Irrigant Flow and Intrarenal Pressure During Flexible Ureteroscopy: The Effect of Different Access Sheaths, Working Channel Instruments, and Hydrostatic Pressure

Renal pelvis pressure and flowrate with a multi-channel ureteroscope: invoking the concept of outflow resistance

Understanding renal pelvis pressure (PRP) during ureteroscopy (URS) has become increasingly important. High irrigation rates, desirable to maintain visualization and limit thermal dose, can increase PRP. Use of a multi-channel ureteroscope (m-ureteroscope) with a dedicated drainage channel is one strategy that may facilitate simultaneous low PRP and high flowrate. We sought to define the relationship between PRP and flowrate across a range of different outflow resistance scenarios with an m-ureteroscope versus a single-channel ureteroscope (s-ureteroscope). The m- or s-ureteroscope was placed into the pelvis of a validated silicone kidney-ureter model. Trials were conducted at irrigation pressures (50-150 cmH20) and five different outflow resistance scenarios simulated with catheters of different lengths and diameters. PRP was measured with a fiber optic pressure sensor positioned in the renal pelvis. Flowrate was determined by measuring the mass of drainage fluid over 60 s. PRP was lower with the m-ureteroscope than the s-ureteroscope when equivalent flowrates were delivered (i.e. 34 vs. 82 cmH20 respectively with 15 ml/min irrigation in a high outflow resistance scenario). Flowrate was higher with the m-ureteroscope than the s-ureteroscope when equivalent irrigation pressures were applied (i.e. 28 vs. 14 ml/min respectively with irrigation pressure 150 cmH20 in a high outflow resistance scenario). The m-ureteroscope has improved pressure-flow dynamics imparting important clinical benefits. More importantly, this approach to framing ureteroscopy in the context of pressure-flow relationships related by resistance values allows quantification of ureteroscopy within a deterministic system, which can be used to streamline future device development and technological innovation.

Intrarenal Pressure in Retrograde Intrarenal Surgery: A Narrative Review

OBJECTIVE

To review the latest evidence on the complications of elevated intrarenal pressures (IRPs) in retrograde intrarenal surgery (RIRS) and the strategies to mitigate the increase of IRP during surgery.

METHODS

A comprehensive literature search of PubMed, Web of Science and EBSCO research databases was conducted from inception to July 31, 2024. The analysis involved a narrative review.

RESULTS

Normal physiological IRP in an unobstructed kidney ranges from 0 to 15 mmHg (0-20 cmH2O). During RIRS, dangerous IRPs are often reached, resulting in complications. These include pyelorenal reflux, which predisposes the patient to fever, urosepsis and postoperative pain, and forniceal rupture, which may result in intraoperative bleeding as well as acute kidney injury, postoperative pain, and fluid overload. To maintain safe IRP, outflow should be as close as possible to inflow. Minimizing the irrigation pressure by controlling the flow rate, reducing the pressure of the irrigant fluid, using a ureteral access sheath and maintaining an empty bladder during the procedure and, more recently, using real-time IRP monitoring are appropriate techniques to mitigate unsafe IRPs.

CONCLUSION

Several complications of RIRS are related to elevated IRPs, which cause pyelorenal backflow and forniceal rupture. Irrigation flow and pressure dynamics drive IRP changes during RIRS. Awareness of these factors will allow urologists to institute strategies to mitigate IRP during RIRS, thereby reducing complications and improving patient outcomes.

Complications of Single-Use Flexible Ureteroscopy vs. Reusable Flexible Ureteroscopy: A Narrative Review

Urolithiasis, or kidney stones, is a painful condition that is becoming increasingly common worldwide. For many, the solution lies in a minimally invasive procedure called flexible ureteroscopy (fURS). This technique involves inserting a tiny, flexible scope into the urinary tract to break up and remove stones. Reusable fURS scopes have traditionally been the norm. However, concerns about infection control and instrument durability have led to the development of single-use scopes. While both methods offer effective treatment, the question remains: which one is safer and more efficient? To answer this, we conducted a comprehensive review of the available research. We analyzed 37 studies that compared single-use and reusable fURS complication rates. While both methods carry risks, such as bleeding, infection, and ureteral injury, the overall complication rates were found to be similar. As technology continues to advance, fURS is becoming even safer and more effective. However, there is still a need for standardized reporting and further research to better understand the potential risks and benefits of both single-use and reusable scopes. Ultimately, the choice between the two will depend on various factors, including patient factors, surgeon preference, and healthcare resource availability.

Assessment of Intrarenal Pressure through Dilatation State of the Renal Collecting System

INTRODUCTION

The aim of the study was to explore the relationship between the dilation states of the renal collecting system in flexible ureteroscopy (f-URS) view and intrarenal pressure (IRP).

METHODS

Fifteen porcine kidneys were randomly selected and numbered 1 through 15. Pressure transducers were inserted into the renal calyx via puncture and adjusted to a zero position. The distal end of the f-URS probe was placed within the renal pelvis. Perfusion rates of 50 mL/min, 80 mL/min, and 100 mL/min were utilized. We observed the relationship between the dilation state of the renal collecting system and changes in IRP. The state of complete dilation was defined as an unchanging spatial morphology of the renal collecting system as visualized during f-URS.

RESULTS

With irrigation rates of 50 mL/min, 80 mL/min, and 100 mL/min, IRP values at the moment of complete dilation of the renal collecting system ranged from 16 to 18 cm H2O, 16-19 cm H2O, and 16-19 cm H2O, respectively. Maximum IRPs ranged from 47 to 49 cm H2O, 82-85 cm H2O, and 97-100 cm H2O, respectively. Prior to complete dilation of the renal collecting system, IRP consistently remained below 20 cm H2O. However, following full dilation of the renal collecting system, IRP rose rapidly and rapidly surpassed 20 cm H2O. Despite sustained elevations in IRP following full dilation, no significant alterations in the renal collecting system dilated morphological were observed with f-URS.

CONCLUSIONS

In vitro experiments indicate that when the renal collecting system is not fully dilated, the IRP is consistently less than 20 cm H2O. Evaluation of IRP being within a safe range can be determined by assessing the dilation status of the renal collecting system.

Intrarenal pressure and flow rate profile using LithoVue™ elite: impact of different irrigation systems and working channel instruments

PURPOSE

To report real-time IRP and FR while performing flexible ureteroscopy in porcine kidney model utilizing LithoVue™ Elite (Boston Scientific®) with different irrigation systems, including automated pumps.

METHODS

Using an ex-vivo model of porcine kidney, IRPs were measured with LithoVue Elite. Ureteroscopic settings (US) were tested with all permutations of irrigation methods (IM), working channel occupant (WCO), and ureteral access sheaths (UAS). IMs included: Single Action Pumping System (SAPS™, Boston Scientific), Thermedx FluidSmart™ (Stryker®), and ENDOMAT™ (Karl Storz®). Pumps were tested at 50, 100, and 150 mmHg. WCOs included a 1.9Fr zero-tip basket, 200 µm, and 365 µm laser fibers. UASs utilized 11/13Fr and 12/14Fr 36 cm.

RESULTS

84 different US were tested (252 experiments). ENDOMAT had higher IRP but the same FR as Thermedx at the same US for 50 and 100 mmHg (p < 0.01). SAPS had higher IRP and FR than pumps in all US studies (p < 0.01). There was positive correlation between pressure set by the pump and both IRP and FR (rho > 0.9). As the diameter of the WCO increased, lower IRP and FR were observed with the pumps (p < 0.01). With SAPS, IRP was similar regardless of WCO, but FR was decreased with the increased diameter of WCO (p = 0.81 and p < 0.01, respectively). There was significantly higher IRP when using 11/13Fr UAS than 12/14Fr (p < 0.01).

CONCLUSION

IRP was higher with SAPS than automated pumps. ENDOMAT showed higher IRP than Thermedx when under 150 mmHg. IRP and FR increase with higher pump pressure and decrease with larger diameter WCO. Likewise, a larger UAS significantly reduced IRP.

The impact of siphoning effect on renal pelvis pressure during ureteroscopy using an in vitro kidney and ureter model

PURPOSE

To experimentally measure renal pelvis pressure (PRP) in an ureteroscopic model when applying a simple hydrodynamic principle, the siphoning effect.

METHODS

A 9.5Fr disposable ureteroscope was inserted into a silicone kidney-ureter model with its tip positioned at the renal pelvis. Irrigation was delivered through the ureteroscope at 100 cm above the renal pelvis. A Y-shaped adapter was fitted onto the model's renal pelvis port, accommodating a pressure sensor and a 4 Fr ureteral access catheter (UAC) through each limb. The drainage flowrate through the UAC tip was measured for 60 s each run. The distal tip of the UAC was placed at various heights below or above the center of the renal pelvis to create a siphoning effect. All trials were performed in triplicate for two lengths of 4Fr UACs: 100 cm and 70 cm (modified from 100 cm).

