Influence of CO2 laser application to the guinea-pig cochlea on compound action potentials.

Hypothesis: Experiments in guinea pigs were performed to clarify which, if any, of the CO2 lasers in different modes (continuous wave [cw] and superpulse) can damage the inner ear on application of the laser parameters required for stapedotomy and to determine their application safety.

Methods: The laser effect connected with perforating the basal convolution of the guinea-pig cochlea (cochleostomy) was examined. Acoustic evoked potentials (compound action potentials [CAPs]) yielded information on inner-ear function.

Results: In cw mode, even single applications of an approximately four times higher power density (60,000 W/cm2) than necessary for stapedotomy at a pulse duration of 50 msec (energies up to 1 J) and 20-fold applications of effective parameters for a footplate perforation (power density 16,000 W/cm2; energy 0.2 J) did not cause CAP changes. Experimental studies with the CO2 superpulse laser used (peak pulse powers: ca. 300 W) have demonstrated that irreversible CAP alterations already occur in the effective laser range in > 40% of the animals.

Conclusions: Because damage is expected only at much higher energies (> 2 J) than those used clinically, the CO2 laser in cw mode has a high application safety for laser stapedotomy. The application of the CO2 laser in superpulse mode with peak pulse powers of approximately 300 W in stapedotomy appears to be more unreliable and dangerous for the inner ear.