CO2 laser stapedotomy safety: influence of laser energy and time on bone-conduction hearing levels.

Total laser energy in CO2 stapedotomy depends on the laser settings and the amount of applications. It is unclear if the amount of total laser energy affects bone-conduction hearing thresholds and if possible effects are temporary or permanent. Alterations of bone-conduction hearing thresholds after single or multiple-shot CO2 laser stapedotomy were analyzed between 1 and 3 weeks and 1.5-6 months after primary (n = 501) or revision surgeries (n = 153) and correlated to time, laser energy, frequency, surgical technique, and pathology encountered in revision stapedotomy. In both time periods, most patients showed a lower bone-conduction threshold in the four-tone puretone average (PTA) at frequencies of 0.5, 1, 2, and 3 kHz that further improved over time. Between 1 and 3 weeks, the improvement was significant in subgroups with cumulative energies lower 1 J and successful one-shot technique or in revisions without laser application. The remaining subgroups with higher total energies showed significant improvements between 1.5 and 6 months. At 4 and 8 kHz, significant improvements were found during 1.5-6 months after primary and revision surgery independent of the used energy. Repeated CO2 laser applications showed no impairment in bone-conduction thresholds and can thus be considered as safe. In most patients, significant, yet unexplained, improvements in bone-conduction hearing thresholds were noticed in a time- and energy-related pattern.