Microperc with Self-Assembled Fr 4.85 Visual Needle and Ureteral Access Sheath

Abstract

Background

Micropercutaneous nephrolithotomy (microperc) is the least invasive among percutaneous nephrolithotripsy (PCNL) procedures. Although microperc has a high stone-free rate and certain advantages over other methods, modifications may be needed to improve the technique. We describe our experience performing microperc using a self-assembled visual needle and ureteral access sheath (UAS).

Methods

Between June 2016 and April 2019, the data of 30 patients with kidney stones undergoing microperc with our self-assembled 4.8 Fr visual needle combined with a UAS was retrospectively analyzed. Patients were placed in an obilique spine lithotomy position.

Results

Two cases were excluded: one due to conversion to mini PCNL and the other required flexible ureteroscopy during microperc. The remaining 28 cases included 18 men and 10 women, age 38.4 ± 7.5 years, stone size 1.7 ± 0.4 cm, and stone density on CT 969 ± 233 HU. Operative time was 47 ± 9.9 minutes, visual analogue scale score of tract pain on postoperative day 1 was 2.5 ± 1.0, hemoglobin decrease was 6.4 ± 1.0 g/L, and hospital stay was 3.1 ± 0.8 days. There was 1 case of fever and urinary infection, 2 cases of hematuria, and 1 case of flank pain. All symptoms resolved after conservative or antibiotic treatment. On postoperative day 1, 12 (42.9%) caseswere stone-free. The stone-free rates at postoperative month 1 and 3 were 92.9% (26/28) and 100% (28/28), respectively.

Conclusions

Our self-assembled visual needle and UAS instrument is effective for microperc. Use of the UAS may improve the operative outcome.

Keywords:

• Micropercutaneous nephrolithotomy
• microperc
• ureteral access sheath
• kidney stones
• percutaneous nephrolithotripsy

Introduction

Percutaneous nephrolithotomy (PCNL) is the first-line option for >2 cm diameter kidney stones and complex renal stones. PCNL has a high stone-free rate (SFR), however, one of its major complications is hemorrhage, which is associated with the size of the percutaneous renal tract.^1–4 Efforts to decrease complications have focused on instrument size. Thus, less invasive and more refined instruments have been developed, such as those used during mini-PCNL and ultramini-PCNL.^2–6 Bader et al.³ established percutaneous renal tracts using a 16-gauge optical puncture system in 2011. Desai et al.⁷ first reported on the puncture and disintegration of urinary stones in a single step without tract dilation and named this innovative PCNL “microperc.” Thereafter, microperc went on to be used to treat moderate-size renal stones in an effort to reduce tract size and tract-related complications.^4,5,8–12 Advantages of the single-step procedure without tract dilation are minimal tract bleeding, high likelihood of terminating the procedure without tubes, and reduced postoperative pain and hospitalization.^5,8,13

Nevertheless, microperc has drawbacks. First, it is performed without an Amplatz sheath, which is intended to facilitate controlling intrapelvic pressure(IPP) and removing fragments.^{5–8,11,14–17} Irrigation fluid may not be actively drained and pressurized irrigation may increase IPP, requiring aspiration through the ureteral catheter during the procedure.^7,8,18 High IPP can cause fluid absorption, intravasation, extravasation, and even renal perforation.^5,8,13,14 Second, similar to extracorporeal shock wave lithotripsy (ESWL) and flexible ureteroscopy, PCNL is a “break and leave” process with stone fragments left to discharge spontaneously after the surgery.^{2,6–8,10,14} However, fragment discharge may be difficult, such as in patients with an abnormal lower calyx and anatomy.^{6,7,10,19–21} Furthermore, residual stone fragments can cause renal colic and postoperative steinstrasse.^{5,6,8,14,16,22–24} Third, stone fragments and powder may impede operator vision and thus reduce efficiency and prolong operative time.^5,20 Fourth, even minimal bleeding can be a concern for vision interference due to a small irrigation channel and in case a suction device is lacking.^{1,5,7,13,14,19,20}

