More energy, same results: high energy settings do not improve the efficiency of dual energy lithotripsy during percutaneous nephrolithotomy

Abstract

Introduction and objective

No prior in vivo clinical trial has investigated the effect of varying energy settings on the performance of a dual-energy lithotripsy. We prospectively evaluated various impact and frequency settings during PCNL procedures to achieve optimal fragmentation and extraction of large stones of varying density.

Methods

Four impact and frequency settings were chosen based on a prior in vitro study and applied sequentially for 1 min each in a randomized manner during PCNL for large renal calculi greater than 3 cm in 24 patients: 4 Hz + 100% impact, 4 Hz + 30% impact, 12 Hz + 100% impact, and 12 Hz + 30% impact. Suction and ultrasonic settings were kept constant. For each setting, all removed fragments were collected, weighed, and dried to quantify stone removal rates. Fragments were categorized based on particle size, < 2 vs. ≥ 2 mm. Extraction rates (g/min), were expressed as medians and interquartile ranges (IQR). Statistical comparisons used the paired Wilcoxon Signed-Rank test. A sub-analysis was conducted based on density (≥ 1000 HU).

Results

24 patients were enrolled. Median stone burden was 36 mm (IQR 32–54) and HU was 1170 (IQR 944–1336). Median extraction rates, 0.50 g/min (IQR 0.24–0.93), 0.55 g/min (IQR 0.22–0.87), 0.40 g/min (IQR 0.22–0.89), and 0.48 g/min (IQR 0.30–0.69), respectively, were not statistically different (Fig. 1a). Particle size was not influenced by impact and frequency settings (Fig. 1b). Fragmentation and extraction efficiency of highly dense stones (HU ≥ 1000) were not influenced by settings (Fig. 2). There was no significant difference in fragmentation or extraction efficiency based on stone composition (primarily calcium-based vs. non-calcium-based).

Conclusion

Increased frequency and impact settings do not improve the efficiency of a dual-energy lithotripsy for clearance of large or hard stones and are unnecessary.

Introduction

Percutaneous nephrolithotomy (PCNL) is the preferred treatment for renal stones larger than 20 mm in diameter [1, 2]. Many devices have been used for stone fragmentation during PCNL and are termed lithotrites. The earliest lithotrites were elecrohydraulic lithotripters, and were based on spark gap technology, akin to a creating an electric charge under water to fragment stones. It was difficult to control the direction of energy, and each firing created variable power, making it less predictable. This energy could also create significant tissue damage and bleeding. These were replaced by more consistent ultrasonic lithotrites that were safer on tissue. These consisted of hollow probes utilizing piezoceramic crystals to create ultrasonic waves that caused the probe’s tip to vibrate and achieve fragmentation (Calcuson, Storz; LUS, Olympus; US-Litho 2271, Richard Wolf). The hollow design permitted simultaneous suction to evacuate fragments [3]. These devices were highly effective but were prone to clogging and were less effective for hard stones, requiring more pressure being applied to the stone which could result in perforation of the collecting system or stone migration. The next generation of lithotrites used compressed air to accelerate a projectile inside a hand piece, which hit a probe to elicit a shock wave that moved through the probe to the stone to cause fragmentation (ballistic lithotripsy, Swiss Lithoclast ^®). These probes, although very powerful, were not hollow and therefore required that fragments be removed using a grasper, limiting their efficiency for larger stone burdens. Combination devices were developed but initially could only use one fragmentation modality at a time, i.e. ballistic alone, or ultrasonic and suction [4–6]. Subsequent variations involved the use of concentric probes mounted within one another to deliver both energies (Cyberwand, Lithoclast Select, Lithoclast Ultra, Lithoclast Master). This resulted in higher efficiency for stone fragmentation, but reduced stone clearance speeds due to the narrowed lumen.

