[Thermographic investigations during stapedotomy using a CO2 laser]

Temporary sensorineural hearing losses after CO(2) assisted stapes surgery have been described in literature. Whether thermal effects are the reason for this side effect is still unclear. The specific aim of this research is to demonstrate the thermal spread during CO(2) laser stapedotomy using a high-speed infrared camera.

Thermal depth effects in physiological saline solutions were examined in cochlea models (glass capillary tube, crystal cuvette and temporal bone preparation). Temperature changes and exchange processes after CO(2) laser application were measured using a high-speed infrared camera. Visualization of gas bubbles triggered by vaporisation underneath the stapes footplate after CO(2) shot was achieved with a high-speed camera. The footplate perforations were performed with a scanner system using a micromanipulator (laser power 20 W, 0.6 mm diameter, continuous wave, duration of 40 ms).

Homogenous temperature increases of more than 100°C were measured on the surface of the footplate and 0.25 mm within the capillary tube after single shot CO(2) laser stapedotomy. Gas bubbles may cause isolated temperature increases of up to 65 K. These effects were found in depths of up to 2 mm underneath the stapes footplate. CO(2) shots on the saline solutions with parameter used for initial laser application may lead to temperature increases between 20-65 K in depths of 3-6 mm.

CO(2) applications to an opened inner ear with the same laser parameter used for initial shot on the stapes footplate should be avoided.