Tepeler et al.²⁵ reported that during all phases of microperc IPP can be significantly higher than conventional PCNL, and the highest levels of IPP during microperc were also markedly higher in the two groups of patients they studied (30.3 ± 3.9 mmHg and 20.1 ± 3.1 mmHg). A 14-gauge intravenous cannula has been used as a micro-Amplatz sheath and another cannula to establish a second tract for relieving intrapelvic pressure.²⁶ However, the extra tract often carries a risk of trauma. Microperc is still in early development and technical improvements are needed to perfect it to establish its place among ESWL, PCNL, and ureteroscopy.^{4,7,8,14,17,27,28}

PCNL can be successfully performed on patients in the oblique supine lithotomyposition.^29,30 During retrograde intrarenal surgery, a ureteral access sheath (UAS) is typically used to maintain low IPP. During flexible uteroscopy, when a UAS is utilized and irrigation flow is <100 cm H₂O, IPP remains lower than 30 mmHg.³¹ Hence, we hypothesize that UAS may facilitate controlling IPP during microperc, flushing out the turbid irrigation fluid, and providing access for flexibleureterscopy in some scenarios, such as stone fragment migration, to improve the success rate.

In this article, we describe the results of applying a self-assembled visual puncture needle combined with UAS to manage kidney stones.

Materials and methods

Patients and study design

We reviewed the case records of 30 patients with urinary calculi who underwent microperc using a self-assembled visual puncture needle between June 2016 and April 2019. This study was conducted in accordance with the Declaration of Helsinki. Inclusion criteria: single stone or multiple stones parallel to the puncture tract that could be fragmented via a single tract;¹² stone size ranged 1.0-3.0 cm in diameter;¹² ≥2 cm nonobstructive pelvic stones; failed ESWL or flexible ureteroscopy due to calyceal neck stricture.¹⁰ Exclusion criteria: multiple stones distributed in different calyces requiring multiple (≥2) puncture tracts;^12,15 other procedure during the same admission, such as flexible ureteroscopy lithotripsy (FURSL) or mini PCNL;renal insufficiency.

Preoperative evaluation included a urine test, urine culture, ultrasound, computed tomography (CT), intravenous pyelogram (IVP), and kidney-ureter-bladder (KUB) study. Stone burden was calculated based on the maximum diameter of a single stone or the sum of maximum diameters of multiple stones.⁸ Surgery was deferred for patients with urinary tract infection (UTI) and positive urine culture until the urine test and culture were both negative. Preoperative, intraoperative, and postoperative data were collected.

Visual needle

The self-assembled visual needle consisted of a 16 G puncture needle (outer diameter 1.6 mm, or 4.85 Fr) (Magnum, MN1616; Becton, Dickinson and Company, Franklin Lakes, NJ, USA), integrated fiber optic microbundle (Fiber Endoscope, YC-LF-A;Youkang Company, Wuhan, China), and two ureteroscopy Y-adapters (Gateway Advantage Y-Adapter; Boston Scientific, Natick, MA, USA) (Figure 1). The diameter of the highly flexible fiber optic bundle was 0.8 mm, with an optic resolution of 10 000 pixels. The two Y-adapters were screwed together: the stem of Y-adapter #2 was screwed into one of the ports of Y-adapter #1. The stem of Y-adapter #1 was then attached to the needle hub. The fiber optic bundle was inserted through the other port of Y-adapter #1 and threaded through the needle shaft until it was flush with the needle tip.⁷ An irrigation tube and a 272 μm holmium:yttrium-aluminum-garnet (Ho:YAG) laser fiber were each introduced through a port of Y-adapter #2. The proximal end of the irrigation tube was connected to a 50 ml syringe to pump irrigation fluid. The proximal end of the fiber optic bundle was connected to anendoscopic camera system (CV-180 CLV-180 Evis Exera II Endoscopy System; Olympus, Tokyo, Japan) and xenon light source.

Figure 1. Self-assembled visual needle: (A) needle sheath; (B) Y-adapter #1; (C) fiber optic bundle (fiber endoscope); (D) Y-adapter #2; (E) Irrigation tube; (F) Holmium laser fiber.