RESULTS

PRP was linearly dependent on the height difference from the center of the renal pelvis to the UAC tip for both tested UAC lengths. In our experimental setting, PRP can be reduced by 10 cmH20 simply by lowering the distal tip of a 4 Fr 70 cm UAC positioned alongside the ureteroscope by 19.7 cm. When using a 4 Fr 100 cm UAC, PRP can drop 10 cmH20 by lowering the distal tip of the UAC 23.3 cm below the level of the renal pelvis.

CONCLUSION

Implementing the siphoning effect for managing PRP during ureteroscopy could potentially enhance safety and effectiveness.

Effect of perioperative tamsulosin on successful ureteral access sheath placement and stent-related symptom relief: A double-blinded, randomized, placebo-controlled study

PURPOSE

This study investigated the effect of administering tamsulosin before surgery on the successful insertion of a 12/14 French (F) ureteral access sheath (UAS) during the procedure, as well as the impact of preoperative and postoperative tamsulosin use on symptoms related to the ureteral stent.

MATERIALS AND METHODS

This study was a randomized, single-center, double-blinded, placebo-controlled trial involving 200 patients who underwent unilateral retrograde intrarenal surgery. Patients received either tamsulosin (0.4 mg) or placebo 1 week before surgery until stent removal. Patients were randomly assigned to one of four groups. Group 1 received tamsulosin throughout the study period. Group 2 received tamsulosin before surgery and placebo after surgery. Group 3 received placebo before surgery and tamsulosin after surgery. Group 4 received placebo before and after surgery. The USSQ (Ureteral Stent Symptom Questionnaire) was completed between postoperative days 7 and 14 immediately before stent removal.

RESULTS

A total of 160 patients were included in this analysis. Their mean age was 55.0±11.0 years, and 48 patients (30.0%) were female. In the group that received preoperative tamsulosin, the success rate of 12/14F UAS deployment was significantly higher than that of the preoperative placebo group (88.0 vs. 75.3%, p=0.038). Preoperative and postoperative tamsulosin did not significantly alleviate symptoms related to the ureteral stent.

CONCLUSIONS

Our results revealed that preoperative administration of tamsulosin improved the success of larger-sized UAS, whereas preoperative and postoperative tamsulosin use did not significantly alleviate symptoms related to ureteral stents.

Fluid dynamics within renal cavities during endoscopic stone surgery: does the position of the flexible ureteroscope and ureteral access sheath affect the outflow rate?

PURPOSE

To evaluate the impact of ureteroscope position within renal cavities as well as different locations of the tip of the ureteral access sheath (UAS) on fluid dynamics during retrograde intrarenal surgery (RIRS).

MATERIALS AND METHODS

A prospective observational clinical study was performed. Measurements with a flexible ureteroscope placed in the upper, middle and lower calyces were obtained with the tip of the UAS placed either 2 cm below the pyelo-ureteric junction (PUJ), or at the level of the iliac crest.

RESULTS

74 patients were included. The outflow rates from the middle and upper calyxes were statistically significantly higher compared to the lower calyx, both with the UAS close to the pyelo-ureteric junction and at the iliac crest. When the UAS was withdrawn and positioned at the level of the iliac crest, a significant decrease in outflow rates from the upper (40.1 ± 4.3 ml/min vs 35.8 ± 4.1 ml/min) and middle calyces (40.6 ± 4.0 ml/min vs 36.8 ± 4.6 ml/min) and an increase in the outflow from the lower calyx (28.5 ± 3.3 ml/min vs 33.7 ± 5.7 ml/min) were noted.

CONCLUSIONS

Our study showed that higher fluid outflow rates are observed from upper and middle calyces compared to lower calyx. This was true when the UAS was positioned 2 cm below the PUJ and at the iliac crest. Significant worsening of fluid dynamics from upper and middle calyces was observed when the UAS was placed distally at the level of the iliac crest. While the difference was statistically significant, the absolute change was not significant. In contrast, for lower calyces, a statistically significant improvement was documented.

Intrarenal pressures during flexible ureteroscopy: an insight into safer endourology

OBJECTIVES

To assess intrarenal pressures (IRPs) and complication rates after flexible ureteroscopy (fURS), and to assess factors that contribute to raised IRPs and postoperative complications.

PATIENTS AND METHODS

After informed consent patients underwent fURS under general anaesthesia. The transducer of a 0.3556 mm (0.014″) pressure guidewire was placed in the renal pelvis for live recording of IRPs. The fURS procedures were performed in a routine manner under antibiotic cover with the aim of dusting the calculus to completion. The operating surgeon was blinded to the live-recorded IRPs.

RESULTS

A total of 40 fURS procedures were performed in 37 patients (26 male and 11 female). The mean age was 50.5 years. As a cohort, the mean of average IRPs was 34.8 mmHg and the mean of maximal IRPs was 128.8 mmHg. Pearson's correlation showed a significant inverse correlation between the mean IRP and age (r[38]: -0.391, P = 0.013). Three cases experienced postoperative deviations from uncomplicated recovery, with two being hypotensive and one case being both hypotensive and hypoxic. Three cases returned to the emergency department within 30 days of surgery, with two cases of flank pain and one case of urosepsis with positive urine cultures. The patient presenting with urosepsis had exhibited IRPs exceeding the mean.

CONCLUSION

The IRPs changed significantly from normal baseline levels during routine fURS. The mean IRP during fURS correlates with patient age, but not with other factors. The IRP may be related to increased complication rates at fURS. Understanding factors that influence IRP will allow urologists to better manage this intraoperatively.

Intrarenal Pressure Measured Using a Novel Flexible Ureteroscope with Pressure Sensing Capabilities: A Study of the Effects of Ureteral Access Sheath, Irrigation, and Working Channel Accessories

Introduction: Intrarenal pressure is emerging as an important monitoring parameter during flexible ureteroscopy (fURS). We measure how intraoperative conditions affect intrarenal pressure using a novel pressure sensing ureteroscope. Methods: The LithoVue Elite (LVE) single-use digital flexible ureteroscope (Boston Scientific) is the first commercial ureteroscope that senses pressure at its tip. LVE was used in a porcine model to measure intrarenal pressure with and without a ureteral access sheath (UAS) with various sizes and placement locations, irrigation methods, and working channel accessories. LVE pressure accuracy was measured in a bench model. This abstract shows the least-square means from multiway analysis of variances used for analysis. Results: Intrarenal pressures were the highest without a UAS (64 mm Hg), followed by the 11/13 UAS (51 mm Hg) and the 12/14 and 13/15, which were not statistically different (39-40 mm Hg). The pressures were highest with UASs placed at the ureteropelvic junction (61 mm Hg), and lowest if placed in the renal pelvis (24 mm Hg). Irrigation methods showed the highest pressures with syringe (57 mm Hg), while irrigation bags (pressurized at 150-300 mm Hg) produced 43 to 46 mm Hg and 25 mm Hg when applied with 80 cm of gravity. Placing a 200 μm laser fiber reduced pressures from 44 to 41 mm Hg. Finally, the bench model showed that LVE was 96% accurate up to 300 mm Hg. Conclusion: Intrarenal pressure significantly varied based on UAS sizes, placement, and irrigation methods. Accordingly, fURS with LVE is poised to be an invaluable tool for clinical decision-making and future studies of intrarenal pressure.

Exploring ureteroscope design with computational fluid dynamics for improved intra-pelvic pressure

High intra-pelvic pressure (IPP) during ureteroscopy can lead to complications including pyelovenous backflow, bleeding, and infection. Our primary goal was to identify the best cross-section and orientation of a ureteroscope within a Ureteral Access Sheath (UAS) to minimize IPP and maximize outflow. Our secondary goal was to validate our findings with a UAS prototype. To determine the optimal ureteroscope cross-section within a UAS, four ureteroscopes of equivalent cross-sectional area were simulated within a 10 Fr UAS using computational fluid dynamics software COMSOL. We then created a corresponding prototype by securing a 3-0 monofilament suture at the inferior aspect of the 12 Fr outer UAS, inducing an offset to the ureteroscope. Mean flow volumes through a 10/12 Fr UAS occupied by a 9.5-Fr single-use flexible ureteroscope were compared (17 iterations) to those through our prototype UAS. During the simulation, the lowest IPP and highest outflow were seen with an offset circular ureteroscope (41% resistance) compared to a ureteroscope centered in the UAS. The unmodified UAS had an average volume of 30.0 mL/min (SD ± 0.35) compared to 33.76 mL/min (SD ± 0.90) for the modified UAS (p < 0.05). We found that using a circular ureteroscope positioned along the sidewall maximizes outflow through a circular UAS. We made a prototype UAS to offset the ureteroscope and observed a 12.5% increase in outflow. This approach can potentially decrease IPP during ureteroscopy without impacting inflow or the working channel. Although modifying a ureteroscope is more difficult, it could create an offset without reducing UAS cross-section.

