Comparison of Moses laser and Raykeen laser in patients with impacted upper ureteral stone undergoing flexible ureteroscopic holmium laser lithotripsy

Abstract

Background

To compare the operative effect and clinical efficacy of the Moses laser mode and the Raykeen holmium laser energy platform powder mode under flexible ureteroscopic lithotripsy in patients with impacted upper ureteral stones.

Methods

From March 2022 to September 2022, 72 patients were divided into a Moses laser group and a Raykeen laser group according to surgical method, with 36 patients in each group. CT and ureteroscopy confirmed that all patients had isolated impacted upper ureteral stones. The stone volume (mm³), stone density (Hu) and severity of hydronephrosis were measured by CT. Postoperative complications were evaluated using the Clavien–Dindo score.

Results

There were no complications of ureteral stenosis related to the laser treatment. The operative time and lithotripsy time were lower in the Moses laser group than in the Raykeen laser group (P < 0.05). The stone-free survival rate did not differ significantly between the two groups (P = 0.722). Stone volume was found to be positively correlated with laser energy and lithotripsy time in both groups (P < 0.01). There was no significant correlation between laser energy and lithotripsy time or ureteral stone density (Hu) in the Moses laser group (P > 0.05) or the Raykeen laser group (P > 0.05).

Conclusions

The contact mode of Moses technology and the powder mode of Raykeen laser lithotripsy can be used for the ablation of a single impacted upper ureteral stone. The ablation speed was related to the stone volume and the severity of polyp hyperplasia, not the stone density. We recommend the use of the powdered mode as a therapeutic measure for the treatment of impacted upper ureteral stones in flexible ureteroscopic lithotripsy.

Background

An impacted upper ureteral calculus leading to hydronephrosis and renal insufficiency has always been a difficult problem in urology [1]. Impacted ureteral stone are defined as the calculi remaining in the same position 2 months and the operator can not pass a wire beyond the stone at the initial attempt [2, 3]. Due to chronic stimulation of the ureteral wall by impacted ureteral upper calculi resulting in proliferation and infiltration of inflammatory cells, ureteral inflammatory edema (UIE) or polyps can form below the calculi [4], which can block vision and distort the ureter [5], resulting in increased surgical complications such as residual stones, ureteral perforation, ureteral rupture, ureteral avulsion and postoperative iatrogenic ureteral stenosis [6]. At present, there is no unified standard for the diagnosis of UIE or ureteral polyps. Jialin Li et al. reported that UIE exceeding 1/3 of the ureteral lumen (i.e., UIE grade 2) significantly affected the surgery time (ST) and ureteroscope placement time (UPT), and this effect further increased with increasing severity of edema, such as the emergence of mucosa stone adherence (MSA), resulting in a severely limited microscopic view and difficulty separating the stone mucosa, indirectly increasing the complexity of the surgery and the risk of anesthesia and infection [4].

The choice of surgical protocol for impacted upper ureteral calculi remains controversial [7]. Flexible ureteroscopy (F-URS) has an active bending function, allowing compliance with the ureteral distortion caused by impacted calculi [8]. A ureteral access sheath (UAS) can reduce perfusion pressure on the kidney during irrigation in the operative region during F-URS. The stone powder and blood oozing from the polyps in the laser lithotripsy may be drained along the ureteral access sheath with the flushing fluid, which significantly improves the operative field. Moreover, the heat generated by the holmium laser can be removed by the flushing fluid, which reduces the local temperature of the ureter, preventing heat injury to the ureter [9]. Traditional Holmium laser such as Raykeen laser whose wavelength is 2120 nm, close to the peak of water absorption (1940nmm), have good efficacy and safety during flexible ureteroscopic lithotripsy (FURL), but the efficiency of lithotripsy is mainly affected by the efficiency of energy transfer.As the distance between laser fibers and stones increases, the efficiency of the rubble decreases and increases the time of operation [10].

