Relocation and evacuation of stone fragments using 7.5 Fr flexible ureteroscope with direct-in-scope suction: an experimental study

Abstract

Introduction

Aim of the study was to evaluate and illustratively depict the aspiration properties of a single-use 7.5 Fr flexible ureteroscope with direct-in-scope suction (DISS) in a specifically designed in vitro setting.

Material and methods

An experimental in vitro study using a 6.5 size sterile glove, natural stone fragments and part of a porcine ureter was performed. A single use 7.5 Fr digital flexible ureteroscope with integrated direct-in-scope suction (PU3033AH, Zhuhai Pusheng Medical Technology Co., Ltd., Zhuhai China) was used for all trials. Five stone fragments ranging from 3 to 5 mm in maximal diameter were used. For each stone, three trials were performed; stones placed in the upper, middle and lower calyx. The experimental trial was defined as partially successful if stone relocation using suction (SRS) was present and successful when subsequent evacuation was reported.

Results

Relocation of stone fragments (partial success) was observed for all stones in different locations. Easy evacuation of the 3 mm stone fragment occurred from all calyces. Complete success was also reported for all 4 mm stones. Complete success was documented with the 5 mm stone positioned in the upper and middle calyces, whereas evacuation of the stone from the lower calyx was not achieved after 5 attempts.

Conclusions

With the 7.5 Fr Pusen DISS integrated scope, stone fragments 3–5 mm in all calyces were successfully relocated. Whilst evacuation from any calyx was successfully done in 3–4 mm fragments, this was only possible for 5 mm fragments located in upper calyx or interpolar region. The lower pole and greater fragment size need further evaluation for optimal management by DISS.

INTRODUCTION

Retrograde intrarenal surgery (RIRS) is the accepted standard of care for small and mid-sized renal stones smaller than 2 cm [1]. With the continuous advancement of technology and materials and relatively lower risk of complications compared to percutaneous nephrolithotomy (PCNL) [2], the modality is gaining popularity also for larger stone burden [3] and complicated anatomies [4].

Several advancements and/or techniques have been reported to improve stone-free rate (SFR) following RIRS and reduce the rate of residual fragments. Among them, the use of high-power and thulium fiber (TFL) lasers was associated with shorter operative time, better efficiency, and production of finer dust [5, 6]. Additional surgical modifications include table tilting techniques [7], percussion inversion diuresis [8], use of external physical vibration lithecbole [9], the use of standard and flexible and navigable suction ureteral access sheaths (SUAS and FANS) [10], specific direct-in-scope suction (DISS) devices [11] and steerable multi-lumen irrigation/aspiration devices [12].

Performing direct aspiration under vision seems the easiest and most logical approach to eliminating minor fragments. In a recent survey sent to the members of Endourological Society, suction feature was considered the future essential development. Out of 208 respondents, 94.3% and 92.3% agreed that fragment and fluid suctioning, respectively, are important future concepts for single-use ureteroscopy [13]. Theoretically, aspiration with SUAS and FANS could evacuate larger stone fragments compared to DISS, since the working channel of DISS is smaller and can accommodate smaller stone particles <1 mm in size [14]. A question that arises and would be worth investigating is whether the aspiration with DISS could potentially attract the bigger stone fragments to the scope and relocate or evacuate them from the collecting system without using a basket or other accessories. The aim of the current study is to evaluate and illustratively depict the aspiration properties of a single-use 7.5Fr flexible ureteroscope with DISS in a specifically designed in vitro setting.

MATERIAL AND METHODS

Study design and setup configuration

We conducted an experimental in vitro study. The experimental setup included a 6.5 size sterile glove, natural stone fragments, and part of a porcine ureter. No pig was sacrificed for the study purpose. Instead, porcine ureter was harvested from the slaughter, thus no ethical approval was required for this study. To mimic the pelvicalyceal system (PCS) of a human kidney, one out of five fingers of the sterile glove (small finger) was tied close to the palm part of the glove, leaving no space for this finger to fill with the saline. The thumb part of the glove was used to introduce a 12/14 Fr ureteral access sheath (UAS). A small incision was made on the tip of the thumb finger. A hydrophilic guidewire (Bioteq Blackwire, Bioteque corporation, Taipei, Taiwan) was introduced first through the lumen of the pig ureter and then into the glove through the artificial opening through the thumb finger. Following the guidewire course, a 12/14 Fr UAS (Cook Medical, Indiana, USA) was introduced from the glove's opening. The glove opening was circumferentially sutured to the part of the harvested porcine ureter over the 12/14 UAS. The remaining three fingers (index, middle, and ring fingers) were tied to decrease their volume and then fixed to the table to form upper, middle, and lower calyces. As a result of the following setup configuration, we constructed a transparent model with hypothetical 3 calyces, dilated pelvis and ureteropelvic junction (the sutured area of the glove to the porcine ureter). This setup allowed realistic movement of the UAS in and out, with a natural tight feel, as a result of used porcine ureter. In addition, when the UAS was pulled to the level of the suture (imaginary uretero-pelvic junction (UPJ)), a narrowing of that segment was present, resembling real UPJ narrowing (Figure 1).