More recently, dual-energy single probe lithotrites were developed, combining ballistic lithotripsy and ultrasound lithotripsy. These devices combine ultrasonic lithotripsy, ballistic lithotripsy and suction capability in single probe (Shockpulse-SE, Olympus Medical,

Center Valley, PA, USA and Lithoclast Trilogy, EMS, Nyon, Switzerland). Several different probe sizes are also available. Studies have suggested that the Trilogy offers faster stone clearance than other ultrasonic and combination ultrasonic devices [3, 7–9]. The Trilogy lithotrite has four modifiable settings: impact (0–100%), frequency (2–12 Hz), ultrasonic lithotripsy (0–100%) and suction (0–100%). The LithoClast^® Trilogy Max is the newest generation model that features a smaller handpiece, an optimized cooling system designed to reduce device downtime, and an upgraded software. However, the settings featured on the LithoClast^® Trilogy have not been tested in an in vivo human model. The objective of this study was to determine the optimal settings (impact and frequency) of the LithoClast^® Trilogy for large stones (> 3 cm).

Methods

Institutional review board (STUDY-24-01300, Ichan School of Medicine at Mount Sinai, 31 March 2025) approval for data collection and evaluation of patients was obtained. Consecutive patients scheduled for outpatient PCNL were prospectively enrolled in a nonrandomized manner from 7 July 2024 to 22 May October 2025. All procedures were performed by two experienced fellowship trained surgeons (M.G. and W.A.) in a regular hospital. Key inclusion criteria included age > 18 years, stone burden exceeding 3 cm in maximum dimension (coronal and axial). Measurements including maximal dimensions and stone volume were measured on non-contrast CT. Patients with a solitary kidney, Chronic kidney disease (CKD) 3 or higher, specific anatomical variations such as horseshoe kidney, pelvic kidney, ptotic kidney, or urinary diversion, or a preexisting nephrostomy were excluded, as well as patients undergoing a mini-PCNL, since they typically have lower stone burdens.

Intravenous antibiotics were administered as per AUA guidelines on antibiotic prophylaxis. Patients were positioned in a modified Barts flank-free position. Cystoscopy was performed, followed by retrograde placement of a 0.035-inch guidewire in the renal pelvis, followed by a ureteral occlusion balloon (Occluder, Boston Scientific, Inc.). Ultrasound (US)-guided access was established, the tract balloon dilated to 24 F with sheath placement (NephroMax, 24 F, Boston Scientific, Inc), and nephroscopy and lithotripsy were conducted with gravity irrigation at a standardized height of 80 cm. Lithotripsy was performed using a 3.9-mm dual energy probe (LithoClast Trilogy^®).

To isolate the impact of specific mechanical parameters on efficiency, suction and ultrasonic power were held constant throughout the study. Four distinct combinations of impact and frequency—4 Hz at 100% impact, 4 Hz at 30%, 12 Hz at 100%, and 12 Hz at 30%—were selected based on prior in vitro data. These settings were applied in a randomized, sequential order. Surgeons were blinded to the parameters, and each setting was utilized for a strictly controlled one-minute interval.

To quantify the efficiency of each setting, a standardized collection protocol was followed. All stone fragments removed during each specific one-minute testing block were captured and isolated. In between the minute testing, the tubing was cleared of fragments. In the end, Fragments were subsequently weighed and dried to ensure accurate measurement of mass. Particles were sorted by size into two categories: small (< 2 mm) and large (≥ 2 mm). Efficiency was defined by the extraction rate (g/min), expressed as medians and interquartile ranges (IQR).

Demographic information and baseline characteristics, including age, sex, body mass index (BMI), prior stone surgery, stone burden, stone volume, and preoperative hydronephrosis, were collected. The primary outcome was the extraction rate (g/min). Statistical comparisons between the four settings were conducted using the paired Wilcoxon Signed-Rank test. Furthermore, the researchers performed targeted sub-analyses to determine if performance varied under specific conditions.