A Pilot Study of a Novel Syphon Ureteral Access Sheath Shows Potential to Reduce Renal Pressures and Improve Irrigant Flow

OBJECTIVE

To describe a novel syphon ureteral access sheath (UAS) intended for use during flexible uretero-renoscopy (fURS). We aimed to report on a pilot study as well as intrarenal pressures (IRP) and irrigant flow volumes compared to traditional UAS.

METHODS

Patients undergoing routine fURS for single, <2cm intrarenal nephrolithiasis were identified, and written informed consent was obtained. Irrigation via the fURS was instilled through the novel 11/13 Fr UAS without (a proxy for a traditional UAS) and with the novel syphon box attached. Measured minute irrigant flow volume, steady state and bolus IRP were compared.

RESULTS

Ten participants (6 males and 4 females) were treated with the syphon UAS. All procedures were completed safely without intraoperative complications. The mean baseline IRP with and without the syphon was 18 vs 29 mmHG (P < .001, SD 4.0 vs 4.8). The mean minute irrigant flow volume with and without the syphon was 31 vs 21 ml (P < .001, SD 6.4 vs 3.3). The mean peak IRP following a 10 ml bolus with and without the syphon was 71 vs 104 mmHg (P = .03, SD 74 vs 59).

CONCLUSION

The described novel UAS is different from traditional devices by incorporating a syphon mechanism. This pilot trial demonstrates that the novel syphon UAS may hold clinical potential to reduce IRP and increase irrigant flow compared to traditional UAS. Firm conclusions about efficacy and safety require assessment of the device in a larger clinical trial.

Comparison of Superpulse Thulium Fiber Laser vs Holmium Laser for Ablation of Renal Calculi in an In Vivo Porcine Model

Introduction and Objectives: We sought to compare the effectiveness and efficiency of the superpulse thulium fiber laser (sTFL to the holmium: yttrium-aluminum-garnet [Ho:YAG] laser for ureteroscopic "dusting" of implanted renal stones in an in vivo porcine model. Methods: Twenty-four porcine kidneys (12 juvenile female Yorkshire pigs) were randomized to Ho:YAG or sTFL treatment groups. Canine calcium oxalate stones were scanned with computed tomography to calculate stone volume and stone density; the stones were randomized and implanted into each renal pelvis via an open pyelotomy. In all trials, a 14F, 35 cm ureteral access sheath was placed. With a 9.9F dual lumen flexible ureteroscope, laser lithotripsy was performed using dusting settings: Ho:YAG 200 μm laser fiber at 16 W (0.4 J, 40 Hz) or sTFL 200 μm laser fiber at 16 W (0.2 J, 80 Hz). Lithotripsy continued until no fragments over 1 mm were observed. No stone basketing was performed. Throughout the procedures, intrarenal and renal pelvis temperatures were measured using two percutaneously positioned K-type thermocouples, one in the upper pole calyx and one in the renal pelvis. After the lithotripsy, the ureteropelvic junction was occluded, the kidneys were bivalved, and all residual fragments were collected, dried, weighed, and then measured with an optical laser particle sizer. Results: Implanted stones were similar in volume and density in both groups. Intraoperative collecting system temperatures were similar for both groups (all <44°C). Compared to Ho:YAG, sTFL ablated stones faster (9 vs 27 minutes, p < 0.001) with less energy expenditure (8 vs 26 kJ, p < 0.001), and a greater stone clearance rate (73% vs 45%, p = 0.001). After sTFL lithotripsy, 77% of the remaining fragments were ≤1 mm vs 17% of fragments ≤1 mm after Ho:YAG treatment (p < 0.001). Conclusions: In an in vivo porcine kidney, using dusting settings, sTFL lithotripsy resulted in shorter ablation times, higher stone clearance rates, and markedly smaller stone fragments than Ho:YAG lithotripsy.

The study of double-J stent free mode of flexible ureteroscopy and laser lithotripsy: a single centre experience

OBJECTIVE

To evaluate the effectiveness and safety of flexible ureteroscopy in the treatment of kidney and upper ureteral calculi under double-J stent free mode.

METHODS

Data from patients who underwent flexible ureteroscopy and laser lithotripsy between February 2018 and September 2021 were retrospectively and analysed. Cases were grouped according to pre- or postoperative use of the double-J stent (6 Fr): Post-F group (preoperative double-J stent but no postoperative double-J stent); Pre-F group (no preoperative stenting but with postoperative double-J stent); and Routine group (preoperative and postoperative double-J stenting).

RESULTS

A total of 554 patients (390 male and 164 female) were included. The mean operation time was similar between the three groups, with no statistically significant difference. Incidence of grade 0-1 ureteral injury was significantly higher in the Pre-F group versus other groups, but there were no significant between-group differences in other operation-related complications. During follow-up, stent-associated complications were observed in the Pre-F and Routine groups, but not in the Post-F group. Stone clearance rates were similar between all groups at 1, 3 and 6 months following surgery.

CONCLUSIONS

Flexible ureteroscopy using double-J stent free mode was found to be safe, feasible and effective in treating renal and upper ureteral calculi.

Upper urinary tract pressures in endourology: a systematic review of range, variables and implications

OBJECTIVES

To systematically review the literature to ascertain the upper tract pressures generated during endourology, the relevant influencing variables and clinical implications.

MATERIALS AND METHODS

A systematic review of the MEDLINE, Scopus and Cochrane databases was performed by two authors independently (S.C., N.D.). Studies reporting ureteric or intrarenal pressures (IRP) during semi-rigid ureteroscopy (URS)/flexible ureterorenoscopy (fURS)/percutaneous nephrolithotomy (PCNL)/miniaturized PCNL (mPCNL) in the period 1950-2021 were identified. Both in vitro and in vivo studies were considered for inclusion. Findings were independently screened for eligibility based on content, with disagreements resolved by author consensus. Data were assessed for bias and compiled based on predefined variables.

RESULTS

Fifty-two studies met the inclusion criteria. Mean IRP appeared to frequently exceed a previously proposed threshold of 40 cmH₂ O. Semi-rigid URS with low-pressure irrigation (gravity <1 m) resulted in a wide mean IRP range (lowest reported 6.9 cmH₂ O, highest mean 149.5 ± 6.2 cmH₂ O; animal models). The lowest mean observed with fURS without a ureteric access sheath (UAS) was 47.6 ± 4.1 cmH₂ O, with the maximum peak IRP being 557.4 cmH₂ O (in vivo human data). UAS placement significantly reduced IRP during fURS, but did not guarantee pressure control with hand-operated pump/syringe irrigation. Miniaturization of PCNL sheaths was associated with increased IRP; however, a wide mean human IRP range has been recorded with both mPCNL (lowest -6.8 ± 2.2 cmH₂ O [suction sheath]; highest 41.2 ± 5.3 cmH₂ O) and standard PCNL (lowest 6.5 cmH₂ O; highest 41.2 cmH₂ O). Use of continuous suction in mPCNL results in greater control of mean IRP, although short pressure peaks >40 cmH₂ O are not entirely prevented. Definitive conclusions are limited by heterogeneity in study design and results. Postoperative pain and pyrexia may be correlated with increased IRP, however, few in vivo studies correlate clinical outcome with measured IRP.

CONCLUSIONS

Intrarenal pressure generated during upper tract endoscopy often exceeds 40 cmH₂ O. IRP is multifactorial in origin, with contributory variables discussed. Larger prospective human in vivo studies are required to further our understanding of IRP thresholds and clinical sequelae.

Quantification of outflow resistance for ureteral drainage devices used during ureteroscopy

PURPOSE

Since renal pelvis pressure is directly related to irrigation flowrate and outflow resistance, knowledge of outflow resistance associated with commonly used drainage devices could help guide the selection of the type and size of ureteral access sheath or catheter for individual ureteroscopic cases. This study aims to quantitatively measure outflow resistance for different drainage devices utilized during ureteroscopy.

METHODS

With measured irrigation flowrate and renal pelvis pressure, outflow resistance was calculated using a hydrodynamic formula. After placement of a drainage device into a silicone kidney-ureter model, a disposable ureteroscope with a 9.5-Fr outer diameter was inserted with its tip positioned at the renal pelvis. Irrigation was delivered through the ureteroscope from varying heights above the renal pelvis. Renal pelvis pressure was measured directly from the port of the kidney model using a pressure sensor (Opsens, Canada). Outflow resistance was determined by plotting flowrate versus renal pelvis pressure. All trials were performed in triplicate for each drainage device inserted.

RESULTS

Flowrate was linearly dependent on renal pelvis pressure for all drainage devices tested. Outflow resistance values were 0.2, 1.1, 1.4, 3.9, and 6.5 cmH₂O/[ml/min] for UAS 13/15 Fr, UAS 11/13 Fr, UAC 6 Fr, UAC 4.8 Fr, and UAC 4.0 Fr, respectively, across the range of commonly used irrigation flowrates.

