Decrease in Dysbaric Osteonecrosis Lesions as a Result of 45‐minute Oxygen Pre‐breathe

Abstract

IntroductionNitrogen (N2) dissolved in long bone fatty marrow can lead to bubble formation in tissue when exposed to sudden decompression. During a disabled submarine escape (DISSUB) hastened decompression is often necessary, and formation of bubbles is likely. If recompression is not administered in a timely manner, bubbles may lead to ischemia and necrosis of marrow and bone, a condition called Dysbaric Osteonecrosis (DON). Oxygen (O2) pre‐breathe has been proposed as a way to reduce N2 in tissue, thus decreasing risk of DON. Previous research has shown that O2 pre‐breathe of 2‐hours resulted in a reduction in DON; however, effects of shorter O2 pre‐breathe are uncertain. This study’s aim is to understand the effect of shorter durations of O2 pre‐breathe on DON formation.MethodEight adult Suffolk ewes (89.5 ± 11.5 kg) were exposed to 33 feet of seawater (fsw) for 24 hours. Animals, separated at random into four groups (n=8) and exposed to either 45, 30, or 15 minutes of O2 (91–88%) pre‐breathe and 21% (controls), were rapidly decompressed. Four weeks after exposure and two weeks prior to euthanasia, Alizarin Complexone was injected intravenously to visualize areas of DON. Right and left long bones (radii, tibiae, femora, and humeri) were analyzed to determine the extent of Alizarin Complexone deposition. Percent deposition in the proximal, middle and distal thirds, as well as over the entire bone was calculated using areas of deposition and total bone to determine for extent of DON. Variance between the groups was found using an unpaired t‐test and Welch’s correction.ResultsA decrease in variance of DON occurrence was seen in the radius when comparing the 45‐minute (min) group to the 30‐min, 15‐min and the controls (p < 0.0001). The humerus also showed a similar decrease in variance when comparing groups (p < 0.05). Both the femur and tibia saw decreases in variance when comparing 45‐min group to the 30‐min and 15‐min group, (p < 0.0005) however no reduction was seen between the 45‐min group and the controls. The radius and tibia saw the highest rates of lesions. The radius mean depositions were 0.05 ± 0.07 in the 45‐min group, 4.8 ± 5.0 in the 30‐min group, 13.2 ± 14.8 in the 15‐min group and 6.4 ± 12.4 for the controls. The tibia mean depositions were 0.13 ± 0.18 in the 45‐min group, 4.8 ± 6.0 in the 30‐min group, 6.8 ± 11.2 in the 15‐min group and 0.6 ± 0.4 for the controls.DiscussionThe 30‐min, 15‐min and controls showed significant amounts of variability, which we hypothesize is due to differences in body composition. Similarly in humans, DON appears sporadically in those exposed to rapid decompression. The decrease of variance in the 45‐min group suggests that 45 minutes of O2 pre‐breathe is required to effectively increase confidence in the reduction of DON. Similar confidence was not reflected in the 30‐min and 15‐min groups. During DISSUB, speed of evacuation is vital for survival, our data suggests a minimum of 45 minutes of pre‐breathe is needed to confidently reduce the risk of developing DON. However, this duration may vary based on depth, time, body mass and bone composition. Future research is needed to understand the relationship between these variables in order to effectively calculate the sufficient O2 pre‐breathe required for an individual.Support or Funding InformationSupported by NAVSEA N00024‐17‐C‐4318