Results

A total of 24 patients were enrolled in this prospective evaluation. The cohort presented with a significant stone burden, characterized by a median stone burden of 36 mm (IQR 32–54, Table 1). The stones were predominantly high-density, with a median attenuation of 1170 HU (IQR 944–1336). Most of the cohort was characterized by a complex stone burden with 75% of the patients having a Guy’s Stone Score of 4 and 87.5% of the patients having a S.T.O.N.E Score of at least 7 or higher. Supine, lower pole anterior calyx access was the most common surgical approach for the PCNL (Table 2). There were no intraoperative complications with a median operative time of 119.5 min (IQR 97.0, 199.0). There were only three 30-day complications (minor, Clavien Dindo I-II) consisting of one postoperative fever and two myocardial infarctions.

Table 1.

Demographic Information and Baseline Characteristics

Variable	Overall1
Age (years)	63.3 (42.4, 76.2)
BMI	27.9 (22.9, 33.6)
ASA
1	1 (4.2%)
2	11 (45.8%)
3	11 (45.8%)
4	1 (4.2%)
Aspirin
No	19 (79.2%)
Yes	5 (20.8%)
Neurological Disease
No	22 (91.7%)
Yes	2 (8.3%)
Diabetes Mellitus
No	17 (70.8%)
Yes	7 (29.2%)
Immunocompromised
No	23 (95.8%)
Yes	1 (4.2%)
Previous Ipsilateral PCNL
No	24 (100.0%)
Yes	0 (0.0%)
Laterality
Left	11 (45.8%)
Right	13 (54.2%)
Guy’s Stone Score
1	2 (8.3%)
2	3 (12.5%)
3	1 (4.2%)
4	18 (75.0%)
Total Number of Stones
1	14 (58.3%)
2	5 (20.8%)
3	3 (12.5%)
4	1 (4.2%)
5	1 (4.2%)
Total Stone Burden (mm)	36 (32.0, 54.0)
Total Stone Surface Area (mm²)	1,080.0 (695, 1,664)
Degree of Hydronephrosis
None	14 (58.3%)
Mild	6 (25.0%)
Moderate	2 (8.3%)
Severe	2 (8.3%)
Number of Calyces with Stones
1–2	3 (12.5%)
3	4 (16.7%)
Full Staghorn	17 (70.8%)
Hounsfield Units	1170 (944, 1,336)
S.T.O.N.E Score
1–6	3 (12.5%)
7–8	10 (41.7%)
9–13	11 (45.8%)

¹Median (Q1, Q3); n (%)

Table 2.

Intraoperative and Postoperative Outcomes

	Overall
	N = 241
Position
Supine	23.0 (95.8%)
Prone	1.0 (4.2%)
Occlusion Balloon Inflated
No	17.0 (70.8%)
Yes	7.0 (29.2%)
Pre-Stented
No	22.0 (91.7%)
Yes	2.0 (8.3%)
Anterior Calyx Accessed
No	3.0 (12.5%)
Yes	21.0 (87.5%)
Location of Access
Lower Pole	22.0 (91.7%)
Interpolar	1.0 (4.2%)
Upper Pole	1.0 (4.2%)
Number of Sticks
1	24.0 (100.0%)
Location in relation to the ribs
Below 12th Rib	23.0 (95.8%)
Between 11th and 12th Rib	1.0 (4.2%)
Size of Sheath
24 F	24.0 (100.0%)
Stent Placed
No	9.0 (37.5%)
Yes	15.0 (62.5%)
Intraoperative Complications
No	0.0 (NA%)
Yes	0.0 (NA%)
Total Operative Time (min)	119.5 (97.0, 199.0)
Transfusion required
No	24.0 (100.0%)
Yes	0.0 (0.0%)
30-Day Complications
No	21.0 (87.5%)
Yes	3.0 (12.5%)
30 Day ED visits/Readmission
No	21.0 (87.5%)
Yes	3.0 (12.5%)

¹n (%); Median (Q1, Q3)

The primary endpoint of stone extraction rate (g/min) demonstrated no statistically significant difference across the four experimental settings. The median extraction rates were as follows: 4 Hz + 100% Impact: 0.50 g/min (IQR 0.24–0.93), 4 Hz + 30% Impact: 0.55 g/min (IQR 0.22–0.87), 12 Hz + 100% Impact: 0.40 g/min (IQR 0.22–0.89), and 12 Hz + 30% Impact: 0.48 g/min (IQR 0.30–0.69).

