Nd-YAG laser damage to metal and silicone endobronchial stents - Delineation of margins of safety using an in vitro experimental model

Study objective: To identify margins of safety within which bronchoscopic N d-YAG laser resection can be performed without damaging indwelling tracheob ronchial stents. Design: Experimental in vitro study simulating a patient-care environment. Methods: Uncovered and covered metal Wallstent (Schneider; Zurich, Switzerl and) and Dumon (Bryan Corporation; Woburn, MA) silicone stents were deploye d in the tracheobronchial tree of a ventilated and oxygenated (fraction of inspired oxygen, 40%) heart-lung block of a dead canine. Rigid bronchoscopi c Nd-YAG (1,064 nm) laser procedures were performed in order to deliver las er energy using fiber-to-target distances of 10 mm and 20 mm, and noncontac t, continuous-mode, 1-s pulses at power settings of 10 W, 30 W, and 40 W. T he major outcome measure was laser-induced stent damage, defined as discolo ration, ignition, or breakage. This was assessed using six power densities: 75 W/cm(2), 172 W/cm(2), 225 W/cm(2), 300 W/cm(2), 518 W/cm(2), and 690 W/ cm(2). Results: The uncovered Wallstent and the silicone stent remained intact at power densities of 75 W/cm(2) (10 W, 20 mm) and 172 W/cm(2) (10 W, 10 mm), but were damaged at power densities > 225 W/cm2 (30 W, 20 mm). The covered Wallstent was damaged at all power densities tested. Conclusion: Uncovered Wallstent and silicone stents are not damaged when Nd -YAG laser energy is delivered using power densities less than or equal to 172 W/cm(2) (10 W, 10 mm). Covered Wallstents, however, had a high likeliho od of ignition at all power densities studied.