Editorial commentary by: Oliver Wiseman, MA, FRCS (Urol), Consultant Urologist, Cambridge, United Kingdom
With recent advancements in technology, flexible ureteroscopy (URS) has become an increasingly favored option to treat kidney stones.1 In fact, the use of URS is increasing in the U.S., the U.K. and across Europe.1-3 In the U.S., for instance, URS increased from 46.3% of stone procedures in 2007 to 60% in 2017.4 However, recent trends associated with URS have had a mixed effect on the goal to increase stone-free rates while decreasing complications rates.
Let’s take a closer look at some of these trends:
Variable use of access sheaths
Ureteral access sheaths may provide a variety of potential benefits including:
• Improved irrigation flow5,6
• Better visibility7,8
• Potential reduced risk of infection8,9
• Instrument protection7,8
• Allowing passive egress of fragments5,10
• Assisting with multiple entries and exits from the kidney10
• Decreased intrarenal pressure (IRP),5,6 which is important because high IRP may lead to complications such as increased risk of infection,11-14 sepsis11-14 and systemic inflammatory response syndrome (SIRS)12,13
However, the practice of using access sheaths is variable and, from my perspective, may have declined in recent years. A 2021 multivariate logistical regression found access sheaths were used in 37.7% of cases, with a surprising degree of variation in the frequency of UAS use depending upon the practice.8 This may be because, as with many surgical techniques, there are risks associated with the way access sheaths are currently used, including bleeding and ureteric injury.15 Additionally, guidelines from the European Association of Urology and the American Urological Association do not offer clear recommendations for using access sheaths during URS procedures.15
Given the purported benefits that access sheaths provide, it’s surprising that use is not more widespread. Concerns regarding the risks of use may account for this, but there are ways to reduce these risks, including care not to use excessive force during placement. Their use may be safer in pre- stented patients. Additionally, the ratio of the size of the access sheath to the outer scope diameter should be considered. It’s important to provide sufficient space between the outer contours of the ureteroscope and the inner wall of the access sheath, in an effort to improve irrigation flow and potentially reduce IRP.9,16
More powerful lasers have led to higher use of dusting
Dusting of kidney stones is now possible with newer high-power lasers that are used to break kidney stones into tiny fragments or “dust” that can be passed out of the kidney. Although high-power lasers can dust more quickly and efficiently, they can also result in more dust and reduced visibility. A 2018 prospective multi-center non-randomized study found that dusting procedures resulted in shorter mean operative time (67.4 vs 35.9 minutes, p <0.001), but stone-free rate was significantly higher in the basketing group on univariate analysis (74.3% vs. 58.2%, p=.04).17 Additionally, a porcine in vivo model showed high-power lasers may cause temperatures to increase enough to damage tissue unless optimal irrigation flow is provided.18
Changes or improvements in pulse modulation can also create a large amount of tiny stone dust fragments – the “snow globe effect.” In vitro stone displacement experiments showed that this technology resulted in significantly higher stone ablation volume (160% higher) and less stone movement (50 times less retropulsion) than the regular mode.19
According to a worldwide survey, 66% and 73% of U.S./Canada and European endourologists, respectively, reported using the laser dusting technique.20 Stone management strategy during URS may have changed to less or no stone basketing,21 and in doing so has negated some of the previously mentioned benefits of using an access sheath.
