Fluid-electrolyte and renal pelvic pressure changes during ureteroscopic lithotripsy

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.

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.

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.

Comparison of intrarenal pressure between convention and vacuum-assisted ureteral access sheath using an ex vivo porcine kidney model

OBJECTIVE

This study aimed to prove the vacuum-assisted ureteral access sheath (vaUAS) is more effective in maintaining a lower IRP than conventional ureteral access sheath (cUAS).

MATERIALS

The model consisted of 12 freshly harvested adult porcine kidneys.

METHODS

Either a 12/14F cUAS or vaUAS was alternately inserted into the ureter to one cm below the renal pelvis. Upper, middle, and lower calyces were punctured, and 6F pressure monitor catheters were introduced. IRP with cUAS was monitored using various irrigation rates. IRP with vaUAS was monitored with the same irrigation rates; various aspiration pressures; and vent fully closed, 50% closed, and fully open.

RESULTS

cUAS with irrigation rate of 50 cc/min resulted in IRP < 30 mmHg. 50 to 100 cc/min should be used with caution. When irrigation rate exceeded 100 cc/min, IRP rose to ≥ 30 mmHg in most instances. With vent closed, vaUAS with vacuum pressure ≥ 150 mmHg and irrigation rate of 50 cc, 100 cc, and 150 cc/min generally resulted in IRPs < 5 mmHg. With vent half closed, vaUAS with vacuum pressure ≥ 300 mmHg and irrigation rate of ≤ 100 cc/min avoided IRP > 30 mmHg. vaUAS with vent open showed limited advantages over cUAS.

CONCLUSION

vaUAS maintains lower IRP than cUAS under same parameters. Both vaUAS and cUAS can be used when irrigation is ≤ 50 cc/min vaUAS showed clear advantages over cUAS in maintaining lower pressure when irrigation rate is ≥ 100 cc/min.

Comparison of intrarenal pressure between convention and vacuum-assisted ureteral access sheath using an ex vivo porcine kidney model

OBJECTIVE

This study aimed to prove the vacuum-assisted ureteral access sheath (vaUAS) is more effective in maintaining a lower IRP than conventional ureteral access sheath (cUAS).

MATERIALS

The model consisted of 12 freshly harvested adult porcine kidneys.

METHODS

Either a 12/14F cUAS or vaUAS was alternately inserted into the ureter to one cm below the renal pelvis. Upper, middle, and lower calyces were punctured, and 6F pressure monitor catheters were introduced. IRP with cUAS was monitored using various irrigation rates. IRP with vaUAS was monitored with the same irrigation rates; various aspiration pressures; and vent fully closed, 50% closed, and fully open.

RESULTS

cUAS with irrigation rate of 50 cc/min resulted in IRP < 30 mmHg. 50 to 100 cc/min should be used with caution. When irrigation rate exceeded 100 cc/min, IRP rose to ≥ 30 mmHg in most instances. With vent closed, vaUAS with vacuum pressure ≥ 150 mmHg and irrigation rate of 50 cc, 100 cc, and 150 cc/min generally resulted in IRPs < 5 mmHg. With vent half closed, vaUAS with vacuum pressure ≥ 300 mmHg and irrigation rate of ≤ 100 cc/min avoided IRP > 30 mmHg. vaUAS with vent open showed limited advantages over cUAS.

CONCLUSION

vaUAS maintains lower IRP than cUAS under same parameters. Both vaUAS and cUAS can be used when irrigation is ≤ 50 cc/min vaUAS showed clear advantages over cUAS in maintaining lower pressure when irrigation rate is ≥ 100 cc/min.

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.

Can Urinary KIM-1 and NGAL Predict Management Endoscopic Surgery in Acute Unilateral Obstructive Stone Disease? Results from a Prospective Cohort Study

INTRODUCTION

Kidney injury molecule-1 (KIM-1) and neutrophil gelatinase-associated lipocalin (NGAL) are the leading novel biomarkers used efficiently in acute kidney injury (AKI). The levels of these biomarkers increase especially in the early period of nephrotoxic and ischemic renal damage. In this study, we aimed to investigate the clinical importance of NGAL and KIM-1 biomarkers used in the effective evaluation of kidney functions in patients with acute unilateral obstructive stone disease (AUOSD) in the management of endoscopic surgery.

