Ureteroscopy has become the most common surgical modality worldwide in the treatment of kidney stones.¹ Since the introduction of the flexible ureteroscope, advancements continue to make them smaller, more maneuverable, and with better image resolution. At this year’s AUA semi-live session, we endeavored to highlight a few of the recent developments that have occurred in this rapidly evolving field.

Single-use ureteroscopes (ie, “disposable” scopes) have been in wide use since 2016 when the LithoVue ureteroscope became widely available.² Since then, dozens of single-use digital ureteroscopes have emerged on the market providing excellent maneuverability and visualization rivaling that of reusable digital ureteroscopes. The next generation of LithoVue ureteroscope, named LithoVue Elite (LVE), has higher resolution due to advancements in chip technology as well as better lighting and contrast from improved LED lighting. The main new advancement in the LVE ureteroscope is that it is able to sense intrarenal pressure (IRP) in real-time intraoperatively.

A number of studies have determined that IRPs above 40 mm Hg (and even as low as 30 mm Hg) will lead to pyelovenous backflow—something theorized to increase the risk of urosepsis and pain.³ Postureteroscopy pain can occur even in the absence of intraoperative complications. Suggestions that pain is related to pressure were supported by a study by Pedersen et al, who studied 15 patients undergoing percutaneous nephrolithotomy.⁴ With the patient awake, they instilled contrast at a rate of 1 cc/sec through a 7F catheter and measured IRP via the nephrostomy tube. Using a visual analog scale they determined that the average threshold when patients experienced pain was when IRP went above ∼34 mm Hg. It remains to be determined if this pain occurs when a spike in IRP occurs or whether it requires a sustained duration of elevated IRP. Previously, measuring IRP during ureteroscopy was cumbersome and was first described only in patients with a preexisting nephrostomy tube.⁵ There are pressure sensing guidewires from the cardiac field that may be used in the kidney, but these require additional monitors as well as the insertion of additional equipment into the ureter.⁶

Figure. Semi-live surgery utilizing LithoVue Elite pressure sensing ureteroscope and holmium:YAG Moses laser.

Currently, the only 2 things we have under our control that we know influence renal pressure are (1) whether a ureteral access sheath is used or not, and (2) the type of irrigation method used during ureteroscopy. With more clinical experience, we are beginning to learn that we do not know all of the factors that influence renal pressure. During this year’s semi-live surgery, we demonstrated a few lessons that we have learned while using the new LVE flexible ureteroscope with pressure sensing capacity: (1) IRP is impossible to predict without measuring it. In general IRP in the renal pelvis is about 28 mm Hg during ureteroscopy but can go much higher when the ureteroscope is in tighter calyces or if irrigation pressure is increased. Additionally, IRP can increase above 100 mm Hg during simple ureteroscopy cases. (2) Anatomy, especially the ureteropelvic junction, can have a significant impact on IRP. A tight ureteropelvic junction can significantly increase IRP—likely because the renal pelvis is less likely to empty the irrigant fluid from the ureteroscope. (3) IRP can be manipulated higher or lower if necessary. For a patient as risk of sepsis from ureteroscopy, IRP can be reduced by using a manual syringe for irrigation and aspirating fluid as necessary during the case to maintain pressure below the pyelovenous backflow threshold. In addition, if the IRP can be continuously monitored, pressure irrigant can be increased when necessary to maximize visualization. The caveat to this is that you need to know what the IRP is in real time as you are operating.

The other part of the semi-live surgery involved the use of the P120 laser with Moses technology (see Figure). With this new technology, the traditional holmium (Ho):YAG laser is improved by modulating the laser pulse to an initial small vapor bubble that separates the water directly in front of it (the Moses effect), and the second part of the pulse is transmitted through the vapor bubble toward the stone. This improves the efficiency of energy transmission toward the stone and reduces retropulsion.

By decreasing retropulsion, this allows more direct contact time with the stone from the laser, thus potentially shortening operative times and decreasing surgeon frustration. Faster stone ablation rates using Moses have been shown compared to regular Ho:YAG.⁷ When using this technology for holmium enucleation of the prostate, Moses technology has shown improved hemostasis and shorter operative times.⁸ The Moses technology and other new high-powered laser technologies have swayed many more procedures toward the dusting technique given the finer dust and decreased retropulsion compared to the traditional Ho:YAG lithotripsy.⁹

It is clear from the early work demonstrated in this semi-live surgery 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? Are patient factors important, and what are their implications and relationship with IRP? Fortunately, with this new flexible ureteroscope with pressure sensing capacity, 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 postureteroscopy to see what role IRP plays in this. Moses laser technology reduces retropulsion and operative time, and future comparative studies will help determine in which circumstances and which conditions each laser is best suited. These new tools will hopefully allow urologists to improve their treatment of kidney stones.