Extracorporeal Shockwave Lithotripsy Treatment & Management

Several factors related to the stone, including stone burden (size and number), composition, and location, affect the outcome of extracorporeal shockwave lithotripsy (ESWL).

Stone size

As stone size approaches 2 cm, the likelihood of success with ESWL decreases, and the need for retreatment and adjunctive therapy increases. ESWL has also been found to be most efficacious in treating nonobstructing renal calculi. In patients with a large stone burden, pre-ESWL stenting may secure drainage and prevent obstructive urosepsis.

Stone composition

The density and ability of a stone to resist ESWL is based in part on the composition of the stone. Stones composed of calcium oxalate dihydrate, magnesium ammonium phosphate, or uric acid tend to be softer and to fragment more easily with ESWL. Stones composed of calcium oxalate monohydrate or cystine, on the other hand, are less susceptible to ESWL. To a degree, this can be predicted with CT scanning by measuring the radio-opacity of stones. A recent retrospective study showed that ESWL monotherapy is more likely to be effective against stones with a lower radio-opacity (551 Hounsfield units [HU]) than those with a higher radio-opacity (926 HU).

In addition, certain radiolucent stones (uric acid, indinavir [Crixivan]) are difficult to visualize on fluoroscopy and therefore require either ultrasonography-guided localization or the addition of retrograde or intravenous contrast to localize a calculus.

Stone location

• Lower-pole calculi: Although ESWL can fragment stones in the lower pole of the kidney, the resulting stone-free rate is decreased because of the difficulty in passing stones from this location. Recent studies have delineated renal morphology associated with improved stone-free rates (eg, lower infundibular length–to–diameter ratio of < 7, lower-pole infundibular diameter of >4 mm, single minor calyx), as well as factors associated with decreased stone-free rates (infundibulopelvic angle of < 70°, an infundibular length of >3 cm, an infundibular width of < 5 mm). Regardless of anatomy, ESWL tends to yield better results in patients with smaller stone burdens.
• Calyceal diverticula with infundibular stenosis: In patients with diverticula caused by or related to infundibular stenosis, fragmented stones cannot easily bypass the obstruction, with resultant retained stone fragments. These patients are best served by more invasive techniques that allow the surgeon to address the obstruction and the stones simultaneously, either with retrograde ureteroscopy or in an antegrade percutaneous fashion.
• Ureteral calculi: Fragmentation of proximal stones is more effective than mid or distal stones. In addition, when associated with hydronephrosis, ureteroscopy yields better stone-free rates for stones larger than 15 mm.

Preoperative and intraoperative stenting

In the modern setting, where access to ESWL and ureteroscopy is readily available, the indications for stenting prior to definitive treatment are much fewer. These indications include (1) obstructed pyelonephritis or pyelitis and (2) newly onset renal insufficiency or renal failure. In these situations, the stent helps to ensure internal drainage and allows passive dilatation of the ureter, facilitating future endoscopic evaluation and treatment. With the advent of newer and smaller ureteroscopic equipment, the rates of endoscopic complications (ie, strictures) have subsequently declined. When preoperative stenting is required, the authors believe that ureteroscopy, especially for ureteral stones, may yield higher stone-free rates without a significant increase in morbidity, time, or cost.

The need for intraoperative manipulation of stones for ESWL (eg, stone pushback) or placement of a ureteral catheter to assist with stone visualization has decreased, as newer machines are capable of treating proximal ureteral stones or visualizing radiolucent stones with ultrasonography. That said, intraoperative ureteral stents should be considered in patients with larger stones, as the rate of steinstrasse (German for “stone street”) increases with stone burden (1-4% in general vs 10% for stones >2 cm).

The optimal shockwave lithotripsy treatment is thought to be about 80-90 shocks per minute. Faster rates have been shown to be associated with decreased stone-free rates, especially for larger stones (11-20 mm). The difference in stone-free rates is less significant for smaller stones. Conversely, slower rates obviously increase the total operative time.

During shockwave lithotripsy, tracking the stone burden becomes an important issue, in part because of the natural movement of the kidney during respiration, with subsequent movement of the stone burden in and out of the focal zone. The smaller focal zone of the newer devices allows for minimal anesthesia, but the patient’s increased ability and susceptibility to cough, shift, or otherwise move requires vigilance to ensure the appropriate targeting accuracy in the application of energy to the stone. This means that the targeting of the machine needs to be adjusted more often.

The decreased anesthetic need during lithotripsy when using the later generation devices provides obvious advantages, such as rapid recovery time and rapid turnover between patients. However, a balance must be struck between the minimal invasiveness of the procedure and the stone disintegration efficacy. The optimal anesthetic regimen to facilitate this remains a subject of debate.

