Extracorporeal Shockwave Lithotripsy

Anatomy and Physiology

Stones can develop anywhere along the urinary tract, from the kidneys to the urethra. While they commonly originate in the renal calyces, they can subsequently obstruct critical points such as the ureteropelvic junction (UPJ), ureter, or ureterovesical junction (UVJ). The physiology underlying stone formation is intricate, involving many factors. See StatPearls' companion reference, "24-Hour Urine Testing for Nephrolithiasis: Interpretation and Treatment Guidelines," for more details.[4] Most renal stones begin as Randall plaques within the kidney. These plaques consist of calcium phosphate concretions deposited in the interstitial tissue of the renal papilla, typically at the collecting duct outlet. In individuals prone to calcium oxalate stone formation, calcification predominantly occurs within the basement membrane of the loops of Henle. 

Randall plaques originate beneath the renal urothelium and gradually enlarge until sections of the plaque are directly exposed to urine within the renal pelvis. Upon continuous contact with urine, crystal layers typically start to organize and accumulate on the nidus through processes of aggregation and epitaxy.[5] Calcium oxalate stones are the most prevalent chemical composition among urinary calculi and are prone to form when the urinary pH is under 7.2, a condition shared with uric acid stones. Additionally, acidic urine (not hyperuricosuria) is the leading cause of uric acid stone formation. Calcium phosphate predominant stones typically develop in urine with a more alkaline pH. The most common renal calculi are those containing calcium, followed by uric acid and struvite (associated with infection) stones. Cystine stones, on the other hand, are relatively rare, accounting for only 1% to 2% of all urinary stones.[6]

Indications

The most common indications for surgery in urolithiasis include intractable or persistent (for more than 72 hours) renal colic pain, nausea, vomiting, infection, or worsening renal function. While treatment with a double J stent can provide immediate relief from blockage or obstruction, enabling symptomatic recovery, definitive management of the calculi typically necessitates an elective stone surgical procedure.

ESWL is an elective procedure suitable for calculi located anywhere in the ureters or kidneys, although it is favored for renal and proximal ureteral calculi. While typically scheduled as an elective procedure, ESWL can also be promptly conducted in urgent situations, such as acute renal colic caused by ureterolithiasis.[4] ESWL is often compared to ureteroscopy, another elective procedure renowned for its higher initial success rate and typically favored for treating distal ureteral stones. However, it is essential to note that ureteroscopy is considerably more invasive than ESWL.

The indications for surgical treatment of urolithiasis encompass several scenarios:

• Failure of a ureteral stone to move or pass within 4 to 6 weeks
• Lack of urinary output (anuria) or severe oliguria (necessitating a double J stent)
• Presence of large calculi (>10 mm)
• Obstructed pyelonephritis (known or suspected) requiring double J stent placement
• Obstructed solitary kidney necessitating a double J stent placement
• Patient preference for surgical intervention
• Persistent or poorly controlled symptoms (including pain, nausea, vomiting)
• Simultaneous bilateral ureteral obstruction necessitating double J stent placement
• Simultaneous urinary tract infection (UTI) requiring double J stent placement
• Urosepsis necessitating double J stent placement
• Worsening kidney failure or loss of renal parenchyma [5][6][7][8]

ESWL is the only outpatient surgical procedure for renal and ureteral calculi that is truly noninvasive. Informed about their options, many patients opt for ESWL due to its safe and noninvasive nature. The choice between ESWL and alternative treatment modalities like ureteroscopy depends on several factors, including stone size, burden, composition, and more. Additionally, patient preference and expectations play a significant role in determining the most suitable treatment approach.

For nonstaghorn renal and ureteral calculi less than 2 cm in size, ESWL is considered a viable first-line treatment. However, success rates of ESWL notably diminish for stones larger than 2 cm.[9] If the patient is not a candidate for general anesthesia, ESWL remains a viable option even for larger stones, as it can be performed under local anesthesia or intravenous sedation.[10] This flexibility in anesthesia options further broadens the accessibility of ESWL as a potential treatment choice for a broader range of patients with larger stones.

Ureteric stent placement is advisable when treating larger stones, particularly those exceeding 15 mm by 15 mm in their largest dimensions, especially if they surpass 20 mm. This approach helps minimize the risk of post-ESWL colic and ureteral blockage resulting from a large collection of obstructing stone fragments (steinstrasse). Stone location is an essential predictor of ESWL success rates. While ESWL can fragment stones in lower renal calyces, their clearance post-treatment is hampered due to the dependent nature of the lower pole. In lower pole stones exceeding 10 mm in size, ESL exhibits lower stone-free rates and outcomes than percutaneous nephrolithotripsy or ureteroscopy in that same region.[11] 

Favorable factors contributing to the clearance of lower pole calyceal stones with ESWL include stone size less than 10 mm, absence of other stones (ensuring maximal shockwave exposure to the solitary calyceal stone for optimal fragmentation), a favorable infundibulopelvic angle, and an infundibular width greater than 4 mm.[12][13][14][15] Stone composition and visibility significantly impact treatment outcomes. While ESWL effectively fragments uric acid stones, their radiolucency can pose challenges for fluoroscopic visualization. In such cases, intravenous contrast or diluted contrast can be gently injected directly into the affected ureter via a retrograde ureteral catheter.

