Is Pulse Modulation the Future of Laser Technology in Endourology: Evidence from a Literature Review - Section of EAU Endourology

Laser activation during endourological surgeries inevitably generates an excess of energy that is ultimately converted into thermal energy, resulting in an increase of the surrounding temperature. As expected from the laws of thermodynamics, higher laser power correlates with higher intraluminal temperature. Ultimately, this temperature rise can potentially lead to complications due to thermal damage to cells, tissues, and organs.

However, tissue injury is not determined solely by a specific temperature threshold. Instead, it depends on both the temperature reached and the duration of exposure - a concept known as thermal dose. This principle, introduced by Sapareto and Dewey to investigate organ damage upon thermal insults, shows that even brief exposure to high temperatures can result in irreversible cell injury. Their model describes this relationship as nonlinear, which emphasizes that an approach based on a fixed temperature value (e.g., avoid exceeding 43°C) may be oversimplistic.

The application of these principles to endourology led us to introduce the thermal safety distance concept. It was defined as the shortest distance from the fiber laser tip to exceed the safety threshold. As a general rule, the closer the laser fiber is to healthy tissue, the higher the local temperature, making available working space a critical factor when planning safe laser settings. Clinically, this translates into different safe power limits for ureteral versus renal procedures, as anatomical constraints and heat dissipation capacity vary by location.

To further complicate matters, several strategies exist to help mitigate excessive intrarenal temperatures. Each offers specific benefits but also presents potential drawbacks:

Increased irrigation flow – While it can help cool the intrarenal environment, insufficient outflow may lead to elevated intrarenal pressure and associated risks.
Intermittent laser activation – Reducing the duty cycle, ideally below 50%, limits cumulative heat generation.
Use of low-power settings – Arguably the most consistent and effective strategy, supported by current evidence and technology, offering a balance between safety and efficacy.

In conclusion, a reasonable safe recommendation is to limit power settings to <20W for intrarenal surgery and <10W for ureteral procedures. This approach is simple, cost-effective, and does not compromise outcomes compared to high-power settings. In addition, thermal safety during laser lithotripsy is multifactorial. Respecting the principles of thermal dese and safety distance by adjusting power accordingly are key steps to reduce complications and optimize results.

Written by: Felipe Pauchard,^1,2,3 Daniele Robesti,⁴ Eugenio Ventimiglia,^1,2,5

Progressive Endourological Association for Research and Leading Solutions, Paris, France
European Association of Urology Endourology Section, Arnhem, The Netherlands
Urology Department, Hospital Naval Almirante Nef, Viña del Mar, Chile
Vita-Salute San Raffaele University, Milan, Italy
Department of Surgical Sciences, Uppsala University, Uppsala, Sweden

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