Figure 1.

Experimental model. Arrow shows the porcine ureter sutured to the thumb of the glove to form pelvi-calyceal system. The stone is positioned in the lower calyx shown with the tip of the forceps.

Flexible ureteroscope

A single-use 7.5 Fr digital flexible ureteroscope with the integrated direct-in-scope suction (PU3033AH, Zhuhai Pusheng Medical Technology Co., Ltd., Zhuhai, China) was used for all trials. The features of the scope include maximum up and down bending flexibility of 270 degrees, a LED light source, and an innovative feature of integrated direct in scope suction (DISS) channel controlled by a suction button attached to the handpiece of the scope. Pressing the button when needed provides easy and intuitive control of the aspiration. The suction channel is 3.6Fr wide, which can aspirate dust and approximately 1 mm particles.

Evaluated parameters

To perform the study, one stone fragment for each trial was placed through the UAS using a flexible ureteroscope and basket. These stone fragments were collected from real-life RIRS with patients' consent. Five calcium-oxalate dehydrate stone fragments ranging from 3 to 5 mm in maximal diameter of different shapes were used. For each stone, three trials were performed; stones placed in the upper, middle and lower calyx. The number of attempts for each trial were separately calculated. Trials were stopped after a maximum of 5 attempts. For the study purposes, two irrigation modes were tested, aspiration with the irrigation “on” and “off”. Two 3 l saline bags were fixed 1 meter above the experimental table. A manual hand-pump (Cook Medical, Indiana, USA) was used for irrigation. Each attempt was initiated following the filling of the “hypothetical pelvicalyceal system”. The suction was connected to the scope and the suction device was set at 100 mBar (× 100 Pa).

The experimental trial was defined as completely successful if stone relocation using suction (SRS) with subsequent evacuation of the was observed. Relocation of the stone fragment from the calyx into the pelvis of the hypothetical pelvicalyceal system was defined as partial success.

Statistical analysis

SPSS v25 software (IBM Statistics, NY, USA) was used for the descriptive statistical analysis.

RESULTS

In total, 15 trials were performed for 5 stones. One stone was 3 mm, 3 stones were approximately 4 mm, and 1 stone was 5 mm in diameter. Relocation of stone fragments (partial success) was observed for all stones in different locations. Suction activation with the irrigation mode “on” and “off” did not affect the success of any of the trial. Easy SRS and evacuation of the 3 mm stone fragment occurred from all locations in the PCS. Two attempts were needed with the stone positioned in the upper and lower calyces, and only one attempt with the stone in the middle calyx. Complete success was also reported for all 4 mm stones, with the attempts ranging from 1 to 4. A five mm stone fragment was more difficult to relocate and evacuate via suction force. Complete success was documented with the 5 mm stone positioned in the upper and middle calyces, whereas SRS and evacuation of the 5 mm stone from the lower calyx was not achieved after 5 attempts (Table 1).

Table 1.

Stone relocation using suction and subsequent evacuation of stone fragments from different in vitro calyces using the 7.5Fr single-use digital PU3033AH flexible ureteroscope with DISS system

Stone	1st trial* (upper calyx)	2nd trial* (middle calyx)	3rd trial* (lower calyx)
N1 (3 mm)	√	√	X√
N2 (4 mm)	XX√	X√	XX√
N3 (4 mm)	√	X√	XXX√
N4 (4 mm)	XX√	√	X√
N5 (5 mm)**	XXX√	XX√	XXXXX

# No difference was observed with the irrigation mode “on” and “off”

^*Maximum 5 attempts performed for each trial

^**Relocation of the stone fragment was observed in all trials

DISS – direct-in-scope suction

DISCUSSION

In our current in vitro experimental study, we evaluated the aspiration potential of a 7.5Fr single-use digital ureteroscope with an integrated direct-in-scope suction to relocate and evacuate stone fragments without the use of any adjunct instruments. We designed to construct a cheap and easily reproducible in vitro model to emulate the human PCS. Having a transparent model, the stone fragments were easily positioned in the desired calyces. In addition, it allowed an illustrative investigation of the suction effect on the constructed PCS and stone relocation.