Surgical methods

After general anesthesia with laryngeal mask or tracheal intubation, patients were placed in the oblique supine lithotomy position, and the perineum and kidney areas were disinfected and draped. For antibiotic prophylaxis cefoxitinor levofloxacin was initiated 30 minutesprior to surgery and did not exceed 24 hours in uneventful cases. A 0.038-inch hydrophilic guide wire (ZIP wire; Boston Scientific) was inserted into the affected ureter and ipsilateral ureteroscopy was performed with 8.0/9.8 Fr semirigid ureteroscope(model #8703.534; Richard Wolf, Knittlingen, Germany) to evaluate ureter diameter and the length from the ureteral orifice to the ureteropelvic junction. Based on the examination, an appropriate UAS (11/13 Fr, 12/14 Fr, or 13/15 Fr) (Navigator; Boston Scientific) was inserted into the ureter along the guidewire. Ultrasound confirmation ensured UAS tip placement was at the ureteropelvic junction or proximal ureter. The UAS core was retained and normal saline was infused to delineate the calyceal anatomy. Puncture was performed under ultrasound guidance. Stone fragmentation with one access was the key for successful puncture.^4,15,16,28 For stones located in a single calyx, the visual needle was advanced directly into the calyx. Stones distributed in different calyces were also managed with one access.Mid-posterior or lower-calyceal puncture was used for pelvic stones. During needle advancement, a surgical assistant continuously perfused normal saline with a 50 ml syringe. The puncture needle allowed visualization of the entire tract in real time during percutaneous access tract establishment and verified the correct pelvicalyceal system. Successful puncture meant that the target calyx was observed and stones were visualized. After successful puncture, a 272 µm laser fiber (Shanghai Raykeen Laser Technology, Shanghai, China) was threaded into the needle through a port of Y-adapter #2. Holmium laser energy was set to high frequency and low energy, such as 30 Hz, 0.5j (Figure 2). During irrigation, if the fluid flowed too slowly from the UAS or the upper ureter mucosa blocked the UAS outlet as observed under direct visualization, the guide wire was inserted to carefully separatethe mucosa. The stones were fragmented into dust or fine particles that were washed out through the UAS and collected for composition analysis (Figure 3). After disintegration, ultrasound confirmed the absence or presence of residual stones. A 5.5 Fr ureteral stent was indwelled transurethrally to prevent urinary tract obstruction due to blood clots or possible residual stones.

Figure 2. Holmium laser lithotripsy during microperc: (A) puncture needle sheath; (B) Holmium laser fiber; (C) kidney stones.

Figure 3. Stone powder and fragments (white arrow) flushed out through the ureteral access sheath (red arrow) during lithotripsy.

Postoperative evaluation

On postoperative day 1, patients underwent renal ultrasonography and KUB to evaluate the absence or presence of peritoneal effusion and hematoma and stent position. Tract pain was assessed using a visual analogue scale (VAS). Postoperative hemoglobin decline was also evaluated. Postoperative temperature >38.5 °C was diagnosed as fever. Complications were classified according to the Clavien-Dindo system.^32,33 The ureteral stent was removed by cystoscopy at postoperative week 2-4 during an outpatient visit. Non-enhancing CT was used to evaluate patients at 1-month and 3-month follow-up. Clinically insignificant residual fragments (CIRFs) were defined as asymptomatic non-obstructing residual fragments <4 mm on CT.^2,7,12

Results

Preoperative data

Two patients were excluded from our analysis: one case was converted to mini PCNL and the second required flexible ureteroscopy during the microperc procedure (Table 1). There were 19 cases of flank pain, 8 gross hematuria, 5 urinary tract infection (UTI), and 5 patients had no symptoms. Five cases had a history of failed ESWL and 4 cases had a history of ureteroscopic lithotripsy. Preoperative urine screening was positive for white blood cells and nitrites in 5 patients, and urine cultures in 4 patients were positive for Escherichia coli, which turned negative after antibiotic treatment.

Table 1. Demographic data and stone characteristics.

Variable	Values
Age, mean (SD), range, y	38.4 (7.5); 28-56
Sex, No. (%)
Male	18 (64.3)
Female	10 (35.7)
BMI, mean (SD), range	26.0 (2.3), 22-32.2
Stone size, mean (SD), range, cm	1.7 (0.4), 1.3-3.0
Laterality, No. (%)
Left	17 (60.1)
Right	11 (39.9)
Stone location
Single stone, No. (%)
Upper pole	2 (7.1)
Middle pole	3 (10.7)
Low pole	13 (46.4)
Pelvic	2 (7.1)
Multiple stones, No. (%)
Calyceal stones	5 (17.9)
Pelvic + calyx	3 (10.7)
CT, mean (SD), range, HU	969 (233), 478-1320
Hydronephrosis, No. (%)
None	6 (21.4)
Mild	13 (46.4)
Moderate	9 (32.1)

Abbreviations: BMI, body mass index; HU, Hounsfield unit.

