Intrarenal pressure during endourologic stone surgery: A systematic review of measurement, clinical impact, and pressure-control strategies

Abstract

BACKGROUND

Intra-renal pressure (IRP) during endoscopic urological procedures, including flexible ureteroscopy (fURS), percutaneous nephrolithotomy (PCNL), and miniaturized PCNL, is increasingly recognized as a critical safety parameter. Elevated IRP may precipitate serious complications such as pyelovenous and pyelotubular backflow, urosepsis, forniceal rupture, and renal parenchymal injury. Although a general knowledge of increased intra renal pressure has been gaining prominence within urology there is no universal or acceptable standard for measuring IRP as well as safe pressure limits.

AIM

To systematically identify all available data on the measurement techniques of IRP, and all clinical outcomes that occur due to various degrees of pressure applied during an endourologic procedure, as well as complications that may arise when IRP reaches excessive levels.

METHODS

Using a systematic search, we searched PubMed/MEDLINE, EMBASE, Cochrane Library, and Scopus using the search terms listed above. Searches were limited to studies published through December 2025. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses 2020 guidelines were followed. Studies measuring IRP during any endourologic procedure of the upper urinary tract were eligible. Two independent reviewers screened the literature, extracted data and assessed the risk of bias utilizing the Cochrane Risk of Bias tool version 2, Newcastle-Ottawa Scale, Murad Tool, and a customized checklist for in vitro research. A narrative synthesis was performed, grouped by measurement techniques, pressure ranges, and clinical outcomes.

RESULTS

Twenty-nine studies met inclusion criteria. IRP during fURS without a ureteral access sheath (UAS) frequently exceeded 40 cmH₂O, with peak pressures reaching up to 437 cmH₂O in human in vivo studies. UAS placement significantly reduced IRP across all measured parameters. In mini-PCNL, pressures ranged from 2.4 cmH₂O to 39.7 cmH₂O, with optimized sheath designs achieving lower pressures. Pyelovenous backflow was demonstrated at pressures ≥ 90 mmHg and pyelotubular backflow at ≥ 60 mmHg in porcine models. The most feared complication was urosepsis, with clinical studies demonstrating significantly higher IRP in patients who developed postoperative urosepsis (81.7 mmHg vs 38.5 mmHg, P < 0.001). Emerging technologies include ureteroscopes with integrated pressure monitoring (e.g., LithoVue Elite) and novel non-invasive monitoring devices.

CONCLUSION

IRP monitoring during endourologic procedures is emerging as an essential component of patient safety. However, no universally agreed safe pressure threshold exists, and the commonly cited 30 mmHg limit is being challenged by newer evidence. Standardized measurement protocols, large prospective multicenter studies, and integration of real-time IRP monitoring into routine clinical practice are urgently needed.

Key Words: Intrarenal pressure; Endourology; Retrograde intrarenal surgery; Flexible ureteroscopy; Ureteral access sheath; Urolithiasis; Irrigation pressure; Suction ureteral access sheath; Mini-percutaneous nephrolithotomy; Pressure monitoring

Core Tip: Intrarenal pressure has emerged as a critical factor influencing infectious complications, pyelovenous backflow, and procedural safety during endourologic stone surgery. This systematic review summarizes current evidence regarding intrarenal pressure measurement techniques, clinically relevant pressure thresholds, and the impact of modern pressure-control strategies including ureteral access sheaths, suction-assisted systems, and mini-percutaneous nephrolithotomy technologies. The review also highlights emerging monitoring technologies and ongoing controversies regarding safe intrarenal pressure ranges during endourologic procedures.

INTRODUCTION

Urolithiasis is a highly prevalent condition affecting approximately 1%-15% of the global population, with recurrence rates exceeding 50% within 10 years of the initial episode[1,2]. The management of kidney stones has undergone a paradigm shift over the past three decades, transitioning from open surgical approaches to minimally invasive endourologic procedures. Flexible ureteroscopy (fURS), also termed retrograde intrarenal surgery (RIRS), and percutaneous nephrolithotomy (PCNL) in its various forms—standard, mini-PCNL, ultra-mini-PCNL, super-mini-PCNL, and micro-PCNL—constitute the backbone of contemporary stone management[3,4]. These procedures have demonstrated excellent stone-free rates with reduced morbidity compared with their open counterparts.

A fundamental requirement of all endourologic procedures of the upper urinary tract is continuous irrigation to maintain adequate visualization, facilitate stone fragment clearance, and cool the operative field during laser lithotripsy. However, the introduction of irrigation fluid into a semi-closed collecting system inevitably raises intra-renal pressure (IRP) above physiological levels[5]. Under normal conditions, IRP is negligible, ranging from 0 to a few cmH₂O[5,6]. During endoscopic procedures, however, IRP can rise dramatically depending on multiple variables, including irrigation method (gravity vs pressurized bag vs hand pump), flow rate, scope diameter relative to the ureteral lumen, presence or absence of a ureteral access sheath (UAS), use of working channel instruments, and individual patient anatomy[7].