While calcium oxalate monohydrate, cystine, and calcium phosphate stones are considered relatively resistant to ESWL, their variable compositions often render them susceptible to fragmentation by lithotripsy.[16] However, staghorn stones are typically better addressed through alternative treatment modalities, primarily due to their substantial size. Stone density, measured by Hounsfield units (HU) on a noncontrast computed tomography (CT) scan, is another crucial consideration before ESWL. Several studies have highlighted that ESWL yields superior outcomes for stones measuring less than 1000 HU, with the stone-free rate declining as the HU value surpasses this threshold.[17][18][19][20][21]  

In addition to stone characteristics, several patient-specific factors help determine the optimal treatment approach for urolithiasis.[22][23]

• Obesity presents challenges with on-table positioning and impacts radiographic quality during procedures.
• A skin-to-stone distance of <10 cm is an independent predictor of a higher stone-free rate following ESWL.
• A higher body mass index (BMI >30 kg/m²) correlates with reduced lithotripsy success.
• Anatomic abnormalities such as calyceal diverticula, kidney malrotation, skeletal abnormalities, and renal fusion anomalies necessitate thorough evaluation and careful consideration when contemplating ESWL.[22][23]

Ureteroscopy is the primary alternative to ESWL but entails notably higher invasiveness and carries a higher complication risk.[24][5] Ureteroscopy has superior initial success rates and lower retreatment rates than ESWL, especially when treating radiolucent or cystine stones. For more information and details on ureteroscopy, see Statpearls' companion reference on "Ureteroscopy."[28]

When repeated ESWL treatments are included, the overall success rates between ureteroscopy and ESWL become comparable.[8][9][27][29][30][31][32][33][34][35] Therefore, the choice between ureteroscopy and ESWL should be carefully weighed, considering factors such as stone characteristics, patient preferences, and potential need for repeated treatments.

Contraindications

ESWL during pregnancy has been linked to numerous serious complications, including low birth weight, miscarriages, gestational diabetes, increased ionizing radiation exposure, and placental displacement.[25] Therefore, ESWL is contraindicated in pregnancy.[5][24][25][26] Patients with a significant abdominal aortic aneurysm face an elevated risk of bleeding and rupture if they undergo ESWL.[27][28] Therefore, caution should be exercised, and alternative treatment options should be considered for this patient population to mitigate the risk of adverse events.

Patients with untreated bleeding diathesis or those on antiplatelet, antithrombotic, or anticoagulant medications are at increased risk of bleeding complications.[29][30][31][32] Discontinue these medications well before the ESWL procedure.[33] In cases where it is unsafe to withhold these medications, delaying ESWL or exploring alternative treatment options, such as ureteroscopy, should be carefully considered and discussed with the patient, as it can be performed in anticoagulated patients.[34] Severe or poorly controlled hypertension is a significant risk factor for bleeding and perinephric hematomas following renal ESWL and is thus considered an absolute contraindication.[12][35][36] Before ESWL, careful assessment and optimization of blood pressure control are imperative to minimize the risk of these complications.

Patients with infected stones, untreated UTIs, or bacteriuria are at an increased risk of pyelonephritis, bacteremia, and sepsis following ESWL. Moreover, whether anatomical or functional, a ureteral obstruction located distal to the stone being treated represents a contraindication to ESWL therapy. The inability to visualize the calculus, even with intravenous or retrograde pyelography, is a relative contraindication, as accurate stone targeting may not be achievable. In such cases, alternative imaging modalities or treatment approaches may need to be considered for optimal stone management.

Equipment

ESWL utilizes a generator to create pressure waves, usually under water. These pressure waves are directed towards a specific target area called F2, corresponding to the stone location following patient positioning. As the pressure wave energy traverses through water and soft tissue, it remains benign until it reaches a concretion (the calculus) at F2, where it becomes focused and intensified, reaching maximum intensity as it converts to kinetic energy. This energy subsequently pulverizes and fragments the stone into smaller pieces.

Stone fragmentation by shockwave forces involves several mechanisms, including cavitation, cleavage, fatigue, shear stress, spall fracturing, squeezing, and superfocusing.[37][38][39][40] These are outlined as follows:

• Cavitation is characterized by forming small gas bubbles in the fluid immediately surrounding the stone.[40] The bubbles are caused by the intense negative pressure of the pressure wave generated by the shockwave upon encountering the stone.[40] As each bubble rapidly collapses, it emits a tiny jet of high-energy fluid that impinges upon the surface of the calculus.[40]
• Cleavage of the stone typically occurs parallel to the plane of wave propagation at higher pressure settings and perpendicular at lower pressures.[37] This process involves the development of microcracks along the plane inside the stone, which gradually coalesce to form a cleavage plane.[37]
• Fatigue refers to the phenomenon wherein the stone fragments at points where the calculus has angles, cracks, or other imperfections. These defects concentrate the energy, producing focal pockets of high stress that create micro-fractures. Over time, these micro-fractures propagate into larger cracks, ultimately leading to stone fragmentation.[37]
• Shear stresses develop as the shockwaves enter the stone, interacting with its internal walls and between layers. Kidney stones typically consist of layers that are especially prone to experiencing shear stress pressure.[37][38]
• Spall fracturing occurs when the shockwave enters the stone and is reflected from its internal rear surface. The energy reflected, combined with other forces, generates foci points of high energy and stress within the stone, forming internal fractures.[37]
• Squeezing produces circumferential pressure and stress on the calculus, resulting from the variation in propagation speed of the shockwave between the stone material (which propagates faster) and the surrounding fluid (which propagates slower).[37]
• Superfocusing refers to the phenomenon where internal energy refracts within the stone, akin to spall fracturing, creating localized areas of high pressure and stress internally. This process leads to the formation of microcracks and fractures within the stone.[37]

