Holmium: YAG Laser Safety Data On Bile Duct Epithelium in the Porcine Model

Abstract

Background: Laser therapy has been increasing used for gastrointestinal and urological applications. Due to a very short wavelength, holmium: YAG can generate high-energy focused shock waves while reducing surrounding thermal injury. This characteristic has led to recent interest in using this technology for the fragmentation of large bile duct stones that have been refractory to conventional endoscopic therapy. Aim: The aim of this study was to establish safety data for holmium: YAG laser lithotripsy within the bile duct in the porcine model. Methods: 6 female 50 kg domestic pigs underwent necropsy and the bile ducts were explanted. The bile ducts were excised longitudinally exposing the epithelial surface and submerged under tension in liquid media. A Slimline holmium YAG laser probe (Lumenis, Sunnyvale, CA) was placed in perpendicular contact with the bile duct epithelium and activated at various energy density settings to evaluate perforation rates. The power density settings ranged from 8 to 15 watts (W) and were accomplished using various combinations of frequencies (Hz) and joules (J). The laser was activated until perforation of the bile duct occurred or for a maximum of 60 seconds. For each setting the probe was placed in similar locations on both the proximal and distal aspects of the duct. Both location and wattage were randomized to avoid physiologic differences that may affect outcomes. The median perforation times at each power setting were then compared using the Kruskal-Wallis One Analysis of Variance. Results: 104 data points were collected from 6 porcine bile ducts using 6 different power settings: 8 W (n=22); 9 W (n=22); 10 W (n=16); 12 W (n=20); 14 W (n=8); 15 W (n=16). The median perforation times were: 8 W (60 s); 9 W (24.5 s); 10 W (28 s); 12 W (24.5 s); 14 W (14 s); 15 W (5 s). Pairwise multiple comparison (Dunn's Method) revealed statistically significant differences (P<0.05) in the perforation times between the following settings: 8 W vs 15 W; 9 W vs 15 W; 10 W vs 15 W; 12 W vs 15 W. Conclusions: Holmium: YAG laser appears to be safe when used in short bursts (< 5 sec) at power settings ranging from 8 W to 12 W. Further studies are required to determine the ideal power settings balancing effective stone fragmentation and perforation risk.