The clinical significance of elevated IRP has been recognized since the pioneering observations by Hinman in 1926 and subsequent experimental work throughout the 20^th century. Elevated IRP may induce pyelovenous backflow—the passage of fluid and potentially bacteria from the renal pelvis into the venous system, which has been identified as a critical mechanism underlying post-procedural urosepsis[8]. Pyelovenous and pyelotubular backflow thresholds were reported in the range of 13.6 cmH₂O to 27.2 cmH₂O in a review conducted by Tokas et al[5], whereas pyelotubular backflow was shown to occur at pressures greater than or equal to 60 mmHg, and pyelovenous backflow at pressures greater than or equal to 90 mmHg in a porcine model[8]. In addition to infectious complications, chronic elevated IRP has also been implicated in forniceal and caliceal rupture, hemorrhage, post-operative pain, and potentially long term renal parenchymal damage[7-9]. Although there are numerous publications on IRP, there are still many issues. Different methods of measuring IRP exist across studies. These include, but are not limited to, pressure transducers attached to the nephrostomy tube or ureteral catheter, fiber-optic sensors, and new ureteroscopes equipped with built-in pressure sensors[10,11]. Due to the wide variety of measurement techniques used, it is difficult to compare the results directly. Additionally, there is no universally accepted “safe” level of IRP. Although a commonly cited limit of 30 mmHg (or approximately 40 cmH₂O) has been challenged by more recent evidence[12]. A recent consensus among international experts using the Delphi technique concluded that the majority of participants believed that IRP levels greater than 61-80 cmH₂O posed a significant risk. It was also determined that the primary safety concern of IRP levels was urosepsis, as stated by 96.2% of the participants[12] A systematic review regarding upper urinary tract pressures in endourology was published, identifying 52 studies and highlighting the substantial variability in reported IRP values[7]. The effects of endourologic procedures on both IRP and temperature were also reviewed[9]. Most recently, a scoping review regarding the current tools, instruments, and future directions for managing IRP during ureteroscopy was performed[13]. Since 2023, several developments have taken place, including the development of intelligent pressure sensing ureteroscopes, integrated pressure-sensing ureteroscopes and non-invasive monitoring methods, Delphi consensus statements, and other non-invasive methods of monitoring IRP.

This systematic review will provide a comprehensive, up-to-date overview of all of the currently available evidence on IRP in endourology, addressing the three main areas of: (1) The measurement techniques of IRP and how they have evolved over time; (2) The ranges of IRP reported during different endourological procedures and what factors contribute to these variations; and (3) Clinical outcomes and complications attributed to elevated IRP. By synthesizing the most recent literature through December 2025, this review will be able to guide clinicians and highlight critical knowledge gaps that require future research.

MATERIALS AND METHODS

Protocol

This systematic review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 statement[14]. The review protocol was developed prospectively but was not formally registered. A meta-analysis was initially planned; however, substantial clinical and methodological heterogeneity among included studies precluded quantitative synthesis, and a narrative review approach was therefore adopted.

Search strategy

A comprehensive electronic database search was completed across four databases. The time limit was set from inception till December 31, 2025. The researcher developed the search strategy. A combination of MeSH terms, Emtree terms, and free-text words were included. The complete search strategies for each database were as follows:

MEDLINE (via PubMed): ("intrarenal pressure"[tiab] OR "intra-renal pressure"[tiab] OR "renal pelvic pressure"[tiab] OR "intrapelvic pressure"[tiab] OR "renal pelvis pressure"[tiab] OR "pelvic pressure"[tiab] OR "collecting system pressure"[tiab]) AND ("endourology"[tiab] OR "ureteroscopy"[MeSH] OR "ureteroscopy"[tiab] OR "percutaneous nephrolithotomy"[tiab] OR "PCNL"[tiab] OR "nephrolithotomy, percutaneous"[MeSH] OR "ureterorenoscopy"[tiab] OR "retrograde intrarenal surgery"[tiab] OR "RIRS"[tiab] OR "flexible ureteroscopy"[tiab] OR "mini-PCNL"[tiab] OR "miniaturized percutaneous nephrolithotomy"[tiab] OR "mini-percutaneous nephrolithotomy"[tiab]).

EMBASE: ('intrarenal pressure': Ti,ab OR 'intra-renal pressure': Ti,ab OR 'renal pelvic pressure': Ti,ab OR 'intrapelvic pressure': Ti,ab OR 'renal pelvis pressure': Ti,ab) AND ('endourology'/exp OR 'ureteroscopy'/exp OR 'percutaneous nephrolithotomy'/exp OR 'percutaneous nephrolithotomy': Ti,ab OR 'PCNL': Ti,ab OR 'retrograde intrarenal surgery': Ti,ab OR 'ureterorenoscopy': Ti,ab OR 'flexible ureteroscopy': Ti,ab OR 'mini-percutaneous nephrolithotomy': Ti,ab).

