Influence of Nd:YAG laser power density and coaxial CO2 on the gastric wall

A detailed understanding is required of the effect of Nd:YAG power density and coaxial CO2 on tissue necrosis in both the acute and healing situation. Lesions were produced by varying peak powers at eight increments of 10 W from 40-110 W/sec for a time duration of 1 sec with and without coaxial CO2 on the rabbit (n = 16) stomach. Surface areas and careful histological examinations were performed at 2 hr and 4 days. In further experiments, a total incident energy of 60 or 120 J with varying peak powers from 30-120 W/sec were applied at a 1-cm distance. The lesion surface area at 1 cm was 21.7 mm2 compared to 12 mm2 when the fiber tip was held 2 cm away (p less than 0.05). Coaxial CO2 at 1 cm reduced the surface area to 10 mm2 (p less than 0.001). There was a positive correlation between surface areas and the incidental power (r = 0.86, p less than 0.01). There was no significant difference in the mean surface area of lesions at 2 hr compared to those at 4 days, nor was there a correlation between the increasing peak powers with the constant incident energy. Histological features were those of coagulative necrosis (81%) with minimal ulceration (1.6%) at 2 hr with ulceration increasing to 22% at 4 days. These results have helped in planning a safe and effective Nd:YAG photocoagulation study in patients in order to obtain maximum hemostasis with minimal tissue injury.