CONCLUSIONS

In this study, outflow resistance of different ureteral drainage devices was quantitatively measured. This knowledge can be useful when selecting which type and size of drainage device to insert to maintain safe renal pelvis pressure during ureteroscopy.

International Alliance of Urolithiasis guideline on retrograde intrarenal surgery

OBJECTIVES

To set out the second in a series of guidelines on the treatment of urolithiasis by the International Alliance of Urolithiasis that concerns retrograde intrarenal surgery (RIRS), with the aim of providing a clinical framework for urologists performing RIRS.

MATERIALS AND METHODS

After a comprehensive search of RIRS-related literature published between 1 January 1964 and 1 October 2021 from the PubMed database, systematic review and assessment were performed to inform a series of recommendations, which were graded using modified GRADE methodology. Additionally, quality of evidence was classified using a modification of the Oxford Centre for Evidence-Based Medicine Levels of Evidence system. Finally, related comments were provided.

RESULTS

A total of 36 recommendations were developed and graded that covered the following topics: indications and contraindications; preoperative imaging; preoperative ureteric stenting; preoperative medications; peri-operative antibiotics; management of antithrombotic therapy; anaesthesia; patient positioning; equipment; lithotripsy; exit strategy; and complications.

CONCLUSION

The series of recommendations regarding RIRS, along with the related commentary and supporting documentation, offered here should help provide safe and effective performance of RIRS.

Determinants of outflow rate through the ureteral access sheath during flexible ureteroscopy: an experimental in vivo study in an anesthetized porcine model

To evaluate the effect of different ureteroscope positions, saline pumping frequency, laser fiber diameter and ureteral access sheath (UAS) on outflow rate during flexible ureteroscopy (fURS). This study was performed in an anesthetized porcine model. The fURS setup included a manual pumping system, a 9.5 Fr single used-digital flexible ureteroscope and a ureteral access sheath (UAS). Outflow was collected and measured from the UAS during 1 min in all experimental settings. The evaluated variables were the position of the ureteroscope, the pumping frequency (2 s, 3 s or 5 s), the diameter of the used UAS (12/14 Fr or 14/16 Fr) and laser fiber (200 μm or a 272 μm). Ureteroscope position in the lower calyx was associated with significantly lower outflow rate (p < 0.05). The use of the 14/16 Fr UAS resulted in improved flow in the renal pelvis and upper calyx (p < 0.05) but not in the lower calyx. The use of a 200 μm laser fiber only improved flow in the upper calyx and when a 14/16 Fr UAS was being used. Pumping frequency did not show a significant correlation with outflow rate. The ureteroscope positioning and UAS size were important determinants of outflow rate through the UAS during fURS, while laser fiber diameter had a limited effect. In the lower calyx the outflow was minimal and was not improved by using a larger UAS.

Comparison of retrograde intrarenal stone surgery with and without a ureteral access sheath using kidney injury molecule-1 (KIM-1) levels: a prospective randomized study

The objective is to compare patients who underwent retrograde intrarenal surgery with and without a ureteral access sheath (UAS) using kidney injury molecule-1 (KIM-1) levels. We also examined the difference in kidney damage between standard and dual lumen UAS. Sixty patients diagnosed with kidney stones and scheduled for RIRS were randomized into three groups: RIRS without UAS (Group 1), 11Fr/13Fr Boston scientific Navigator™ UAS (Group 2), and 11Fr/13Fr dual lumen ClearPetra™ UAS (Group 3). Data were prospectively collected in consecutive patients. Urine KIM-1/Cr levels were measured preoperatively, at postoperative 4 h, and on a postoperative day 14. Stone size, location, number, pre- and postoperative stent use, operation time, stone-free rate (SFR), post-ureteroscopic lesion scale (PULS) grade, hospitalization duration, and complications were recorded. There was no significant difference in demographical parameters and preoperative KIM-1/Cr levels among the groups. Postoperative 4th-hour urine KIM-1/Cr levels were higher in patients without UAS than patients with UAS (1.86, 0.67, 0.63 Groups 1, 2, 3, respectively). In comparing group 1 with groups 2 and 3 separately, Group 1 had a statistically significantly higher value than both groups (p = 0.002, p = 0.001, respectively). According to UAS type, there was no significant difference between groups 2 and 3. The use of UAS during RIRS has been shown to reduce kidney injury in the evaluation with KIM-1. Different UAS types on kidney injury and which one can protect the kidneys more during the procedure; will be elucidated by prospective randomized studies involving larger patient groups and UAS types.

Comparison of retrograde intrarenal stone surgery with and without a ureteral access sheath using kidney injury molecule-1 (KIM-1) levels: a prospective randomized study

The objective is to compare patients who underwent retrograde intrarenal surgery with and without a ureteral access sheath (UAS) using kidney injury molecule-1 (KIM-1) levels. We also examined the difference in kidney damage between standard and dual lumen UAS. Sixty patients diagnosed with kidney stones and scheduled for RIRS were randomized into three groups: RIRS without UAS (Group 1), 11Fr/13Fr Boston scientific Navigator™ UAS (Group 2), and 11Fr/13Fr dual lumen ClearPetra™ UAS (Group 3). Data were prospectively collected in consecutive patients. Urine KIM-1/Cr levels were measured preoperatively, at postoperative 4 h, and on a postoperative day 14. Stone size, location, number, pre- and postoperative stent use, operation time, stone-free rate (SFR), post-ureteroscopic lesion scale (PULS) grade, hospitalization duration, and complications were recorded. There was no significant difference in demographical parameters and preoperative KIM-1/Cr levels among the groups. Postoperative 4th-hour urine KIM-1/Cr levels were higher in patients without UAS than patients with UAS (1.86, 0.67, 0.63 Groups 1, 2, 3, respectively). In comparing group 1 with groups 2 and 3 separately, Group 1 had a statistically significantly higher value than both groups (p = 0.002, p = 0.001, respectively). According to UAS type, there was no significant difference between groups 2 and 3. The use of UAS during RIRS has been shown to reduce kidney injury in the evaluation with KIM-1. Different UAS types on kidney injury and which one can protect the kidneys more during the procedure; will be elucidated by prospective randomized studies involving larger patient groups and UAS types.

Novel syphon ureteric access sheath has the potential to improve renal pressures and irrigant flow

OBJECTIVE

To describe a novel syphoning ureteric access sheath (UAS) intended for use during flexible ureterorenoscopy (URS). We aimed to assess if in vitro it could reduce intrarenal pressure (IRP) and increase irrigant flow compared to traditional UASs.

MATERIALS AND METHODS

A validated phantom kidney with fibre optic pressure sensing capabilities was used to assess the IRP. Standardised 80 cmH₂ O irrigation via a ureterorenoscope was instilled through traditional UASs (11/13 and 12/14 F) and compared to the novel 11/13-F syphoning UAS. The measured minute volume, calculated hourly flow volume, and steady state IRP were compared.

RESULTS

The traditional 11/13 and 12/14-F UASs had statistically poorer irrigant flow than the novel syphoning UAS, at 19.3 vs 29.3 mL/min (P < 0.001) and 22.7 vs 29.3 mL/min (P = 0.002), respectively. The steady state IRP was 20 mmHg for the traditional 11/13 F and 13 mmHg for the 12/14 F compared to 0 mmHg for the novel UAS.

CONCLUSION

The described novel UAS is different from traditional devices by incorporating a syphon mechanism. Our in vitro assessment demonstrates that the novel UAS holds clinical potential to reduce IRP while allowing a significant increase in irrigant flow compared to larger diameter traditional UASs.

The Impact of One Week of Pre-stenting on Porcine Ureteral Luminal Circumference

OBJECTIVES

Larger ureteral access sheaths (UAS) have the potential to improve ureteroscopic stone removal outcomes, but are often avoided by surgeons due to concerns of ureteral injury. Using our novel UAS force sensor and previously defined force thresholds for ureteral injury, we sought to evaluate the impact of one week of stenting on the maximum safe dilation of ureteral luminal circumference.

METHODS

Twelve juvenile female Yorkshire pigs (24 ureters) were evaluated. The inner (i.e. luminal) circumference of each ureter was determined using Cook urethral dilators ranging from 8-24Fr in 2Fr increments, 37cm in length. Each dilator was sequentially passed while applying the UAS force sensor to measure insertion force before and after one week of stent placement. Each ureter was randomized to receive either a 4.7Fr or 7.0Fr stent (20cm). Maximum ureteral luminal circumference was defined as successful passage of the dilator to the ureteropelvic junction with <6 newtons (N) of force (the force threshold previously defined by porcine and clinical studies to avoid ureteral damage). Following passage of the largest dilator at 6N, flexible ureteroscopy was performed and a post-ureteroscopic lesion score (PULS) was recorded.

RESULTS

After one week of stent placement, the median ureteral luminal circumference increased to 15Fr representing a mean increase of 3.8Fr + 2.8 (p<0.001). Twenty-one (88%) of the pre-stented ureters had an increase in luminal circumference, with 12 ureters (50%) dilated to >16Fr (p=0.032), six ureters (25%) dilated to >18Fr, and in two cases a maximum size of 24Fr was recorded. The PULS grade was < 2 in all cases, indicating no high grade ureteral injuries. Laterality and stent size did not impact ureteral luminal circumference after pre-stenting (p=0.232 and p=0.337, respectively).