The Moses technique, a new type of pulse modulation technique, divides energy into two pulses. The first pulse generates microbubbles in the water, and the second pulse directly acts on the target stone through the bubbles; consequently, the energy will not dissipate in the medium, and this greatly improves the efficiency of lithotripsy [10]. In vitro studies have shown that the Moses holmium laser has a greater rate of stone ablation and a lower rate of stone displacement than traditional holmium lasers [11]. However, the available data on the use of this new system for the treatment of impacted ureteral stones are insufficient.

Therefore, we conducted a retrospective clinical study to compare the efficacy of a holmium laser using the contact mode of Moses technology and the powder mode of the Raykeen holmium laser system in the treatment of impacted ureteral stones and to evaluate the effect of the severity of hydronephrosis and different polyp hyperplasia grades on the duration of lithotripsy. The main stone composition, short-term clinical outcomes and complications were also analyzed.

Methods

Patients

After approval from the institutional review board (S2022-154-01), we retrospectively analyzed patients who underwent surgical treatment for impacted upper ureteral stones at the First Medical Center of the Chinese PLA General Hospital from March 2022 to September 2022. Patients underwent flexible ureteroscopic lithotripsy (FURL) using the contact mode of a Moses Technology P120 laser (Lumenis) or a powder model of a Raykeen laser. According to the surgical method, the patients were divided into a Moses laser group and a Raykeen laser group, with 36 patients in each group. The inclusion criteria were as follows: (a) patients with upper urinary tract calculi who were scheduled to undergo URSL preoperatively; (b) patients whose complete clinical information was available; and (c) patients whose calculi were located above the fourth lumbar vertebra and had been present for more than 8 weeks. The exclusion criteria were as follows: (a) patients with renal dysfunction and coagulation disorders; (b) patients with a history of ureteroscopic procedures within the preceding 3 months; (c) patients undergoing preoperative ureteral stent placement or preoperative nephrostomy; (d) the operator can pass a wire beyond the stone at the initial attempt .

Postoperative outcomes and complications

Postoperative characteristics, used as study outcomes, included changes in the postoperative hemoglobin concentration and postoperative serum creatinine, stone composition, postoperative hospital stay, stone-free rates and postoperative complications according to the Clavien–Dindo grading system.Low-dose nonenhanced CT (slice thickness 1.25 mm) was performed 28 days after the operation to evaluate the stone-free rate (SFR was defined as clinically insignificant residual fragments ≤ 3 mm).At 3 months after surgery, the patient underwent urological ultrasound to assess hydrops.At 6 months after surgery, the patient underwent urological ultrasound to assess hydronephrosis and ureteral stenosis.

Surgical procedures

All patients were indwelled with ureteral stents for one week before the operation, and the operation was performed under general anesthesia. After an electronic flexible ureteroscope (STORZ German FLEX-XC 11278VS) was inserted to the stone location, the stone was treated with a holmium laser fiber of 200 μm. A Moses fiber (Moses SIS EZ) was used in the Moses laser group (output energy of 0.3–0.4 J, frequency of 80 Hz, and laser output power of 24–32 W), while a Raykeen holmium laser fiber was used in the Raykeen laser group (output energy of 0.6–0.8 J, frequency of 40 Hz, and laser output power of 24–32 W). In the case of any stone drifting into the renal pelvis, the flexible ureteroscope was advanced for further lithotripsy. If the flexible ureteroscope failed to reach the stone location or if the stones drifted to the renal pelvis before lithotripsy and could not be pulverized, the operation was considered to be a failure.

Statistical methods

Statistical analysis was performed using the Statistical Package for Social Sciences (SPSS, version 26.0). Quantitative variables are described herein using means and standard deviations, and qualitative variables are described using frequencies and percentages. To compare outcomes between groups, Pearson’s chi-square or Fisher’s exact test was used for dichotomous and categorical variables. Student’s t test was used for continuous normally distributed variables, and the Mann–Whitney U test was used for skewed variables. The significance level was set at 0.05. The strength of the relationships between variables was determined by the Spearman correlation coefficient, and the significance was set at 0.05. GraphPad Prism 9.4.1 (681) was used for the statistical analysis.