Cochrane library: ("intrarenal pressure" OR "intra-renal pressure" OR "renal pelvic pressure" OR "intrapelvic pressure") AND (ureteroscopy OR "percutaneous nephrolithotomy" OR PCNL OR "retrograde intrarenal surgery" OR endourology).

Scopus: TITLE-ABS-KEY [("intrarenal pressure" OR "intra-renal pressure" OR "renal pelvic pressure" OR "intrapelvic pressure" OR "renal pelvis pressure") AND (endourology OR ureteroscopy OR "percutaneous nephrolithotomy" OR PCNL OR ureterorenoscopy OR "retrograde intrarenal surgery" OR "flexible ureteroscopy" OR "mini-PCNL")].

A manual screening of reference lists of all included studies and relevant review articles was performed to identify further eligible publications. During search phase, language restrictions were not applied. In the final analysis, only English-language articles were included. Lastly, a search of grey literature was also performed. It included conference abstracts from the European Association of Urology, American Urological Association, and Société Internationale d'Urologie.

Eligibility criteria

Inclusion criteria: (1) Original studies [randomized controlled trials (RCTs), prospective and retrospective cohort studies, case-control studies, cross-sectional studies, case series, and case reports] measuring IRP during any endourologic procedure of the upper urinary tract; (2) In vitro and in vivo (animal) experimental studies measuring IRP in endourologic models; (3) studies reporting IRP measurement techniques, IRP values during procedures, and/or clinical outcomes or complications associated with IRP levels.

Exclusion criteria: (1) Editorials, commentaries, and letters to the editor; (2) Narrative reviews lacking a systematic methodology; (3) Studies not measuring IRP or not involving endourologic procedures of the upper urinary tract; (4) Non-English language publications; (5) Duplicate publications reporting the same dataset.

Study selection

All retrieved records were imported into Covidence systematic review software (Veritas Health Innovation, Melbourne, Australia) for deduplication and screening. Two independent reviewers screened titles and abstracts against the eligibility criteria. Full texts of potentially eligible studies were subsequently retrieved and assessed independently by both reviewers. The study selection process is presented in the PRISMA 2020 flow diagram (Figure 1).

Figure 1 PRISMA 2020 flow diagram of study selection. Flow diagram illustrating the identification, screening, eligibility assessment, and inclusion of studies evaluating intrarenal pressure during endourologic stone surgery. Records were identified through searches of MEDLINE, EMBASE, Cochrane Library, Scopus, manual reference screening, and grey literature sources. The study selection process followed the PRISMA 2020 guidelines. IRP: Intra-renal pressure.

Data extraction

Data were extracted independently by two reviewers using a standardized, piloted data extraction form (Table 1). The following variables were collected: First author, publication year, country, study design, sample size (number of patients, kidneys, or experimental units), type of endourologic procedure, IRP measurement method (including sensor type and placement), irrigation parameters (method, flow rate, pressure), mean and/or peak IRP values reported, use of UAS or suction sheaths, clinical outcomes (stone-free rate, operative time) and follow-up durations. No included studies reported bleeding, forniceal rupture, postoperative pain, or long-term renal injury in relation to IRP.

Table 1 Data extraction summary of included studies.

