Background:Acute acoustic trauma (AAT) is an acute hearing impairment caused by intense noise-impact.The current management strategy for AAT with substantial hearing loss in the Dutch military is the combination therapy with corticosteroids and hyperbaric oxygen therapy (HBOT).In a previous study,early initiation of the combination therapy was associated with better outcomes.Therefore,we performed a new analysis to assess the difference in hearing outcome between patients in whom combination therapy was started within two days,versus after more than two days.Methods:A retrospective analysis was performed on military patients diagnosed with AAT with sub-stantial hearing loss who presented between February 2018 and March 2020.Absolute and relative hearing improvement between first and last audiograms were calculated for all affected frequencies(defined as loss of ≥20 dB on initial audiogram).We also determined the amount of patients who recovered to the level of Dutch military requirement,and performed speech discrimination tests.Results:In this analysis,30 male patients (49 ears) with AAT were included.The median age was 24.5 years (IQR 23-29).The median time to initiation of therapy with corticosteroids and HBOT were one and two days,respectively.HBOT was started within two days in 31 ears,and after more than two days in 18 ears.The mean absolute and relative hearing gains were 18.8 dB (SD 14.6) and 46.8％ (SD 31.3) on all affected frequencies.The 100％ discrimination/speech perception level improved from 64.0 dB to 51.7 dB(gain 12.3 dB ± 14.1).There was significantly more improvement in absolute and relative hearing improvement when HBOT was started in ≤2 days,compared to ＞2 days.Conclusion:Our analysis shows results in favor of early initiation (≤2 days) of the combination treatment of HBOT and corticosteroids in patients with AAT.