Decompression Illness Incidence and Hypoxia Symptoms After Prebreathing in Hypobaric Hypoxia Training.

Hypobaric hypoxia training utilizing the environmental chamber is often preceded by prebreathing of 100% oxygen with the goal of reducing decompression illness (DCI). We aimed to study the impact of prebreathing 100% oxygen for 30 min prior to hypobaria exposure to 7600 m (25,000 ft) on the incidence rate of DCI, as well as the impact of prebreathing on hypoxia symptoms felt during training. Records of participants who underwent hypobaric hypoxia training in the Republic of Singapore Air Force (RSAF) from 2011 to 2014 (before introduction of prebreathing) were compared to those who underwent similar training from 2014 to 2017 (after introduction of prebreathing) to determine the incidences of DCI for both groups. Participants who underwent hypobaric hypoxia training from January 2017 to July 2017 completed a survey to assess the impact of prebreathing on the presentation and severity of hypoxia symptoms. Two DCI events were recorded in 1530 hypobaric chamber exposures without prebreathing while two DCI events were recorded in 1729 exposures with prebreathing. There was no significant difference in the incidence of DCI between the two groups. The survey findings showed no significant difference in the presentation and severity of hypoxia symptoms with 30 min of prebreathing. Incidence of DCI remains low during hypobaric chamber training, with no statistical difference with or without prebreathing. Possible reasons were the short duration of hypobaric exposure of 10 min during hypoxia training, and that 30 min of prebreathing was insufficient to further decrease or eliminate the risk of DCI in short duration hypobaric exposures.