Comparative analysis between these groups yielded p-values ranging from 0.51 to 0.77, indicating that increasing the frequency or impact power did not enhance the mass of stone removed per minute (Fig. 1a).

Fig. 1.

Comparison of extraction rates(g/min) between the different settings. (a) overall extraction rates, (b) Proportions of extracted particles: small (<2 mm, light colored) vs. large (≥2 mm, dark colored)

The physical characteristics of the fragmented stone were likewise unaffected by the energy parameters. The proportion of small particles (< 2 mm) versus large particles (≥ 2 mm) remained consistent across all settings (Fig. 1b).

To determine if high-energy settings were beneficial for more “difficult” stones, targeted sub-analyses were performed. For the hardest stones in the cohort, fragmentation and extraction efficiency remained independent of the impact and frequency settings (Fig. 2). Efficiency was compared between primarily calcium-based stones and non-calcium-based stones. No significant differences in extraction rates were observed between these chemical compositions, with p-values for calcium-based stones ranging from 0.33 to 0.87 and non-calcium stones from 0.16 to 0.82 (Fig. 3a and b).

Fig. 2.

Comparison of extraction rates (g/min) between the different settings among highly dense stones. (a) overall extraction rates, (b) Proportions of extracted particles: small (< 2 mm, light colored) vs. large (≥ 2 mm dark colored)

Fig. 3.

(a) Comparison of extraction rates (g/min) between the different settings among Calcium based stones. (b) Comparison of extraction rates (g/min) between the different settings among Non-Calcium based Stones

Discussion

The LithoClast^® Trilogy has consistently yielded high stone clearance rates with minimal device malfunctions in various clinical studies [10–12]. Yet the question remains, what are the optimal settings for this device? The clinical management of large renal calculi during percutaneous nephrolithotomy (PCNL) often relies on the assumption that “more is better”—specifically, that increasing the power and frequency of a lithotripter will lead to faster stone clearance. However, our prospective in vivo evaluation of the LithoClast^® Trilogy demonstrates that increasing impact and frequency parameters does not yield a statistically significant improvement in stone extraction rates. Several physiological and mechanical factors may explain why higher energy settings failed to translate into increased surgical efficiency.

In a dual-energy system like the Trilogy, fragmentation and suction occur simultaneously. The Trilogy has already been shown to be the fastest lithotripter due to its large probe diameter and greater downward tip displacement during both ultrasonic and impactor functions [13]. Therefore, our results suggest that the “rate-limiting step” in stone clearance is likely the physical capacity of the suction to evacuate fragments through the 3.9-mm probe, rather than the speed of the ballistic impact itself. Once a stone is comminuted into fragments small enough to be aspirated, providing additional mechanical energy does not accelerate the removal process. This is supported by the fact that suction and ultrasonic settings were kept constant throughout the study to isolate the impact of frequency and power. Furthermore, there is a point of diminishing returns regarding energy delivery in a fluid-filled renal pelvis. At higher frequencies (12 Hz) and maximum impact (100%), the increased kinetic energy may lead to “stone dance” or retropulsion. This phenomenon pushes the stone away from the probe tip, disrupting the continuous contact required for efficient fragmentation and aspiration. By contrast, lower settings (4 Hz) allow for more stable contact between the probe and the stone, maintaining a consistent fragmentation-suction cycle.

