Abstract
We have read the article by Kim et al. entitled “The Clinical Efficacy of Dual-Lumen Catheter Technique in Retrograde Intrarenal Surgery for the Management of Nephrolithiasis: A Propensity Score Analysis.” 1 We would like to congratulate the authors for their innovative and novel technique of removing stone dust during retrograde intrarenal surgery.
Although the authors have quoted their own experience that stone dust show long spontaneous passage time with a high probability of growth in size, Hecht and Wolf 2 have noted spontaneous passage of stone dust without long-term sequalae, which is also consistent with our experience.
Our first concern is regarding the difficulty in the use of ureteral access sheath (UAS) 11/13F especially in unstented ureter. Only 4 (16%) out of 25 patients in the group with Dual Lumen Technique (DLC) have stented ureter, whereas 21 (84%) patients had unstented ureter. Traxer and Thomas 3 in their study have found the incidence of ureteral injuries in 46.5% of patients with the use of UAS size 12/14F and they further noted that the incidence of severe ureteral injuries is largely decreased by preoperative Double-J stenting. Another series of 101 patients with the use of UAS sizes of 9.5/11.5F (in 77 patients) and 12/14F (in 24 patients) reported mucosal lesions in 38.6% and involvement of smooth muscle layers in 2.9% of patients. 4
Worldwide there is a trend of miniaturization of endoscopes and ancillary equipments, allowing the use of smaller diameter UASs, which may lower the risk of ureteral damage. The introduction of a device that requires use of a larger access sheath thus contradicts the current modern practice.
We would like to know the methods used for accurate assessment of the size of the fragments after lithotripsy intraoperatively, as it determines the method of removal of fragments using stone basket or DLC technique. Clear distinction of residual fragments (RFs) and stone dust based on size is important as the authors have stated in the article that DLC technique has adverse effect on removal of RF.
Our last concern is suctioning of stone dust or fragments through DLC technique. The two lumens have caliber of 0.97 mm and 1.27 mm with pressure and flow rate of 50 to 80 cm of Hg and 1–1.5 L/min, respectively. With this pressure and flow, there is a possibility of increase in pelvicalieal pressure after blockage of the suctioning channel by gravel leading to pyelovenous reflux, forniceal rupture, bacteremia, and sepsis.