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 superpu lse) can damage the inner ear on application of the laser parameters requir ed 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 pote ntials (compound action potentials [CAPs]) yielded information on inner-ear function. Results: In cw mode, even single applications of an approximately four time s higher power density (60,000 W/cm(2)) 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/c m2; 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 rang e 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 applicati on safety for laser stapedotomy. The application of the CO2 laser in superp ulse mode with peak pulse powers of approximately 300 W in stapedotomy appe ars to be more unreliable and dangerous for the inner ear.