Patient-controlled analgesia has been suggested to enable urologists to achieve better patient compliance through more accurate pain control and, hence, more effective treatment.^[3] To this end, Parkin et al studied preoperative diclofenac alone versus diclofenac and alfentanil PCA. Pain scores based on a visual analog score (VAS) were similar between the 2 groups but PCA patients showed a statistically significant increased level of satisfaction with the experience.^[4]

Kumar et al compared 3 forms of adjunctive analgesia for ESWL patients: preoperative diclofenac, topical eutectic mixture of lidocaine/prilocaine (EMLA), and the 2 in combination. Stone free rates at 3 months were the highest in the combination group at 88.75%, and the retreatment rate was the lowest, both reaching statistical significance.^[5]

Thus, excellent stone free rates can be achieved with minimal to no general anesthesia using modern lithotripters. Analgesic adjuncts certainly have a role in facilitating these outcomes.

Common adverse effects associated with ESWL include flank petechiae, hematuria, and passage of stone fragments with associated renal colic. Many patients are issued a urine strainer to help collect stone fragments, which can later be chemically analyzed to assist with prevention of future stones. Hydration and analgesia alleviate most flank discomfort and symptoms caused by the passage of fragments.

Some groups have initiated trials of pharmacologic aids similar to those involved in medical stone-passage protocols to facilitate stone passage. In the treatment arm, pharmacologic aids (stone-free rate of 86% with nifedipine and 82% with tamsulosin) were superior to placebo (stone-free rate of 52-57%). Quantification of residual stone burden and resolution of hydronephrosis was defined with postoperative radiography or ultrasonography.

It is the practice of the authors to obtain postoperative imaging, typically a KUB or ultrasound, within 6 weeks following the procedure or sooner if the patient is symptomatic.

Stone-prevention strategies

All patients who undergo surgery for stones should be given information about kidney-stone prevention. General measures include increased fluid intake and restriction of dietary sodium and purine. In patients with calcium oxalate stones, intake of foods high in oxalate (eg, spinach, nuts, beer, chocolate, rhubarb, green leafy vegetables) should be discouraged. Calcium intake should be moderated; extremely high or low levels of calcium can increase stone production.

Blood work and 24-hour urine collections measuring for pH, urinary volume, citrate, calcium, oxalate, uric acid, sodium, magnesium, phosphates, and electrolytes can assist in identifying and alleviating risk factors for future stone production. Following treatment of the initial stone event, testing should be performed in all children and in patients with solitary kidneys, chronic diarrhea, a history of bariatric surgery, renal failure, and nephrocalcinosis, as well as in any patient with kidney stones who has sufficient motivation to follow long-term treatment recommendations to prevent future stones. Twenty-four–hour urine-testing protocols are available from a number of sources, including Mission, Dianon, UroCor, Quest, LabCorp, and Litholink.

The National Kidney and Urologic Diseases Information Clearinghouse (NKUDIC), which is part of the National Institutes of Health (NIH), is a good general patient information Web site.

The NIH has also recommended The Kidney Stones Handbook (Savitz and Leslie, 2000). This award-winning patient guide to kidney stones can be ordered directly from the publisher (Grant Gibbs) by email (gsavitz@earthlink.net) or by telephone (530-889-1727).

Renal complications

Bacteriuria develops in 7.7-23.5% of patients undergoing extracorporeal shockwave lithotripsy (ESWL) and is more likely to develop in patients with infection-related stones. Bacteremia is less common, developing in up to 14% of patients, with fewer than 1% developing clinical sepsis (although this number increases to 2.7% in patients with staghorn calculi). Although preoperative antibiotic coverage remains controversial, antibiotics may be recommended in patients with infection-related stones, positive urine cultures results, or recurrent urinary tract infections.

Post-ESWL hematuria is usually mild and transient. In the event of significant hematuria with clots or frank clot retention, imaging the kidneys should be considered to identify a perinephric hematoma. Perinephric, subcapsular, or intranephric hematomas may be associated with severe pain, ileus, and, infrequently, shock or hypotension. Unexplained or unusually severe pain or any unusual drop in blood pressure may suggest a hematoma. Subcapsular hematoma following ESWL usually responds to bedrest, transfusions, and supportive care. If the patient requires multiple transfusions, arteriography and selective embolization should be considered.

