Effect of CO2 milliwatt laser on peripheral nerves: Part I. A dose-response study.

In order to explore further the role of laser for microneural repair, the effect of CO2 laser irradiation on intact rat sciatic nerves was investigated. In total 40 rat sciatic nerves were exposed to 12 different combinations of laser power (50, 100, and 150 mW) and pulse duration (0.1 to 3 s) normally used for CO2 laser-assisted nerve repair. The results were evaluated 24 hr after surgery with functional toe-spreading test and light microscopy. Irradiations of 50 and 100 mW for up to 1 s exposure time per pulse resulted in almost no deficit in motor function, while 100 mW power with prolonged exposure times and 150 mW power resulted in a significant decrease in motor function. Light microscopy showed significant focal injury to the epi/perineurium and the subepineunal nerve fibres proportional to the laser energy applied to the nerve, consisting of Wallerian degeneration and thrombosis of blood vessels. In conclusion, a power of 50-100 mW in combination with a pulse duration of 0.1-1 s produced no or minimal thermal damage with no or a negligible loss of motor function. Therefore, combinations of power and pulse duration above these thresholds are considered less suitable for CO2 laser nerve repair.