Ref.	Study design	n	Procedure	IRP measurement method	Key IRP findings
Auge et al[17], 2004	Prospective clinical	5 patients	fURS ± UAS	Nephrostomy tube + pressure transducer	Without UAS: 94.4 mmHg; with UAS: 40.6 mmHg
Nagele et al[18], 2007	In vitro (porcine)	Porcine kidneys	Mini-PCNL	Urodynamic workstation	Conventional sheath: 136 cmH2O; new sheath: 20 cmH2O
Jung et al[19], 2008	RCT	12 patients	fURS	Ureteral catheter + pressure transducer	Saline: 33 ± 12 mmHg; ISO: 19 ± 3 mmHg; peak: 328 mmHg
John et al[33], 2024	In vivo porcine	17 renal units	fURS	Pressure-sensing guidewire	Mean IRP reduction: 29% (95%CI: 13%-53%)
Hong et al[8], 2023	Ex vivo porcine	21 renal units	fURS	Pressure-sensing wire	Pyelotubular: ≥ 60 mmHg; pyelovenous: ≥ 90 mmHg
Doizi et al[23], 2021	In vitro (silicone model)	Kidney model	fURS, mini-PCNL, PCNL	Pressure transducer	fURS: 1.4-46.2 cmH2O; mini-PCNL: 2.4-39.7 cmH2O; PCNL: 1.4-7.3 cmH2O
Patel et al[22], 2020	Prospective clinical	8 patients (45 calyces)	fURS	Cardiac pressure guidewire	12/14 Fr UAS lower pole: 49.2 ± 40.3 mmHg; 14/16 Fr: 16.2 ± 3.5 mmHg (P = 0.004)
Lazarus et al[26], 2022	In vitro (phantom kidney)	Phantom model	fURS	Fiber-optic pressure sensing	Traditional 11/13 Fr: 20 mmHg; 12/14 Fr: 13 mmHg; novel UAS: 0 mmHg
Doizi et al[21], 2020	Prospective pilot	4 patients (5 procedures)	fURS	Digital pressure sensor wire	Baseline: 6 cmH2O; f-URS: 63 cmH2O; laser mean: 115.3 cmH2O; peaks: 289-437 cmH2O
Sierra et al[27], 2022	Prospective pilot	20 patients	fURS	Vascular PressureWire	Baseline: 13.6 cmH2O; laser + forced irrigation: 61.2 cmH2O; UTI: 15%
Jung and Osther[20], 2015	Prospective clinical	12 patients	fURS	Ureteral catheter + pressure transducer	Baseline: 10 ± 4 mmHg; stone management: 54 ± 18 mmHg; peaks: 328 mmHg
Bhojani et al[28], 2023	Retrospective observational	50 patients	fURS	LithoVue Elite (integrated sensor)	Median IRP: 28.5 mmHg; max: 174 mmHg; < 60 mmHg for 92% of time
Chew et al[11], 2023	In vivo porcine + bench validation	Porcine + bench	fURS	LithoVue Elite (integrated sensor)	No UAS: 64 mmHg; 11/13 Fr: 51 mmHg; 12/14 Fr: 39-40 mmHg; accuracy: 96%
Croghan et al[29], 2023	Prospective multi-institutional	120 patients	fURS + semi-rigid URS	COMET II pressure guidewire	Baseline: 16.45 ± 5.99 mmHg; urosepsis IRP: 81.7 ± 49.52 vs controls 38.53 ± 22.6 (P < 0.001)
Yekani et al[32], 2023	Prospective pilot	10 patients	fURS	Not specified (syphon UAS study)	Without syphon: Baseline 29 mmHg, peak bolus 104 mmHg; with syphon: Baseline 18 mmHg (P < 0.001), peak bolus 71 mmHg (P = 0.03)
Gadzhiev et al[38], 2025	In vitro (cadaveric porcine)	Porcine kidneys	fURS	Pressure transducer via ureteral catheter	FANS + suction: 1.7 ± 0.6 cmH2O; conventional UAS + machine irrigation: 39.6 ± 0.8 cmH2O
Croghan et al[36], 2024	RCT	34 patients	fURS	COMET II pressure guidewire	PB mean: 38.16 ± 16.84 mmHg; HP mean: 62.29 ± 27.45 mmHg (P = 0.005); PB max: 68.04 mmHg; HP max: 192.71 mmHg (P < 0.001)
Chen et al[37], 2025	Retrospective observational	25 patients	fURS	LithoVue Elite (integrated sensor)	Median IRP: 22.0 (15.0-36.5) mmHg; < 60 mmHg for 94.1% of time
Zhu et al[43], 2025	Prospective clinical trial	100 patients	fURS	FANS with IRP monitoring	IRP within 30 mmHg; operative time: 50.9 minutes vs 67.6 minutes (P < 0.01)
Yuen et al[42], 2025	In vitro comparative validation	Bench model	fURS	Urodynamic system (gold standard)	LithoVue Elite: 0.26 ± 1.75 mmHg difference; ICC 0.975; all devices ICC > 0.915
Kayano et al[39], 2025	Retrospective two-center	30 patients	fURS	LithoVue Elite (integrated sensor)	% time > 30 mmHg: 3.31%; > 40 mmHg: 0.01%; 0% febrile UTI
Vergamini et al[35], 2024	Ex vivo porcine	252 experiments	fURS	LithoVue Elite (integrated sensor)	SAPS higher IRP/FR than pumps (P < 0.01); larger UAS → lower IRP (P < 0.01); rho > 0.9
Omar et al[40], 2025	In vitro bench-top validation	30 paired measurements	fURS	Handheld meter vs sphygmomanometer	Mean bias: 0.02 ± 0.35 mmHg; 95% limits: -0.664 to +0.704 mmHg; P = 0.756
Han et al[30], 2023	Ex vivo porcine	11 kidneys	fURS	6F pressure catheters (upper/lower calyces)	cUAS: IRP 30 mmHg at 60-70 cc/minute; vaUAS: IRP < 10 mmHg up to 120 cc/minute; Backflow at 40 mmHg
Ostergar et al[31], 2023	Ex vivo porcine	3 kidneys	fURS	Percutaneous catheter	IRP drop: 42.30→24.45 mmHg with suction (P < 0.0001); paradoxical increase > 5 sec at > 200 mmHg
MacCraith et al[25], 2021	Ex vivo porcine	Porcine kidneys	fURS	Pressure measurement system	12/14F UAS: 16.45 ± 5.3 cmH2O; 11/13 F: 32.73 ± 35.66 cmH2O (P = 0.006); safest: 11.6 ± 3.65 cmH2O; most dangerous: 100.6 ± 16.1 cmH2O
Lazarus et al[24], 2021	Ex vivo porcine (cadaveric)	Porcine model	fURS	Arterial invasive pressure system	With UAS: Bolus < 5 mL safe; without UAS: 2 mL bolus unsafe; 10/12 Fr UAS inadequate drainage
Samaras et al[34], 2024	In vivo porcine	3 pigs	fURS	ZebraScope (integrated sensor)	No UAS: 28.25 ± 11.2 mmHg to 35.46 ± 10.08 mmHg; 12/14 Fr UAS: 7.64 ± 3.08 mmHg to 9.25 ± 1.42 mmHg
Tanaka et al[41], 2025	Ex vivo porcine	Porcine kidneys	fURS	LithoVue Elite vs PNC (gold standard)	11/13 Fr UAS: < 30 mmHg all settings; 10/12 Fr UAS: HP > 100 mmHg; LVE accurate vs PNC (P > 0.05 for calyces)

