(UroToday.com) At the WCET 2024 conference in Seoul, Dr. Robert Medairos from the Department of Urology at Duke University Medical Center presented a study that investigates the potential for thermal injury during the use of the thulium fiber laser (TFL) in stone dusting procedures. The increasing popularity of TFL for stone dusting aims to minimize or eliminate the need for fragment extraction. However, concerns have been raised regarding the possibility of thermal injury to the urothelium due to the TFL's high water absorption properties.
The study was conducted using an in-vivo porcine model involving two anesthetized pigs. Cylindrical BegoStones, measuring 4-6 x 10 mm, were implanted and treated in both the kidneys and ureters of the pigs. Throughout the procedure, temperatures near the stone-tissue boundary were monitored using K-type thermocouples. The research team performed ureteroscopy with TFL laser lithotripsy (LL), utilizing a 200-μm fiber and room temperature saline irrigation at a flow rate of 20 mL/min. Each TFL treatment was compared against a sham control to assess its effects.
Three kidney treatments were conducted at a setting of 1 J/20 Hz, and three ureter treatments were performed at settings of 0.8 J/12 Hz, 0.2 J/100 Hz, and 1 J/20 Hz. Post-procedural examinations analyzed both the kidneys and ureters for any signs of thermal tissue injury. The thermal dose, expressed as cumulative equivalent minutes at 43°C (CEM43), was calculated based on the recorded temperature data.
The results revealed significant findings regarding the thermal impact of TFL. In the kidney, the maximum sustained temperatures recorded were 40°C, 60°C, and 95°C, with corresponding CEM43 values of 4.63, 1.32E+5, and 1.14E+194 minutes, respectively. The lower temperatures were observed in a calyx with a wide infundibulum, whereas the higher temperatures were noted in calyces with a narrower infundibula. In the ureter, temperatures reached 32°C (at 0.8 J/12 Hz), 63°C (at 0.2 J/100 Hz), and 73°C (at 1 J/20 Hz), with corresponding CEM43 values of 1.44E-8, 8.50E+9, and 7.82E+7 minutes.
The study also found that kidney and ureter treatments with higher temperatures and thermal doses resulted in extensive visible damage to the urothelium, as confirmed by gross pathology and histologic evaluation. Specifically, high thermal doses led to significant heat-induced damage, characterized by acellular tissue and collagen homogenization, findings that were not present at lower thermal doses.
In conclusion, the study demonstrates that using TFL at 20 W with 20 mL/min irrigation in an in-vivo porcine model can result in elevated intraluminal temperatures and extensive thermal tissue damage in both the kidney and ureter. These findings underscore the importance of considering thermal dose as a critical factor in the safe application of TFL in clinical settings.
Following the presentation, the Q&A session provided additional insights. An audience member asked if urologists in clinical practice typically use the 20 W setting for TFL and whether they are able to visualize thermal damage during procedures. Dr. Medairos acknowledged that some clinicians do use the 20 W setting, but at their facility, they have opted to switch to a lower setting of 10 W to mitigate the risk of thermal injury.
The moderator then posed a question about whether they had considered using cold temperature irrigation fluids during the procedures. Dr. Medairos responded affirmatively, noting that they are currently conducting a study investigating the impact of irrigation temperature on thermal injuries.
Another audience member raised a concern regarding the study's methodology, specifically that the laser was fired for 30 seconds followed by a 30-second pause, which is different from typical clinical practice. Dr. Medairos explained that this approach was used to reduce variability in the experimental conditions, making it easier to measure and compare the effects of different settings.
This project received support from the National Institutes of Health (NIH) through grants 1P20DK135107-02 and 2R01DK052985-26.
Presented by: Robert Medairos, MD, Faculty Physician from the Department of Urology at Duke University Medical Center.
Written by: Seyedamirvala Saadat, Research Specialist at Department of Urology, University of California Irvine, @Val_Saadat on X during the 2024 World Congress of Endourology and Uro-Technology (WCET) Annual Meeting, August 12 -16, 2024, Seoul, South Korea