Hyperbaric Oxygen Therapy for Idiopathic Sudden Sensorineural Hearing Loss: Factors Affecting Benefits of Earlier Start and Longer Treatment Duration

<b>Background/Objectives</b>: The study aimed to evaluate the efficacy of hearing gain using hyperbaric oxygen (HBO) therapy on patients with idiopathic sudden sensorineural hearing loss (ISSHL), and to provide recommendations with reference to treatment session, intervention time and the impairment severity. <b>Methods</b>: In this retrospective chart-review study, we analyzed data of ISSHL patients referred to us from the department of Ear, Nose and Throat (ENT) between January 2016 and December 2024. Hearing sensitivity improvements were assessed using pure-tone audiometry (PTA). <b>Results</b>: We found that 50.7% of patients (<i>n</i> = 148) had improved after 5 HBO sessions and 47.7% (<i>n</i> = 107) had improved after 10 HBO sessions. While no difference was found between different treatment cycles, we found treatment effects varied significantly depending on disease severity. Specifically, 64.3% of patients with profound ISSHL had improved (<i>p</i> = 0.010) after 5 sessions, and 69.2% (<i>p</i> = 0.002) after 10 sessions. Such improvements in patients with profound ISSHL were 3.681-fold larger than in those with mild to moderate ISSHL. In addition, patients who had received HBO therapy within 12 days of diagnosis showed the best response, with an odds ratio (OR) of 7.768 (95% CI: 2.785-21.664) (<i>p</i> = 0.000 *); those receiving HBO between 13 and 27 days had an OR of 3.974 (95% CI: 1.243-12.702), (<i>p</i> = 0.020 *); both groups were compared with those receiving HBO after 27 days. <b>Conclusions</b>: Patients with more severe ISSHL showed greater improvement with HBO therapy. Also, patients who started HBO therapy earlier showed better response; those who started later, like after 27 days, showed poorer or even no response at all.