CONCLUSIONS

One week of ureteral stenting resulted in nearly a 4Fr increase in the luminal circumference of porcine ureters.

Comparison of irrigation flows between different irrigation methods for flexible ureteroscopy: An in vitro study

OBJECTIVE

To compare the irrigation flows between different irrigation methods for f-URS.

METHODS

We compared the automatic irrigation system Endoflow II to gravity-based irrigation, and gravity-based irrigation with pressure cuff. Irrigation pressures were set at 40 and 100cmH₂O. A LithoVue f-URS with a 3.6Fr working channel was used for the experiments. The f-URS was placed in straight alignment without active deflection on the operating table. For each irrigation pressure level, we evaluated the influence of the occupation of the working channel of the f-URS with an empty working channel, a 272μm laser fiber, a 1.9Fr nitinol basket. The outflow from f-URS was measured by the volume of irrigation fluid collected using a graduated glass at 1min, 2min, 3min and 5min.

RESULTS

Irrigations flows remained constant over the time for the Endoflow II and the gravity-based irrigation methods regardless of the irrigation pressure and setting. For the pressure cuff method, the irrigation flow remained constant only when the working channel was occupied either by the nitinol basket or the laser fiber. Irrigation flow with the Endoflow II were constantly higher than gravity-based irrigation methods. Irrigation flow significantly increased with increased irrigation pressure. In the presence of any instruments at any irrigation pressure, the flow decreased as the size of the instrument in the working channel increased.

CONCLUSIONS

Automatic irrigation system Endoflow II provided higher irrigation flows than gravity-based irrigation methods. The irrigation flow decreased as the size of the instrument in the working channel increased. Further studies conducted in vivo are needed to investigate if the differences found between irrigation methods result in higher intrarenal pressure during procedures.

LEVEL OF PROOF

4.

Ureteral access sheath-related injuries vs. post-operative infections. Is sheath insertion always needed? A prospective randomized study to understand the lights and shadows of this practice

OBJECTIVE

To compare intraoperative ureteral injuries in RIRS with UAS insertion with the rate of postoperative infections after RIRS without UAS insertion.

PATIENTS AND METHODS

In this randomized trial, patients who received an indication for RIRS between January 2017 and December 2017 were divided into two groups. Group A had no UAS insertion and Group B had UAS insertion. Post-Ureteroscopic Lesion Scale (PULS) grading was performed after UAS or flexible ureteroscope removal. Proximal, middle and distal ureteral lesions were evaluated and compared according to the PULS scale. Additionally, patients in both groups were followed postoperatively to assess any infective complication.

RESULTS

The evaluation comprised 181 patients, 89 for group A and 92 for group B. Overall stone-free rate, clinically insignificant residual fragments, and final stone-free rate were 41.4%, 53.5%, and 95%, respectively. There were 33 (37.1%) patients with ureteral lesions in group A while 42 (45.6%) patients had ureteral lesions in group B, with no significant difference. On the other hand, the overall presence of postoperative infection rate was much higher for Group A (37.1% vs 16.3% P = 0.03).

CONCLUSIONS

UAS insertion does not result in a higher number of ureteral injuries. UAS insertion during RIRS allows a lower rate of postoperative infections.

CLINICAL TRIAL REGISTRATION NUMBER (ISRCTN REGISTRY NUMBER)

55546280.

Ex-vivo Renal Stone Dusting: Impact of Laser Modality, Ureteral Access Sheath, and Suction on Total Stone Clearance

INTRODUCTION AND OBJECTIVES

Conventional renal stone dusting is challenging; the holmium laser (Ho:YAG) and holmium with MOSES Effect (Ho:YAG-MOSES) fail to uniformly produce fragments <100 microns (i.e. dust). The superpulse thulium fiber laser (sTFL) may more effectively render uroliths into "dust," and may thus improve stone free rates. Accordingly, we performed ex-vivo evaluations with all three laser modalities, assessing stone fragments and stone clearance.

METHODS

Seventy-two ex-vivo porcine kidney-ureter models were divided into 12 groups of six: laser type (Ho:YAG, Ho:YAG-MOSES, sTFL), ureteroscope (URS) with and without applied suction, and presence or absence of a 14Fr ureteral access sheath (UAS). Calcium oxalate stones were pre-weighed and implanted into each kidney via a pyelotomy. Stones were treated at 16 watts using dusting settings of 0.4Jx40Hz (Ho:YAG) 0.2Jx80Hz (Ho:YAG-MOSES), and 0.2Jx80Hz (sTFL) for up to 20 minutes. No stone basketing was performed. Kidneys were bi-valved and residual fragments were collected, dried, weighed, and sieved to determine fragment size and stone clearance.

RESULTS

Initial stone mass (mg), procedure time (sec), and laser energy expenditure (kJ) were similar in all 12 groups. The greatest stone clearance was seen with sTFL+suction+UAS (94%) compared to a conventional technique (Ho:YAG+no suction+no UAS) (65%, p<0.01). The use of sTFL provided greater stone clearance than Ho:YAG or Ho:YAG-MOSES. Aspiration improved stone clearance for sTFL (p=0.01) but not for Ho:YAG or Ho:YAG-MOSES, consistent with the creation of smaller fragments with sTFL. Presence of a 14F UAS improved stone clearance in all scenarios (p<0.01).

CONCLUSIONS

In this ex-vivo study, stone clearance was optimized under the following conditions: sTFL laser, 14F ureteral access sheath, and aspiration. This combination resulted in 94% of stone fragments cleared; the 6% remaining fragments were all <2 mm. In all scenarios, deployment of a 14Fr UAS improved stone clearance.

Role of Intrarenal Pressure in Modern Day Endourology (Mini-PCNL and Flexible URS): a Systematic Review of Literature

PURPOSE OF REVIEW

To review the latest evidence about intrarenal pressures (IRPs) generated during flexible ureteroscopy (fURS) and mini percutaneous nephrolithotomy (mPCNL) and present tools and techniques to maintain decreased values.

RECENT FINDING

fURS and PCNL constitute the primary means of stone treatment. New flexible ureterorenoscopes with small diameter and miniaturized PCNL instruments achieve optimal stone-free rates (SFRs) while decreasing invasiveness and morbidity. Nevertheless, endourologists must remain cognizant regarding the dangers of increased IRPs to avoid complications. Current research presents essential information for urologists regarding this topic. During fURS, using a ureteral access sheath (UAS), we avoid extremely high IRPs with all irrigation types. During mPCNL, pressure remains low, mainly using the purging effect or a vacuum-assisted sheath. Devices of intraoperative IRP measurement and intelligent pressure control have proven their feasibility, accuracy and efficacy. These will have an increasing role to play in the future management of stone disease.

Impact of Preoperative Stenting on the Outcome of Flexible Ureterorenoscopy for Upper Urinary Tract Urolithiasis: A Systematic Review and Meta-Analysis

PURPOSE

This study aimed to investigate the effect of preoperative stenting (POS) on the perioperative outcomes of flexible ureterorenoscopy (fURS).

MATERIALS AND METHODS

A systematic review and meta-analysis was conducted based on the PRISMA statement. From the initially retrieved 609 reports, we excluded the ineligible studies at 2 stages. We only included studies that contained fURS patients with and without POS in the same report. Data of patients who underwent semirigid ureteroscope only were excluded from the analysis. The Newcastle-Ottawa Scale (NOS) system was applied for risk of bias assessment.

RESULTS

A total of 20 studies including 5,852 patients were involved. 48.5% of the patients had preoperative stent. Stone-free rate was significantly higher with prestenting; odds ratio (OR) was 1.98 (95% CI: 1.51-2.58) (Z = 5.02; p = 0.00001). It also displayed tendency toward lower complications; OR was 0.74 (95% CI: 0.52-1.05) (Z = 1.67; p = 0.09). POS significantly increased the use of ureteral access sheath; OR was 1.49 (95% CI: 1.05-2.13) (Z = 2.22; p = 0.03). Risk of bias assessment showed 13 and 7 studies with low and moderate risk, respectively.

CONCLUSIONS

POS clearly improves the stone-free rates after fURS. It might reduce the complications, especially ureteral injury. These findings might help solve the current debate and can be useful for urologists during patient counselling for a proper decision-making.

Ureteral access sheath-related injuries vs. post-operative infections. Is sheath insertion always needed? A prospective randomized study to understand the lights and shadows of this practice

OBJECTIVE

To compare intraoperative ureteral injuries in RIRS with UAS insertion with the rate of postoperative infections after RIRS without UAS insertion.