Lithotripters are categorized according to the mechanism of shockwave generation, with 3 main types: electrohydraulic, electromagnetic, and piezoelectric. These devices generally offer comparable efficacy and stone-free rates.[41] These lithotripters are described as follows: 

Electrohydraulic (spark-gap) technology uses an electrical discharge from an underwater spark plug positioned at one focal point (F1) of an ellipsoidal reflector, usually crafted from solid brass. The spark creates gas for a fraction of a second, producing the pressure generating the shockwave. Patients are positioned such that the stone aligns precisely with the reflector's focus, known as F2.

This original shockwave generator model is generally acknowledged as highly effective in fragmenting stones, offering a relatively large treatment area (F2). However, it is susceptible to significant pressure variations between shocks, and the shockwave's nature changes as the electrode wears down. Furthermore, the spark plug electrode has a short lifespan and necessitates frequent replacement. 

A recent development is electroconductive ESWL generators, which utilize carbon and graphite-based solutions to enhance energy delivery efficiency and reduce shockwave production variability compared to standard electrohydraulic ESWL machines. Predictors of successful ESWL therapy include stone chemical composition, density, stone size, and skin-to-stone distance. These factors play crucial roles in determining the efficacy and outcomes of shockwave lithotripsy.

Electromagnetic generators produce a shockwave inside a cylindrical tube generated by a vibrating metallic membrane activated by a high-voltage electromagnet. Subsequently, an acoustic lens or parabolic reflector is employed to focus the shockwave energy.

These generators produce shockwaves that are not notably predictable and consistent. Their delivery over a vast body surface reduces patient discomfort, and the machines themselves are highly durable. However, the treatment area or target is relatively small, necessitating precise targeting, which can pose a challenge. Nevertheless, the machines offer very accurate targeting. Due to their highly focused energy, electromagnetic generators induce more subcapsular renal hematomas than other ESWL machine types.

Piezoelectric machines utilize unique ceramic crystals with vibrating properties upon exposure to a high-frequency electrical pulse. These ceramic crystals are arranged in a hemispherical or ellipsoidal dish, each with a predetermined focal point. When the ceramic crystals vibrate collectively, they concentrate and focus to create a shockwave. Piezoelectric shockwave generators offer several advantages, including a high degree of focusing accuracy and machine durability. Like electromagnetic machines, piezoelectric-generated shockwaves enter the body over an extensive surface area, resulting in minimal patient discomfort. However, the target area is relatively small and narrow.

Despite its accuracy and durability, piezoelectric technology has limitations in delivering high energy to the stone target compared to other ESWL machines, thereby restricting its stone-breaking capability. To address this drawback, a double piezoelectric layer has been implemented.[42][43][44] In addition to the shockwave generator, essential equipment for ESWL includes ultrasound or fluoroscopy for stone localization and targeting, a specialized table for patient positioning and access to the ESWL machine, and a coupling mechanism to optimize shockwave delivery while minimizing acoustic impedance or energy loss.

Personnel

Medical professionals involved in ESWL include the performing provider, an assistant, and an anesthetist. The anesthetist's role is to ensure adequate anesthesia and analgesia to reduce the patient's stress and prevent patient movement due to pain during the procedure, which may result in decoupling. The provider should be present to localize the stone at the beginning of the procedure and ensure proper targeting throughout the procedure. The stone commonly disintegrates, moves, or even starts with multiple stones. Therefore, it is paramount that the provider is present to primairly plan the treatment session and adapt the targeting to any variation during the procedure itself.

Preparation

Before proceeding with ESWL, a comprehensive evaluation is imperative, comprising a detailed patient history and a thorough physical examination. This assessment aims to identify any contraindications to ESWL, locate the stones precisely, assess potential complications related to urolithiasis, ascertain positive and negative risk factors for ESWL therapy, and uncover any hidden risk factors or underlying pathology. This meticulous approach ensures patient safety and optimizes treatment outcomes.

An x-ray of the kidneys, ureters, and bladder (KUB) or renal ultrasound is frequently employed as the initial screening test for significant nephrolithiasis. Ultrasound can detect noncalcified stones larger than 5 mm, identify obstruction and hydronephrosis, and calculate the renal resistive index to aid in identifying ureteral obstruction. However, KUB provides greater detail regarding the shape of the stone and its fluoroscopic visualization, which is essential for accurately targeting calculi during ESWL.

