Sepsis is one of the most serious complications following ureteroscopy. We recently reported that the rate of sepsis after ureteroscopy in North America is 5.5%.¹ Furthermore, we also showed that health care utilization and cost associated with sepsis after ureteroscopy is magnitudes higher than for those who do not develop sepsis.¹ Sepsis after ureteroscopy has also been shown to significantly increase all cause in patient mortality (HR 17).² Pressure within the renal collecting system, also known as intrarenal pressure (IRP), ranges from 0 to 6 mm Hg at baseline but can increase significantly during endoscopic surgery. IRP has recently garnered a lot of attention due to the possibility that higher IRP can result in complications such as pain, infection, and even renal damage.³ The main cause of elevated IRP is thought to be the type of irrigation used and whether or not a ureteral access sheath (UAS) is in place. It has been shown that a UAS can reduce IRP when using a 12/14Fr- or 14/16Fr-sized UAS.⁴

A number of studies have determined that IRPs above 40 mm Hg (and even as low as 20 mm Hg) will lead to pyelovenous backflow—something theorized to increase the risk of urosepsis and pain.³ Post ureteroscopy pain can occur even in the absence of intraoperative complications. Suggestions that it is related to pressure were supported by a study by Pedersen et al, who studied 15 patients undergoing percutaneous nephrolithotomy.⁵ With the patient awake, they instilled contrast at a rate of 1 cc/sec through a 7Fr catheter and measured IRP via the nephrostomy tube. Using a visual analog scale, they determined that the average threshold of when patients experienced pain was when IRP went above ∼34 mm Hg. It remains to be determined if occurrence of this pain occurs with a spike in IRP or whether it requires a sustained duration of elevated IRP.

It is important to recognize that a number of factors can impact IRP. As discussed, the type and amount of irrigation used has a direct impact on IRP. Pressure irrigation will produce a higher IRP than gravity irrigation. Hand irrigation with a syringe is variable and depends on the amount of force being used to irrigate the collecting system. A retrospective study examined the impact of irrigant flow rate and volume on post-ureteroscopy systematic inflammatory response syndrome (SIRS). Both flow rate and irrigant volume were found to be independent predictors of SIRS.⁶ A randomized study by Omar et al comparing irrigation pressures of 80 mm Hg vs 200 mm Hg in patients undergoing percutaneous nephrolithotomy determined that higher irrigation pressure was an independent predictor of postoperative SIRS.⁷

One of the hypotheses behind the relationship between high IRP and postoperative infections is pyelovenous/renal backflow leading to absorption of bacteria. A recent AUA abstract used a porcine model to test sterile saline irrigation fluid compared to saline infected with a standardized concentration of uropathogenic Escherichia coli for 60 minutes at IRPs of 37 mm Hg or 75 mm Hg.⁸ It was determined that irrigation with the E. coli infected saline produced an inflammatory response with positive kidney cultures (pyelonephritis) even at the lower 37 mm Hg pressure. At the higher IRP of 75 mm Hg they found positive kidney cultures as well as bacteremia with positive blood cultures. If bacteria is present in the collecting system, a higher IRP may lead to bacteremia and possibly a septic event.

In a study by Schwalb et al, a porcine model was used to examine the impact of exceptionally high IRP during ureteroscopy.⁹ A nephrostomy tube attached to a transducer was placed in order to measure IRP. It was determined that IRPs above 204 cm H₂O produced significant pathological changes to the kidney compared to pressures less than 122.4 cm H₂O.⁹

Previously, measuring IRP during ureteroscopy was cumbersome and has been described in patients with a pre-existing nephrostomy tube during ureteroscopy.⁹ There are pressure-sensing guidewires that may be used but these also require additional monitors as well as the insertion of additional equipment into the ureter. Single-use ureteroscopes (ie, “disposable” ureteroscopes) have been commonly used since 2016 when the LithoVue (Boston Scientific Corporation) ureteroscope became widely adopted.¹⁰ Recently, the next generation of LithoVue ureteroscope, LithoVue Elite (LVE), was approved for use in Canada. A major advancement of the new LVE ureteroscope is its ability to sense IRP in real time giving readings every second (see Figure). It is clear from early work that a number of questions need to be answered regarding IRP. Is there a safe IRP? At what IRP do complications occur? Is there one maximum threshold pressure that, when exceeded, opens a floodgate for a complication to occur, or is it based on an average pressure over a minimum time period? What patient factors affect IRP? Fortunately, with the new LVE ureteroscope, IRP can be measured in every case and we can begin to answer some of these questions. Currently, we have an ongoing study to evaluate and correlate patient pain and infection post ureteroscopy to see what role IRP may play. There are many questions that need to be answered regarding IRP and its effect on ureteroscopy outcomes. Now there is a convenient tool to measure it.

In summary, IRP is hypothesized to be associated with a number of important complications. One of the most serious complications is postoperative sepsis. Therefore, renal pelvis pressures should be investigated in order to mitigate this dangerous complication. With a tool that can be easily used in every case to measure IRP, further studies will be able to define those limits and determine cutoffs to help us determine safe IRP levels to reduce complications.