PATIENTS AND METHODS

In this randomized trial, patients who received an indication for RIRS between January 2017 and December 2017 were divided into two groups. Group A had no UAS insertion and Group B had UAS insertion. Post-Ureteroscopic Lesion Scale (PULS) grading was performed after UAS or flexible ureteroscope removal. Proximal, middle and distal ureteral lesions were evaluated and compared according to the PULS scale. Additionally, patients in both groups were followed postoperatively to assess any infective complication.

RESULTS

The evaluation comprised 181 patients, 89 for group A and 92 for group B. Overall stone-free rate, clinically insignificant residual fragments, and final stone-free rate were 41.4%, 53.5%, and 95%, respectively. There were 33 (37.1%) patients with ureteral lesions in group A while 42 (45.6%) patients had ureteral lesions in group B, with no significant difference. On the other hand, the overall presence of postoperative infection rate was much higher for Group A (37.1% vs 16.3% P=.03).

CONCLUSIONS

UAS insertion does not result in a higher number of ureteral injuries. UAS insertion during RIRS allows a lower rate of postoperative infections. Clinical Trial Registration Number (ISRCTN registry number): 55546280.

An irrigation system for noninvasively estimating intrarenal pressure during flexible ureteroscopy

BACKGROUND

High intrarenal pressure (IRP) during flexible ureteroscopy (FURS) may lead to severe complications. Reported methods for measuring IRP are often inconvenient to use, expensive and involve instruments that occupy the narrow ureter.

METHODS

We proposed an irrigation system, which can noninvasively estimate IRP based on the principle of fluid mechanics. To determine the feasibility of our system, we conducted irrigation experiments on a kidney phantom and a porcine kidney. The estimated IRPs were compared with the ground truth IRPs.

RESULTS

When no surgical instrument was inserted into the flexible ureteroscope's working channel, our system can estimate IRP with high accuracy. When a surgical instrument was inserted, our system can approximately estimate the level of IRP.

CONCLUSIONS

Our proposed irrigation system can noninvasively estimate IRP, presenting a new thought for clinical practice. In future studies, in vivo experiments are needed to further validate and improve the system.

Tips and Tricks to Improve Ergonomics, Efficacy, Versatility, and Overcome Limitations of Micro Percutaneous Nephrolithotomy

Percutaneous Nephrolithotomy (PCNL) has evolved over the decades from Standard to Mini to Ultramini PCNL to Micro-perc, with miniaturisation being the dominant theme and supine approach gaining momentum world over.

Aim: In literature, miniaturised PCNL with microperc needle access system has raised concerns of intrarenal pressure and has some limitations with its success for larger stones. Our tips and tricks explain how to overcome these pitfalls by utilising the full construct of the needle system to its maximum potential. These will in turn help make the procedure versatile, precise, ergonomical, and enhance a surgeon's experience with improved outcomes for patients especially in large renal stones.

Materials and Methods: We describe the limitations of microperc needle access as stated in literature and proposals by the co-authors using microperc for miniaturised access on how to overcome the same.

Results: A simplified table describing the limitations and tips and tricks on overcoming these is provided for quick reference.

Conclusion: As Technological advancements and techniques for miniaturised access in urolithiasis improve, we believe our suggestions will help surgeons overcome the quoted limitations of microperc needle access for miniaturised PCNL, making this a versatile, safe and efficacious technique even in large and complex stones. A multi centre trial will be the best way to validate the suggestions proposed in this article.

Development and Testing of an Anatomic in vitro Kidney Model for Measuring Intrapelvic Pressure During Ureteroscopy

OBJECTIVES

To create an in vitro anatomic bench model that can mimic in vivo intrapelvic pressure (IPP) during ureteroscopy (URS) and compare it against existing in vivo and ex vivo data.

METHODS

A silicone kidney model (Simagine Health) that permits intrarenal endoscopic navigation was engineered to have a fluid-tight seal for the ureteral opening and a Tuohy-Borst valve in the renal pelvis incorporating a 0.2 mm pressure sensor (Opsens). To calibrate the model, a Cobra ureteroscope (Wolf) was inserted to the pelvis with 200cmH₂O irrigation, and the valve adjusted until an IPP of 54cmH₂O was obtained (prior human data). All experiments were conducted with a laser fiber in the working channel, with and without ureteral access sheaths (UAS) (11/13F, 13/15F) at irrigation setting of 61, 102, 153, and 193cmH₂O using an automated system (Rocamed). Study outcome was mean steady-state IPP for each UAS/irrigation condition.

RESULTS

Fluid leakage through the Tuohy-Borst valve, which could be adjusted, was critical to simulate ureteric outflow during URS. IPP values for each condition corresponded with data from in vivo and ex vivo models. In the no UAS condition, IPP increased with increasing irrigation pressures, and surpassed 40cmH₂O when ≥153cmH₂O. When using a UAS, IPP was below 40cmH₂O for all irrigation pressures.

CONCLUSIONS

An in vitro kidney model can simulate in vivo and ex vivo IPP profiles, and be tailored to different conditions by controlling fluid outflow. This bench model can be useful for testing of new technologies and their impact on IPP.

High pressure endoscopic irrigation: impact on renal histology

Purpose:

High intra-renal pressures during flexible ureteroscopy have been associated with adverse renal tissue changes as well as pyelovenous backflow. Our objective was to investigate the effect of various intra-renal pressures on histologic changes and fluid extravasation during simulated ureteroscopy.

Materials and Methods:

Twenty-four juvenile pig kidneys with intact ureters were cannulated with an Olympus flexible ureteroscope with and without a ureteral access sheath and subjected to India ink-infused saline irrigation for 30 minutes at constant pressures ranging from sphygmomanometer settings of 50mm, 100mm and 200mmHg. Renal tissue samples were collected, processed and stained, and were evaluated by a blinded pathologist for depth of ink penetration into renal parenchyma as a percentage of total parenchymal thickness from urothelium to renal capsule.

Results:

The mean percentage of tissue penetration for kidneys with ink present in the cortical tubules at sphygmomanometer pressure settings of 50, 100, and 200mm Hg without a ureteral access sheath was 33.1, 31.0 and 99.3%, respectively and with ureteral access sheath was 0, 0 and 18.8%, respectively. Overall, kidneys with an access sheath demonstrated a smaller mean tissue penetration among all pressure compared to kidneys without a sheath (6.3% vs. 54.5%, p=0.0354). Of kidneys with sheath placement, 11% demonstrated any ink compared to 56% of kidneys without sheath placement.

Conclusions:

Pressurized endoscopic irrigation leads to significant extravasation of fluid into the renal parenchyma. Higher intra-renal pressures were associated with increased penetration of irrigant during ureteroscopy in an ex-vivo porcine model.

Evaluation of a Novel Female Gender Flexible Ureteroscope: Comparison of Flow and Deflection to a Standard Flexible Ureteroscope

Introduction: The advent of single-use disposable flexible ureteroscopes allows for rapid prototyping of novel endoscopes. In this regard, we sought to develop a female-specific ureteroscope, with a shorter working length, to account for the female anatomy. We hypothesized that the shorter, female-specific single-use flexible ureteroscope would engender higher irrigation flow at a given pressure than that of the standard-length ureteroscope. Methods: An in vitro analysis of a standard 65 cm Dornier Axis™ ureteroscope and a shorter, 45 cm female-specific Dornier Axis ureteroscope was performed. All other aspects of the endoscopes were identical. Each ureteroscope was oriented vertically and connected to a Thermedx^® irrigation system to provide uniform pressurized flow. The average flow rate was computed over five, 2-minute periods at pressure settings of 50, 100, 150, and 200 mm Hg. Data were collected with the working channel unoccupied, after placement of a 200 μm (0.6F) holmium laser fiber and after passage of a 1.7F stone basket. The procedure was then repeated with the endoscopes at maximum deflection. Results: The female gender ureteroscope had significantly higher irrigation flow rates than the standard-length ureteroscope under all conditions by an average of 11% (p < 0.02). The highest average percent increase, 17% (p < 0.001), was seen with the 1.7F NGage^® basket in the working channel with the endoscope straight. The maximum angle of deflection was not significantly different between the female gender and standard ureteroscopes with an open working channel (314° vs 315°, p = 0.86), with the 1.7F NGage basket in place (314° vs 315°, p = 0.15), and with the 200 μm holmium laser in place (316° vs 309°, p = 0.09). Conclusions: A 45 cm female gender ureteroscope allows for a higher irrigation flow rate than the standard-length ureteroscope under all test conditions. There is no added benefit with regard to deflection capabilities.