An unenhanced, noncontrast CT scan of the abdomen and pelvis is the most sensitive diagnostic tool for localizing calculi and detecting associated complications. Although not mandatory, it offers valuable insights into the internal renal anatomy, skin-to-stone distance, number of calculi, stone density (measured in HU), and other factors influencing treatment.[32] This comprehensive assessment aids in formulating an effective treatment plan tailored to the individual patient's needs.

Additional investigations, such as urinalysis, urine culture, and white blood cell count with differential, are essential to rule out infections and assess the patient's overall health status. These tests provide valuable information regarding urinary tract health and help guide treatment decisions in cases of suspected infection or inflammatory processes associated with urolithiasis. Coagulation profiling should be conducted to identify any underlying bleeding diathesis, as ESWL does not allow immediate surgical intervention for unexpected or unusual bleeding complications. This proactive approach ensures patient safety and appropriately manages any potential bleeding risks during the procedure.

Shared decision-making discussions should be conducted with the patient and their family to provide education and discuss the various treatment options available, along with their associated benefits and potential risks. Ensure the patient fully understands the implications of their choices. Obtaining informed consent before initiating the procedure is crucial. This affirms the patient is fully aware of the procedure's nature, potential outcomes, and associated risks, empowering them to make informed decisions about their care. In discussions surrounding ESWL, critical factors such as the potential for requiring a second ESWL treatment should be addressed. This consideration should be thoroughly compared to alternative management options, such as ureteroscopy, ensuring a fair and comprehensive assessment of the available choices.

Advantages of ESWL compared to ureteroscopy include:

• Less invasive and very well-tolerated
• Much lower complication rate.
• Inherently safer procedure
• Optimal for brittle stones (<900 HU on unenhanced CT scans)
• Surgical time is relatively short and predictable
• Comparable stone-free rate
• Can be performed anywhere in the urinary tract
• Best used for proximal ureteral and renal calculi
• Can usually be done with just intravenous sedation
• No double J stents are typically required
• No pre-stenting is needed except for symptomatic relief or infection control before the procedure
• No need for ureteral dilation or ureteral access sheaths
• Best used in the kidney and proximal ureter
• Can be used to treat a ureteroscopy failure or complication
• Preferred by many patients who wish to avoid more invasive surgeries
• Appropriate for patients who are frail, pediatric, or older
• ESWL is much more cost-effective than endourological procedures, even though additional procedures are required more often [32][45][46][47]

Disadvantages of ESWL compared to ureteroscopy include:

• Not optimal for radiolucent, ESWL resistant, or very hard stones such as brushite, cystine, calcium oxalate monohydrate, and uric acid
• May not be effective for very radiodense stones (>1,000 HU on unenhanced CT scans)
• Less effective for larger stones, especially if >20 mm
• Will not yield optimal results in patients with a skin-to-stone distance >10 cm or in morbidly obese individuals
• Not ideal if multiple stones not grouped together are targeted, as each kidney should only receive a maximum total of 3000 to 4000 shocks per ESWL session
• Lower calyceal stones can be fragmented with ESWL but are much less likely to pass, resulting in lower rates of stone clearance.
• While the stone-free rate is comparable to ureteroscopy, achieving this may require more than one lithotripsy treatment and typically takes longer
• Ureteroscopy is generally preferred and easiest for distal ureteral calculi
• Stones that fail 2 ESWL treatments will most likely require a different therapeutic modality, such as ureteroscopy
• Salvage ureteroscopy after an ESWL failure has a lower success rate and more complications than primary ureteroscopic surgeries
• ESWL is contraindicated in pregnancy, active anticoagulation, severe or poorly controlled hypertension, aortic aneurysms in the therapy or blast path, and untreated coagulopathies [45][32][48]

Technique or Treatment

ESWL was pioneered and used in Germany in 1980, receiving Food and Drug Administration (FDA) approval in the US in 1984. Since then, millions of renal and ureteral calculi have been successfully treated with this modality, solidifying its status as one of the primary surgical interventions for ureteral stones.[5][24] Widely regarded as the least invasive urological surgical modality for urinary calculi, ESWL boasts good efficacy and an extremely low complication rate.[49]

Coupling refers to the interface between the shockwave generator and the patient's body. Modern ESWL machines require direct contact with the patient using a fluid medium, typically facilitated by a water-filled balloon infused with ultrasound gel to enhance shockwave energy transmission.[50] An essential therapy objective is to minimize pressure loss during coupling, as air gaps and bubbles impede efficient shockwave energy transmission, leading to significant power losses.[29][36][51][52]

Even a small air pocket covering just 2% of the treatment head can diminish shockwave transmission energy efficiency by up to 40%.[51] This highlights the importance of meticulously applying the gel to minimize energy loss, as it can profoundly impact the efficacy of ESWL treatment.[51]

The recommended approach is to apply a generous amount of transmission gel directly from the stock container onto the treatment head, allowing it to spread upon contact with the patient. This method effectively minimizes air gaps and bubbles, improving coupling and maximizing shockwave delivery.[20][29][36][51][52][53][54] Applying gel to the treatment head and the patient's skin can create additional air gaps.[54] Similarly, using smaller gel bottles or gloved hands for application is discouraged, as these methods tend to introduce more air bubbles and gaps.[54]

Once optimal acoustic coupling is established, breaking contact, such as for repositioning purposes, can reduce shockwave energy transmission substantially by up to 50% or more.[51] This underscores the importance of aintaining continuous and uninterrupted contact throughout the ESWL procedure to ensure consistent and effective shockwave delivery.

