Category: Clinical Stones: Ureteroscopy

MP24-11 - “Operator Duty-Cycle” effect of heat generation during holmium laser lithotripsy

Sun, Sep 23
10:00 AM - 12:00 PM

Introduction & Objective :

Recent in vitro studies with test-tube models have demonstrated that temperature elevation sufficient to cause thermal tissue damage can occur with certain laser and irrigation settings.  These studies were standardized with continuous laser activation for 60 seconds which does not replicate the patterns of laser activation in the clinical scenario. The aim of this study was to characterize the thermal dose from high power laser lithotripsy using a more realistic 50% operator duty-cycle and compare to the same energy applied with a 100% duty cycle.

Methods :

The experimental system consisted of a glass test tube (inner diameter 10 mm/length 75 mm) filled with deionized water. Real time temperature was recorded using a wire thermocouple attached alongside the ureteroscope. A 242 µm laser fiber (Flexiva, Boston Scientific, MA) was inserted through a ureteroscope (Lithovue, Boston Scientific, MA) and positioned 10 mm above the bottom. Irrigation with room temperature saline was provided through the working channel of the ureteroscope at medium irrigation (14-15 mL/min) - 100 cm gravity, low irrigation (7-8 mL/min) – 60 cm gravity, or no irrigation. The test tube was placed in a water bath maintained at 37°C. During each experiment temperature was monitored continuously and 40 W laser energy (0.5 J, 80 Hz, short pulse) was applied (pulse 120; Lumenis, CA) starting at 20 seconds. The laser was activated in three modes of operation:  60 continuous seconds (100% operator duty-cycle), 5 second on and off cycles for 120 seconds (50% operator duty-cycle), and 10 second on and off cycles for 120 seconds (50% operator duty-cycle). Each experiment was repeated 3 times. Thermal dose for each trial was calculated based on Dewey and Sapareto t43 equivalence calculations.

Results :

Thermal dose exceeded the safety threshold (t43 >120 min.) for all experiments when using no irrigation and for all experiments with 100% duty cycle (Figure 1A). Temperature curves for no irrigation experiments are demonstrated in Figure 1B.

Conclusions :

High power (40 W) laser settings can induce concerning temperature rise of calyceal fluid even when activating the laser at 50% operator duty cycle with no or low irrigation rate. Further studies are needed to investigate the effects of lower operator duty-cycle on calyceal fluid temperatures.

Ali H. Aldoukhi

Research fellow
University of Michigan
Ann Arbor, Michigan

I'm a research fellow in the Urology department at the University of Michigan. In our lab we study factors affecting stone fragmentation during holmium laser lithtotripsy.

Timothy L. Hall

Associate Research Scientist
University of Michigan
Ann Arbor, Michigan

Khurshid R. Ghani

Associate Professor of Urology
University of Michigan
Ann Arbor, Michigan

Khurshid Ghani is an Associate Professor of Urology at the University of Michigan. His research interests include novel techniques of endoscopic and robotic surgery for renal stone disease, health services research and surgical quality improvement. In particular Dr Ghani has been focused on advancing a Dusting technique for endoscopic stone surgery and has extramural funding to study optimal laser settings for holmium laser lithotripsy. He is the Course Director of the Developments in Ureteroscopic Stone Treatment (D.U.S.T.) symposium. In addition, Dr Ghani serves as Co-Director of the Michigan Urological Surgery Improvement Collaborative, which is a consortium of 44 urology practices aiming to improve the quality of urological care in the state of Michigan.

William W. Roberts

University of Michigan
Ann Arbor, Michigan

William W. Roberts, MD is Professor of Urology and Biomedical Engineering at the University of Michigan. He earned a B.S. in Physics from the Massachusetts Institute of Technology in 1992, an M.D. from the Johns Hopkins University School of Medicine in 1997, and completed his urology training at the Brady Urological Institute at Johns Hopkins. He joined the faculty of the University of Michigan in 2004 and is now Director of the Division of Endourology. His clinical practice is focused on minimally invasive surgery, endourology, and urinary stone disease.

Dr. Roberts is part of the multidisciplinary scientific team at the University of Michigan that developed histotripsy, a non-invasive, focused ultrasound technology that induces controlled cavitation to mechanically ablate targeted tissues within the body. He is the director of the Translational Histotripsy Laboratory and has led the research effort to apply histotripsy for treatment of urologic diseases in preclinical models.

Dr. Roberts has presented his work at international and national meetings and has authored over 100 peer-reviewed publications. His research contributions have been recognized in the form of multiple grants and awards from the National Institutes of Health, American Urological Association Foundation, Coulter Foundation, and Engineering and Urology Society. He was the 2014 recipient of the prestigious AUA Gold Cystoscope Award.