were placed into individual custom-designed Plexiglas ™ boxes (26 x 54 x 38 ) inside a steel-hulled hyperbaric chamber reported elsewhere ( 11 ). Each box allowed for a hyperbaric oxygen environment in which the subjects could breathe without requiring restraints.…”

“…by 77 -85% ( 15 ). More recently, OPB for 45, 15, and even 5 min after saturation at 18 msw signifi cantly reduced both Type I and II DCS with 45 min of OPB eliminating Type II DCS completely ( 11 ). In humans, OPB at 18 msw (2.52 ATA) saturation signifi cantly reduced DCS, allowing for a safe 8 -10-h decompression schedule ( 9 ).…”