Needle-Perc: A New Instrument and Its Initial Clinical Application
Percutaneous nephrolithotomy (PCNL) has gained significant acceptance over the past decade, largely due to the minimization of instruments and improvements in flexible scopes. Research has demonstrated that the size of the tract used in PCNL is positively correlated with the rate of bleeding and renal injuries. Building on this concept, a new PCNL technique called “needle-perc” was developed, which utilizes a needle even thinner than that used in the micro-perc technique. This study presents the initial clinical experience with the needle-perc method for treating small renal stones and assesses its feasibility and safety as a new instrument in minimally invasive endourology.
The clinical trial was approved by the ethics committee of Beijing Tsinghua Changgung Hospital. The inclusion criterion was the presence of a single small kidney stone measuring less than 1.5 cm. Patients meeting this criterion were informed that PCNL would be performed using a new instrument, and all provided informed consent. The disposable instruments, including the needle-perc sheath, were provided free of charge. From March 2019 to July 2019, 24 patients with renal stones underwent PCNL using the needle-perc technique at the hospital. All operations were performed by an experienced surgeon.
The novel instruments included reusable optical microfibers with a diameter of 0.6 mm and a resolution of 10,000 pixels. The microfiber, equipped with a light lead, was inserted into the working sheath through the central port of a three-way connector at the proximal end of the sheath. The depth of the fiber could be manually adjusted during the operation to ensure clear visualization. One lateral port of the connector was for the irrigation system, which could use a pump system or gravity irrigation with saline bags. The other lateral port was designed for the laser fiber, a 200-mm fiber used for dusting or fragmenting the stones during surgery. The optic fiber was connected to a standard endoscopic camera system and light source via a zoom ocular and light adapter.
Procedures were performed under general anesthesia. A 5F catheter was inserted with the patient in the lithotomy position, after which the patient was placed in the prone position for the puncture. The needle-perc was introduced to the target calyx under ultrasonography guidance. The stone was fragmented or dusted with the laser power set at 8 to 12 W (0.8–1.0 joules/10–15 Hz) using long or short pulses. After the procedure, any residual stones were assessed by ultrasonography. The ureteral catheter was removed on the first post-operative day. The stone-free rate was evaluated one month after surgery. Hemoglobin loss and the pain index were evaluated 24 hours post-operatively.
A total of 24 renal units underwent PCNL with the needle-perc technique in 16 male (67%) and eight female (33%) patients. The mean age of the patients was 42.5 years, ranging from 1 to 67 years. There were 13 left-sided and 11 right-sided renal units. The mean calculus size was 12 mm, ranging from 5 to 15 mm. Among the 24 patients, 20 were treated with a single puncture, while the other four required re-puncture to confirm correct positioning. Two patients underwent conversion to the use of a mini-perc (16F) to remove stones that had been transferred to the proximal ureter during surgery. The mean operative time was 49.2 minutes, ranging from 22 to 75 minutes. The mean hemoglobin loss was 5.2 g/L, ranging from 0 to 13.8 g/L. The mean visual analog scale score for pain was 3.2, ranging from 1 to 6, based on the 20 adult patients whose procedures were performed with the needle-perc.
Of the 24 patients, 20 (83%) had no residual stones according to the kidneys-ureters-bladder examination on the first post-operative day, while four patients had residual calculi measuring 2 to 3 mm (three in the lower pole calyx and one in the upper ureter). At the one-month follow-up, two of these patients had expelled the residual stones, resulting in a stone-free rate of 91%. Significant complications were assessed using the modified Clavien classification system. Fever (>38.5°C, grade II) was observed in two (8%) patients, who were treated with intravenous antibiotics. One patient experienced transient renal colic (grade II) on the first post-operative day and was managed conservatively with anti-spasmodic drugs. The ureteral catheter was maintained for two additional days in patients with residual ureteral stones. None of the patients required blood transfusion, and no complications classified as Clavien III or above occurred.
Traditional PCNL with 24 to 30F channels is believed to achieve better stone clearance, particularly for staghorn stones. However, evidence suggests that smaller channels may be associated with lower morbidity rates. By keeping the access route as small as possible, such as with the initial puncture needle, complications like bleeding can be minimized. The design of the needle-perc was based on the goal of achieving the highest stone clearance with minimal kidney damage. Compared to the micro-perc, the needle-perc has a smaller outer sheath, resulting in less damage to the kidney. Similar to the micro-perc, stones cannot be removed using the sheath due to its limited size, so most stones must pass spontaneously. Therefore, the “dusting effect” should be maximized.
To achieve this effect, the laser parameters were set to “lower energy, higher frequency, and long pulse duration” modes to avoid large fragments. For conventional access, intra-pelvic pressure can be easily controlled. However, for small tracts, pressure during the procedure must be adjusted with caution. Intra-pelvic pressure was measured using a pre-placed ureteral stent, as described by Sameh et al. The pressure throughout the procedure ranged between 16 and 35 cmH2O, effectively avoiding bacterial reflux. Due to the small size of the intra-sheath space, gravity irrigation was preferred for the needle-perc procedure. The small volume of water used could explain the lower intra-renal pressure and even the absence of outflow during the procedures.
The miniaturization of PCNL offers advantages in special anatomical situations, such as upper urinary tract stones in pediatric patients. The needle-perc technique was recently used in three cases of renal stones in infants, although these cases were not included in this study due to insufficient follow-up and the limited number of cases. Compared to retrograde intra-renal surgery, the tubeless needle-perc technique may offer benefits such as a shorter hospital stay, less discomfort, and fewer patients requiring general anesthesia, which is particularly important for infants. Another potential use of the needle-perc is as an auxiliary channel to standard channels. Patients with parallel calyx renal stones may require multiple channels for conventional surgery. The needle-perc can serve as a “satellite access” point, allowing parallel calculi to be fragmented or pushed into the renal pelvis. The main access can then be used for stone removal, avoiding the need for multiple channels and effectively protecting kidney function.
This study has several limitations. First, only patients with small stones were enrolled, so it is unclear whether the same therapeutic effect can be achieved in patients with larger stones. Second, the needle-perc is still in the early stages of clinical application, leaving room for improvement in its handling, materials, and performance. The first-generation needle-perc was used in this study, but a second-generation needle-perc has since been developed. The second-generation instrument includes a vacuum suction device to allow more effluent discharge, maintaining lower pressure in the collection system intra-operatively. Future studies will explore the application of the second-generation needle-perc to removing larger kidney stones (>2 cm). Finally, randomized studies are needed to define the needle-perc’s place in the treatment of renal calculi compared to previous instruments such as ultra-mini PCNL, super-mini nephrolithotomy, and micro-perc devices.
In conclusion, the needle-perc is a promising instrument for PCNL, particularly in managing special cases. For small, low calyceal stones, it can serve as an appealing alternative to extracorporeal shock wave lithotripsy and flexible ureteroscopy. Pediatric patients may benefit more from this new technique than from flexible ureteroscopy. Complex and large stones typically require conventional and multiple tracts to achieve a high stone-free status. The use of the needle-perc could increase the stone-free rate without adding complications.
doi.org/10.1097/CM9.0000000000000692
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