Intrarenal pressure (IRP) is a principle that first came to light in the 1920s and continues to be at the forefront of endourology 100 years later. Even in the early 20th century, there were robust data that renal pressures over 30 mm Hg could cause pyelovenous lymphatic backflow.¹ From this rudimentary study, the theoretical risks of increased IRP have expanded to include barotrauma, irrigant absorption, forniceal rupture, and fluid extravasation.² When bacteria are present in irrigant fluid, irrigant absorption results in the translocation of bacteria into the systemic circulation. Using a live swine model, Hinojosa Gonzalez et al³ demonstrated that there were significant differences in the rate of bacteremia after ureteroscopy (URS) depending on the renal pelvis pressure during the procedure. During this randomized controlled trial, irrigation with Escherichia coli–infused saline resulted in an inflammatory response and positive kidney cultures. However, bacteremia was only seen in animals in the high IRP group (75 mm Hg) compared with the lower IRP group (37 mm Hg).³ Further studies have looked at the clinical sequelae in humans of IRP during flexible URS and demonstrated that irrigation flow rate and irrigation volume are independent risk factors for systemic inflammatory response syndrome after flexible URS.⁴ Rates of urinary tract infection after URS are 0.95% while 0.3% of patients undergoing URS will develop sepsis.⁵

In addition to infection, renal hemorrhage is a rare but potentially life-threatening complication of URS. One systematic review including 7 studies reported an incidence of 0.45% of post-URS perirenal hematoma. Risk factors included high perfusion pressure, moderate to severe hydronephrosis, prolonged time in operating room, hypertension, existing chronic kidney disease, prior renal surgery, sheath usage, stents, and thin renal cortex. Of these, intrarenal perfusion pressure is one of the few modifiable risk factors for the urologist.⁶ While increased pressures in the renal pelvis during URS have historically been thought to cause increased pain postoperatively, there are gaps in the literature, and higher-quality data are needed.

Given the theoretical and clinical adverse effects of increased IRP, monitoring pressure during URS has become a focal point of endourology. There are a variety of devices that allow for liver IRP monitoring, including wires, sheaths, and disposable ureteroscopes. With real-time IRP monitoring, we can now utilize these data to reduce IRP.

Decreasing IRP depends on reducing irrigant inflow and increasing outflow. Suction technology has emerged as a revolutionary way to increase outflow and minimize IRP through passive and active suction. Aspiration devices include ureteroscopes (direct in-scope suction) and access sheaths (flexible and navigable suction sheaths). A retrospective analysis of patients undergoing flexible URS evaluated IRP with the ClearPetra Ureteral Access Sheath. With set pressure irrigation and suction, IRP remained lower than 40 mm Hg for 76% of the total procedure time and lower than 60 mm Hg for 94% of the total procedure time, which demonstrated that flexible and navigable suction ureteral access sheaths are effective at maintaining lower IRP even with higher irrigation pressures.⁷ Further studies have looked at the rate of adverse events of suction technology compared with traditional ureteroscopes and ureteral access sheaths. Zhu et al⁸ compared the efficiency and safety of traditional ureteral access sheaths and suctioning access sheaths during flexible URS. The incidence of overall complications was significantly higher in the traditional sheath group (24.8% vs 11.5%; P < .001), including a higher incidence of fever (13.9% vs 5.5%; P = .009) and urosepsis requiring additional antibiotics (6.7% vs 1.8%; P = .029).⁸ Suction devices have come to the market as an attractive option to achieve lower IRP and decrease the risk of unfavorable adverse events, overall complications, infectious complications, and length of hospital stay, and improve stone-free rates in URS (Figure).⁹

Although the outcomes of utilizing suction technology are promising, it is essential to remember that there are potential obstacles, such as stone debris in outflow channels, which can increase outflow resistance and thus IRP.¹⁰ As mentioned above, one recent study showed IRP remained lower than 40 mm Hg for 76% of the total procedure time, which is encouraging but also means that 24% of procedures had IRP at levels that could lead to pyelovenous lymphatic backflow and its potential sequelae.⁷ Further limitations to suction technology include availability, cost, failure of the technology, and human error. Without aspiration devices, there still exist ways to facilitate drainage, including bladder catheterization in the absence of a ureteral access sheath and using smaller ureteroscopes to allow for better irrigation outflow.

Pressurized irrigation carries potential risks and can result in life-threatening adverse outcomes, including infection, sepsis, barotrauma, renal hemorrhage, and possibly increased postoperative pain. Understanding the pathophysiology of IRP can help urologists employ risk reduction practices that minimize adverse events after stone treatments. By minimizing inflow and maximizing outflow of irrigation, IRP can be regulated and reduced throughout a case. Live monitoring of IRP can be advantageous for patients who are at high risk of experiencing adverse events from the surgical treatment of stones. Suction devices offer another layer of protection by reducing IRP and reducing the risk of adverse events like infection and sepsis. Actively monitoring IRP and utilizing suction devices that reduce IRP will be a field that continues to evolve in the practice of endourology. Nonetheless, until data consistently show that aspiration devices have NO complications related to high pressures and demonstrate in real-life cases that pressures remain less than 40 mm Hg for the entire duration of 100% of procedures, IRP will continue to matter.

Conflicts of Interest: Dr Semins is a consultant for Boston Scientific. No other disclosures were reported.