Stone fragments may pass with a minimal amount of discomfort. In some patients, the comminuted stone fragments pile up in the ureter, creating a virtual column of stone called steinstrasse. The overall rate of steinstrasse is 1-4%, with the rate progressively increasing for greater stone burdens (10% for stone burdens >2 cm²) and approximately 40% for complete staghorn calculi. Patients with asymptomatic nonobstructing steinstrasse can be monitored closely with serial imaging.

Asymptomatic or mildly symptomatic steinstrasse with mild dilatation of the upper urinary tract can be managed conservatively. If fragments fail to progress within 3-4 weeks or if patients develop significant symptoms or obstruction, endoscopic lithotripsy or percutaneous drainage should be performed. Patients with high-grade obstruction and concomitant pyelonephritis require prompt percutaneous nephrostomy drainage with appropriate antibiotic coverage, followed by staged endoscopic removal of stone fragments.

Renal atrophy, although uncommon, can result from renal vascular or severe atherosclerotic disease. Patients with underlying renal parenchymal disease are at a higher risk of renal atrophy. However, studies of ESWL in patients with a solitary kidney have shown no statistical evidence of renal function deterioration secondary to shockwave lithotripsy.

Medical complications

Hypertension is an unusual complication of ESWL but may occur as a sequela of a large perinephric hematoma (ie, page kidney). Older patients with abnormal renal perfusion may develop hypertension within 26 months after the ESWL session.

Patients who undergo ESWL may have a slightly higher likelihood of eventually developing hypertension and diabetes than patients who undergo other therapies for stone removal, based on a 2006 study by Krambeck et al. This study retrospectively identified 630 patients who were treated with ESWL 19 years prior, and queried them regarding development of hypertension and diabetes mellitus. Compared with a control group treated conservatively for nephrolithiasis at the same time, diabetes and hypertension were more common, a finding that persisted in multivariate analysis when BMI was controlled for. The authors suggested injury to pancreatic islet cells by the shock waves as an explanation for this observation.^[6]

In response to the above study, Wendt-Nordahl et al measured pancreatic enzymes post-ESWL in patients treated for proximal ureteral and renal stones to evaluate for acute pancreatic injury. The control group consisted of patients treated with ESWL for lower ureteral stones and no difference was demonstrated between the 2 groups. The authors concluded that the hypothesis that ESWL causes acute trauma to pancreatic islet cells, leading to an endocrine insufficiency resulting in DM, therefore seems unlikely.^[7]

In a recent study, Makhlouf et al examined a cohort of almost 2000 patients who underwent ESWL between 1999 and 2002. The control group consisted of matched individuals from a national database. At 6 years of follow-up, the number of patients in the study group and the control group who had developed DM were the same.^[8]

Based on these studies, the relationship between ESWL and the development of diabetes, remains unclear. One of the criticisms of Krambeck et al^[6] is that the study patients were treated with first generation lithotripters, with significantly wider focal areas than current lithotripters. On the other hand, this study was based on 19 years of follow-up while Antoine et al only reported on 6 years of follow-up. Further studies are necessary to elaborate this relationship.

Other possible complications

Less-common complications may include (1) pulmonary contusion, (2) pancreatitis, (3) splenic hematoma, (4) elevated liver functions (transient), and (5) biliary colic with inadvertent fragmentation of adjacent biliary stones.

In appropriately selected patients, the overall success rate of extracorporeal shockwave lithotripsy (ESWL) is higher than 90% for stone clearance, with patients remaining stone-free for up to 2 years. Compared with ureteroscopic removal of stones, ESWL leads to less complications and shorter hospital stays. However, ureteroscopy was shown in one review to achieve a greater stone-free rate than ESWL.^[9]

ESWL is safe and effective. Although small series have shown successful treatment of stones in young children, long-term follow-up of the potential complications, including hypertension and decreased renal function, are not yet mature.

As the degree of stone burden increases and exceeds 2 cm, the stone-free rate drops significantly. In patients with stones sized 2-3 cm, the stone-free rate with ESWL monotherapy is typically 50%. Stone-free rates in patients with larger stones (complete and incomplete staghorn calculi) are correspondingly lower.

The location of the stone also affects the efficacy of ESWL. In a meta-analysis of 2927 patients from 14 centers, Lingeman et al (1996) found that the overall stone-free rate for all lower-pole stones treated with ESWL (59.2%) was lower than the stone-free rate associated with percutaneous nephrolithotomy (90%).^[10] Some studies have suggested that select patients with appropriate renal collecting system anatomy may see good results with ESWL despite lower-pole stone location. In these studies, the overall stone-free rate was approximately 50%, with a stone-free rate of 85% in patients with favorable anatomy versus 7% in those with unfavorable anatomy.

