Role of ESWL in Era of Miniatured Endourological Modalities

Abstract

Extra corporeal shock wave lithotripsy (ESWL), being the first noninvasive stone treatment, was a landmark development. With its relatively good safety profile, cost effectiveness, and good results in certain types of stone management, it remained a prominent modality for three decades. However, because of the redefined indications for ESWL and the advancement of endourological equipment, its role has become limited. This chapter discusses the indications, advantages, limitations, and new developments of ESWL in this era of rapidly progressing minimally invasive stone surgeries.

1. Introduction

“I will not cut, even for the stone…” Hippocrates

As indicated in the Hippocrates oath, urolithiasis has affected mankind since ancient times, and it also reflects that its surgical management has always been challenging. ESWL invention in the 1980s thus straightaway attracted health care providers and patients towards this modality [1].

Despite the notable successes of newer surgical procedures to deal with renal tract stones, the ESWL, which uses ultrasonic shock waves, holds its place in urolithiasis treatment. It remains the first choice of therapy for relatively small, soft, and suitable-positioned stones [2].

ESWL’s advantages:

1. It is relatively painless, and most patients can return home the same day.

2. It is a safe procedure with a low risk of complications.

3. It is a cost-effective procedure, making it more attractive in monetary terms for health care providers and patients too.

ESWL’s disadvantages:

1. May not be as effective in treating relatively larger stones with increased density and in the lower pole of the kidneys.

2. There are chances of residual stone bulk, necessitating further treatment.

3. There is a small risk of complications, e.g., bleeding, infection, and renal parenchyma damage.

Overall, ESWL is a valuable tool in the treatment of stone disease, as long as the patient selection is correct [3, 4, 5].

2. The shockwave lithotripters

Prior to the development of ESWL in 1980, open stone surgery was the only treatment option for the management of renal tract stones, which were unlikely to pass spontaneously. Over the ensuing years, the modality was put to use mainly for upper renal tract stones [2].

The lithotripsy machines have four basic components:

1. Shockwave generator/energy source

2. Focusing system

3. Coupling mechanism

4. Localizing unit

With time, improvement in the lithotripters has mainly been focused on refining the shockwave generator. In the quest for the most effective lithotripter, there was a shift from electro-hydraulic to piezoelectric and finally to electromagnetic generators. The ultimate objective has been to have an ESWL system that is effective, results in minimal complications, and is cost-effective [2, 3].

3. The technical features of shockwave generators

3.1 Electrohydralic lithotripter

EHL was invented in Kyiv (Kiev) in 1954 and was used in the first model of ESWL in the 1980s by Dornier as HM3. The original method of shockwave is spark-gap technology. The energy that is generated by the spark gap results in vaporization bubbles that collapse and expand in a vicious cycle, and those bubbles strike and fragment the surface of stones (Figure 1).

Figure 1.

Courtesy: ESWL. Electrically produced shock waves can fracture renal calculi. From Polaski and Tatro (1996).

3.2 Piezoelectric

The piezoelectric effect produces electricity via the application of mechanical stress. It was first described by the Curie brothers in 1880. The piezoelectric lithotripter contains ceramic crystals in a water container. These ceramics are activated by high-frequency electrical pulses. These pulses result in the production of shockwaves for the fragmentation of stones (Figure 2).

Figure 2.

Piezoceremic lithotripter. Courtesy: M. Pearle. Shock-wave lithotripsy for renal calculi. Published in the New England Journal of Medicine 2012.

Electromagnetic lithotripters are the latest generation of lithotripters. A high voltage is applied to an electromagnetic coil that creates high-frequency vibration in an attached metallic membrane. The oscillation is then transmitted to a wave-propagating medium to produce shockwaves (Figures 3 and 4).

Figure 3.

Electromagnetic coil: this figure was uploaded by Achim M. Loske.

Figure 4.

Physics of electromagnetic lithotripsy: this figure was uploaded by Achim M. Loske.

There have been multiple studies comparing different machines for lithotripters. Sofras et al. conducted a comparative study with the Dornier HM3 and EDAP LT01 in 1000 patients. The stone-free rate (SFR) in 3 months was 87.5% vs. 90.4%. There was no significant difference for renal stones up to 1 cm [6]. The same findings were reported by Garber and Portis on HM3 lithotripters [7, 8]. A recent comparative trial among three lithotripters concluded that Dornier MPL 9000 resulted in superior treatment outcomes regarding stone-free rates and incidence of re-treatment when it was compared with Piezolith 2300 and Dornier Compact Delta [9]. All those comparisons have inherent flaws due to human, machine, and system biases [7]. Others compared different generations of machines. A comparative study of 13,864 calculi between an unmodified Dornier HM3 (5698 patients) and Medstone STS (8166 patients) found no complications or implications. This study showed SFR was 69.5% with the Dornier HM3 and 72.1% with the Medstone for single renal stones. While comparing the Piezolith 3000 to the previous Piezolith 2300 by matched-pair analysis, for single ureter stones, in 25 pairs [7], there were no differences in outcome.

