Evaluating temperature dynamics: a single-center prospective randomized pilot study of holmium versus thulium laser fiber for renal stones.

Background: We aimed to evaluate and compare the rise in the temperature for the safety of the kidney parenchyma on firing the Holmium: Yttrium Aluminium Garnet laser and the Thulium Fiber Laser during laser lithotripsy in humans.

Method: We included 30 pre-stented patients with renal calculi undergoing Retrograde intra-renal surgery. They were randomized into two groups - 15 patients underwent holmium laser lithotripsy and 15 patients underwent TFL laser lithotripsy. We used Philips paediatric esophageal probe to measure rise in temperature on firing holmium or TFL laser with irrigation at 10 ml/min and pressure at 100 mmHg. Different laser settings were used.

Result: The mean size of the calculi was 0.8 mm. The rise in temperature with holmium and TFL lasers depended on the firing time and irrigation flow, keeping power constant. On continuous firing for 10s, 20s, and 30s, the average rise in temperature went up to 28.67 °C, 29.70 °C, and 37.17 °C with holmium and with TFL it was 28.77 °C, 29.83 °C, and 37.62 °C, respectively. The difference in rise in temperature between two groups was statistically insignificant with p-values > 0.05. The maximum temperature reached with TFL was 39.4 °C with a 30s lasing time, and that with Ho: YAG was 38.9 °C.

Conclusions: The rise in temperature was almost equivalent with holmium and TFL. Hence, both Ho: YAG and TFL can be safely used in laser lithotripsy. Adequate irrigation is a must during the surgery. The continuous lasing time should be strictly restricted to less than 20s.