MATERIALS AND METHODS

We prospectively included patients who underwent endoscopic surgery due to AUOSD between January 2018 and December 2019. Urine KIM-1 and NGAL values of the patients were measured preoperative period, postoperative 4th h, and postoperative 7th day. The patients were evaluated according to the location and size of the stone, the degree of renal hydronephrosis, the duration of the operation, complications, and JJ stent placement.

RESULTS

The study enrolled 50 patients. Urinary KIM-1/Cr and urinary NGAL/Cr ratios were higher in postoperative 4th h than in others (p < 0.001). Also, we found that urinary KIM-1/Cr and urinary NGAL/Cr ratios with Grade 2 and higher hydronephrosis were statistically higher than Grade 0-1 hydronephrosis (p < 0.001 and p: 0.042, respectively). Additionally, a preoperative urinary KIM-1 value of 1.24 ng/mL had a sensitivity of 78% and a specificity of 63% to predict the presence of hydronephrosis. When urine KIM-1 and NGAL results were compared with surgery time, stone size and location, serum creatinine (sCr) value, and Post-Ureteroscopic Lesion Scale grade, the difference was not statistically significant. Postoperative 7th day NGAL/Cr and KIM-1/Cr ratios were statistically higher in those with JJ stents placed (p: 0.03 and p: 0.004, respectively).

CONCLUSION

KIM-1 and NGAL can be used in our assessment of renal function in patients with AUOSD, even if sCr is normal. Also, these biomarkers can predict the presence of hydronephrosis. It can be helpful in determining the time of surgical treatment, as well as providing information in the follow-up of patients with JJ stents after treatment.

A simple fluid dynamic model of renal pelvis pressures during ureteroscopic kidney stone treatment

Ureteroscopy is an endoscopic kidney stone removal procedure which increases the internal pressure in the renal pelvis, the kidney's urinary collecting system. Elevated renal pelvic pressure may result in systemic absorption of irrigation fluid and urine, which can increase the risk of postoperative fever and sepsis. Urologists have investigated the effects of various surgical parameters on the renal pelvic pressure. However, it still remains unknown which surgical parameter has the most dominant effect on the renal pelvic pressure over time. Here we develop a physical model that computes the renal pelvic pressure as a function of time based on parameters that can be varied during ureteroscopy. The model is developed by applying pipe network analysis to the regions of the urinary tract that are involved in a representative ureteroscopic procedure. Our model unifies the findings of the previously published studies on this topic; an ex-vivo porcine study and an in-vivo human study. Furthermore it allows simulation of surgical procedures based on various techniques. Our simulation demonstrates that the two strong regulators of renal pelvis pressure during ureteroscopy are the size of the gap between ureteroscope and ureteral access sheath and the frequency and duration of ureteroscope withdrawal.

Pressure matters 2: intrarenal pressure ranges during upper-tract endourological procedures

PURPOSE

To perform a review on the latest evidence related to intrarenal pressures (IRPs) generated during upper-tract endourology, and present different tools to maintain decreased values, to decrease complication rates.

METHODS

A literature search was performed using PubMed, restricted to original English-written articles, including animal, artificial model and human studies. Different keywords were: percutaneous nephrolithotomy, PCNL, ureteroscopy, URS, RIRS, irrigation flow, irrigation pressure, intrarenal pressure, intrapelvic pressure and renal-pelvic pressure.

RESULTS

IRPs reported during retrograde intrarenal surgery (RIRS), PCNL, miniPCNL, and microPCNL range 40.8-199.35, 3-40.8, 10-45 and 15.37-41.21 cm H₂O, respectively. By utilizing ureteral access sheaths (UASs) IRPs usually remain lower than 30 cm H₂O at an irrigation pressure (IP) of ≤ 100 cm H₂O but could increase to > 40 cm H₂O at an IP of 200 cm H₂O. By utilizing the minimally invasive PCNL system, IRPs remain low at 20 cm H₂O even at high IPs. Utilizing endoluminal isoproterenol during RIRS, could reduce IRP increases with a rate of 27-107%, and maintain low IRPs values, usually below 50 cm H₂O.

CONCLUSIONS

Increased IRP values have been reported during RIRS and UASs constitute the most efficient tool for decreasing them. IRPs during mini-PCNL can be decreased utilizing the vacuum-cleaner and purging effects but might remain uncontrolled during micro- and ultra-mini PCNL. Intraluminal pharmacological treatment could play a role in IRP decrease, with isoproterenol being the most studied agent.