Results

Comparison of baseline data between the two groups

According to our inclusion criteria, a total of 79 patients were included in the original cohort. 7 patients were excluded from the study, because the operator can pass a wire beyond the stone at the initial attempt.So a total of 72 patients were included in the study.There was no statistically significant difference in age, sex, body mass index, side of treatment, combined medical disease (diabetes, hypertension or heart disease), positive rate of preoperative urinary culture, severity of ureteral polyp hyperplasia, severity of renal pelvis separation, stone volume, stone density or main stone composition between the two groups (P > 0.05), as shown in Table 1.

Table 1 Comparison of baseline data between the two groups

Comparison of clinical efficacy between the two groups

Table 2 shows that there was no statistically significant difference in intraoperative stone displacement, stone-free rate, postoperative hospital stay, change in postoperative hemoglobin concentration, change in postoperative serum creatinine, or laser energy between the two groups (P > 0.05). The operation time and lithotripsy time of the Moses laser group were shorter than those of the Raykeen laser group (P < 0.05).

Table 2 Comparison of clinical efficacy between the two groups

Endoscopic features of severity of polyp hyperplasia

Since polypoid lesions at the site of impacted stones cannot be diagnosed by routine CT, an electronic flexible ureteroscope was used to evaluate the severity of polyp hyperplasia. We graded the severity of polyp hyperplasia based on endoscopic features, as shown in Fig. 1.

Fig. 1

Grading results for the severity of polyp hyperplasia under the flexible ureteroscope: A. Grade 1 = Mild polyp hyperplasia, i.e., more than half the size of the ureteral stone is visible; B. Grade 2 = Moderate polyp hyperplasia, i.e., no more than half the size of the ureteral stone is visible; C. Grade 3 = Severe polyp hyperplasia, i.e., complete obstruction of flexible ureteroscopic visual field, and the ureteral stone is invisible. D. Holmium laser lithotripsy for ureteral stones under a flexible ureteroscope

Correlation analysis

Moses laser group

Figure 2 shows the relationships of laser energy and lithotripsy time with stone volume, stone density, polyp hyperplasia and hydronephrosis in the Moses laser group. The laser energy required was more closely related to stone volume (R² = 0.823, P < 0.01) than to stone density (R² = 0.107, P = 0.536). The required lithotripsy time was more strongly correlated with stone volume (R² = 0.800, P < 0.01) than with stone density (R² = 0.141, P = 0.413). Moreover, the lithotripsy duration was more strongly correlated with the severity of polyp hyperplasia (R² = 0.564, P < 0.01) than with the severity of hydronephrosis (R² = 0.076, P = 0.659).

Fig. 2

Correlation analysis in the Moses laser group: A. Relationship between laser energy and stone volume; B. Relationship between lithotripsy time and stone volume; C. Relationship between laser energy and stone density; D. Relationship between lithotripsy time and stone density; E. Relationship between lithotripsy time and polyp hyperplasia; F. Relationship between lithotripsy time and hydronephrosis

Raykeen laser group

Figure 3 shows the relationships of laser energy and lithotripsy time with stone volume, stone density, polyp hyperplasia and hydronephrosis in the Raykeen laser group. The laser energy required was more closely related to stone volume (R² = 0.693, P < 0.01) than to stone density (R² = 0.327, P = 0.052). The required lithotripsy time was more strongly correlated with stone volume (R² = 0.678, P < 0.01) than with stone density (R² = 0.273, P = 0.107). Moreover, the lithotripsy duration was more strongly correlated with the severity of polyp hyperplasia (R² = 0.495, P < 0.01) than with the severity of hydronephrosis (R² = 0.152, P = 0.376).

Fig. 3

Correlation analysis in the Raykeen laser group: A. Relationship between laser energy and stone volume; B. Relationship between lithotripsy time and stone volume; C. Relationship between laser energy and stone density; D. Relationship between lithotripsy time and stone density; E. Relationship between lithotripsy time and polyp hyperplasia; F. Relationship between lithotripsy time and hydronephrosis

Postoperative complications

There was no perirenal hematoma, severe hematuria or sepsis in either the Moses laser group or the Raykeen laser group. As shown in Table 3, the proportions of patients with fever were 3 (8.3%) and 2 (5.6%) in the two groups, respectively, all of whom were treated with oral antibiotics and improved. There was no significant difference between the two groups (P = 0.643). One patient in the Moses laser group had Clavien‒Dindo grade I complications, while 3 patients in the Raykeen laser group had Clavien‒Dindo grade I complications, which were cured after symptomatic treatment. There was no statistically significant difference between the two groups (P = 0.303). One patient in the Raykeen laser group developed stent-related pain that required analgesic medication. One patient in the Moses laser group required early removal of the ureteral stent because of stent-related pain.3 patients developed ureteral stenosis at 6 months after surgery, and there was no statistically significant difference between the two groups (P = 0.555).