Intraoperative results

In our cohort, all microperc procedures were performed unilaterally. Two cases were excluded from our analysis. One case was converted to mini PCNL because the visual field was obscured due to intraoperative bleeding. In the second case, flexible ureteroscopy was required during the microperc procedure because large stone fragments had migrated, which precluded use of the visual needle. The fragments were retrieved using a Zero Tip nitinol stone retrieval basket (Boston Scientific) and moved to a better location for laser disintegration. Microperc was successfully performed on the remaining 28 cases using a single tract. In 2 cases, each of the target calyces was filled with stones. Both the calyx and stones were clearly observed on ultrasound when the needle tip entered the target calyx. But the calyx and stones were not seen with the visual system. The needle was then advanced further to penetrate through the calyceal mucosa into the calyx at which point the stones were clearly visualized. Under direct visualization, the stones were pushed aside to confirm calyx entry. After fragmentation, the stone fragments and dust were flushed out through the UAS.

Operative time for microperc was defined as the duration between initial retrograde ureterscopy to placement of indwelling stent and urethral catheter. Operative time for our cohort was 47 ± 9.9 minutes.

Postoperative results

Postoperative tract pain VAS was 2.5 ± 1.0 (range of 1-6) (Table 2). Hospital stay was 3.1 ± 0.8 days. Patients were discharged on postoperativeday 1, except for 2 cases of hematuria (Clavien I), 1 case of urinary infection and fever (Clavien II), and 1 case of flank pain (Clavien I). Hematuria and flank pain resolved on postoperative days 2–3 after conservative treatment and fever on postoperative day 3 following antibiotic therapy. Ultrasound examination did not show obvious peritoneal or pleural effusion, or retroperitoneal hematoma. There were no cases of urine or blood exudate at the skin puncture site. Hemoglobin decline was 6.4 ± 1.0 g/L on postoperative day 1. There were no residual stone fragments in 12 (42.9%) cases on postoperative day 1 (Figure 4). At postoperative month 1, the stone-free rate was 92.9% (26/28). In the two cases with residual stones, their diameters were 2 and 4 mm. These fragments disappeared by the 3-month follow-up visit.

Figure 4. Pre-and post-operative CT and abdominal plain film (KUB) of left low calyceal stone treated with microperc: (A) preoperative CT; (B) KUB; (C) stone and fragments disappeared on postoperative day 1.

Table 2. Intra-and postoperative Findings.

Variable	Values
Operative duration, mean (SD), range, min	47 (9.9), 35-75
Pain VAS, mean (SD), range	2.5 (1.0), 1-6
Hospitalization, mean (SD), range, day	3.1 (0.8), 2-5
Hemoglobin decrease, mean (SD), range, g/L	6.4 (1.0), 5-9
Stone free rate post-op month 1, % (n)	92.9, (26/28)
Complication, No.
Clavien I	3
Clavien II	1

Abbreviation: VAS, visual analog scale.

Stone analysis showed 15 cases of calcium oxalate monohydrate, 4 cases of uric acid, and 3 cases of ammonium magnesium phosphate hexahydrate, 6 case of a mixture of calcium oxalate monohydrate and calcium oxalate dihydrate.

Discussion

In this study, we successfully performed microperc on 28 patients using a self-assembled visual needle combined with a ureteral access sheath (UAS). Results, such as stone-free rate (SFR), were comparable to conventional microperc. Patients placed in the oblique spine lithotomy position allowed for both transurethral and percutaneous renal access without repositioning.^315.0-7.0 UAS facilitateda clear operative field of vision, controlled IPP, and combined with flexible ureteroscopy during microperc resulted in an improved postoperative SFR compared with microperc alone.