Pressure matters: intrarenal pressures during normal and pathological conditions, and impact of increased values to renal physiology

PURPOSE

To perform a review on the latest evidence related to normal and pathological intrarenal pressures (IRPs), complications of incremented values, and IRP ranges during endourology.

METHODS

A literature search was performed using PubMed, restricted to original English-written articles, including animal, artificial model, and human studies. Different keywords were: percutaneous nephrolithotomy, PCNL, ureteroscopy, URS, RIRS, irrigation flow, irrigation pressure, intrarenal pressure, intrapelvic pressure and renal pelvic pressure.

RESULTS

Normal IRPs range from zero to a few cm H₂O. Pyelovenous backflow may occur at pressure range of 13.6-27.2 cm H₂O. During upper tract endourology, complications such as pyelorenal backflow, sepsis, and renal damage are directly related to increased IRPs. Duration of increased IRPs and concomitant obstruction are independent predictors of complication development.

CONCLUSIONS

IRP increase remains a neglected predictor of upper tract endourology complications and its intraoperative monitoring should be taken into consideration. Further research is necessary, to quantify pressures generated during upper tract endourology, and introduce means of controlling them.

Verapamil Inhibits the Pelvic Pressure Increase Corresponding to Flow Perfusion in the Porcine Percutaneous Renal Puncture Model

PURPOSE

To estimate the effects of verapamil on pelvic pressure and investigate the possible systemic side effects in the porcine model during the procedure of increasing perfusion rates.

MATERIALS AND METHODS

In the experimental group, the pelvic pressure was recorded with increasing perfusion rates of the renal pelvis (0, 2, 4, 6, 8, 10, 14 and 20 ml/min) in response to intraluminal administration of increasing concentrations of verapamil (0, 0.1, 1, 10 and 100 µg/ml) in isotonic saline. In the isotonic saline group, the pressure flow study was also done by increasing perfusion rates of the renal pelvis per animal using isotonic saline without verapamil.

RESULTS

Perfusion with 1, 10 and 100 µg/ml verapamil caused a decrease in pelvic pressure as a response to increasing flow rates, whereas perfusion with 0.1 µg/ml verapamil did not obviously inhibit the increase of pelvic pressure at all perfusion rates compared with other concentrations. Importantly, the mean systolic blood pressure and mean heart rate were stable despite the increase of flow rates and verapamil concentrations. In the isotonic saline group, perfusion with isotonic saline resulted in an increase in the pelvic pressure with an increase in flow rates each time.

CONCLUSIONS

Endoluminal administration of verapamil reduces pelvic pressure significantly without any untoward systemic cardiovascular side effects.

Systemic Inflammatory Response Syndrome after Percutaneous Nephrolithotomy: A Randomized Single-Blind Clinical Trial Evaluating the Impact of Irrigation Pressure

PURPOSE

We evaluated the impact of intraoperative irrigation pressures on the risk of systemic inflammatory response after percutaneous nephrolithotomy.

MATERIALS AND METHODS

Between January 2014 and March 2015, 90 patients with renal stones planned for percutaneous nephrolithotomy were randomized between low (80 mm Hg) and high (200 mm Hg) irrigation pressure. Patient demographics, perioperative outcomes and systemic inflammatory response incidence rates were compared using the chi-square and Wilcoxon signed rank tests.

RESULTS

Mean patient age, gender, body mass index and other perioperative outcomes were similar in both arms. High pressure irrigation was associated with a higher risk of systemic inflammatory response syndrome (46%) compared to low pressure irrigation (11%, p=0.0002). On multivariate analysis only high irrigation pressure, paraplegia or neurogenic bladder and nonquinolone perioperative medication were predictive of postoperative systemic inflammatory response syndrome.

CONCLUSIONS

High pressure fluid irrigation fluid increases the risk of postoperative systemic inflammatory response syndrome after percutaneous nephrolithotomy.

Oxidative Damage and Mitochondrial Injuries Are Induced by Various Irrigation Pressures in Rabbit Models of Mild and Severe Hydronephrosis

OBJECTIVE

We aimed to study whether tolerance to irrigation pressure could be modified by evaluating the oxidative damage of obstructed kidneys based on rabbit models experiencing different degrees of hydronephrosis.

