Pressure-Controlled and Suction-Assisted Ureteroscopy: A Systematic Review and Meta-analysis of Fluid Dynamics and Perioperative Safety

1. INTRODUCTION

Ureteroscopy (URS) is a widely adopted procedure for managing upper urinary tract stones, supported by continuous advancements in flexible ureteroscopes, laser lithotripsy, and Ureteral Access Sheaths (UAS) [1, 2]. Despite its efficacy, URS carries risks related to Intrarenal Pressure (IRP) and irrigation fluid absorption. Elevated Renal Pelvic Pressure (RPP) has been associated with pyelovenous and pyelolymphatic backflow, potentially leading to postoperative fever, urosepsis, and ureteral injury [3-6]. Clinical studies report that infectious complications such as postoperative fever occur in approximately 4–8% of URS cases, while urosepsis develops in 0.5– 5% depending on patient risk factors and intraoperative pressure levels [7, 8].

To address these concerns, a new generation of intrarenal pressure–modulating devices, including suction-assisted UAS, negative-pressure access sheaths, and intelligent pressure-control platforms, has been introduced. These systems aim to stabilize RPP, enhance outflow, minimize pressure surges, and reduce intrarenal fluid absorption, thereby improving procedural safety [9-13]. Early clinical trials suggest that device-based pressure regulation may reduce fluid absorption, shorten operative time, and maintain high Stone-Free Rates (SFR), positioning these technologies as promising adjuncts in modern URS [14, 15].

However, available evidence remains fragmented. Studies differ substantially in their pressure measurement techniques (pressure wires, fiber-optic sensors, ethanol absorption models), irrigation strategies, and definitions of clinical outcomes [10, 16, 17]. Although both randomized trials and observational cohorts have evaluated individual devices, no prior systematic review has specifically synthesized their impact on fluid absorption, pressure dynamics, and patient outcomes during URS.

Therefore, this systematic review aims to critically evaluate current evidence on intrarenal pressure–modulating devices, focusing on their effects on fluid absorption, pressure dynamics, and clinical outcomes during URS.

2. METHODS

3. RESULTS

3.1. Study Selection

The database search identified a total of 337 records (PubMed = 114, Cochrane =54, EBSCOhost = 169). After removal of 76 duplicates, 261 records remained for screening. Following title and abstract screening, 207 records were excluded. A total of 54 full-text articles were assessed for eligibility, of which 50 were excluded (irrelevant population or procedure, n = 18; no outcomes on intrarenal pressure or fluid absorption, n = 12; review articles, n = 11; conference abstracts, n = 6; animal/in vitro studies, n = 3). Finally, 4 studies met the inclusion criteria and were included in both qualitative and quantitative synthesis (Fig. 1).

As shown in Table 1, four primary studies were included, comprising two randomized controlled trials and two observational cohorts, with sample sizes ranging from 73 to 231 patients. Across all studies, participants were adult patients undergoing ureteroscopy or retrograde intrarenal surgery for upper urinary tract stones, with mean or median ages generally ranging from the mid-40s to the late-50s. The sex distribution was relatively balanced, although the multicenter cohort by Bai et al. [10] included a higher proportion of male patients. Stone size differed by study design: both RCTs enrolled patients with stones measuring approximately 15–17 mm, whereas the retrospective multicenter series evaluated larger stone burdens, with a median size of 26 mm.

Table 1.

Author (Year)	Country / Setting	Design	Total N	Intervention (N)	Control (N)	Age (yrs)	Sex (M/F)	Stone Size	Inclusion Criteria	Exclusion Criteria
Croghan et al. (2022) [17]	Ireland (4 hospitals)	Prospective, multi-institutional, blinded IRP measurement	120	–	–	57.5 ± 13.4	70/50	NA	≥18 yrs, undergoing URS or FURS for stones/diagnostic	<18 yrs, refusal
Chen YJ et al. (2024) [19]	China (Ganzhou People’s Hospital)	RCT, single center	76 (80 enrolled, 4 excluded)	A:0 mmHg (18) B:–5 mmHg (19) C:–10 mmHg (19)	D: uncontrolled (20)	47.5 (mean)	NR	15–17 mm	ASA I–II, ≥18 yrs, upper tract stones	Prior surgery, systemic disease, ethanol allergy, uncontrolled UTI, malpositioned UAS.
Deng et al. (2024) [14]	China	RCT, single center	73 (80 enrolled, 7 excluded)	A:–5 mmHg (19) B:0 mmHg (17) C:+5 mmHg (18)	D: uncontrolled (19)	46.5–49.5	38/35	15–17 mm	Stones <2 cm, age 18–70, elective FURS	Stricture, prior surgery, fibrosis, severe hydronephrosis, pregnancy, infection.
Bai et al. (2024) [10]	China (6-center Fujian cohort)	Retrospective multicenter	231(254 screened)	FANS- UAS: 231	–	Median 55 (21–80)	147/84	Median 26 mm (20–57)	Stones ≥2 cm, RIRS with FANS-UAS	Failed UAS, conversion to PCNL, contraindications.

