An in vitro study evaluating the internal pressure during RIRS of suction ureteral access sheath versus traditional sheath

ABSTRACT

Introduction

Flexible ureteroscopy (fURS) remains the gold standard for managing ureteral and renal calculi. The integration of vacuum suction ureteral access sheaths has demonstrated improved stone clearance rates. Through an in vitro fURS model, this study systematically validates the sheath’s efficacy in regulating intraluminal pressure across diverse operational parameters, providing mechanical insights for clinical optimization.

Methods

An 8.6Fr disposable flexible ureteroscope was utilized to measure intraluminal pressure within a silicone urinary tract model fabricated using 3D printing technology. The experiment was conducted under three configurations of ureteral access sheaths (UAS): (1) conventional UAS, (2) negative pressure suction sheath with an open vent, and (3) negative pressure suction sheath with a fully closed vent. Intraluminal pressure and irrigation flow rate were recorded for various UAS sizes under irrigation pressures ranging from 10 to 240 mmHg.

Results

Under varying infusion pressure conditions, the negative pressure sheath with an open vent exhibited slightly lower intraluminal ureteral pressure compared to the traditional sheath; however, this difference was not statistically significant (p = 0.56). In contrast, when using the closed vent method, the negative pressure aspiration sheath demonstrated a significantly distinct change in intraluminal pressure compared to both the traditional sheath and its open vent mode (p < 0.01). Additionally, the choice of ureteral sheath size had a profound impact on intraluminal pressure, with larger sheath sizes associated with lower pressure levels under the same infusion pressure (p < 0.01).

Conclusions

During ureteroscopy procedures, intraluminal pressure within the ureter increases proportionally with irrigation pressure. However, the application of negative pressure using a closed vent can effectively mitigate this rise in intraluminal pressure.

Introduction

Nephrolithiasis imposes substantial clinical-economic burdens as a globally prevalent disorder, with rising incidence per European Association of Urology (EAU) epidemiological surveillance [1,2]. Current management aligns with EAU 2023 guidelines endorsing retrograde intrarenal surgery (RIRS) as primary intervention for calculi ≤2 cm or proximal ureteral stones ≥1 cm, complementing extracorporeal shockwave lithotripsy and percutaneous approaches [3,4].

Flexible ureteroscopy (fURS) has evolved through three decades of innovation, notably with ureteral access sheaths (UAS) enhancing stone-free rates, operative efficiency, and upper tract protection via intraluminal pressure (IRP) modulation [5–8]. While novel suction-UAS (S-UAS) systems demonstrate improved lithotripsy efficacy and IRP control in preliminary studies [9–12], critical knowledge gaps persist regarding pressure dynamics across operational parameters. This in vitro study pioneers systematic quantification of S-UAS-mediated IRP reduction under variable irrigation intensities and sheath configurations, establishing foundational evidence for clinical protocol optimization.

Materials and methods

3D printing silicone model

This study employed 3D printing technology to fabricate a silicone urinary tract model that replicates the human renal collecting system for simulating ureteroscopy during stone fragmentation. A disposable intraoperative pressure-measuring ureteroscope (8.6Fr; HUS-M100, Anhui Happiness Medical Equipment, Anhui, China) was utilized to measure intraluminal pressure. During the testing process, the pressure-measuring ureteroscope was consistently positioned at the same lumen location within the model prior to each measurement. This standardization, along with zeroing adjustments, minimized the potential impact of depth variations within the inner lumen. Additionally, the ureteroscope was aligned to a zero-degree horizontal plane to reduce the minor influence of fluid retention caused by the angle of the ureteral sheath (Figure 1).

Figure 1.

Schematic overview of in vitro experiments to evaluate the intrarenal pressure during RIRS of suction UAS and traditional UAS.

Pressure fluid irrigation device

For irrigation, a medical fluid pressurizer (ISA-IIIa, Hawk, Shenzhen, China) was used to provide constant-pressure fluid irrigation. Before each test, zeroing procedures were performed to ensure measurement accuracy and minimize the influence of residual pressure in the irrigation bottle on the experimental results. The irrigation pressure was initiated at 0 mmHg and gradually increased in increments to the target pressure range of 10–240 mmHg.