In a prospective, randomized, multicenter clinical trial performed by the Lower Pole Study Group, patients with lower-pole stones treated with ESWL or percutaneous nephrolithotomy had overall stone-free rates of 37% and 95%, respectively. In contrast, this prospective study did not show any difference in stone-free rates based on renal anatomy, but an inverse relationship was found between stone size and stone-free rate. In patients with stones or stone aggregates measuring larger than 1 cm, percutaneous nephrolithotomy was the most efficacious modality to render patients stone-free.

Sheir et al (2003) evaluated the safety and efficacy of ESWL in patients with an anomalous kidney, including 49 patients with a horseshoe kidney, 120 patients with a malrotated kidney, and 29 patients with a duplex kidney.^[11] Two second-generation lithotriptors were used. Although the type of renal anomaly and the type of lithotriptor did not affect the stone-free rate, stone length and number (stone burden) significantly influenced the stone-free rate. The prone position facilitated treatment in 38% of the patients with a horseshoe kidney and in 31% of patients with a duplex kidney. The overall retreatment success rate was 64.1%. However, with an overall stone-free rate of 72.2%, Sheir et al deemed ESWL to be safe and reliable in patients with an anomalous kidney and to be considered the primary treatment option for stones smaller than 20 mm.

Early-generation lithotriptors required pushback of stones into the renal pelvis for treatment. With advancements, specifically higher-amplitude waveforms with smaller focal zones, newer lithotriptors are able to treat ureteral stones in situ. Results tend to be better for proximal stones, with stone-free rates of 65-81%, versus 58-67% for distal ureteral stones.

Technical improvements, such as bidirectional synchronous twin-pulse technique with variable angles between the shockwave reflectors, have been attempted to increase the quality and rate of stone disintegration. With this technique, shock waves are produced simultaneously from separate reflectors through nonopposing directions to the same F2 and appear to be particularly effective with right angle orientation between the two. This effect was demonstrated in vitro and then demonstrated by Sheir in a study of 50 patients with renal or ureteral stones (mean size, 12.3 mm; range, 9-18 mm). Using this technique, 17 patients (34%) were rendered stone-free, 20 patients (40%) had less than 5 mm of residual stone, and 13 patients (26%) had 6-9 mm of residual stone at 14 day follow-up. Thirteen patients (26%) with more than 5 mm of residual stone underwent repeat ESWL.^[12]

The same authors followed this initial clinical study with one that randomized patients to the twin-pulse technique versus standard ESWL. The study group included 240 patients with single radio-opaque stones less than 2.5 cm. Stone disintegration rates were significantly greater in the twin-pulse group while stone free rates were high in both groups but not significantly different for stones less than 10 mm (67% and 74%; standard and twin-pulse, respectively).^[13]

An additional purpose of this study was to compare collateral parenchymal damage caused by each technique. N-acetyl-B-glucosaminidase (NAG), a high-molecular weight enzyme not typically filtered by the glomerulus, was measured post-ESWL. The degree to which this enzyme is lost in the urine immediately after ESWL is thought to be reflective of the severity of tubular damage. Both groups in this study had elevated post-ESWL NAG levels, but the levels normalized in the twin-pulse group after 2 days and remained elevated up to 7 days in the control group. Patients also underwent dynamic MRI post-ESWL to assess changes in renal perfusion. Decreased renal perfusion was demonstrated in the standard ESWL group (control), but not in the twin-pulse group.

The authors of these studies concluded that bidirectional synchronous twin-pulse lithotripsy has superior efficacy to standard lithotripsy while possibly decreasing damage to surrounding parenchyma.

Other groups have attempted to improve the fragmenting capability of the cavitation bubbles created during lithotripsy by forcing their collapse with a second weaker pulse timed immediately after the initial pulse. Using a porcine model with BegoStone phantoms, Young et al (2003) used a 22-kV shock from an HM3 followed with a 4-kV shockwave 500-600 ms later from a separate piezoelectric source. Their initial results showed increased stone comminution rates with reduced renal injury.

The smaller focal zone and newer lithotripter tabletop designs have increased the indications for treatment and lowered the anesthetic requirements, but some have demonstrated decreased overall efficacy of the treatment. Many newer generators require precise localization, with little margin for error in light of the greatly reduced focal zones. Future studies are necessary to define the preferable anesthetic regimen, localization technique, and shock-wave delivery sequence to optimize outcomes.

A prospective study comparing the clinical effectiveness of the HM3 to the newer MODULITH SLX-F2 lithotripter found that the HM3 showed higher stone-free rates for solitary ureteral stones and multiple stones at 3-month follow-up. The HM3 also required fewer shock waves and led to fewer kidney hematomas.^[14]