Effect of Chilled Irrigation on Caliceal Fluid Temperature and Time to Thermal Injury Threshold During Laser Lithotripsy: In Vitro Model

Introduction: High-power lasers (100-120 W) have widely expanded the available settings for laser lithotripsy and facilitated tailoring of treatment for individual cases. Previous in vitro and in vivo studies have demonstrated that a toxic thermal dose to tissue can result from treatment within a renal calix. The objective of this in vitro study was to compare thermal dose and time with tissue injury threshold when using chilled (CH) irrigation and room temperature (RT) irrigation. Materials and Methods: A glass tube attached to a 19 mm diameter bulb simulating a renal calix was placed in a 37°C water bath. A 242 μm laser fiber was passed through a ureteroscope with its tip in the center of the glass bulb. A wire thermocouple was placed 3 mm proximal to the ureteroscope tip to measure caliceal fluid temperature. RT at 19°C or CH at 1°C irrigation was delivered at 0, 8, 12, 15, or 40 mL/minute. The laser was activated at 0.5 J × 80 Hz (40 W) for 60 seconds. Thermal dose was calculated using the Sapareto and Dewey t43 methodology with thermal dose = 120 equivalent minutes considered the threshold for thermal tissue injury. Results: At each irrigation rate, CH irrigation produced a lower starting temperature, a lower plateau temperature, and less thermal dose compared with RT irrigation. The threshold of thermal injury was reached after 13 seconds of laser activation without irrigation. With 12 mL/minute irrigation, the threshold was reached in 46 seconds with RT irrigation but was not reached with CH irrigation. Conclusion: As higher power laser lithotripsy techniques become further refined, methods to mitigate and control thermal dose are necessary to enhance efficiency. CH irrigation slows temperature rise, decreases plateau temperature, and lowers thermal dose during high-power laser lithotripsy.

Consultation on kidney stones, Copenhagen 2019: aspects of intracorporeal lithotripsy in flexible ureterorenoscopy

Purpose

To summarize current knowledge on intracorporeal laser lithotripsy in flexible ureterorenoscopy (fURS), regarding basics of laser lithotripsy, technical aspects, stone clearance, lithotripsy strategies, laser technologies, endoscopes, and safety.

Methods

A scoping review approach was applied to search literature in PubMed, EMBASE, and Web of Science. Consensus was reached through discussions at the Consultation on Kidney Stones held in September 2019 in Copenhagen, Denmark.

Results and conclusions

Lasers are widely used for lithotripsy during fURS. The Holmium laser is still the predominant technology, and specific settings for dusting and fragmenting have evolved, which has expanded the role of fURS in stone management. Pulse modulation can increase stone ablation efficacy, possibly by minimizing stone retropulsion. Thulium fibre laser was recently introduced, and this technology may improve laser lithotripsy efficiency. Small fibres give better irrigation, accessibility, and efficiency. To achieve optimal results, laser settings should be adjusted for the individual stone. There is no consensus whether the fragmentation and basketing strategy is preferable to the dusting strategy for increasing stone-free rate. On the contrary, different stone scenarios call for different lithotripsy approaches. Furthermore, for large stone burdens, all laser settings and lithotripsy strategies must be applied to achieve optimal results. Technology for removing dust from the kidney should be in focus in future research and development. Safety concerns about fURS laser lithotripsy include high intrarenal pressures and temperatures, and measures to reduce both those aspects must be taken to avoid complications. Technology to control these parameters should be targeted in further studies.

Comparison of intrapelvic pressures during flexible ureteroscopy, mini-percutaneous nephrolithotomy, standard percutaneous nephrolithotomy, and endoscopic combined intrarenal surgery in a kidney model

PURPOSE

To compare intrapelvic pressure (IPP) levels achieved during f-URS, mini-PCNL, standard PCNL, and endoscopic combined intrarenal surgery in a kidney model.

METHODS

A silicone model simulating the complete urinary tract was used for all the experiments. We compared: a 9.5Fr f-URS, a 12Fr mini-nephroscope and a 26Fr nephroscope. The irrigation pressure was set at 40 and 193 cmH₂O. We compared: f-URS-S ± ureteral access sheath (UAS, 10/12Fr, 11/13Fr, 12/14Fr) ± 273 μm laser fiber, Mini-PCNL with different sizes of operating sheath (15/16Fr, 16.5/17.5Fr, 21/22Fr) ± 365 μm laser fiber, Standard PCNL with an operating sheath of 30Fr ± Lithotripter LithoClast Master 11.4Fr.

RESULTS

f-URS: IPP values ranged between 1.4 and 46.2 cmH₂O. Factors reducing IPP were an irrigation pressure at 40 cmH₂O, an occupied working channel, and the use of a UAS except with the 10/12Fr at 193 cmH₂O. Mini-PCNL: IPP values ranged between 2.4 and 39.7 cmH₂O. Factors reducing IPP were irrigation pressure at 40 cmH₂O, a large operating sheath (> 15/16Fr). The occupation of the working channel did not affect the IPP at 40 cmH₂O, while it decreased at 193 cmH₂O. Standard PCNL: IPP values ranged between 1.4 and 7.3 cmH₂O. Occupancy of the working channel did not affect IPP at 40 cmH₂O, while it increased at 193 cmH₂O.

CONCLUSION

We recorded for the first time IPP values according to different endourological techniques and configurations. IPP never exceed 50 cmH₂O irrespectively of the assessed technique/setup. The factors reducing IPP were a low irrigation pressure (40 cmH₂O), the use of a UAS or a working sheath appropriate to the diameter of the endoscope, as well as the occupation of the working channel in the case of f-URS.

The effect of preoperative ureteral stenting in retrograde Intrarenal surgery: a multicenter, propensity score-matched study

Background

Stent placement before retrograde intrarenal surgery (RIRS) can theoretically expand the ureter to improve access and remove stones. The purpose of this study was to investigate the effect of preoperative ureteral stenting on access and surgery.

Methods

We retrospectively analyzed patients who underwent RIRS between January 2010 and December 2016 at multiple centers. The patients were divided into two groups based on whether or not a ureteral stent was inserted preoperatively. The characteristics of the stone (size, number, density, and location), the success rate of the access sheath placement, perioperative complications, operative times, hospitalization periods, the period for which the stents remained, postoperative urinary tract infection rates, stone-free rates, and additional treatment rates were analyzed.

Results

Overall, 727 patients were included in the study (113 were pre-stented and 614 were non-stented). The median stone size was 12.2 mm. The overall stone-free rate (SFR) was 85.8% for the pre-stented group and 83.2% for the non-stented group, showing no significant (p = 0.498) difference between the two groups. Preoperative ureteral stenting improved the success rate of sheath placement (93.8% vs. 85.3%, p = 0.023) during surgery. The access sheath size in participants in the pre-stented group showed a tendency to be larger than that in participants in the non-stented group. However, there were no differences in perioperative complications, operative times, additional treatment rates, and stone-free rates.

Conclusions

Although preoperative ureteral stenting did not affect operative outcomes, it increased the success rate of access sheath placement. Depending on the patient’s characteristics, preoperative ureteral stenting can be considered as an adjunctive option when access sheath insertion is considered during RIRS.

Effects of irrigation parameters and access sheath size on the intra-renal temperature during flexible ureteroscopy with a high-power laser

OBJECTIVES

To investigate the effect of different laser power settings on intra-renal temperature (IRT) under different irrigation conditions during flexible ureteroscopy (FURS) in a live-anesthetized porcine model.

METHODS

Following ethics approval, 2 female pigs weighing ~ 28 kg were used. Under general anesthesia, a percutaneous access was obtained to fix a K-type thermocouple inside the pelvi-calyceal system for real-time recording of IRT during FURS without UAS, UAS-10/12, UAS-12/14, and UAS-14/16F. A high-power holmium laser was used and the IRT was recorded during laser activation for up to 60 s at a laser power of 20 W, 40 W, and 60 W under gravity irrigation and manual pump irrigation.

RESULTS

Under gravity irrigation, FURS without UAS was associated with hazardous IRT at a laser power as low as 20 W for as short as 20 s of laser activation. The IRT was rendered borderline when UAS was used. This UAS buffering effect disappeared with the use of higher laser-power settings (40 W and 60 W) with the maximal IRT exceeding 60 °C. Moreover, laser activation at 60 W was associated with very rapid increase in IRT within few seconds. Under pump irrigation, laser activation at the highest power setting (60 W) for 60 s was associated with a safe IRT, even without the use of UAS. The maximal IRT was below 45 °C.

CONCLUSION

The use of high-power Ho:YAG laser carries potentially harmful thermal effect when used under gravity irrigation, even when large-diameter UAS is used. High-power settings (> 40 W) require high irrigation flow. The use of UAS is advisable to reduce the IRT and balance any intra-renal pressure increase.

Impact of ureteral access sheath on renal stone treatment: prospective comparative non-randomised outcomes over a 7-year period

PURPOSE

To compare the outcomes (stone free rate and complications) of renal stone treatment with and without the use of ureteral access sheath (UAS). The worldwide use of UAS has risen over the last decade; however, questions still remain on the safety and outcomes with its use. We wanted to look at the role of UAS for treatment of consecutive renal stones over a 7-year period.

METHODS

The outcomes of flexible ureteroscopy and stone treatment (FURS) for renal stones with and without the use of UAS was prospectively compared from March 2012 to July 2018. Patients were divided into two groups: group-1 where UAS was used for stone treatment and group-2 where a UAS was not used. Data were collected prospectively on consecutive patients for demographics, stone size, location and number, pre and post-operative stent usage, operative time duration, stone free rate (SFR), length of stay and complications.

