Ni 2004.

Methods	Double blind, randomised controlled trial
Participants	52 patients (aged 12 to 66 years), randomly assigned to 2 different treatment groups. Gender data were unavailable.
Interventions	Group 1: carbogen and drug course (IV dexamethasone + vitamin B + LMW dextran + salvise miltiorrhiaze + oral intake of vitamin C + vitamin E); carbogen inhalation for 30 minutes, 30 minutes break followed by another 30 minutes of inhalation Group 2: drug course only
Outcomes	1. Complete recovery: normal hearing in 0.25 to 4 kHz frequency range 2. Significant recovery: > 30 dB in 0.25 to 4 kHz frequency range 3. Some recovery: 15 to 30 dB in 0.25 to 4 kHz frequency range The proportion of patients who had some degree of recovery was 76.9% in group 1 (treatment) and in group 2 (control) was 50 %. The difference in outcome between the 2 groups reached statistical significance (P < 0.05).
Notes	Adverse effects: 5 patients in group 1 (treatment, carbogen) complained of a sensation of swelling in the area of the head, which settled spontaneously and did not interfere with their treatment
Risk of bias
Bias	Authors' judgement	Support for judgement
Allocation concealment?	Low risk	Allocation concealment up to the point of assignment