Conventional PCNL, including mini and ultramini PCNL, comprises three steps: tract establishment, tract dilation, and nephroscopy.¹⁴ Their common shortcomings include: the procedures require multiple steps, tract bleeding, calyceal neck tearing, and pelvic perforation.^7,13,14,22 However, reducing the size of the percutaneous renal tract does decrease injury and associated complications.²³ Microperc using a 4.85 Fr needle has the smallest tract size, avoids tract dilation during stone disintegration, and the fragments are left to pass spontaneously.^7–9,12,22 In this study, ureteral stents were not placed preoperatively as describedin our previous study,²⁹ since after ureteroscopy the appropriate UAS was selected and placed successfully under ultrasound guidance. However, flexible ureteroscopy and a stone retrieval basket were used in one case to move the stone fragments to a better location for lithotripsy without repositioning the patient.

Similar to flexible ureterscopy, bleeding and stone powder are major factors affecting the operative field of vision during microperc, necessitating conversion to mini PCNL,^1,8,17,34,35 However, when a UAS is utilized during microperc, fragments and blood clots are easily flushed out through the sheath than through a 5.0-7.0 Fr ureter catheter,^4,7,10,16 thus facilitating a clear operative field of vision and a reduced postoperative stone burden. Pressurized irrigation may improve the postoperative stone-free rate,^7–9,20,36 however, this can increase IPP and related complications such as renal pelvic-venous reflux and even calyceal perforation.^1,5,7,8 Using a UAS, a low IPP is easily maintained, whereas intermittent aspiration is needed to decrease IPP if a ureteral catheter is used.^1,4,7,16 With a Holmium laser, stones of different compositions can be powdered into fragments <1-2 mm, which can be easily flushed out through a UAS.¹⁶ In fact, even fragments as large as 3-4 mm can pass througha 13-14 Fr UAS. In the past, conversion to mini PCNL was a solution to remove displaced stones during microperc.¹³ Now, UAS may provide another access during flexible ureteroscopy to reposition and remove fragments.²⁹

Our self-assembled visual needle is disposable and less costly than the all-seeing needle. The latter is of narrow caliber and is prone to bending and breakage during lithotripsy.^4,10 Our visual needle is easily assembled just prior to skin puncture and requires only the insertion of the laser fiber into the needle sheath once the tract is established. In comparison, the all-seeing needle necessitates multiple steps during assembly and usage: after skin puncture and tract establishment, the stylet is removed and the 3-way connector is attached, followed by the telescope, the irrigation system, and the laser fiber.^3,7,19 Manipulation of our needle is simple and efficient. Another advantage of our setup is that all tissue layers are displayed on the camera during puncture,^7,20 which permits accurate tract establishment under direct vision, thus improving the success rate of surgery.^7,20,24 In two cases that had calyces full of stones, ultrasound showed that the needle tip had reached the target calyx and stones, and the operator even felt the needle tip contact the stones. However, the calyx and stones were not observed with the visual system. After advancing the needle further, the tip of needle penetrated through the calyceal mucosa and entered the calyx at which point the calyx and stones were visualized. Thus, in this scenario, direct visualization helped to accurately establish the tract while under ultrasound and x-ray the calyceal mucosa was unable to be identified.

In this study, the mean operative time including ureterosopy was 47 minutes, which was consistent with the duration of 40-104 minutes in previous reports.^{2,6,12,14–16,22,37} Thus, better irrigation and visualization contributed to the high efficiency. Postoperative tract pain was VAS 2.5, which is in line with previous reports.^7,15 Mean hospital stay was 3.1 days, which was also similar to other studies.^7,37 In the absence of nephrostomy tube insertion, postoperative pain is significantly less and hospital stay is shortened.¹ Hemoglobin decrease was 6.4 g/L on postoperative day 1, which was comparable with the previously reported 6.3-14 g/L.^{2,7,8,13,15,16,24,37} In our study, fever occurred in 1 case (Clavien II) and disappeared after antibiotic treatment. Insertion of ureteral stent due to renal colic (Clavien IIIa) after microperchas been reported.^{8,13,14,16,22–24,37} In our cohort, this complication did not occur, which could be related to ureteral stent placement and fewer residual fragments. SFR at postoperative month 1 was 92.9% (26/28), which was similar to previous results of 80.9-95.7%.^{2,6–8,13,14,16,22,24,37} Furthermore, 12 cases were fragment-free on postoperative day 1. Therefore, our method appears to render patients stone-free earlier in the postoperative period. In addition, we thought that fragment clearance was affected by the location of the UAS. However, in 1 case the UAS outlet was obstructed by the upper ureter wall, which was then nudged out of the way by inserting the guidewire through the sheath, thus allowing for smooth drainage. Therefore, drainage should be continually monitored during the procedure.

