A temperature model for laser lithotripsy

J G Williams,D E Moulton,B W Turney,S L Waters,L Goldsmith

doi:10.1007/s00345-020-03357-y

Abstract

ObjectiveTo derive and validate a mathematical model to predict laser-induced temperature changes in a kidney during kidney stone treatment.MethodsA simplified mathematical model to predict temperature change in the kidney for any given renal volume, irrigation flow rate, irrigation fluid temperature, and laser power was derived. We validated our model with matched in vitro experiments.ResultsExcellent agreement between the mathematical model predictions and laboratory data was obtained.ConclusionThe model obviates the need for repeated experimental validation. The model predicts scenarios where risk of renal tissue damage is high. With real-time knowledge of flow rate, irrigating fluid temperature and laser usage, safety warning levels could be predicted. Meanwhile, clinicians should be aware of the potential risk from thermal injury and take measures to reduce the risk, such as using room temperature irrigation fluid and judicious laser use.

Highlights

Over the last 30 years, Holmium lasers have been used to fragment stones within the urinary tract
An unintended consequence is the risk of thermal tissue damage due to heating of the irrigation fluid within the ureter or renal pelvis
We subsequently derived a mathematical model from conservation of energy principles, neglecting spatial temperature variation and considering only the volume-averaged temperature over time

Summary

Introduction

Over the last 30 years, Holmium lasers have been used to fragment stones within the urinary tract. Lasers for stone surgery have become more powerful (up to 120 Watts) to provide the ability to modulate the frequency and pulse energy across a greater range. This has made the technique of “dusting” feasible. In this technique, the laser is used at a higher frequency with a lower energy to gradually break off tiny pieces of stone that can be passed spontaneously in the urine and do not require time-consuming extraction. An unintended consequence is the risk of thermal tissue damage due to heating of the irrigation fluid within the ureter or renal pelvis

Methods

Results

Discussion

Conclusion