RESULTS

During the study period, 338 patients underwent FURS for renal stones, of which a UAS was used for 203 (60%) patients. The mean age of patients was 56 years (range 2-89 years) with a male:female ratio of 204:134. The mean cumulative stone size and the mean number of stones was 16.5 ± 10.8 mm and 11.37 ± 8.08 mm (P < 0.001), and 2.17 ± 1.99 and 1.66 ± 1.50 (P = 0.009) for groups 1 and 2 respectively. The pre and post-operative stent insertion rates were similar in the two groups. The procedural time was longer in group-1 (54.8 ± 25.8 min) compared to group-2 (41.3 ± 22.2 min) (P < 0.001). The SFR for group-1 (88%) was slightly lower than group-2 (94%) although this was not statistically significant (P = 0.07). There were no intra-operative complications in either of the groups. Post-operative complications were seen in eight patients in group-1 (7 Clavien I/II and 1 Clavien IVa) and two patients in group-2 (Clavien I) (P = 0.19).

CONCLUSION

The use of UAS for renal stones is safe with no intra-operative complications noted in our series. Good stone-free rates were obtained for large and multiple renal stones with a small risk of minor complications post-operatively.

The role of preoperative ureteral stenting in retrograde intrarenal surgery in renal stone patients: a propensity score-matched study

Background

The purpose of this study was to investigate the effect of preoperative ureteral stenting on retrograde intrarenal surgery (RIRS).

Methods

We retrospectively analyzed RIRS cases from October 2014 to June 2017. Patients were divided into two groups according to preoperative ureteral stent insertion. The characteristics of the patients [age, body mass index (BMI), sex, previous disease history, hemoglobin, creatinine, estimated glomerular filtration rate (eGFR)], characters of stone (size, number, density, location), ureteral access sheath (UAS) success rate, perioperative complication, operative time, hospitalization time, period with stent, postoperative urinary tract infection (UTI) rate, stone free rate (SFR), and additional treatment rate were analyzed.

Results

RIRS was performed for 122 patients. Seventy-three patients had preoperative ureteral stents before RIRS, while 49 patients did not have preoperative ureteral stents. The median size of the stone was 14.5 mm. Overall SFR was 87.7%. Preoperative eGFR was relatively high in patients who underwent preoperative stenting (68.18 vs. 79.01 mL/min/1.73 m², P=0.042). Preoperative stenting led to improvement in the success rate of UAS insertion (97.3% vs. 87.8%, P=0.038) during surgery. Before and after propensity score matching revealed a significant difference in operation time when the diameter of the stone was smaller than 1 cm (P=0.019 and P=0.004). However, there was no significant difference in operation time, postoperative UTI rate, additional treatment rate, or SFR.

Conclusions

Preoperative ureteral stenting can facilitate UAS insertion, and reduce operation time in RIRS for stones with a diameter less than 1 cm.

Effects of flexible ureteroscopy on kidney: A prospective clinical trial

OBJECTIVE

To investigate the effects of flexible ureteroscopy (F-URS) on the operated side of a kidney by assessing the renal damage markers, urine neutrophil gelatinase-related lipocalin (NGAL) and serum cystatin-C (Cys-C), and overall kidney function with the measurements of standard serum creatinine and urine albumin and protein levels.

MATERIAL AND METHODS

A total of 30 patients who underwent F-URS for treatment of upper urinary stone disease were prospectively evaluated. Preoperative serum urea, creatinine, and Cys-C levels were noted. Levels of urine albumin, protein, creatinine, and NGAL in spot urine samples from the operated side of a kidney obtained through the access sheath preoperatively and through the ureteral catheter 1 and 24 hours postoperatively were also measured. Preoperative and postoperative parameter levels were statistically compared.

RESULTS

The patients' mean age was 46.6±15.9 years. The mean operative and fluoroscopy times were 90.67±32.5 and 3.15±1.43 minutes, respectively. The urine creatinine, albumin, protein, albumin/creatinine, and protein/creatinine levels were similar in preoperative and postoperative periods. Postoperative serum urea, creatinine, and Cys-C levels and urine NGAL and NGAL/creatinine levels were not also found with remarkable changes from the baseline levels.

CONCLUSION

F-URS is a safe therapeutic intervention in the treatment of urolithiasis, especially regarding renal damage, and functional outcomes.

The Fluid Mechanics of Ureteroscope Irrigation

Purpose: To develop a physical understanding of ureterorenoscopy irrigation, we derive mathematical models from basic physical principles and compare these predictions with the results of benchtop experiments. Mathematical modeling can be used to understand the role of inlet pressure, tip deflection, the presence of working tools, geometric properties of the instruments used, and material properties of the irrigation fluid on resulting flow rate.

Materials and Methods: We develop theoretical models to describe irrigation flow in an idealized setup and compare with benchtop experiments for flow through a straight scope, a scope with a deflected tip, and a scope with a working tool inserted. The benchtop experiments were performed using Boston Scientific LithoVue ureteroscope and a variety of Boston Scientific working tools. Standard ureteroscope working channels have circular cross sections, but using theoretical models we investigate whether modifications to the cross-sectional geometry can enhance flow rates.

Results: The theoretical flow predictions are confirmed by experimental results. Tip deflection is shown to have a negligible effect on flow rate, but the presence of working tools decreases flow significantly (for a fixed driving pressure). Flow rate is predicted to improve when tools are placed at the edge of the channel, rather than the center, and modifying the cross-sectional shape from a circle to an ellipse can further increase flow rate.

Conclusions: A mathematical framework is formulated and shown to accurately predict the properties of ureteroscope irrigation flow. The theoretical approach has significant potential in quantifying irrigation flow and improving ureteroscope design.

Outcomes of ureteroscopy (URS) for stone disease in the paediatric population: results of over 100 URS procedures from a UK tertiary centre

PURPOSE

To report the outcomes of paediatric ureteroscopy (URS) for stone disease from a specialist endourology centre in the UK. Ureteroscopy for management of stone disease has increased worldwide and is now being done more commonly in the paediatric age group.

METHODS

Data were analysed retrospectively from a database maintained between April 2010 and May 2018. Consecutive patients ≤ 16 years of age undergoing semi-rigid or flexible URS for stone disease were included. Stone size and stone-free rate (SFR) were routinely assessed using an ultrasound (USS) and/or plain KUB XR. Complications were graded according to the Clavien-Dindo classification and recorded within 30 days post-procedure and readmissions within 90 days after the procedure were also captured.

RESULTS

Over the 8-year period between April 2010 and April 2018, 81 patients with a mean age of 8.8 years (range 18 months-16 years) and a male to female ratio 1:1.1 underwent 102 procedures (1.28 procedure/patient to be stone free). Of the 81 patients, 29 (35.8%) had comorbidities, with 26 (32%) having multiple comorbidities. The mean (± SEM) single and overall stone size was 9.2 mm (± 0.48, range 3-30 mm) and 11.5 mm (± 0.74, range 4-46 mm) respectively, with 22 (27.1%) having multiple stones. Thirty-five (34.7%) had stent in situ pre-operatively. The stone location was in the ureter (26.6%), lower pole (35.4%), and renal pelvis (16.5%), with 22/81(27%) having multiple stones and 21/102 (20.5%) where a ureteral access sheath (UAS) was used. With a mean hospital stay of 1.2 days, the initial and final SFR was 73% and 99%, respectively, and 61/102 (60%) had ureteric stent placed at the end of the procedure. While there were no intra-operative complications, the readmission rate was less than 1% and there were only three early complications recorded. This included a case each of prolonged admission for pain control (grade I), urinary retention (grade II) and post-operative sepsis requiring a brief ITU admission (grade IV).

CONCLUSION

Our study demonstrates that in appropriate setting a high stone-free rate can be achieved with minimal morbidity for paediatric patients. There is potentially a need to factor the increasing role of URS in future paediatric urolithiasis guidelines.

[Role of pressure and temperature in ureterorenoscopy and percutaneous nephrolitholapaxy : Pressure and temperature changes during stone treatment]

Ureterorenoscopy and percutaneous nephrolitholapaxy are minimally invasive procedures and are the standard procedures for the treatment of kidney stones and ureteral calculi. To achieve an adequate view, in both methods an optimal and sufficient irrigation flow is necessary. The intrarenal pressure is influenced by the irrigation pressure and irrigation volume and has to be controlled. Pathologically elevated intrarenal pressure can lead to irreversible damage of the kidneys. Lasers are frequently used for stone fragmentation. It has been shown in studies that the laser energy can lead to an increase in the temperature and that thermal effects can also damage the kidneys. This article provides the surgeon with an overview about the effects of temperature and pressure changes during ureterorenoscopy and percutaneous nephrolitholapaxy and how damages can be avoided.