Inhalation of carbon dioxide mixtures for sensorineural deafness. Evaluation of a rebreathing method

A laboratory study in 11 healthy subjects was conducted to evaluate the performance of a rebreathing device as a means of raising the effective carbon dioxide level in the inspiratory mixture. In all subjects, there was a sustained rise in end-tidal carbon dioxide levels and a transient rise in end-tidal nitrogen tensions associated with an equivalent fall in end-tidal oxygen levels. Although the rise in end-tidal carbon dioxide tensions was variable, the mean elevation for the 11 subjects (from 36 to 43 mm Hg) was not equivalent to elevations reported to follow inhalation of 5% carbon dioxide mixtures. Nevertheless, the volume of the device was sufficient to cause a marked depression of the end-tidal oxygen level (to 67 mm Hg) in one subject. Despite the simplicity and cost-effectiveness of the rebreathing method, it cannot be recommended in the treatment of sudden or fluctuant sensorineural deafness.