Clayman defined the stone-free rate at a three-month interval better by the following formula: Effectiveness quotient = 100% stone free/100% stone free + % re-treatment + % auxiliary procedure %. Though this formula is very helpful in defining effectiveness, it still puzzles the researcher regarding clinically significant residual fragments [9].

4. Indications of ESWL in the twenty-first century

Recent literature contains important recommendations about ESWL concerning:

1. Predictors for stone fragmentation.

2. Predicting factors for treatment failure in lower pole and ureteric stones.

3. Contribution to the formulation of guidelines.

4. Maneuvers in procedures, e.g., slower rate and twin-pulse technique, for increasing efficacy and decreasing complications.

5. Comments on the potential role of medical treatment.

6. The role of ESWL in calyceal stones, clinically insignificant residual fragments, anomalous kidneys, obesity, and the ESWL pediatric population.

Before embarking on shockwave lithotripsy, the patient must be counseled for available alternate treatment options, allowing the patient to choose the mode of treatment. The clearance rate, the expected complications, and the procedure will be discussed in detail. A pre-procedure workup, like history, physical examinations, and biochemical profiles, is mandatory to exclude any contraindications to the treatment.

With the invention of advanced modalities like flexible ureteroscopy and mini percutaneous nephrolithotomy, shockwave lithotripsy is still being mentioned and recommended in European and American guidelines for small- to medium-sized suitable stones.

Several factors, such as stone burden, its location, the density in Hounsfield units (HU), pelvicalyceal anatomy, and the body mass index of the patient, determine the successful outcome of ESWL.

4.1 Stone size

Stones with a size less than 2 cm and favorable anatomy, such as upper midpole and pelvis stones, are more amenable to treatment.

However, in certain cases, where either the patient is not fit to undergo PCNL or is unwilling to have a surgical procedure, ESWL may be considered for stones a little larger than 2 cm. Obviously, in such patients, there are potential problems related to stone clearance and other complications, which are to be borne in mind.

4.2 Lower pole stones

Lower pole stones are difficult to clear with ESWL, but stones of appropriate size and low density may also be considered for ESWL. In addition, their clearance is also dependent on some anatomical features. The latter includes the lower pole-draining infundibular width, its length, and the infundibular pelvic angle. Stones with a size less than 1 cm have been reported to have a satisfactory clearance [3]. The details are shown in Figure 5.

Figure 5.

Details of a anatomical predictive factors of Lower calyx for stone free rates in ESWL.

In a randomized trial comparing the clearance of 14 mm lower pole calculus, the SFR was dramatically better with PCNL than ESWL, i.e., 95% vs. 37% [3]. Although stone-free rates are relatively lower in lower pole stones, tactics to facilitate fragments after shockwave lithotripsy are postural inversion, diuresis, and mechanical percussion, which can label 60% of these patients free of stone [5].

4.3 Ureteric stones

ESWL treatment of proximal ureteric stones between 1 cm and 1.5 cm has also been reported in the literature and guidelines. In a large randomized controlled study, ureteroscopy showed a marginally improved outcome in terms of stone clearance; nevertheless, shockwave lithotripsy had better results in terms of health care costs [8].

4.4 In transplanted kidneys

Stones in transplanted kidneys have also been reported and successful, but caution must be exercised in dealing with such cases as patients are immunocompromised and anatomically different from the normal population. Distal patency for stone clearance post-procedure must be made ensured [10].

4.5 In bladder stones

Extracorporeal shockwave lithotripsy for bladder calculi has also been deemed safe and effective [11]. Bladder calculi are mobile and not ideal for ESWL; however, patients reluctant to undergo endoscopic procedures with stone sizes less than 2 cm can safely opt for ESWL.

4.6 Pre-ESWL Ureteric stents

The Pre-ESWL ureteric stent has been under a lot of controversy. For stones between 15 and 20 mm, a stent would prevent obstruction due to larger fragments. The stent itself requires the patient to undergo anesthesia and experience stent-related morbidity. Therefore, the placement of a stent is a personalized choice, keeping in mind the patient’s condition, accessibility to the hospital in case of post-ESWL stone impaction, and other socioeconomic factors.

4.7 ESWL in obese patients

Controversy exists about the use of ESWL in obese patients as an important factor in predicting the outcome. Patients with a high body mass index, i.e., a BMI > 30 kg/m² are less likely to benefit from extracorporeal shockwave lithotripsy due to the increased skin-to-stone distance. A recent study proved the stone-free rates after 3 months in obese patients are 68% versus 80–85% in non-obese patients [5]. Obesity is also associated with a greater number of ESWL sessions. It is mentioned in the literature that patients with a waist circumference >10² cm require more than two sessions.

4.8 ESWL in the pediatric population

ESWL is still considered the most favorable therapeutic option in the pediatric population. ESWL is dramatically effective in stone fragmentation with low complication rates. Its effectiveness has been reported at a range of stone-free rates in children. For stones sized <20 mm, it’s 67–93% in the short term and 57–92% in the long term. Stone-free rates in children after ESWL should be periodically assessed at a 3-month interval. A complete metabolic profile is mandatory for children with urolithiasis. Piezoelectric lithotripters are frequently mentioned with a lesser degree of pain in children. Our greatest invention is human curiosity. Minimal Access Surgery: Keeping in view the effectiveness quotient, the space of relative less clinical effectiveness of ESWL in terms of SFR was filled by the curiosity of scientists involved in making tools for minimal access surgery (MAS). In the second decade of the twenty-first century, MAS surpassed ESWL in clinical practice, evidence-based medical literature, and clinical effectiveness.

