Thermal Damage during Thulium Laser Dissection of Laryngeal Soft Tissue is Reduced with Air Cooling: Ex vivo Calf Model Study

Abstract

The 2-microm-wavelength thulium laser has recently been shown to be an effective cutting instrument in endolaryngeal surgery, although there is increased thermal trauma as compared with the carbon dioxide laser. This study investigated temperature changes and thermal trauma during thulium laser dissection of laryngeal tissue, with and without air cooling, in an ex vivo model. A continuous-wave thulium laser (400-microm fiber, 4-W continuous power, 4-second duration) was used to incise 10 calf vocal folds. Paired cooled and uncooled cuts were made in each fold with a dermatologic cooling device. A thermistor inserted into the glottic subepithelium was used to measure tissue temperatures. Thermal damage was analyzed histologically by measuring the depth of the zone of lactate dehydrogenase inactivation surrounding the mucosal incision. The initial vocal fold temperature averaged 24.3 degrees C without cooling and 4.4 degrees C with cooling. The peak temperature during cutting averaged 59.1 degrees C without cooling and 28.0 degrees C with cooling. The thermal damage zone surrounding the cooled incisions was approximately 27% less than that surrounding the uncooled incisions. Air cooling can reduce the extent of thermal trauma associated with thulium laser surgery of the vocal folds, and the high-temperature plume generated during laser cutting is effectively cleared.