Ureteral access sheath and vacuum suction device

The negative pressure suction ureteral access sheath (10/12Fr, 11/13Fr, 12/14Fr, 13/15Fr; Reborn Medical, Zhuzhou, China) is a novel UAS featuring an advanced bendable tip that passively adjusts during actively bending fURS procedures. The UAS handle consists of a handle site and a chimney site equipped with a pressure-regulating vent connected to a vacuum device, as illustrated in Figure 1. The wall vacuum negative pressure suction device was set at 0.06 MPa for the experiments.

The experiment was conducted under three configurations of the UAS: (1) traditional UAS (T-UAS), (2) negative pressure suction sheath with an open vent, and (3) negative pressure suction sheath with a fully closed vent (closed-system vacuum). Intraluminal pressure and irrigation flow rate were measured for various UAS sizes under irrigation pressures ranging from 10 mmHg to 240 mmHg.

Statistical method

Statistical analysis was performed using IBM SPSS Statistics 27. A one-way ANOVA test was utilized to analyze the data and identify any significant differences among the groups. Furthermore, Fisher’s least significant difference (LSD) analysis was conducted to examine the statistical differences between specific group combinations.

Results

The experimental protocol employed three ureteral access sheath configurations (Traditional UAS, S-UAS with open vent, and S-UAS with closed vent) across 12/14Fr sheath sizes. Using a computer-controlled pressure infusion system (20–300 mmHg gradient), we recorded hemodynamic performance metrics (intraluminal pressure and irrigation flow) at 10 mmHg intervals. (Table 1)

Table 1.

Irrigation velocity change and ureteral pressure change difference.

	Mean Difference	95% Confidence Interval	P value
Irrigational velocity Change difference in various setting (ml/min)			< 0.001
S-UAS OPENED VENT Vs S-UAS CLOSED VENT	−38.42	(-54.17, -22.66)	< 0.001
T-UAS Vs S-UAS CLOSED VENT	−44.71	(-60.47, -28.95)	< 0.001
T-UAS Vs S-UAS OPENED VENT	−6.29	(-22.05, 9.47)	0.428
Pressure Change difference in various setting (mmHg)			< 0.001
S-UAS OPENED VENT Vs S-UAS CLOSED VENT	19.92	(15.86, 23.97)	< 0.001
T-UAS Vs S-UAS CLOSED VENT	21.12	(17.07, 25.18)	< 0.001
T-UAS Vs S-UAS OPENED VENT	1.21	(-2.85, 5.26)	0.560
Pressure Change difference in various sheath size (mmHg)			< 0.001
F12/14 VS F13/15	2.42	(-0.80, 5.63)	0.140
F11/13 VS F13/15	12.20	(8.98, 15.41)	< 0.001
F10/12 VS F13/15	50.89	(47.68, 54.11)	< 0.001
F11/13 VS F12/14	9.78	(6.57, 13.00)	< 0.001
F10/12 VS F12/14	48.48	(45.26, 51.69)	< 0.001
F10/12 VS F11/13	38.70	(35.48, 41.92)	< 0.001

a VS b Mean Difference = Mean b-Mean a

Effect of vent status on intraluminal pressure

Primary endpoint analysis revealed the closed-vent S-UAS demonstrated significantly lower intraluminal pressures (−32.7 ± 5.4 mmHg, p < 0.01) compared to T-UAS across all irrigation scales. Secondary outcomes showed closed-vent configuration maintained 18–26% pressure reduction versus open-vent models, particularly pronounced at high-pressure thresholds ( > 200 mmHg).

Regardless of the ureteral access sheath size, the intraluminal pressure change was significantly lower in the S-UAS closed vent group compared to the T-UAS group (mean difference [MD] = −21.12 mmHg, p < 0.001). Additionally, the irrigation flow rate was significantly higher in the S-UAS closed vent group (MD = 44.71 ml/s, p < 0.001).