The study findings were particularly notable for highly dense stones (≥ 1000 HU) and various calcium-based compositions. Traditionally, surgeons might increase power settings when encountering “hard” stones. However, our data suggests that the baseline energy provided at 4 Hz and 30% impact is already sufficient to overcome the structural integrity of the densest calculi. Therefore, the extra energy provided by higher settings is mechanically redundant and does not facilitate finer comminution or faster extraction. Our clinical findings both support and provide necessary nuance to existing laboratory data. Regarding hard stone data, our results align with ex vivo studies using Begostone phantoms, which found that “hard” stone types were cleared most efficiently at lower settings of 30% impact and 4 Hz.¹⁰ However, a clinical divergence was noted; while ex vivo models suggested that “soft” stones were cleared more efficiently at maximum settings, our in vivo study found no significant difference in efficiency based on stone composition, including non-calcium-based stones. This highlights that the complexities of the operative environment—such as continuous irrigation, unpredictable stone movement, and tissue proximity—may neutralize the theoretical advantages of high-frequency impacts seen in controlled lab settings.

Operating at more conservative settings provides several practical advantages for the urologist. Utilizing lower impact and frequency settings may significantly reduce mechanical wear and tear on the handpiece and expensive lithotripsy probes. Tissue safety studies have shown direct contact trauma caused by dual-energy lithotripters heal without long-term tissue effects [14, 15]. However, no studies have examined potential thermal injury to the urothelium from the heat generated by the probes. While the LithoClast^® Trilogy Max features an optimized cooling system, lower energy settings inherently generate less heat, potentially reducing this risk. From a workflow perspective, because efficiency was independent of stone density and composition, surgeons can utilize standardized “low” settings for all cases, removing the need for intraoperative adjustments based on visual stone characteristics or Hounsfield unit measurements. Finally, supporting research indicates that maintaining suction levels 30–40% is critical to prevent negative intrarenal pressure and renal pelvis collapse, which can lead to loss of vision and bleeding [16]. Some studies have shown that suction levels as low as 10% can maintain stable intrarenal pressures that facilitate fragment removal in porcine kidney models [17].

This study is limited by the one-minute testing intervals for each setting. While this standardized approach allowed for a randomized internal control within each patient, it may not fully capture the cumulative effects of device fatigue or surgeon exhaustion over a multi-hour procedure. Additionally, the study utilized a 3.9-mm probe; results may vary with smaller diameter probes used in mini-PCNL procedures, which were explicitly excluded from this cohort. Ultimately, the Trilogy device has revolutionized PCNL and newer iterations are likely to improve its use, such as a recent study that showed significantly less surgeon effort required for lithotripsy with the use of the lighter weight handle [18].

Conclusion

Higher frequency and impact settings on dual energy lithotripters does not translate to improve efficiency for clearance of large or hard stone. Instead, lower settings may facilitate a more controlled surgical approach to lithotripsy of large, complex stones while minimizing workflow inefficiencies and wear and tear on the equipment.

Abbreviations

BMI

Body mass index

CKD

Chronic kidney disease

CT

Computed tomography

ED

Emergency department

Hz

Hertz

HU

Hounsfield units

IQR

Interquartile range

PCNL

Percutaneous nephrolithotomy

S.T.O.N.E.

(A scoring system for complexity based on Size, Topography, Obstruction, Number of stones, and Essence/density)

US

Ultrasound

Author contributions

Author Contributions: Conceptualization – Kavita Gupta, Ziv Savin, Mantu Gupta.Data Curation –Eve Frangopoulos, Kavita Gupta, Vinay Durbhakula.Formal Analysis – Ziv Savin, Juan Serna.Methodology – Kavita Gupta, Mantu Gupta.Project Administration – Blair Gallante.Resources – Mantu Gupta.Supervision – Mantu Gupta.Writing – Original Draft – Kavita Gupta, Ziv Savin, Juan SernaWriting – Review & Editing – William Atallah, Mantu Gupta.

Funding

This investigator-sponsored study was funded in part by an educational grant from Boston Scientific.

Data availability

The data that supports the findings of this study are available on request from the corresponding author. The data is not publicly available due to ethical issues and the privacy of the participants.

Declarations

Conflict of interest

The authors declare no competing interests.

Ethical approval

Ethical approval to report this study was obtained from our institutional review board (STUDY-24-01300, Ichan School of Medicine at Mount Sinai, 31 March 2025).