Stone localization for targeting is usually conducted using fluoroscopy.[49] In the past, the original HM-3 machine utilized 2 fluoroscopes positioned at a 90° angle. The alignment of the target stone at the precise center of each fluoroscope indicated its optimal focus point for F2. Newer models have streamlined this process, often employing a C-arm, facilitating straightforward determination of length (forward and backward) and width (right to left). However, rotation of the C-arm is required to determine the stone's height. Once the other parameters have been optimized, only a 30° angle of the C-arm is necessary to determine the height for targeting. This streamlined approach simplifies stone localization and ensures efficient and accurate targeting during ESWL procedures.

Ultrasound can be an alternative method for targeting and stone localization during ESWL procedures. Unlike fluoroscopy, ultrasound does not involve ionizing radiation and can visualize even radiolucent stones. However, identifying smaller calculi, especially in the mid-ureter or in the presence of a ureteral stent or catheter, can be more challenging with sonography.[55][56] Ultrasonographic targeting relies heavily on the operator's proficiency, with more experienced practitioners typically achieving superior results. Some newer machines offer the capability for both fluoroscopic and sonographic stone localization and targeting, allowing clinicians to leverage the strengths of both imaging modalities.[12][57][58]

Useful predictors of successful ESWL therapy include known or suspected stone chemical composition, CT density measured in HU, stone size, number, grouping, and patient characteristics such as obesity (BMI). Additionally, factors such as internal renal anatomy (nephrolithiasis), skin-to-stone distance, and degree of ureteral stone impaction play crucial roles in treatment outcomes. When multiple negative predictive factors are present, consideration should be given to alternative therapies, such as ureteroscopy for patients with urolithiasis.[34][45]

• The chemical composition of the calculus plays a crucial role in determining the success rate of ESWL therapy, as certain stones exhibit greater resistance to shockwave fragmentation, such as brushite, cystine, and pure calcium oxalate monohydrate.[5][24] Alternative treatments like ureteroscopy and laser lithotripsy may yield better outcomes for these stones.[5][24] 
  • Uric acid stones fragment easily with ESWL therapy, although they pose challenges in visualization without retrograde pyelography or intravenous contrast.[5][24] 
  • To enhance stone visualization during ESWL, a ureteral catheter can be inserted before the procedure, with diluted contrast injected periodically to aid in stone visualization.[5][24] 
• A high body mass index (BMI >30 kg/m²), indicative of significant obesity, correlates with poorer outcomes from ESWL due to fatty tissue attenuating the shockwave energy.[49][59][60][61]
• Enhanced clearance of renal calyceal fragments is observed in kidneys characterized by short, wide infundibula (>4 mm wide), minimal distance from the calculus to the lower lip of the calyx, upper and middle pole calyces versus lower pole, the degree of stone fragmentation, solitary stone size less than 10 mm, and a more obtuse angle between the calyceal stone target and the renal pelvic outflow channel.[12][13][14][15][36][62]
• Stone density, as measured in HU on unenhanced CT scans, is a useful indicator of the stone's relative density and responsiveness to ESWL therapy. Generally, stones measuring 900 HU or less are conducive to effective fragmentation with ESWL, while those exceeding 1000 HU tend to resist shockwave therapy.[5][17][18][19][20][21][24][61] Lower HU density readings correlate with higher success rates in ESWL treatment.[20]
• A skin-to-stone distance exceeding 10 cm is associated with a higher failure rate in treating ureteral and renal calculi with ESWL, regardless of other contributing factors.[17][63][64]
• Stone size is a crucial predictor of successful ESWL treatment.[17][65]
  • Stones <10 mm in size are typically excellent candidates for ESWL therapy.
  • Stones ranging from 10 mm to 20 mm may be treated with careful consideration of factors such as location, density, and composition.
  • ESWL is not generally recommended for stones >20 mm, although it may be considered in some situations, with a stent recommended to minimize the risk of steinstrasse.
• A higher degree of ureteral stone impaction presents a challenge for successful fragmentation with ESWL. Negative predictive factors include the following:
  • A greater degree of hydroureteronephrosis
  • A higher renal resistive index calculations
  • Absence of ureteric jets
  • Thicker ureteral walls
  • Ureteral stone size and number [12][36][66]

Stent placement before ESWL therapy is not required but can offer benefits such as symptom relief or infection control before definitive stone surgery.[5][24] A stent is recommended for patients with specific conditions, including those with a solitary kidney, larger renal stones (>15 mm x 15 mm) that might cause steinstrasse, and cases where locating the stone for treatment would otherwise be challenging.[5][24][67] 

A double J stent is less critical for ureteral calculi unless there is significant obstruction.[36][68] Stent placement does not increase the overall stone-free rate after ESWL but tends to lower it.[5][24]

Antibiotics are not required before ESWL. However, a preoperative urinalysis should be conducted, and any infection or bacteriuria should be treated and eliminated before therapy.[29][31] Antibiotics should be considered in patients with a history of UTIs or if the likely stone composition suggests infection.[36]

Medical treatment appears to be reasonably helpful in ESWL. 

