Presented by: Ron Marom MD
University of Michigan

Introduction

Higher power laser settings can yield smaller stone fragments and faster endoscopic treatments but also impose a thermal risk to the surrounding healthy renal tissues. While high fluid temperatures have been seen in both in-vitro and in-vivo studies with laser lithotripsy, the thermal distribution within the renal parenchyma has not been characterized. Additionally, the heat-sink effect of vascular perfusion remains uncertain. In this in-vivo study we sought to map the renal temperature distribution in response to laser activation in a calyx in both perfused and non-perfused states.

Materials

Ureteroscopy was performed in three porcine subjects with a prototype ureteroscope containing a temperature and a pressure sensor at its tip. The distal end of the ureteroscope was positioned in the middle of a calyx and maintained there for the entire experiment. A multi-point needle with four thermocouple sensors located 5, 15, 25, and 35 mm from the tip was introduced percutaneously into the same calyx using US guidance. The first sensor was positioned inside the calyx. Three trials of 60 second laser activation (40 W) were conducted with irrigation of 8 ml/min. After euthanasia, three trials with the same settings were repeated. Thermal dose was calculated from the time-temperature curves for each thermocouple using the Sapareto and Dewey methodology. The threshold of thermal tissue injury was considered to be t43 = 120 equivalent minutes.

Results

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The collecting system fluid temperature increased by over 30 °C and surpassed the thermal threshold in all trials. The temperature at the second thermocouple in the medulla increased to a lesser degree, but still surpassed thermal threshold in some trials. Comparing perfused and non-perfused trials, temperature curves were similar except at the 3rd thermocouple in the renal cortex where temperatures increased much more without perfusion.

Conclusion

High-power laser settings (40 W) with lower irrigation rates can induce potentially injurious temperatures in the in-vivo porcine model, particularly in the region adjacent to the collecting system. Furthermore,  vascular perfusion appears to have limited effect on mitigating thermal spread in the medulla.

Funding

Research grant from Boston Scientific

Disclaimer: Prototype ureteroscope used in this study was a concept device/technology, which was not available for sale at the time the study was conducted. Pre-clinical study results may not necessarily be indicative of clinical performance.

Lead Authors

William W. Roberts, MD
University of Michigan

Co-Authors

Julie J. Dau, DVM
University of Michigan

Timothy L. Hall, PhD
University of Michigan

Khurshid R. Ghani, MBChB, MS, FRCS
University of Michigan