Administration of free-radical scavengers (vitamins C and E) before oxygen diving did not improve eustachian tube ventilatory function.

Clinical Bottom Line: 1. Administration of vitamins C and E promoted negative middle ear pressures after oxygen diving. 2. The magnitude of middle ear negative pressure was less after the second dive in both groups.

    • Appraised by: Mike Bennett, Dept. of Diving and Hyperbaric Medicine, Prince of Wales Hospital, Sydney; Sunday, 17 September 2000
    • Clinical Scenario: A diver exposed to hyperbaric oxygen displayed negative middle ear pressures.
    • Three-part Question: In divers using high inspired oxygen, does the administration of vitamins C and E, compared to placebo, prevent negative middle ear pressure after diving?
    • Search Terms: Middle ear, eustachian tube
    • The Study:

Double-blinded concealed randomised controlled trial with intention-to-treat. Fit volunteer naval divers

    • Control group (N = 8; 8 analysed): Placebo medication at least three hours before diving (oxygen rebreather at 4m for 30 minutes average) on two consecutive days.
    • Experimental group (N = 7; 7 analysed): 1g vitamin C and 600 IU of vitamin E at least three hours prior to diving (same exposure).
    • The Evidence:
Non-event outcomes Time to outcome Placebo group Vitamin group P-value
Middle ear impedance (1st dive) 24 hours -5 daPa -17.5 daPa 0.017
Middle ear impedance (2nd dive) 24 hours -2.5 daPa -7.5 daPa 0.64
    • Comments:

1. Administration of vitamins was associated with significantly worse eustachian tube function- this finding was the reverse of that hypothesised. 2. The putative action of vitamins was to reduce free-radical mediated mucosal damage that might explain the development of negative middle ear pressures after oxygen diving. 3. Report in abstract only

    • Expiry date: June 2020
    • References:

1. Mutzbauer T, Mueller P, Tetzlaff K et al. Is eustachian tube ventilatory function (ETVF) impairment after oxygen diving mediated by free radicals? Undersea and Hyperbaric Medicine 2000; 27(suppl):16.