THERMAL EFFECTS IN THE VESTIBULE DURING LASER STAPEDOTOMY WITH PULSED-LASER SYSTEMS

Background and Objective: Apart from the ablation properties at the st apes footplate, the degree of thermic loading in the inner ear is impo rtant in determining the suitability of pulsed lasers for stapedotomy. The aim of the study is to compare the thermic effects in the vestibu le with different pulsed laser systems. Study Design/Materials and Met hods: Temperature increases and heat exchange processes in the fluid ( physiological saline) were examined in a calorically and physiological ly approximated cochlea model for applying the laser parameters effect ive in creating footplate perforations. Results: With all systems, inc reases in the energy density, number of pulses, and thus resultant tot al energy lead to higher temperatures. In the effective energy density range, the highest temperature increases achieved with the requisite number of pulses at a distance of 2 mm behind the perforation are 26 d egrees C with the Ho:YAG laser. The lowest temperature maxima are 5.5 degrees C with the Er:YAG and <5 degrees C with the Er:YSGG laser. The excimer laser, investigated at only one energy density, showed maxima l temperatures of 10 degrees C, Conclusion: The Er:YSGrG and Er:YAG la ser can be applied in laser stapedotomy in a relatively broad energy d ensity range without a risk of inner ear damage by thermic loading. On the other hand, the Ho:YAG laser is not recommended for stapedotomy b ecause of the higher energy density and pulse rate required for suffic ient perforation and the resultant higher temperature increases in the perilymph. Though likewise achieving perforations with only slight te mperature increases in the fluid of the cochlea model, the excimer las er does not seem appropriate for stapedotomy because of the long perio d of heat exposure (ca. 60 s) due to the lower ablation rate at the st apes necessitating a longer application time. Lasers Surg. Med. 23:7-1 7, 1998. (C) 1998 Wiley-Liss, Inc.