• N-acetylcysteine pretreatment has been observed to minimize renal tissue damage and injury during renal ESWL, especially when combined with the slow ramping-up protocol.[69] A dosage of 600 mg before bed was used, starting 2 days before ESWL therapy and continuing for 1 day postoperatively.[69]
• NSAIDs administered immediately before ESWL therapy minimize postoperative patient discomfort and decrease the requirement for post-procedure analgesics.[12][20][36][52][53][70][71][72]
• Intravenous hydration and intravenous furosemide have shown to be beneficial during ESWL of renal stones, although their efficacy in treating ureteral calculi remains uncertain.[73]
• After lithotripsy, the use of medical expulsive therapy (tamsulosin, alfuzosin, silodosin) facilitates the clearance of stone fragments, improves the overall ESWL success rate, reduces the risk of steinstrasse, improves the stone-free rate, lowers the risk of major adverse events, and shortens the stone clearance time.[5][12][20][24][74][75]

Extracorporeal Shockwave Lithotripsy Therapy: Tips, Tricks, Advice, and Suggestions

Patient selection

Patient selection criteria for ESWL should consider several factors:

• Stone size: ESWL is less effective for stones >20 mm, as it will likely leave large fragments requiring additional procedures and a double J stent.[5][24] This size limit may be increased to 30 mm for stones with lower density (<900 HU), which would be expected to be brittle and easily fragmented.[36][76] Stones approaching 20 mm that are cystine, pure calcium oxalate monohydrate, or brushite may also warrant reconsideration due to their hardness and resistance to ESWL.[36]
• Timing of N-acetylcysteine: If N-acetylcysteine is used, it should be initiated 48 hours before the scheduled ESWL procedure.[69]
• Pre-stenting: A brief period before surgery can improve the stone-free rate for larger renal calculi treated with ESWL by facilitating ureteral dilation.[53][77]
• Special populations: ESWL can be considered for stones in transplanted kidneys and frail, pediatric, and elderly urolithiasis patients, as it is generally the safest surgical option for them.[32][78][79][80]
• Contraindications: Ensure that the patient has no contraindications to ESWL, such as a new UTI, and confirm that the patient has stopped any anticoagulation drugs when instructed.
• Informed consent: Before the ESWL procedure, provide an objective review of the proposed treatment, alternatives, risks, and benefits as part of the informed consent process. Address all patient questions satisfactorily to ensure shared decision-making. 

Preparation, setting up, and targeting

• Perform a KUB x-ray immediately before administering anesthesia or entering the operating room for ESWL treatment. This step ensures the target stone is still visible and has not shifted significantly or passed spontaneously. 
• Ultrasound can be used for stone targeting in ESWL, yet its efficacy can vary based on the location and nature of the stone. While it is effective for renal calculi, its utility for ureteral stones is limited due to factors such as the absence of distinct landmarks, the typically smaller size of ureteral stones, and the interference caused by bowel gas. Nonetheless, ultrasound can yield outcomes comparable to those of skilled operators of other imaging modalities for ureteral stone targeting.[12][29]
• If the stone is not visible, several options can be discussed with the patient calmly: 
  • Rescheduling imaging for a later outpatient appointment
  • Conducting an ESWL simulation 
  • Proceeding with a cystoscopy accompanied by a retrograde pyelogram
• Based on the findings of the retrograde pyelogram:
  • The ESWL procedure may be canceled
  • Placement of a double J stent could be considered
  • Ureteroscopy may be indicated
  • Retrograde catheter could be retained and intermittently injected with diluted contrast to aid in stone visualization and targeting during ESWL
• Retrograde catheters can be inserted in the operating room immediately before ESWL therapy for radiolucent stones. Periodic injection of small amounts of diluted contrast can aid in visualizing radiolucent stones, facilitating ESWL, especially for uric acid calculi.
• Stones situated above the iliac crest and bony pelvis can still undergo ESWL therapy. Certain ESWL machines permit the rotation of the treatment head by 180°. In cases where this is not feasible, placing the patient in a prone position is an alternative approach.[29][81]
• Trans-gluteal shockwave delivery with the patient in the supine position has demonstrated superior results in a few studies; this may be beneficial in selected cases where targeting the stones adequately is otherwise challenging.[82]
• Rotating the head of the ESWL machine anteriorly may aid in treating lower calyceal stones in obese patients.[83]
• An NSAID should be administered immediately before ESWL to reduce postoperative patient discomfort.[12][20][36][52][53][70][71][72]
• Intravenous sedation is typically adequate anesthesia for most patients undergoing ESWL, although general anesthesia may also be used.[29]
• Consider alternative techniques if the stone cannot be targeted without including significant bowel gas in the blast path, as this can attenuate the shockwave energy treatment and reduce fragmentation efficacy.[36]
• Patients with significant bowel gas may benefit from pretreatment with simethicone, although laxatives do not appear to be helpful.[36][81]

Coupling

• Optimizing coupling, where the water-filled balloon contacts the patient's skin directly for shockwave transmission, can dramatically improve efficiency by eliminating the air bubbles and gaps hindering shockwave energy transmission.[51] Taking the time to apply the gel properly to minimize energy loss can make a dramatic difference in the efficacy of ESWL treatment.[51]
• Applying a large volume of the transmission gel directly from the container to the treatment head, rather than immediately to the patient, tends to minimize air gaps and bubbles, thereby improving coupling and maximizing shockwave delivery.[20][29][36][51][52][53]
• If necessary, consider using a bag of saline for very thin patients or children to achieve proper focal length and distancing. Ensure that transmission gel is applied carefully to both coupling surfaces.

