Endourological procedures, including ureteroscopy and percutaneous nephrolithotomy for management of urolithiasis, are associated with temporary elevation in intrarenal pressures (IRPs).

Historically, one of the first applications for collecting system pressures was the Whitaker test, an antegrade pressure/perfusion study developed in the 1960s to evaluate upper renal collecting system obstruction. Intraluminal pressures in the renal pelvis and ureter have since been measured using pressure transducers in animal and human studies. However, characterization of the intrarenal ramifications of elevated pressures and associated clinical sequelae did not occur until several decades later.

IRP is influenced by external compression, wall tension, wall thickness, and the difference between internal and external pressures. IRP values across a variety of conditions have been described in several recent systematic reviews. In humans, the normal physiologic IRP in the absence of obstruction is estimated to range from 0 to a few cm H₂O; however, the IRP has the potential to increase significantly during endourological procedures; ie, retrograde renal surgery (40.8-199.35 cm H₂O), percutaneous nephrolithotomy (PCNL) (3-40.8 cm H₂O), mini-PCNL (10-45 cm H₂O), and micro-PCNL (15.37-41.21 cm H₂O).¹ Animal models suggest elevated IRP can lead to pyelovenous backflow, forniceal rupture, hematoma formation, and focal renal scarring. Human studies have examined but failed to clearly define a relationship between specific IRP thresholds with postoperative pain and infectious complications.² Normal vs pathological IRP values or ranges are not well established for humans, and there is currently no evidence-based ceiling for maximum IRP considered safe during endoscopic procedures.

The current AUA guideline recommends clinicians ‘‘make every effort to maintain low intrarenal irrigation pressure’’ to avoid the consequences of high IRP during endourological procedures.³ Based on limited data, a pressure of approximately 40 cm H₂O is referenced in the European Association of Urology guidelines as a goal threshold beneath which IRP should be maintained during endourological procedures.⁴ An established method to measure IRP intraoperatively is using a ureteral catheter connected to an invasive blood pressure monitor.⁵ Additionally, 2 promising new technologies with pressure monitoring, including pressure-sensing wires (COMET II Pressure Guidewire; Boston Scientific) and the recent Food and Drug Administration–approved pressure-sensing single-use ureteroscopes (LithoVue Elite Single-Use Digital Flexible Ureteroscope; Boston Scientific), are increasingly being used to understand the clinical significance of IRP. Currently, studies are limited to pilot studies and are limited by high costs. However, as more researchers apply these new real-time in vivo pressure-sensing technologies, true IRP profiles during endoscopic procedures may potentially be defined, such as baseline IRP, maximum peak IRP, and duration of elevated IRP.

The clinical usefulness of the routine inclusion of IRP-monitoring technology outside of a research setting is yet to be determined. Strategies to minimize IRP focus on decreasing inflow and maximizing outflow from the system. Ureteral access sheath placement has been shown to significantly reduce IRP. Other practical suggestions include avoiding use of pressurized-bag or annual irrigation, limiting height of irrigation fluid, and maintaining a decompressed bladder.⁶ Use of intelligent pressure-sensing equipment may further provide real-time feedback on the efficacy of these maneuvers. IRP measurement may also help direct further research on strategies on how to minimize IRP. For example, IRP monitoring can help qualify the usefulness of new devices such as flexible or rigid vacuum-assisted ureteral access sheaths⁷ or vacuum-assisted mini-PCNL sheaths.⁸ IRP measurements have also been used in pilot studies for calculating irrigation inflow,⁹ as well as for evaluating ureteral patency after PCNL,¹⁰ which may assist with intraoperative clinical decision-making. In addition, intraluminal pharmacological treatment, particularly with isoproterenol, has been studied for a potential role in IRP decrease. However, more human prospective studies are needed to adopt these into everyday clinical practice.

In summary, increases in IRP during endourological procedures are becoming increasingly recognized in the urologic community. While a “safe level” has not yet been clearly defined, and theoretical benefits of lowering IRP on infectious complications and postoperative pain after endourology procedures are yet to be demonstrated, advances in real-time pressure-sensing technologies may help define safety thresholds. Ultimately, IRP monitoring in its current state is mainly investigational; however, these newly available tools hold great promise towards the evidence-based application of IRP limits to enhance patient outcomes.