IRP: Intrarenal pressure; fURS: Flexible ureteroscopy; UAS: Ureteral access sheath; RCT: Randomized controlled trial; PCNL: Percutaneous nephrolithotomy; Mini-PCNL: Mini-percutaneous nephrolithotomy; FANS: Flexible and Navigable Suction Ureteral Access Sheath; UTI: Urinary tract infection; ISO: Isoproterenol; ICC: Intraclass correlation coefficient; PNC: Percutaneous nephrostomy catheter; SAPS: Sterile automated pressure system; FR: Flow rate; HP: Hand-pump irrigation; PB: Pressurized-bag irrigation.

Risk of bias assessment

Two reviewers independently assessed the risk of bias. Validated tools appropriate to each study design were employed. The Cochrane Risk of Bias 2 tool was used to appraise RCTs across five domains. These include randomization process, deviations from intended interventions, missing data for outcomes, measurement of outcomes, and selection of results to be reported[15]. The Newcastle-Ottawa Scale (NOS) was used to assess the quality of non-randomized comparative studies. Studies that scored 7 or greater out of 9 stars on the NOS were considered to have high quality[16]. No case reports or case series met the inclusion criteria. The in vitro and ex vivo experimental study design and data quality were evaluated by using a checklist that included standardized experimental model, instrument calibration, blinding, reproducibility, and completeness of reporting (Table 2).

Table 2 Risk of bias assessment of included studies.

Study type	Tool used	Overall assessment
RCTs (Jung et al[19], 2008, Croghan et al[36], 2024)	ROB 2	Low-moderate risk
Prospective clinical studies	Newcastle-Ottawa Scale	Moderate-high quality
Retrospective studies	Newcastle-Ottawa Scale	Moderate quality
Animal studies	Customized checklist	Moderate risk
In vitro studies	Customized checklist	Low-moderate risk
Validation studies	Customized checklist	Low risk

RCTs: Randomized controlled trials; ROB 2: Cochrane Risk of Bias tool version 2.

Data synthesis

Due to the variety in the study designs used in this research, as well as the methods of measuring the variables involved in the research, as well as the experimental conditions under which the studies took place and the results that each researcher chose to report, a qualitative narrative synthesis was chosen to be the primary method by which the researchers combined their study data. The data collected from all of the studies in this systematic review were organized and then synthesized into these three themes: (1) Measurement techniques for IRP; (2) Range of IRP values measured during different procedures & factors influencing IRP; and (3) Clinical outcomes and complications that can occur with elevated IRP.

Meta-analysis could not be conducted because there were such large amounts of heterogeneity among the studies on how they measured their variable(s), what types of pressures they measured using (e.g., millimeters of mercury vs. centimeters of water), and what type of outcome measures were reported.

RESULTS

To facilitate comparison across studies, pressure values were reported in their original units. Where relevant, conversion between units was considered using the relationship 1 mmHg = 1.36 cmH₂O.

Study selection

The systematic search identified 1247 records across the four databases. It included 498, 389, 87, and 273 from MEDLINE, EMBASE, Cochrane Library, and Scopus. 412 duplicate records were found. After their removal, the title and abstracts of 835 unique records were screened. Then, 689 were excluded as they were not relevant to the research question. Then, 146 full-text articles were assessed for eligibility. Following full-text review, 117 articles were excluded for the following reasons: Not measuring IRP (n = 34), not involving endourologic procedures of the upper tract (n = 22), review articles without original data (n = 15), non-English language (n = 8), editorials or letters without data (n = 6), and duplicate datasets (n = 32). Ultimately, 29 studies met all inclusion criteria and were included in the qualitative synthesis.

Study characteristics

The included studies were published between 2004 and 2025. A notable increase in publication frequency was seen since 2018, with 18 of 29 studies (62%) published between 2023 and 2025, reflecting growing interest in IRP research. For reporting purposes, studies were categorized into six predefined groups: Randomized controlled trials, prospective clinical studies, retrospective observational studies, in vitro/ex vivo experimental studies, in vivo animal studies, and validation studies evaluating pressure-monitoring technologies.