ESWL technique

• Starting the treatment with reduced pressure settings and at a slower rate (≤60 shocks per minute) is crucial if the kidneys are in the therapy field. This allows for renal arteriolar vasoconstriction, reducing contusions, bruising, hematomas, and hematuria.[32][84][85] The shockwave energy settings and frequency can then be slowly increased or "ramped up" after about 250 to 500 shocks and a brief pause of several minutes.[32][86][87][88][89][90][91][92]
• Ramping-up is less critical when treating ureteral stones away from the kidneys.
• Optimal treatment frequency rates vary somewhat depending on the machine used, but a shockwave frequency of over 120 shocks per minute appears counterproductive.[5][24] Cavitation induces gas bubbles around the stone, requiring some time to dissipate before the next shockwave, or they may interfere with the therapy. Sixty shocks per minute is likely the most effective rate for ESWL but extends the total procedure time.[36]
• Based on multiple studies, systemic reviews, meta-analyses, and published guidelines, the consensus recommendation is to utilize a shockwave frequency rate between 60 and 90 shocks per minute.[5][20][24][93][94][95][96][97][98][99][100][101]
• However, several studies have indicated that a shockwave frequency as low as 60 shocks per minute, or even fewer, can enhance fragmentation efficacy and improve stone-free rates.[102][103][104]
• Periodic imaging rechecks of stone position and targeting are recommended at least every 500 shocks to ensure accurate and effective treatment delivery.[29]
• The usual recommendation for most ESWL machines is to use no more than roughly 3000 total shocks per treatment for each kidney, but this depends on the individual machine and if the kidney is in the target area.[5][24][42] If the kidney is not being treated, the risk of renal bruising, bleeding, contusion, hematuria, and kidney damage is reduced, allowing for the safe delivery of more shocks.
• The usual maximum is 4000 shocks per treatment, but even this can be safely exceeded in selected cases of ureteral calculi.[5][24][42][105][106]
• ESWL can sometimes cause cardiac arrhythmias. If these are encountered, the shockwave generator can be directly tied or "gated" to the electrocardiogram (ECG) to avoid delivering the shockwave directly on the T wave. However, this may reduce the shockwave frequency to the lower heart rate and extend the surgical time. Atropine can be used to increase the heart rate, if necessary.[36]
• The number of ESWL treatments to a single stone should be limited. Studies have indicated that more than 2 ESWL therapy sessions offer little additional benefit.[24][107]
• If a second ESWL treatment is deemed necessary, it can be performed in as little as 2 or 3 days for ureteral calculi, but at least a week is recommended after ESWL for renal stones.[5][24]
• If this second ESWL treatment session fails, ureteroscopy is recommended.
• Postoperative mechanical percussion can help improve renal stone fragment passage.[12][108]

Double J stents are not required for most ESWL cases but are recommended for larger stones (15 mm x 15 mm or larger) to minimize steinstrasse and post-ESWL complications.[32] Stents may be needed before ESWL for symptomatic relief and infection control. They may also help identify smaller stones in the ureter that would otherwise be difficult to visualize and target. While double J stents generally will not significantly affect the clearance rate for renal stones, they do appear to decrease the stone-free rate for ureteral stones less than 10 mm by 15% to 22%.[53][109][110][111][112]

An ESWL simulation can be beneficial in questionable or borderline clinical situations, and is also recommended in patients with complex anatomy, morbid obesity, or skeletal deformities.[36][53] The patient is positioned on the ESWL treatment table but is not anesthetized. An attempt is made to target the stone without actually starting therapy. This simulation may be the only way to know if a borderline stone can be successfully treated with ESWL.

• If the patient passes the simulation, anesthesia is given, and ESWL is performed. 
• If the patient fails the simulation, the ESWL procedure can be quickly canceled, or a ureteroscopy can be performed instead.

Contraindications for ESWL Therapy 

ESWL therapy during pregnancy is contraindicated due to its association with increased risks of gestational diabetes, low neonatal birth weight, miscarriages, preeclampsia, and spontaneous abortions, as well as the potential for a direct injury to the fetus.[45][12][29][25][36][49][113][114]

Other contraindications include:

• Active UTI
• Distal ureteral obstruction (anatomical or functional)
• Inability to safely stop anticoagulation therapy long enough for the procedure
• Obstructed blast path due to tumor, organ, aneurysm, or other structure
• Pregnancy
• Uncorrected coagulopathy
• Ureteropelvic junction obstruction (renal calculi)

Complications

Complications of ESWL include: 