Abbreviations: FURS = Flexible ureteroscopy; UAS = Ureteral access sheath; IRP = Intrarenal pressure; RCT = Randomized controlled trial; ASA = American Society of Anesthesiologists; PCNL = Percutaneous nephrolithotomy.

3.3. Meta-Analysis Results

Across the two randomized controlled trials that provided quantitative data, pressure-controlled ureteroscopic systems consistently demonstrated physiological advantages over standard UAS. Fluid absorption was significantly lower in the pressure-controlled groups, with the pooled estimate showing a reduction of −159.71 mL (95% CI −264.05 to −55.37; p = 0.003), as illustrated in Fig. (2). Similarly, operative time favored pressure-controlled techniques, with a combined mean difference of −22.93 minutes (95% CI −45.28 to −0.58; p = 0.04), despite substantial heterogeneity (I² = 77%; Fig. 3). These findings indicate that maintaining a fixed or negative renal pelvic pressure may enhance surgical efficiency and reduce fluid ingress during RIRS. In contrast, postoperative fever did not differ significantly between groups. The pooled risk difference was −0.05 (95% CI −0.18 to 0.08; p = 0.43), with moderate heterogeneity (I² = 47%; Fig. 4). This lack of statistical difference likely reflects the low incidence of infectious complications and limited sample sizes across studies. Overall, the meta-analysis supports the physiological benefits of pressure-modulating devices during ureteroscopy, while highlighting that their impact on short-term infectious outcomes remains inconclusive.

3.4. Risk of Bias

The risk of bias assessment indicated acceptable methodological quality across studies. The two RCTs (Chen YJ et al. 2024 [19]; Deng et al. 2024 [14]) were rated as having overall some concerns due to deviations from intended interventions and selective reporting, despite low risk in other domains (Fig. 5). The observational studies scored 7/9 (Bai et al. 2024) [10] and 8/9 (Croghan et al. 2022) [17] on the NOS, indicating low to moderate risk of bias Table 3.

Table 3.

Study	Representativeness of exposed cohort	Selectio n of non- exposed cohort	Ascertainment of exposure	Outcome not present at start	Comparability of cohorts	Assessment of outcome	Follow-up long enough	Adequacy of follow-up	Total (0–9)
Bai et al., (2024) [10]		–							7
Croghan et al., (2024) [17]									8

4. DISCUSSION

This review highlights the consistent association between Intrarenal Pressure (IRP) and perioperative outcomes in Ureteroscopy (URS) and Retrograde Intrarenal Surgery (RIRS). Across two Randomized Controlled Trials (RCTs) and two observational cohorts, pressure-controlled and suction-assisted Ureteral Access Sheaths (UAS) were consistently shown to reduce intrarenal pressure, limit irrigation fluid absorption, and shorten operative time while maintaining high Stone-Free Rates (SFR) [10, 20]. These findings are consistent with the hypothesis that elevated Renal Pelvic Pressure (RPP) promotes pyelovenous and pyelolymphatic backflow, potentially leading to infectious complications. Clinical studies have reported that postoperative fever occurs in approximately 4–8% of URS cases, while urosepsis develops in 0.5–5% of cases, depending on patient risk factors and intraoperative conditions [8, 21, 22].

The prospective study by Croghan et al. demonstrated that intraoperative IRP can peak at 334 mmHg, and that greater pressure variability was strongly associated with postoperative pyrexia and urosepsis [17]. Although elevated intrarenal pressure has been implicated in postoperative infectious events, an exact pressure threshold associated with these complications remains uncertain. Croghan et al. reported substantial variability in intraoperative pressure measurements, with peak values exceeding 300 mmHg in some cases. Notably, postoperative pyrexia and urosepsis appeared to be associated with greater pressure fluctuations rather than a distinct pressure cutoff. Consequently, current evidence supports strategies aimed at reducing pressure variability and avoiding excessive intrarenal pressure excursions during URS and RIRS [4, 16, 17, 23, 24].

Intrarenal pressure is also influenced by irrigation settings. Across the included studies, irrigation protocols ranged from gravity-assisted irrigation to automated pump systems delivering 50–150 mL/min, with or without suction-assisted outflow. Because irrigation flow rate, ureteroscope deflection, and ureteral access sheath characteristics all affect intrarenal pressure, direct comparison of absolute pressure values between studies remains challenging. Standardized irrigation protocols will be essential for defining clinically relevant pressure thresholds in future investigations [10, 14, 17, 25, 26].

In contrast, both Chen et al. and Deng et al. showed that negative or fixed RPP control significantly reduced fluid absorption and procedure duration without compromising SFR [14, 19]. Similarly, Bai et al. reported excellent stone clearance (>95% at 30 days) and minimal complication rates (1.7%) using a negative-pressure FANS-UAS system [10]. These data align with experimental studies that identified high pelvic pressures as a risk factor for infectious sequelae, although systematic reviews on this topic remain scarce and fragmented [3, 4, 25, 27].