The 29 included studies are summarized in Table 1[17-43]. Study designs comprised 5 prospective clinical studies[17,21,27,32,43], 11 in vitro or ex vivo experimental studies[18,23,25,26,30,31,35,38,40-42], 2 randomized controlled trials[19,36], 3 validation studies[20,22,24], 4 retrospective observational studies[28,29,37,39], and 4 in vivo animal studies[8,11,33,34]. The total number of human participants across clinical studies was approximately 430 patients, with individual study sample sizes ranging from 4 to 120. The endourologic procedures studied focused primarily on fURS/RIRS, which was the subject of 24 studies. One study included semi-rigid ureteroscopy data[29]. Standard PCNL was examined in one study[23]. Mini-PCNL was examined in two studies[18,23]. Several studies compared multiple techniques within the same experiment[23,25,35].

Measurement techniques

Over the course of the four-decade study period, the development of IRP measurement techniques was characterized by the increasing sophistication and miniaturization of pressure-sensing technologies[11,17-19,21,22,28,34,42].

Pressure transducers via nephrostomy tubes or ureteral catheters: This technique is now accepted as the gold standard for measuring intrarenal pressures[41-43]. It involves attaching an external pressure sensor to a nephrostomy tube, an antegrade ureteral catheter, or a retrograde catheter that is positioned in the renal pelvis[17,19,20]. It is also important to note that this technique produces reliable real-time pressure readings[17,19,20,22,31].

However, this technique may be limited by the fact that it requires either an existing nephrostomy tract, or the placement of an additional catheter along with the endoscope[17,41]. In doing so, the additional catheter could alter the pressures being measured by occupying space within the ureteral lumen[11,25,41].

Novel ureteroscopes with integrated pressure sensing: A significant advancement was the testing of an innovative flexible ureteroscope equipped with integrated pressure-sensing functionalities[11,28,34,41,42]. The LithoVue Elite system (Boston Scientific) features a pressure sensor at the tip of the ureteroscope, facilitating continuous, real-time intrarenal pressure monitoring without requiring supplementary catheters or sensors[11].

This technology eliminates confounding effect of putting in extra catheters and is a big step toward making IRP monitoring work smoothly in clinical settings[11,28,41].

Non-invasive monitoring devices: A recent 2025 study detailed innovative non-IRP monitoring devices, potentially obviating the necessity for any intracorporeal sensor placement[42]. This approach is still in its early stages, but it could entirely change IRP monitoring from a research tool to a normal part of clinical practice[11,28,42].

IRP ranges during procedures

Different studies reported varying IRP values[11,17-19,21,22,28,29,34,41]. This shows differences in measurement techniques, experimental conditions, irrigation parameters, and patient or model characteristics[19,20,23,25,35,36]. The following ranges were identified for each procedure type, pressure-monitoring technology, clinical outcomes, and pressure-mitigation strategies:

Normal physiological IRP: Under resting conditions, IRP in the non-obstructed collecting system is negligible, ranging from 0 to a few cmH₂O (0 to approximately 5 cmH₂O)[20,21,29]. This serves as the baseline against which procedural IRP elevations are measured[17,19,27].

Flexible ureteroscopy without UAS: URS without a UAS consistently generated the highest IRP values reported in the literature[11,17,25]. A mean IRP of 49.5 ± 29.36 cmH₂O during fURS without a UAS was reported[25]. In human studies, peak pressures have reached 289-437 cmH₂O, which shows how high transient pressure spikes can get[19-21,29]. The mean IRP values varied from 47.6 cmH₂O to more than 200 cmH₂O, depending on the method of irrigation[21,25,29]. Pressurized irrigation always produced higher pressures than gravity-feed systems[21,27,35,36].

Flexible ureteroscopy with UAS: In all studies that looked at this variable, putting a UAS in place consistently and significantly lowered IRP during fURS[11,17,25]. Mean IRP decreased from > 94 mmHg to approximately 40 mmHg with UAS placement during fURS[17]. The amount of IRP reduction depended on the inner diameter of the UAS[11,22,25,41]. Bigger sheaths provided more decompression[11,22,25]. However, even with UAS, IRP could transiently exceed proposed safety thresholds during active irrigation or when the UAS became partially obstructed[29,31,41].

Standard PCNL: IRP during standard PCNL was generally lower than during URS, ranging from 1.4 cmH₂O to 7.3 cmH₂O[23]. The large caliber Amplatz sheath used in standard PCNL provides effective decompression of the collecting system, allowing free egress of irrigation fluid around the nephroscope[23]. Optimized sheath design significantly decreased IRP during PCNL procedures[18].

