CO2 laser used through the operating channel of laser laparoscopes: in vitro study of power and power density losses.

The purpose of this study was to measure the effects of several variables on energy transmission and power density through the CO2 laser laparoscope. The factors studied included the laser beam diameter, coupler optics, laparoscope lumen size, and absorption of the laser wavelength by the insufflation gas. The addition of CO2 insufflating gas to the operating channel at higher power settings not only reduced the energy transmitted to tissue by 35-58% with a 7.2-mm laparoscopic operating channel and by as much as 61% with a 5-mm operating channel, but also increased the spot size. This "blooming" of the laser beam definitely reduced power density at tissue and eliminated the pinpoint spot size needed for microdissection. Even under optimal conditions regarding lumen size and beam diameter, our data indicate a point of diminishing returns for power density above 40 W for the systems tested. Power densities obtainable at laparotomy were not possible. Clinically, this effect resulted in optimal cutting (vaporization) at low power settings and coagulation accompanying cutting at higher settings.