A Cochrane review included 7 studies with a total of 392 subjects. Pooled data from two trials involving 114 patients did not show any significant improvement in the chance of a 50% increase in hearing threshold on Pure Tone Average (PTA) when HBOT was used (relative risk [RR] with HBOT 1.53, 95% CI 0.85 to 2.78), but did show a significantly increased chance of a 25% increase in PTA (RR 1.39, 95% CI 1.05 to 1.84). There was a 22% greater chance of improvement with HBOT, and the NNT to achieve one extra good outcome was 5 (95% CI 3 to 20). A single trial involving 50 subjects also suggested significantly more improvement in the mean PTA threshold with HBOT, expressed as a percentage of baseline (WMD 37%, 95% CI 22% to 53%, P < 0.001). There was also an absolute improvement in average pure tone audiometric threshold following HBOT (MD 15.6 dB greater with HBOT, 95% CI 1.5 to 29.8). The significance of any improvement in tinnitus could not be assessed.
There were no significant improvements in hearing or tinnitus reported in the single study to examine chronic presentation (6 months) of idiopathic sudden sensorineural hearing loss (ISSHL) and/or tinnitus.
Comment: The quality of evidence was downgraded by study quality (inadequate allocation concealment) and inconsistency (heterogeneity in treatments and outcomes).