Re: Comparison of retrograde intrarenal stone surgery with and without a ureteral access sheath using kidney injury molecule‑1 (KIM‑1) levels: A prospective randomized study by Gökhan Ecer, Mehmet Giray Sönmez, Arif Aydın, Cemile Topçu, Haider Nihad Izaddin Alalam, Selçuk Güven, and Mehmet Balasar

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This is a very interesting article where the authors used urine KIM-1/Cr levels to assess the damages to the kidneys during retrograde flexible ureteroscopy (RIRS) without and with the use of ureteral access sheath (UAS) in the treatment of renal calculi [1]. The major flaw of this manuscript is that the authors failed to understand the design and function of the ClearPetra^® UAS, which the authors mistakenly referred to as a dual lumen UAS. ClearPetra does not have dual lumen, rather it has a single straight lumen but with an oblique side branch. This side branch is devised to be connected to a vacuum apparatus; thus, ClearPetra sheath is often referred in the literature as vacuum assisted sheath. There is a longitudinal air vent on this side branch which allows the operator to adjust the vacuum pressure by covering and uncovering the vent. If the ClearPetra UAS is not connected to vacuum, as it was applied in this study, it would perform same as a standard UAS; hence, the same outcome as reported in this manuscript. The drainage of fluid from the kidney during RIRS is directly proportional to the space between the scope and the sheath. In the standard UAS, the drainage is passive, whereas in the ClearPetra, the drainage is active. Active drainage will be more efficient than passive drainage with the similar size UAS. This should result in lower intrarenal pressure and less renal damage. We had reported our researches [2, 3] comparing the intrarenal pressure in ex-vivo porcine kidneys using ClearPetra versus standard UAS. ClearPetra UAS demonstrated significantly lower intrarenal pressure under the same trial condition. Thank you. …