Effects of hyperbaric oxygen therapy initiation latency on auditory outcomes following acute acoustic trauma.

Introduction: Hyperbaric oxygen (HBO) is a potential adjunct treatment to improve hearing following acute acoustic trauma. However, the optimal time frame for HBO initiation has not been elucidated. Methods: Patients exposed to intense noise as part of active military service that met our audiometric criteria were referred for combined HBO (253 kPa for 80 min, treatment numbers titrated to response) and corticosteroid treatment. The primary outcome was defined as an improvement of at least 10 dB in any of the measured high pure tone frequencies (3, 4, 6 or 8 kHz). Additional outcomes included the absolute change in high pure tone (3, 4, 6 and 8 kHz) summation (HPTS), relative change in HPTS compared to baseline (rHPTS) and the proportion of patients returned to auditory combat readiness. Results: Of 129 ears (103 patients) included in the final analysis, 59/67 (88%) of the patients treated within seven days but only 14/25 (56%) of patients treated 21 days or more from exposure met the primary outcome (Bonferroni adjusted P = 0.002). Similarly, HPTS improvement (55 dB vs -5dB), rHPTS improvement (55% vs 3%) and return to combat readiness (32/56 (57%) vs 3/20 (15%)) were significantly (P < 0.001, P < 0.001 and P = 0.017, respectively) more pronounced in patients treated earlier. These results were unchanged despite adjusting to age, degree of initial hearing loss and the mechanism of injury. Conclusions: Early initiation of HBO following acute acoustic trauma is associated with improved response to therapy. The optimal treatment latency appears to be within seven days from injury, with response rates dropping when treatment is delayed beyond three weeks.