Mini-PCNL and variants: IRP during miniaturized PCNL variants showed greater variability than during standard PCNL due to the smaller tract size and reduced outflow capacity. IPP values ranging from 2.4 cmH₂O to 39.7 cmH₂O during mini-PCNL in a kidney model were reported, compared to 1.4 cmH₂O to 7.3 cmH₂O for standard PCNL[23]. An optimized sheath design for mini-PCNL significantly reduced IRP from 136 cmH₂O (conventional sheath) to 20 cmH₂O (new sheath)[18].

Factors influencing IRP: Multiple variables were identified as significant determinants of IRP across studies[11,17,25,35,36]: (1) Irrigation method—pressurized bag and hand pump irrigation generated significantly higher pressures than gravity-feed systems[21,27,36]; (2) Irrigation flow rate—higher flow rates correlated with higher IRP[35,30]; (3) UAS presence and size—larger inner diameter UAS provided greater IRP reduction[11,22,25]; (4) Scope diameter relative to ureteral lumen—larger scopes relative to the ureter created greater resistance to outflow[25,41]; (5) Working channel accessories—insertion of laser fibers, baskets, or guidewires through the working channel reduced irrigation flow and consequently lowered IRP[11,23,34]; and (6) Patient anatomy—ureteral strictures, tortuous ureters, and stone-related obstruction all elevated IRP[28,29,37].

Clinical outcomes and complications

The correlation between increased IRP and negative clinical outcomes was examined from various perspectives:

Pyelotubular and pyelovenous backflow: A study utilizing a porcine model effectively illustrated the pressure-dependent characteristics of fluid backflow from the renal pelvis. Pyelotubular backflow, representing fluid passage from the collecting system into the renal tubular system, was observed at IRP levels ≥ 60 mmHg. Pyelovenous backflow, the more clinically consequential pathway whereby bacteria-laden irrigation fluid enters the venous circulation, occurred at IRP ≥ 90 mmHg. At 200 mmHg, ink staining was observed in supportive tissue, venous tributaries in the sinus fat, peritubular capillaries, and glomerular capillaries, illustrating the progressive tissue penetration with increasing pressure. This study provided essential mechanistic evidence connecting elevated IRP to systemic infectious complications[8].

Urosepsis: Urosepsis was seen as the most feared complication linked to increased IRP. The mechanism linking IRP to urosepsis is now well-established: Elevated pressure drives bacterial translocation from infected or colonized urine into the renal venous system via pyelovenous backflow, producing bacteremia and potentially septic shock[8]. Several clinical studies reported associations between higher intraoperative IRP and increased rates of postoperative urosepsis[27,29], although prospective controlled data in humans remain limited.

Strategies to Mitigate Elevated IRP

The included studies identified several strategies to reduce or control IRP during endourologic procedures:

UAS: The most extensively studied IRP mitigation strategy, UAS placement consistently reduced IRP during fURS by providing a low-resistance outflow pathway for irrigation fluid alongside the ureteroscope[11,17,25]. Efficacy of IRP reduction was contingent upon inner diameter of UAS, with 12/14 Fr and larger sheaths yielding enhanced decompression[11,17,22,25].

Suction sheaths and vacuum-assisted systems: In flexible ureteroscopy, active aspiration suction sheaths gave excellent control over IRP[31,37,38,43]. FANS (flexible and navigable suction UAS) with machine irrigation and suction achieved the lowest IRP among all conditions tested (1.7 ± 0.6 cmH₂O)[38]. Vacuum-assisted UAS reduced IRP from 42.30 mmHg to 24.45 mmHg with suction activation (P < 0.0001)[31]. IRP was maintained within 30 mmHg using FANS in a prospective clinical trial of 100 patients, with significantly reduced operative time (50.9 minutes vs 67.6 minutes, P < 0.01)[43]. A median IRP of 22.0 mmHg with FANS was reported, with IRP remaining below 60 mmHg for 94.1% of procedure time[37]. These findings demonstrate that suction sheaths provide effective IRP control during fURS.

Limiting irrigation pressure and flow: Studies in this review consistently demonstrated that hand pumps and SAPS irrigation generate significantly higher IRP than gravity-feed or automated pump systems[25,27,35,36]. Forced on-demand irrigation produced mean IRP of 115.3 cmH₂O with peaks of 289-437 cmH₂O, compared to 63 cmH₂O without forced irrigation, supporting the principle of using the minimum irrigation necessary to maintain adequate visualization[21].

DISCUSSION

This systematic review offers an extensive synthesis of the existing evidence on IRP in endourology, incorporating 29 studies published between 2004 and 2025[11,17-19,21,22,28,29,34,41]. The results highlight the significant advancements in comprehending IRP dynamics[8,31,38] and the considerable deficiencies that persist in applying this knowledge to standardized clinical practice[29,28].