As expected, the intraluminal pressure change was significantly lower in the S-UAS closed vent group compared to the S-UAS open vent group (MD = −19.92 mmHg, p < 0.001). Similarly, the irrigation flow rate was significantly higher in the S-UAS closed vent group (MD = 38.42 ml/s, p < 0.001).

However, no significant differences were observed in intraluminal pressure changes between the S-UAS open vent group and the T-UAS group (MD = −1.21 mmHg, p = 0.56). Similarly, there were no significant differences in irrigation flow rate changes between these two groups (MD = 6.29 ml/s, p = 0.428).

Effect of UAS size on intraluminal pressure

In the intragroup analysis of various ureteral access sheath sizes, independent of other setting conditions, intraluminal pressure changes were significantly lower in larger UAS groups. Specifically, the F13/15 group showed significantly lower pressure changes compared to the F11/13 group (mean difference [MD] = −12.20 mmHg, p < 0.001) and the F10/12 group (MD = −50.89 mmHg, p < 0.001). Similarly, the F12/14 group exhibited significantly lower pressure changes compared to the F11/13 group (MD = −9.78 mmHg, p < 0.001) and the F10/12 group (MD = −48.48 mmHg, p < 0.001). Additionally, the F11/13 group demonstrated significantly lower pressure changes compared to the F10/12 group (MD = −38.70 mmHg, p < 0.001).

Surprisingly, no significant differences in intraluminal pressure changes were observed between the F13/15 and F12/14 groups (MD = −2.42 mmHg, p = 0.140).

In conclusion, we believe that larger ureteral access sheaths were associated with significantly lower intraluminal pressures, regardless of other conditions. Pressure reductions were progressively greater as sheath size increased, with the F13/15 and F12/14 groups showing significantly lower pressures compared to smaller sizes, particularly F10/12.

Effect of procedure time on intraluminal pressure

Our pressure-controlled trials demonstrated that intraluminal perfusion pressure (IPP) stabilized after a 2–3 sec equilibration phase, exhibiting dynamic steady-state characteristics. For RIRS using 8.6Fr ureteroscopes, sheath sizes ≥F11/13 should be prioritized (max IPP 34.14 mmHg under physiological perfusion parameters), while F10/12 sheath use necessitates maintaining irrigation pressure < 80 mmHg (critical IPP threshold: 40.03 mmHg) to prevent renal pelvic barotrauma.

Discussion

Since the introduction of retrograde intrarenal surgery (RIRS) and its associated instruments, ureteroscopic lithotripsy has become the most widely used treatment among urologists in many countries [4]. In terms of irrigation, traditional manual irrigation has gradually been replaced by electric-powered irrigation pumps, which offer more precise control over irrigation flow rate and pressure [7]. However, despite advancements in clinical research, postoperative infections related to elevated intraluminal pressure (IPP) caused by excessive irrigation remain a significant concern that cannot be overlooked [13].

One of the primary factors contributing to infection complications during RIRS is elevated IPP. Studies have demonstrated that the application of negative pressure techniques during RIRS can reduce infection complications by lowering IPP [14,15]. Unlike traditional UASs, which are typically positioned at the ureteropelvic junction (UPJ), S-UAS can be adjusted to reach the renal pelvis, targeting specific calyces to ensure adequate irrigation space. This adjustment helps prevent mucous blockage of the UAS opening at the pelvis-ureter junction and maintains lower IPP levels.

The integration of S-UAS with a vacuum device facilitates continuous irrigation-suction cycles, enhancing renal fluid outflow and maintaining reduced intraluminal pressure (IPP) levels.

To our knowledge, this is the first study to investigate the effectiveness of S-UAS in reducing intraluminal pressure under various conditions. Our findings demonstrate that the S-UAS closed vent group exhibited a significant reduction in intraluminal pressure compared to both the S-UAS open vent group and the T-UAS group, with reductions of 21.12 mmHg and 19.92 mmHg, respectively. These results confirm that S-UAS with a closed vent is superior to T-UAS in lowering intraluminal pressure.