Formal guidance on application of microperc is still lacking. Most reports on its use are for moderate size stones (10-20 mm) and lower calyceal stones that are difficult to handle using extracorporeal shock wave lithotripsy (ESWL) or retrograde intrarenal surgery (RIRS).^{4,6–8,10,12,13,15,16,20,23,38–40} Microperc is also performed for pediatric renal stones,^1,7,18,20,40 pelvic ectopic kidney stones,^4,7,8,20,40 kidney stones following partial nephrectomy,²¹ kidney stones in severe kyphoscoliosis,^14,26 bladder stones,⁶ stones in the isthmus of a horseshoe kidney,^7,21 and awkward lower calyceal anatomy.^7,21 The ideal scenario for microperc is a single calyceal stone, pelvic stone, or multiple stones parallel to the percutaneous renal tract so that lithotripsy can be completed with a single tract and multiple punctures avoided.^{1,4,7,13,15,16,22,37} The upper limit of stone burden for microperc has not been identified,^1,6,8,14 although stone burden ≥30 mm has been successfully treated.^1,13,26 However, large stones require a longer lithotripsy time and carry more risk of complications,^7,20 and can even necessitate conversion to mini PCNL.⁸ Stones that completely obstruct the urinary tract, such as obstructive ureter due to ureteral stones and impacted pelvic stones, are predisposing factors for a higher IPP, therefore microperc should be avoid in these scenarios.^{1,5,8,13,14,24} Patients with marked hydronephrosis were not included in our cohort due to the risk of converting to mini-PCNL or other procedures since lithotripsy might be difficult because of poor operative field of vision or displacement of stones.^4,6,14,15,26

There are several limitations of this study. First, it was a retrospective case series analysis with a small sample size. Second, our results were not compared with those of the commercial all-seeing needle (PolyDiagnost, Pfaffenhofen, Germany) and other methods. Third, all patients in our cohort were indwelled with ureteral stents. This may have offset the advantage of microperc, which is intended to accomplish a totally tubeless kidney stone management procedure without a nephrostomy tube or double-J stent.^{5,6,13–15,21,40,41} However, some cases of >20.0 mm calculus that necessitate long operative times or result in more residual fragments are also indwelled with ureteral stents.^{1,4,6,7,12,14,15,19,37,38} In addition, stent insertion can be required due to postoperative renal colic and steinstrasse.^10,13,14,23 Therefore, indications for ureteral stent placement warrants further validation.⁶ Fourth, use of UAS leads to increased cost, ureteral spasms, swelling, obstruction, pain due to removal of the stent, and even future stricture.^6,34 Fifth, ureteroscopy performed prior to UAS insertion may increase the complexity, duration, and cost of surgery. Finally, this was an exploratory study, and as such we did not measure IPP during our procedures because irrigation flow was constant, which allowed for continual flushing of fragments and powder through the UAS. This likely decreased IPP and improved SFR.

In summary, the self-assembled visual puncture needle combined with UAS in the oblique lithotripsy position integrates visualized puncture, stone disintegration, and intraoperative stone discharge. Furthermore, it has the advantage of combining flexible ureteroscopy at any time during the procedure. This modification of microperc reduces postoperative stone burden and complications, allows for intraoperative acquisition of stone samples for composition analysis, and increases SFR. The self-assembled visual puncture needle is technically simple and is effective for performing microperc. Furthermore, it is less costly compared with the commercial all-seeing needle. However, its widespread application needs to be validated in large prospective clinical trials.

Authors’ contributions

All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Jiqing Zhang, Ning Kang, and Yuguang Jiang. Jiqing Zhang and Junhui Zhang provided the concept and design the instrument and perform the surgery. The first draft of the manuscript was written by Jiqing Zhang, and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Acknowledgment

The authors thank Nissi S. Wang for developmental editing of this manuscript. We thank all the cases for their participation in this study.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Availability of data and material

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.