Presentation Authors: Ali H Aldoukhi*, Kristian M Black, Timothy L Hall, Khurshid R Ghani, Ann Arbor, MI, Adam D Maxwell, Brian MacConaghy, Seattle, WA, William W Roberts, Ann Arbor, MI
Introduction: High-power laser settings are commonly employed for stone dusting techniques. Previous in vitro and in vivo studies have demonstrated that a toxic thermal dose can result from treatment within a renal calyx. The risk of thermal damage with laser lithotripsy within the ureter is hypothesized to be even greater than in a renal calyx given the smaller volume of fluid adjacent to the laser fiber. The aim of this study was to experimentally measure temperature and calculate thermal dose for a range of laser power and irrigation parameters in a simulated ureteral model.
Methods: The experimental system consisted of a rounded glass tube (inner diameter 6 mm/length 130 mm) simulating a ureter that ends with a 19 mm sphere simulating a renal pelvis. A 242 Î¼m laser fiber (Flexiva, Boston Scientific) was inserted through a ureteroscope (Lithovue, Boston Scientific) and positioned 60 mm away from the simulated pelvis wall. Real time temperature was recorded using two wire thermocouples; one at the level of the ureteroscope and another in the simulated pelvis. The model was placed in a water bath maintained at 37Â°C. Irrigation with room temperature fluid was provided at 25,12, or 6 mL/min. Laser energy was applied (pulse 120; Lumenis) for 60 seconds. Thermal dose for each trial was calculated based on Dewey and Sapareto t43 equivalence calculations. Thermal toxicity (cell death) was considered attained when t43= 120 minutes, the equivalent of maintain 43Â°C for 120 minutes. The probability of exceeding t43 = 120 equivalent minutes was determined for strategically selected power levels and irrigant flow rates in order to map the safety margin. Each experiment was repeated 5 times.
Results: Thermal dose within the ureter for each parameter pair (power, irrigation rate) is represented by a circle in Figure 1. The percentage of trials that exceeded t43= 120 minutes is indicated on each circle. Temperature in the renal pelvis was not elevated by laser lithotripsy in the ureter.
Conclusions: We have defined a thermal safety threshold between safe and unsafe laser/irrigation parameter set pairs. Further studies are needed to map out the safety thresholds for other locations within the urinary tract. This methodology will also provide a framework in which to assess effectiveness of various strategies to control and mitigate thermal dose.
Source of Funding: Research grant from Boston Scientific