• Abdominal aneurysm leakage or rupture
• Bacteremia, sepsis, and infection (The postoperative risk of infection is about 10%.)
• Gastrointestinal lesions of various types, with a global incidence of 1.8%
• Hematuria, typically self-limiting
• Inability to find or target the calculus, which may necessitate additional imaging or ureteroscopy
• Incomplete fragmentation leads to ureteral blockage from multiple fragments (steinstrasse) or a single, larger fragment
  • Steinstrasse occurs in about 3% of all ESWL cases, with only 6% requiring surgical intervention
  • Treatment is usually conservative but may require a double J stent, ureteroscopy, or a repeat ESWL
• Perirenal, subcapsular, or intrarenal hematomas occur in about 1% to 4.6% of cases, with increased risk in anticoagulated patients and those with significant or untreated hypertension
  • Treatment is usually conservative and supportive with regular monitoring of hemoglobin and hematocrit
• Renal colic in about 40% of patients is usually treated medically with alpha-blockers and analgesics, with a potential need for double-J stenting or ureteroscopy
• Renal parenchymal trauma or contusion is typically managed conservatively
• Skin contusions and bruising
• Failure to fragment may warrant repeat ESWL or consideration of alternative therapies such as ureteroscopy if no fragmentation occurs after 2 treatments [12][28][36][114][115][116][117][118]

Clinical Significance

The primary treatment modalities for nephrolithiasis are ESWL, ureteroscopy, and percutaneous nephrolithotomy. ESWL is uniquely noninvasive and can achieve stone-free rates approaching 75%. This procedure is considered a first-line treatment for smaller stones (<2 cm in size).[119] 

For stones that exceed 2 cm, a more invasive approach, such as ureteroscopy or percutaneous nephrolithotomy, is recommended. However, some patients may still prefer ESWL despite the potential need for additional surgeries instead of a more invasive procedure.

While the single-treatment success rates of ESWL may not match those of ureteroscopy or percutaneous nephrolithotomy, employing adjunctive treatments, careful patient selection, optimizing ESWL technique, and considering a second treatment session when necessary can yield stone-free rates comparable to other modalities, but with less invasiveness and greater safety.[5][24][120]

Research suggests that both ureteroscopy and ESWL yield comparable stone-free rates for treating calculi. However, ESWL may necessitate multiple treatments, albeit at a substantially lower overall cost.[5][6][24][29][121][122][123][124][125]

ESWL offers a significant advantage in complication rates with a reported 0%, compared to 3.2% with ureteroscopy. Meta-analyses comparing resolution rates for proximal stones between shock wave lithotripsy and ureteroscopy have found no statistical difference between the 2 modalities.[5][6][24]

The advantages of ESWL are numerous, as it offers a high stone-free rate, requires minimal anesthesia (typically intravenous sedation or light general anesthetic), is well tolerated, can be used for stones anywhere in the urinary tract, is noninvasive, can easily be repeated, and is associated with minimal risk of serious complications. As a general rule, it is preferable to repeat ESWL therapy than to risk unnecessary renal tissue trauma, preventable complications, or excessive bleeding.[36]

Kidney Stone Prevention Testing

The key to kidney stone prevention is increasing fluid intake (urinary volume) and employing specific therapeutic measures guided by 24-hour urine testing. Though this approach is standard for determining long-term prophylactic treatment, its success relies heavily on patient compliance. Therefore, such testing should be extended to all patients with urolithiasis, especially following ESWL surgical treatment.

24-hour urine testing is particularly recommended for patients with the following: 

• Abnormal or surgically altered urinary anatomy (reimplanted ureters, etc)
• Gastrointestinal bypass surgery
• High anesthesia or surgical risk factors
• Irritable bowel syndrome or chronic diarrheal states
• Kidney stone composition primarily composed of cystine, calcium phosphate, or uric acid
• Morbid obesity
• Multiple previous urinary stone surgeries
• Nephrocalcinosis
• Positive family history of kidney stones
• Recurrent or multiple UTIs
• Renal failure
• Solitary kidney (anatomically or functionally)
• Young age of first known kidney stone (<21 years)[2][126][127]

Enhancing Healthcare Team Outcomes

When a patient presents with renal calculi, the clinician must comprehensively understand medical and surgical treatment options. The patient should be thoroughly educated about the available options, including their relative risks and benefits. With ESWL, explaining the heightened likelihood of retreatment and the potential need for adjunctive therapies is essential.  Preoperative evaluation and preparation play a crucial role in maximizing the success rate of ESWL while minimizing the risk of unforeseen complications. The role of an anesthetist is essential to ensure adequate analgesia and patient comfort throughout the procedure. 

During the procedure, a nurse is vital for patient monitoring and medication administration, if necessary, to ensure the patient's safety and comfort. Nurses are among the many members who provide the safety, comfort, and well-being of patients undergoing ESWL procedures. After undergoing ESWL, educating the patient about dietary modifications and informing them about the option of 24-hour urine testing with directed therapy to reduce the risk of recurrent urolithiasis and renal calculi is essential. This proactive approach can significantly contribute to the long-term prevention and management of kidney stones.

Close cooperation and communication among the patient's healthcare team members are vital to reinforce this message and ensure optimal treatment results with minimal recurrences. By working together effectively, healthcare professionals can provide comprehensive care and support to patients throughout their treatment journey, improving outcomes and enhancing overall satisfaction.