Positioning- the preferred position is the modified supine Valdivia position. The patient is lying supine and positioned at the edge of the bed to avoid collision between the bed and the nephroscope. The ipsilateral flank is elevated using an inflatable bag while the contralateral hip is flexed at about 45 degrees. The supine position provides better draining of the irrigation fluid through the smaller tract and thus decreases intrarenal pressure. This position also allows for two surgeons to work in tandem as retrograde pyelography and kidney puncture are done simultaneously (this can save about 15 minutes of procedure time).
Kidney Puncture- percutaneous access traverses the posterior axillary line into the lower pole of the kidney. The kidney puncture is performed using both ultrasound and fluoroscopy. The ultrasound probe is positioned parallel with the 12th rib and Doppler image is used to avoid puncture of major blood vessels. Cranio-caudal tilt of the C-arm facilitates alignment of the puncture needle and the desired calyx.
Tract Dilation- a single reusable metallic dilator is used to dilate the tract under fluoroscopic control, and an 18 Fr Amplatz sheath establishes the percutaneous tract. This has eliminated the costs associated with disposable balloon dilators.
Stone Fragmentation- a large diameter laser fiber is preferred because of its ability to produce a higher energy density at its tip (energy transmitted through a unit area, defined as Joule/cm2). Therefore, a 550µm laser fibers yields an energy density that is 5.3 times that of a 200µm fiber. While activating the laser, the stone is pushed against the urothelium. This maneuver fixes the stone and prevents retropulsion.
Stone Extraction- removal of stone fragments is facilitated by a suction device or an aspiration system. Fragments as large as 5.5 mm can be extracted through the sheath.
At the end of the procedure, a ureteral catheter is placed for 24 hours and a small nephrostomy tube is removed if its clamping causes no flank pain. Another alternative is the insertion of a double J stent. In either case, the majority of patients are discharged on postoperative day one.
Presented by Anrdas Hozneck, MD, Henri-Mondor Hospital, Créteil, France
Written by Dr. Shlomi Tapiero, Department of Urology, University of California-Irvine, medical writer for UroToday at the 36th World Congress of Endourology (WCE) and SWL - September 20-23, 2018 Paris, France