A principal conclusion of this review is the remarkable variability in IRP measurement methodologies among studies[11,17,19,22,42]. The field has seen a lot of technological progress, from pressure transducers connected to nephrostomy tubes[17] to pressure guidewires[21,22,27] and integrated ureteroscope-based monitoring[11,28,34,41,42]. But this wide range of methods makes it challenging to compare studies. It is not possible to directly compare IRP values recorded with different sensor types, at different anatomical positions, and under different irrigation conditions[25,35,36]. This makes meta-analysis impractical for most outcomes. In this field, standardizing measurement protocols is likely the most crucial task.

No one knows what a “safe” IRP threshold is yet. The often-cited limit of 30 mmHg (about 40 cmH₂O), which comes mostly from animal experiments and theoretical ideas, has been a useful clinical guide for many years. Recent evidence, however, calls this threshold into question on several levels. Pyelotubular backflow occurs at IRP levels ≥ 60 mmHg and pyelovenous backflow at ≥ 90 mmHg, both significantly higher than the conventional threshold[8]. Patients who developed postoperative urosepsis had a mean IRP of 81.7 mmHg during surgery, compared to 38.5 mmHg in patients who did not develop urosepsis (P < 0.001)[29]. These results indicate that the safe pressure threshold may be contingent upon various factors, including the existence of infection[29], individual patient anatomy[28,37], and UAS size and placement[11,25,41].

This field has undergone technological progress. The advent of ureteroscopes equipped with integrated pressure sensors (e.g., LithoVue Elite) is poised to facilitate IRP monitoring as a standard aspect of routine ureteroscopy, thereby removing the logistical and technical obstacles that have previously restricted IRP measurement to research environments[11,28]. Non-invasive monitoring devices, although still in the nascent stages of development, have the potential to enhance the accessibility of IRP monitoring[42].

Notwithstanding these advancements, a significant deficiency remains: The absence of extensive, prospective, multicenter clinical studies directly linking intraoperative IRP levels with patient-centered outcomes. Most of the IRP data in this review comes from in vitro models, ex vivo experiments, animal studies, and small clinical series (11 in vitro/ex vivo studies, 4 animal studies, and 9 small clinical series). Although these studies have been instrumental in elucidating the fundamental science of IRP dynamics[8,31,38], they cannot replace substantial clinical evidence. Prospective human studies remain a priority research direction.

Strengths and limitations

This systematic review has several strengths. It offers the most thorough and current compilation of IRP evidence in endourology, including studies up to December 2025 and reflecting the major technological and conceptual progress made in recent years[11,17-19,21,22,28,34,42]. The systematic methodology, extensive multi-database search, independent dual screening and extraction, and stringent risk of bias evaluation, conforms to the utmost standards of evidence synthesis.

There are several limits to this study. First, there was too much variability among study designs, measurement tools, and reporting[19,20,23,25,35,36]. Thus, most of the outcomes studied did not allow for a formal meta-analysis. Second, publication bias is an issue with these data since those studies showing significant (or extreme) findings on IRPs would likely have received more attention from publishers. Third, many of the studies selected to include in this review had relatively small samples which limit their applicability (17 - n = 5; 21 - n = 4; 32 - n = 10; 39 - n = 30). Fourth, restricting the literature search to studies written in English may have excluded studies done in other languages. Fifth, the rapid changes in technology mean that some older studies will reflect methods that are no longer clinically applicable[17]. Conversely, the newer technologies have not yet been validated over time[11,42].

Future directions

Based on the findings of this review, several priority research directions are identified: (1) Large, prospective, multicenter studies directly correlating real-time IRP measurements with postoperative infectious, hemorrhagic, and pain outcomes[27,29]; (2) Development and adoption of standardized IRP measurement protocols to enable valid cross-study comparisons[25,35,36]; (3) Validation of pressure-dependent backflow thresholds in human subjects[8]; (4) Long-term follow-up studies assessing the impact of intraoperative IRP on renal function preservation; (5) Clinical trials evaluating the impact of real-time IRP monitoring and automated pressure management on complication rates[11,28]; and (6) Cost-effectiveness analyses of routine IRP monitoring during endourologic procedures[40].

CONCLUSION

The IRP associated with endourology has many factors which contribute to its variability and dynamic nature and can directly affect patient safety. A systematic review of 29 studies was conducted to examine how often IRP exceeded recommended limits during typical endoscopic procedures; these pressures were most elevated when performing flexible ureteroscopy without a UAS. Pressure-dependent mechanisms such as pyelovenous and pyelotubular backflow are the primary mechanism by which endourologic-induced urosepsis and other systemic complications occur. Technology developments such as integrated pressure-sensing ureteroscopes may facilitate broader clinical adoption of real-time IRP monitoring in the future. No standardized definition of “safe” pressure level currently exists. The 30 mmHg limit on pressure referenced in literature is being challenged; there is very little clinical data available that correlates IRP levels with patient outcomes. Thus, there is an urgent need for standardization of methods for measuring IRP, multicenter prospective studies correlating specific levels of IRP with patient outcomes, and incorporation of real-time IRP monitoring into selected endourologic procedures may improve patient safety and warrants further evaluation in prospective studies.