The journey of miniaturization from conventional PCNL to mini PCNL and ultra mini PCNL has so far taken a short stop on micro PCNL. All these miniaturizations have resulted in enhanced safety along with better stone fragmentation with the development of newer intracorporeal lithotripsy devices like lithoclast, trilogy, and holmium lasers. The development of effective flexible ureteroscopes with access sheaths has encouraged urologists to use mini PCNL in the supine position along with flexible URS in the same setting. All these developments in MAS, or natural orifice surgery, have studded the evidence-based medical literature. In a recently published meta-analysis by Kim et al. in 2020 [9], that, firstly, PCNL had the highest stone-free rates than others regardless of stone sizes, and RIRS showed higher stone-free rates than ESWL in <2 cm stones. Secondly, ancillary procedures were higher in ESWL than others. Finally, in stones <2 cm, the re-treatment rate of ESWL was higher. ESWL is still safer than other modalities, with a higher complication rate in PCNL than in URS and ESWL [9]. The 2023 EUA and AUA guidelines also endorse the better stone-free rates for endourological options of PCNL/URS in stone sizes above 20 mm, lower pole stones above 15 mm, and ureteric calculi. In upper ureteric calculi, the URS offers better SFR and ESWL a better safety profile. The safety profile of ESWL has also been enhanced by using losartan and selenium-based multivitamins. Other recent papers favor PCNL and URS as equally safe and effective in the low-volume disease of urolithiasis. A meta-analysis of 2927 patients with lower calyceal stones showed a decreased SFR for ESWL (52.9%) versus PCNL. The conclusion was that even stones of 11–20 mm are best treated by PCNL, with no difference in complication rates or quality of life [6, 9]. Thus, it is important to identify the patients likely to achieve failure in ESWL. With this, we can save the ESWL as one of the most effective modalities in the management of renal stones. For this purpose, the right patient selection should ensure the exclusion of persons with obesity, bleeding diathesis, failure of ESWL, complicated renal anatomy, hard stones on CT KUB, lower calyceal stones with unfavorable anatomy, struvite stones, and large stone burdens.

4.9 Safety profile of ESWL versus PCNL

Though literature suggests that PCNL and retrograde intra renal surgery (RIRS) are more effective in achieving stone-free rates in the management of urolithiasis than ESWL, however, ESWL still has, to its credit, a better safety profile than all sorts of percutaneous treatments. The complications of PCNL include intraoperative bleeding, hypotension, and postoperative hematuria. The need for blood transfusions in PCNL is about 3.5%. A recent meta-analysis published states that ESWL had lower complication rates than percutaneous nephrolithotomy (p < 0.001). However, there was no significant difference between complications of ESWL and RIRS [7, 8, 9].

4.10 ESWL, a landmark invention, from fading into oblivion

The first and foremost solution is that the established usefulness of ESWL must not be overlooked, and secondly, efforts to develop better-performing upgraded lithotripters must be hastened. In this regard, the new innovative technical developments are already underway.

The newer developments in SWL include twin-head and dual-pulse shock-wave generators; broad focus; low pressure systems; augmented coupling; self-operating location; and auditory tracking systems. The new developments, including evaluating lasers and histotripsy, have raised new hope for more effective ESWL. These innovations will contribute to a better SFR. As mentioned before, special emphasis should be drawn on attempting ESWL in obese patients, as it negatively affects the SFR not only for ESWL but also for endourological modalities [12].

It is worth mentioning that if the urologists get more familiar with the pathophysiology and physics of shock waves, much better results can be achieved in the future. This may lead to promoting the ESWL as one of the first lines of treatment in the management of urolithiasis in the era of miniature endoscopic equipment.

5. Summary

Despite all these years of the notable ESWL role and its exceptional importance as the only noninvasive stone treatment modality, the feeling of its diminishing importance is creeping in. This impression has developed due to the rapid development and success of MAS.

Nevertheless, with further refinements in the Lithotripters and attention paid to the correct patient selection for lithotripsy, ESWL still has a role in the treatment of certain renal or upper ureteric stones, especially in patients who cannot or prefer not to have stone surgery.

Ureteroscopy and PCNL offer higher success rates and greater versatility in treating larger or complex stones, but in terms of a better safety profile and cost effectiveness, ESWL still has an important place in the armamentarium for managing nephrolithiasis.

The European Union guideline suggests the use of ESWL or RIRS for the primary treatment of renal stones smaller than 2 cm and PCNL for stones larger than 2 cm. Although SFR is one of the essential points to consider when choosing among treatments, one also has to bear in mind the advantages and disadvantages of different methods of treatment when choosing the one that is most suited to that particular patient.