LAUSR

With great interest, I read a study by Lu et al. [1] in a recent issue of the journal. It is a randomized, controlled trial to compare the clinical efficacy and safety between the retrograde intrarenal surgery (RIRS) with 365 μm and conventional 200 μm holmium laser. The authors concluded that 365 μm holmium laser in RIRS is safer and highly efficacious for treating kidney stones with similar low complication and less operation time, especially for those located in lower pole and larger than 2 cm. It is a promising result, and I would like to highlight some issues. Many studies focus RIRS on the challenges for treating > 2 cm kidney stones because of less invasiveness with less bleeding. However, the low stone clearance rate and the long lithotripsy time along with high risk of postoperative infection limit its broad clinical use. The most exciting point in Lu et al. study is that the lithotripsy time can be significantly shortened, which is a very favorable reason for expanding the clinical application and indication of RIRS. In one study using a custom bench model, the 365 μm laser showed improved stone fragmentation efficiency compared with 200 μm laser (80 mg/min vs 52 mg/min) [2]. Therefore, large stones and more complex stones, such as multiple renal calyceal calculi, which are often treated by PCNL even with multiple tracts, might be treated successfully as well by RIRS with the high lithotripsy efficiency of 365 μm holmium laser. Although some problems, such as timeliness of debris stone discharge and possible postoperative infections and renal colic secondary to steinstrasse, are need to be further studied, it still has a bright prospect in stone-surgery field. Temperatures over 43 °C, the threshold (as body temperature is 6 °C below 43 °C) for cellular injury may be achieved during holmium laser lithotripsy. Winship et al. reported that the time to reach and subsequently clear high temperatures was related to laser power settings and irrigation pressures, and high temperatures were achieved in vitro model in as little as 1 s at common irrigation pressures and laser settings, and with laser cessation, temperatures quickly returned to a safe level at each irrigation pressure [3]. Others also demonstrated that temperature increased with increasing laser power output and decreasing irrigation flow rate in vitro ureteral system [4, 5]. The authors recommended that “Awareness of this risk allows urologist to implement a variety of techniques (higher irrigation flow rates, intermittent laser activation, and potentially cooled irrigation fluid) to control and mitigate thermal effects during holmium laser lithotripsy” to potentially reducing ureteral tissue injury [5]. Therefore, although low complications are observed in Lu et al. study, the more concerns about the possibility of thermal damage in calyceal neck and renal papilla in the renal collection system are required, which may cause a bad longterm impact. We find the study valuable and we believe the prospect of 365 μm holmium laser in RIRS technique when the safety of thermal response to high-power holmium laser lithotripsy was confirmed.