Additionally, we observed that when using the same type of ureteroscope and ureteral access sheath, the application of S-UAS maintained lower intraluminal pressure even with increased irrigation flow rates. Higher irrigation flow rates can improve stone clearance, enhance visual field clarity, and reduce operative time. Furthermore, although we used an 8.5F pressure-measuring ureteroscope (larger than the standard 7.5F disposable fURS, Pusen, Zhuhai, China) in experiments with various smaller-sized ureteral sheaths, the results demonstrated that negative pressure suction sheaths can still effectively reduce intraluminal pressure. Therefore, using the standard 7.5F fURS with a negative pressure suction sheath may result in even lower intraluminal pressure than observed in our study.

Regarding ureteral access sheath size, our study confirmed that larger sheath sizes are associated with lower intraluminal pressure. However, no significant difference was observed between the F13/15 and F12/14 groups, indicating that increasing the sheath size beyond F12/14 May not further reduce intraluminal pressure. Nonetheless, larger sheath sizes may offer other advantages, such as improved irrigation flow and the ability to clear smaller stones.

Moreover, according to Hinman and other studies, an intraluminal renal pressure (IRP) exceeding 30–35 mmHg can lead to pyelovenous backflow, resulting in fluid absorption and increasing the risk of urinary tract infections [16]. In our study, most static intraluminal pressures in the S-UAS groups were below this threshold, with some even recording negative values in the larger-sized S-UAS closed vent group. However, excessive negative pressure suction may collapse the collecting system, potentially compromising intraoperative visibility. Therefore, further in vivo experiments are necessary to determine the optimal balance between these factors.

Our study has several limitations. First, although the experimental design is theoretically sound, the use of silicone models may differ in elasticity compared to human ureters, and the anatomical structure of the model may not fully replicate the human renal collecting system, which includes the renal pelvis and multiple calyces. These differences could lead to variations in intraluminal pressure measurements, necessitating further in vivo validation. Second, due to the lack of narrower ureteroscope models, we used a larger 8.6F ureteroscope for experiments with smaller ureteral sheaths, which may have contributed to higher measured intraluminal pressures. Future studies should explore alternative methods to investigate intraluminal pressure changes using appropriately sized ureteroscopes and varying ureteral sheath sizes.

Conclusion

Ureteroscopic lithotripsy continues to advance technologically, but the potential risks associated with intraoperative pressure changes during RIRS should not be overlooked. Our initial in vitro study demonstrates that the application of a negative pressure suction sheath can effectively reduce intraluminal pressure within the experimental model under various conditions. These findings may reflect similarities in fluid dynamic characteristics between the in vitro model and in vivo conditions, providing valuable insights for the clinical application of this advanced technology.

Funding Statement

This work was financed by grants from the National Natural Science Foundation of China [grant number 82070721 and 82270822], the Young Talent Support Project of Guangzhou Association for Science and Technology, the Guangzhou Science Technology and Innovation Commission [grant number 202102010150 and 2023A04J0574]. The sponsors played no direct role in the study.

Disclosure statement

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

Author contributions

Shusheng Liu had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Study concept and design: Guohua Zeng, Wei Zhu.

Acquisition of data: All authors.

Analysis and interpretation of data: Shusheng Liu, Wei Zhu, Guohua Zeng.

Drafting of the manuscript: Shusheng Liu, Wei Zhu.

Critical revision of the manuscript for important intellectual content: Chu Ann Chai.Pasin Limudomporn.

Statistical analysis: Shusheng Liu, Yuqun Li, Wei Zhu.

Obtaining funding: Wei Zhu, Guohua Zeng.

Administrative, technical, or material support: Shusheng Liu, Wei Zhu, Weijie Liu, Jian Zhong, Xuliang Pang, Guoyao Ai, Zhicong Huang.

Supervision: Guohua Zeng.

Other: None.

Financial disclosures

Wei Zhu certifies that all conflicts of interest, including specific financial interests and relationships and affiliations relevant to the subject matter or materials discussed in the manuscript (eg, employment/affiliation, grants or funding, consultancies, honoraria, stock ownership or options, expert testimony, royalties, or patents filed, received, or pending), are the following: None.

Data sharing statement

Raw data are available on reasonable request.