METHODS

A total of 66 rabbits were randomly divided into two experimental groups and a control group. In the experimental groups, the rabbits underwent a surgical procedure inducing mild (group M, n=24) or severe (group S, n=24) hydronephrosis. In each experimental group, the rabbits were then randomly divided into 4 subgroups (M0-M3 and S0-S3) consisting of 6 rabbits each. Group 0 received no perfusion. Groups 1 through 3 were perfused with 20, 60 and 100 mmHg fluid, respectively. For the control group, after a sham operation was performed, the rabbits were divided into 4 subgroups and were perfused with fluid at 0, 20, 60 or 100 mmHg of pressure. Kidney injuries was evaluated by neutrophil gelatinase associated lipocalin (NGAL). Oxidative damage was assessed by analyzing superoxide dismutase (Mn-SOD) activity, malondialdehyde (MDA) levels, glutathione reductase (GR), catalase (CAT) and peroxide (H2O2) levels, mitochondrial injuries was assessed by mitochondrial membrane potential (MMP), the mitochondrial ultrastructure and tubular cell apoptosis.

RESULTS

In the experimental groups, all results were similar for groups 0 and 1. In group 2, abnormalities were observed in the S group only, and the kidneys of rabbits in group 3 suffered oxidative damage and mitochondrial injuries with increased NGAL, decreased Mn-SOD, GR and CAT,increased MDA and H2O2, lower levels of MMP, mitochondrial vacuolization and an increased apoptotic index.

CONCLUSION

In rabbits, severely obstructed kidneys were more susceptible to oxidative damage and mitochondrial injury than mildly obstructed kidneys when subjected to higher degrees of kidney perfusion pressure.

Acute kidney injuries induced by various irrigation pressures in rat models of mild and severe hydronephrosis

OBJECTIVE

To clarify whether tolerance to irrigation pressure could be modified over varying degrees of kidney obstruction during the endoscopic treatment of kidney stones in a rat model.

METHODS

A total of 126 rats were randomly allocated into 2 experimental groups and a control group. The experimental groups underwent a surgical procedure to induce mild (group M, n = 60) or severe (group S, n = 60) hydronephrosis. In each group, the rats were then randomly allocated into 4 subgroups (M0 to M3 and S0 to S3) of respectively 6, 18, 18, and 18 rats. Groups 0 to 3 were respectively perfused with 0 (no irrigation), 20, 60, and 100 mm Hg pressure fluid. The control group underwent no surgical procedures and was only perfused with 100 mm Hg pressure fluid. Acute kidney injuries were assessed by analyzing the kidney microstructure, tubular cell apoptosis, kidney injury molecule-1, and cysteine-rich 61 (Cyr61/CCN1) expression using immunohistochemistry.

RESULTS

No abnormalities were observed for the control group, groups 0, or 1. In group 2, abnormalities were observed only in the S group, whereas all kidneys in group 3 suffered acute kidneys injuries, along with occurrence of tubular cells necrosis, increased apoptosis, and increased expression of kidney injury molecule-1 and Cyr61.

CONCLUSION

Rats with severely obstructed kidneys were more likely to suffer acute kidney injuries than those with less obstructed kidneys when exposed to higher kidney irrigation pressures. This suggests that the pressure should be controlled and reduced when performing endourologic procedures in the context of kidney obstruction.

Effects of renal pelvic high-pressure perfusion on nephrons in a porcine pyonephrosis model

The aim of this study was to investigate the effects of various renal pelvic pressure gradients on nephrons with purulent infection. Five miniature test pigs were selected. One side of the kidney was used to prepare the pyonephrosis model and the other side was used as the healthy control. A piezometer and a water fill tube were inserted into the renal pelvis through the ureter. Prior to perfusion, punctures were made on the healthy and purulent sides of the kidneys to obtain tissues (as controls). Subsequently, a puncture biopsy was conducted on the kidneys at five pressure levels: 10, 20, 30, 40 and 50 mmHg. Once the renal pelvic pressure had increased, the healthy and injured kidneys presented pathological changes, including dilation of the renal tubule and capsule and compression of the renal glomerulus. When the renal pelvic pressure exceeded 20 mmHg, the injured kidney presented more damage. Electron microscopy revealed that the increase in pressure resulted in the following: the podocyte gap widened, the epithelial cells of the renal capsule separated from the basement membrane, the basement membrane thickness became uneven, the continuity of the basement membrane was interrupted at multiple positions and the renal tubule microvillus arrangement became disorganised. The manifestations in the pyonephrosis model were more distinct compared with those in the healthy kidney. As the renal pelvic pressure exceeds 20 mmHg under a renal purulent infection status, the nephrons become damaged. The extent of the damage is aggravated as the pressure is increased.