With the increasing number of RIRS procedure worldwide, achieving stone-free status still remains a challenge. Despite the advantages of RIRS, in a recent study a SFR defined as the absence of any stone fragments was 56.7% following a single RIRS session for stones >2 cm [15], and as per the FLEXOR Registry, 51.5% of patients with residual fragments would eventually require re-intervention following RIRS [16]. Anomalous kidneys represent another entity; the reports have shown a SFR of 76.6% with almost 1/4 of the patients suffering from residual fragments [17]. While 2 to 4 mm residual stones have been considered as clinically insignificant fragments [18], the risk of reintervention ranges from 12% to 35% when residual fragments are present [19].

Several surgical methods have been described to improve the SFR. In addition, there have been recent advancements in endourological instrumentation. FANS and DISS [10, 11] are believed to be one of the promising features added to the endourological armamentarium. In case of DISS, the scope itself acts as the aspiration conduit. In an in vitro experimental study, Schneider et al. evaluated the feasibility of suctioning of sub-millimeter fragments through the working channel of the flexible ureteroscope [14]. A Luer Lock syringe was used to aspirate the phantom stone fragments of ≤1 mm and ≤0.5 mm sizes. In both of the groups, the mean percentage of suctioned fragments was 86%. Trapping of the working channel requiring further cessation of the procedure occurred in 64% and 78% of stones in the ≤0.5 mm and ≤1 mm groups, respectively [14]. A recent in vitro comparison of endoscopic clearance rates between manual syringe suction and integrated direct in-scope suction demonstrated significantly faster rates in favor of DISS (3.01 g/min vs 0.41 g/min). The authors reported complete stone clearance for dust particles <250 µm [20].

In a clinical setting, vacuum-assisted ureteroscopic lithotripsy has been shown to improve the SFRs significantly. Zhang et al. [21] compared vacuum suction rigid ureteroscopy with standard ureteroscopy and flexible ureteroscopic lithotripsy for impacted upper ureteral stones. Modified vacuum suction ureteroscopy group demonstrated significantly higher SFRs both at 3–5 days (90.0% vs 61.9% vs 55.6%) and 1-month (96.4% vs 77.7% vs 74.0%).

Gauhar et al. [11] were the first to coin and describe the DISS technique using a modified flexible ureteroscopy with in-scope suction potential. In their study, two 3-way stoppers were connected to each other and subsequently to the used scope. In a direct comparison of SUAS and DISS, Gauhar et al. reported no significant differences in residual fragments [11]. With the significantly bigger stone burden, comparable SFR were reported between the group, the DISS group showing 33.3% residual fragments. Yet, significantly more patients treated with DISS were shown to have multiple residual fragments and required subsequent treatment. It was also highlighted that the dusting technique should be used to evacuate the generated dust with DISS. The feasibility of the DISS technique using similar add-on instruments was also challenged in a patient with a transplanted kidney with a large ureteral stone [22]. The authors reported a successful procedure achieving complete stone-free status following antegrade ureteroscopic lithotripsy with DISS technique. Recently, a prospective multicentric study using the DISS scope in 57 patients showed a stone-free rate (SFR) of 84% with integrated suction deemed helpful by 94.7% of users, and all surgeons were willing to use the scope in the future [23].

Despite the promising results, the DISS technique may be associated with several drawbacks. The method may require an increased irrigation flow rate and some additional learning curve. During the active suction, not only dust, but also blood clots can be aspirated, blocking the working channel and requiring further maneuvers [11]. In addition, due to the smaller size of the suction/working channel, stone fragments smaller than 1mm can potentially be considered to be aspirated through the scope [14]. Our paper introduces a new concept of the action of flexible ureteroscopes with the DISS feature. We were able to show that the suction force was sufficient to relocate and in most of the cases to evacuate stone fragments 3–5 mm in size. In all experimental trials, naturally collected calcium oxalate stones were used, which further strengthens our paper.

Several limitations can be encountered in our paper. Our current study was performed in an artificially constructed in vitro model. Although the model was specifically designed to mimic human PCS, not all the factors could be controlled. Additional criticism may include the use of only one stone type and one size of the glove to construct the PCS. In the clinical setting, we deal with patients with different anatomy of the PCSs and stone composition, which may affect the outcomes. Nevertheless, this experiment spreads light on the aspiration properties of newly introduced single-use ureteroscope with integrated DISS. Further in vivo experimental and clinical studies are warranted.

CONCLUSIONS

The 7.5 Fr Pusen DISS integrated scope successfully relocated stone fragments 3–5 mm in all calyces. Whilst evacuation from any calyx was successfully done in 3–4 mm fragments, this was only possible for 5 mm fragments located in the upper calyx or the interpolar region. The lower pole and bigger fragment size need further evaluation by DISS for optimal management.

Funding Statement

FUNDING This research received no external funding.

CONFLICTS OF INTEREST

The authors declare no conflict of interest.

ETHICS APPROVAL STATEMENT

The ethical approval was not required.