The pooled analysis performed in this review supports these findings by demonstrating significant reductions in both irrigation fluid absorption and operative time. Pressure-controlled UAS significantly reduced fluid absorption (MD −159.71 mL, 95% CI −264.05 to −55.37) and shortened operative time (MD −22.93 minutes, 95% CI −45.28 to −0.58). However, postoperative fever did not differ significantly between groups (RD: −0.05; 95% CI: −0.18 to 0.08), likely due to the inherently low event rates and limited sample sizes. These results suggest that pressure modulation improves physiological and operative efficiency, although its impact on infectious outcomes may require larger populations to demonstrate statistical significance.

From a clinical standpoint, suction-enabled or pressure-regulated UAS represent a practical strategy to enhance safety in RIRS, as these systems stabilize RPP, minimize pressure spikes, and reduce the volume of absorbed irrigation fluid [10, 14, 17, 19]. Although infectious outcomes did not consistently reach statistical significance, this is plausibly attributed to underpowered sample sizes and the relatively low frequency of severe postoperative infections. In the absence of clear, evidence-based pressure thresholds, pressure-modulating systems may represent a useful strategy for improving intraoperative fluid dynamics, particularly in patients at increased risk of infectious complications. However, additional evidence is required before their routine adoption can be universally recommended. Current international guidelines (EAU, AUA) acknowledge the potential harms of elevated IRP but do not define safe pressure limits or recommend specific UAS technologies, underscoring the need for stronger clinical evidence [28, 29].

This review also reveals important knowledge gaps. Only four eligible studies were identified, resulting in limited statistical power despite the feasibility of pooled analyses for selected outcomes. The heterogeneity in devices (Storz, Olympus, PUSEN, and FANS-UAS), pressure-monitoring techniques (pressure guidewires, fiber-optic sensors, and ethanol-based absorption methods), and irrigation protocols limits the ability to define a universal safe intrarenal pressure threshold [10, 14, 17, 19, 27, 30]. Furthermore, all but one study were conducted in China, with a single European cohort, raising questions about the generalizability of the findings to other healthcare settings. None of the included studies evaluated patient-reported outcomes such as pain or quality of life, nor did they assess long-term renal function recovery. The economic impact of suction UAS and pressure-control platforms also remains unexplored. Future multicenter RCTs are needed to standardize IRP thresholds, harmonize clinical outcome definitions, evaluate cost-effectiveness, and incorporate patient-centered measures, while technological advancement should continue toward real-time IRP-guided surgical systems [20, 21, 31].

A specific limitation warranting explicit acknowledgment is the small number of eligible studies and the correspondingly limited statistical power of the pooled estimates. Only four studies met the inclusion criteria, and the quantitative synthesis for fluid absorption and operative time was derived from just two randomized controlled trials, while the risk-difference estimate for postoperative fever pooled data from a similarly small number of studies. With such small numbers of trials, the pooled effect estimates are inherently imprecise, as reflected in the wide confidence intervals accompanying each outcome (fluid absorption: 95% CI −264.05 to −55.37 mL; operative time: 95% CI −45.28 to −0.58 minutes; postoperative fever: 95% CI −0.18 to 0.08), and the analysis was not supported by a formal a priori power or sample-size calculation, which is a recognized constraint of meta-analyses conducted on emerging surgical technologies with few available trials [27, 30]. The non-significant result for postoperative fever most plausibly reflects a type II error arising from the low baseline event rate of infectious complications in URS/RIRS combined with the small pooled sample, rather than a true absence of effect, consistent with sample-size considerations raised in comparable meta-analyses of ureteral access sheath interventions [27, 30, 32]. Consequently, the findings on fluid absorption and operative time should be interpreted as indicative rather than definitive, and the fever outcome should be regarded as inconclusive because the review was underpowered to detect a clinically plausible reduction in infectious complications rather than because no such reduction exists. These considerations also limit the generalizability of the pooled estimates, since the included cohorts predominantly originated from single-center or regional settings; larger, adequately powered multicenter randomized trials with prespecified sample-size calculations are required before firm conclusions on infectious outcomes can be drawn.

CONCLUSION

This systematic review and meta-analysis demonstrate that pressure-controlled and suction-assisted ureteral access sheaths significantly reduce intrarenal fluid absorption and shorten operative time during URS/RIRS, while maintaining high procedural efficacy. Although postoperative fever did not differ significantly between pressure-controlled and standard systems, this likely reflects the low incidence of infectious complications and limited sample sizes across available studies. Collectively, the available evidence suggests that pressure modulation improves intraoperative fluid dynamics and procedural efficiency, although its impact on postoperative infectious complications remains uncertain. Larger multicenter randomized trials with standardized pressure metrics and patient-centered outcomes are needed to establish safe intrarenal pressure thresholds and inform future guideline recommendations.

References