Table 3 Comparison of complications between the two groups

Discussion

In previous ureteroscopic holmium laser lithotripsy, polyps needed to be removed first, and then the incision of the narrowed ureter was performed using holmium laser cutting and hemostasis technology before holmium laser lithotripsy. This approach increases the difficulty of surgery and the risk of complications [5]. In this study, an electronic flexible ureteroscope was used to evaluate the severity of inflammatory polyp hyperplasia. The results showed that the application of an electronic flexible ureteroscope with a small diameter can overcome the adverse effects on the surgical visual field caused by inflammatory polyps and ureteral distortion.

Some studies have shown that the application of a high-energy holmium laser for the treatment of ureteral stones may increase the risk of ureteral stenosis [12]. In our study, 3 patients developed ureteral stenosis. One patient had a ureteral stent re-inserted and two patients underwent laparoscopic surgery.The mechanism of ureteral stenosis formation following URL is not fully understood. The contributing factors of postoperative ureteral stenosis may include intraoperative ureteral injury and a long-term inflammation reaction caused by the stones.Ischemia, granuloma and fibrosis caused by impacted ureteral stonesalso play critical roles in the formation of stenosis [13, 14]. Although the tissue penetration of the Ho: YAG laser is only 0.4 mm, the thermal effect of Holmium lasers on ureteral mucosal injury remains a risk of stenosis from scarring of the ureter [15]. Therefore, a high-power laser should not be used between the stones and the mucosa during the lithotripsy surgery of impacted upper ureteral stone, and the method of gradually crushing the stones from inside to outside can be used to to avoid thermal injury to the ureteral mucosa [16].

Stone displacement was found in both groups during the operation. In FURL, stones may move back, which leads to stone displacement; therefore, a flexible ureteroscope is used to trace the stones, resulting in a prolonged operative time [17, 18]. In lithotripsy using a new generation of holmium lasers, this backward effect is effectively reduced by a double pulse. Elhilali et al. reported that stone displacement under the Moses mode decreased and that the amount of stone ablation significantly increased (increased by 160%, P < 0.001) [19]. We also found in clinical practice that the stone displacement was minimal even in the Moses mode with a high energy of (0.6–0.7) J × (70–80) Hz.

The lithotripsy time was shorter in the Moses laser group than in the Raykeen laser group (P = 0.049). Stone volume was positively correlated with lithotripsy time and laser energy during surgery in both groups, which was similar to the findings of previous studies [20, 21]. Stone density is not a reference factor in the treatment of ureteral stones, although a previous study showed that stone density may affect the lithotripsy time [22]. The stone volume can be used to predict the lithotripsy time. The type of laser was not related to the stone composition in the two holmium laser lithotripsy procedures.

This study has several limitations. First, ureteral polyps and hydronephrosis were evaluated, but ureteral distortion caused by stones was not evaluated. Ureteral distortion may affect the lithotripsy time of FURL. Second, in our study, predilation was performed for all patients with indwelling ureteral stents before the operation, which was conducive to implantation of the ureteral access sheath and objectively alleviated the effect of hydronephrosis and the use of an upper ureteral hydroureter on the difficulty of the operation.Third, The follow-up time is short, which is one of our limitations, and further improvement is needed in future studies.

Conclusions

The Moses mode has a faster lithotripsy time than the common holmium laser platform. We found that preoperative CT evaluation of the stone volume and the severity of inflammatory polyp hyperplasia intraoperatively observed under the ureteroscope can be used as indicators to determine the lithotripsy time of Holmium laser treatment of impacted ureteral stones.