Study design
This retrospective study considered patients with urinary calculus who underwent f-URS from September 2014 to November 2019 at St. Luke’s International Hospital and Tohoku Medical and Pharmaceutical University Hospital, Japan. A self-retrieval basketing method during f-URS was performed to extract stones. While more than 200 consecutive patients underwent f-URS during the above period, we included 100 patients treated with a single surgeon (G.A) who had the experience of performing over 100 cases of f-URS. The inclusion criteria included patients between 20 and 90 years of age. We excluded patients who were initially scheduled for two-stage surgery because the stone size was too large as well as those with malformations in the urinary tract, such as cases after urinary diversion. The ethical committee of Tohoku Medical and Pharmaceutical University Hospital School of Medicine, Sendai, Japan approved the study protocol based on the guidelines of the Declaration of Helsinki (no. 2019-2-056).
Equipment
The following equipment was used a 100-W holmium:yttrium aluminum garnet (YAG) laser (VersaPulse PowerSuite; Lumenis, Yokneam, Israel) with a 200 or 365 μm laser fiber (SlimLine 200 or 365 μm; Lumenis, Yokneam, Israel), a flexible ureteroscope (7.5- French (Fr) FlexX2; Karl Storz, Tuttlingen, Germany or 7.95-Fr URF-P6; Olympus, Tokyo, Japan), a semirigid ureteroscope [6.0/7.5 or 8.0/9.8 Fr; Wolf, Knittlingen, Germany], an irrigation system (single action pumping system; Boston Scientific, Natick, MA, USA), a ureteral access sheaths (Flexor12/14 Fr; Cook Medical, Bloomington, IN, USA), a single-use basket holder (M-arm; MC Medical, Tokyo, Japan), and a basket catheter (N-gage, 1.7 Fr, Cook Medical, Bloomington, IN, USA).
Surgical technique
All patients underwent a standard surgical procedure. In brief, a semirigid ureteroscope (6.0/7.5 or 8.0/9.8 Fr rigid ureteroscope) was inserted into the urethra, and the bladder was examined under general anesthesia. A straight guidewire was inserted into the ureteral orifice on the diseased side, and the semirigid ureteroscope was passed over the guidewire through the ureteral orifice, as far as was safely achievable up to the renal pelvis region or to the ureteric stone. The presence or absence of ureteral stenosis or ureteral stones was confirmed using a rigid ureteroscope before a UAS insertion in all cases. When there was ureteral stenosis, ureteral dilation was performed or a ureter stent was placed, and two-stage f-URS procedure was scheduled.
Next, a UAS (12/14Fr Cook Flexor sheath) was introduced over the guidewire and positioned under the ureteral stone or in the renal pelvis to reduce intrarenal pressure and to facilitate the extraction of large or multiple renal stones. A holmium laser was used to crush the stones to sizes of 2–4 mm by f-URS (Storz FlexX2 or Olympus P6). All stones were managed by laser fragmentation (0.5–1.0 J × 5–10 Hz). In the case of upper ureter stones or pelvic stones, mostly 365 μm laser fibers were used because this size of fibers, due to a larger surface area offers a higher degree of lithotripsy efficiency. In the above cases, the patient position was changed to head-down to prevent the stone fragments from moving to the lower pole because the difficulty of retrieving the fragments can be increased in such a scenario. In kidney pole stone cases, mostly 200 μm laser fibers were used because the flexibility of f-URS could be deployed maximally. After crushing the observed stones into fragments that could easily be extracted (≤4 mm), a basket catheter (N-gage, 1.7-Fr; Cook Medical, Bloomington, IN, USA) (Figure 1) with an M-arm (MC Medical, Tokyo, Japan) attached to a flexible ureteroscope was inserted.
This basket catheter typically took up about one-quarter of the screen view in front or to the side of the target stone (Figure 2a). The flexible ureteroscope was manipulated with the nondominant hand, and the basket catheter was manipulated with the dominant hand. The basket was half-opened, and the flexible ureteroscope moved from the near side to the calculus position (Figure 2b). The self-retrieval basketing technique was executed in one of two ways: the front catch (Figures 3a–3d) or the side catch (Figures 3e–3h) method. In large spaces, such as the renal pelvis, the basket catheter was moved straight ahead to capture stones using the front catch technique, whereas, in narrow spaces such as a renal pole, the basket catheter was moved laterally, and stones were captured using the side catch technique. The calculus was confirmed to have entered the basket catheter, and the basket catheter was closed slowly with the dominant hand (Figure 2c). The basket catheter holding the calculus was moved a little closer to the flexible ureteroscope, and an endoscope monitor was used to confirm that the calculus had entered the tip of the access sheath. The fragments were removed from the body via the access sheath. This procedure was repeated by solo surgeons until all fragments that could be enclosed by the basket catheter had been retrieved. In all cases, a 5-Fr ureteral stent was placed just after f-URS and later removed via flexible cystoscopy with local anesthesia at two weeks after f-URS.
During f-URS, we used the single action pumping system to provide a high irrigation flow to ensure a clear view was present to help avoid ureter injury when the flexible ureteroscope was inserted from the access sheath into the ureter and renal pelvis. Essentially, the single action pumping system was not used except for in cases of poor visual access when the stones were being crushed and retrieved in the renal pelvis and kidney pole. This procedure prevented overpressure within the renal pelvis. In most cases, a 5-Fr double-J stent was placed just after f-URS and later removed via flexible cystoscopy with local anesthesia at two weeks after f-URS.
Parameters
The total operating time, stone fragmentation time, and stone retrieval time were evaluated. All patients were assessed two weeks postoperatively for ureteral stent removal and postoperative stone status. The definition of being stone-free was ≤2 mm with KUB 1 month after f-URS. We also reviewed intraoperative complications, such as heavy hematuria and ureteral injury, and postoperative complications such as postoperative fever and postoperative ureteral stenosis. Postoperative fever was defined as a significant fever over 38.0°C. Complications were evaluated according to the modified Clavien grading system [16].