Extracorporeal shock-wave lithotripsy of renal calculi

Extracorporeal _ Anthony Atala,

Shock-Wave Lithotripsy of Renal Calculi MD,

Greg S. Steinbock,

Extracorporeal shock-wave lithotripsy (ESWL) is a noninvasive technique that utilizes focused shock waves to fragment stones into sand-sized particles, which then pass spontaneously witb urination. The clinical use of this technique was introduced in 1980 in Germany by Chaussy and associates and has replaced most open surgery and percutaneous endoscopy for stone removal. The physics of shock waves, equipment, techniques, and patient selection in ESWL are discussed. Results of treatment of renal, upper ureteral, and lower ureteral calculi are reviewed and compared. Complications of treatment, including ureteral obstruction, hemorrhage, and tissue damage, are discussed. The advent of second-generation lithotripters has widened the parameters for patient selection in the treatment of ESWL and has increased the availability of this treatment modality.

U

rinary calculi haveafflicted mankind sinceantiquity. Two to 3 percent of the adult population in the United States is affected by urinary stone disease, an incidence comparable with that of diabetes. Most stones pass spontaneously; however, in up to 30 percent of patients, the stone does not pass and urologic intervention is required. About 1 in 10 Americans will require treatment for a stone disease in his or her lifetime. Recurrence is common, occurring in 20 to 50 percent of patients within a 5-year period [Z-4]. Treatment remained unchanged for many years and included transurethral manipulation of calculi in the lower ureter and open surgical procedures for calculi lodged in the upper ureter (ureterolithotomy) and in the renal collecting system (pyelolithotomy). The introduction of percutaneous nephrolithotomy, along with the ureteroscopic techniques in the late 197Os,provided an effective alternative to open surgery. Extracorporeal shock-wave lithotripsy (ESWL), a noninvasive technique of fragmenting urinary stones by the use of shock waves, was introduced in 1980 in Germany and in 1984 in the United States as another treatment alternative. From the Division of Urology, Department of Surgery, University of Louisville School of Medicine, Louisville, Kentucky. Requests for reprints should be addressed to Anthony Atala, MD, Department of Surgery, University of Louisville, 550 South Jackson Street, Louisville, Kentucky 40292. 350

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MD, Louisville, Kentucky

HISTORICAL

PERSPECTIVE

In 1969, the Domier System of Friedrichshafen, West Germany received a grant from the German Ministry of Defense to study the effects of warfare-related shock waves. Research on the cause of pitting seen on supersonic aircraft and spacecraft traveling at high velocity demonstrated that pitting was caused by shock waves generated upon the collision of the craft with water droplets. Shock waves were administered to animal tissue to determine the effect that vibration from a high-velocity projectile when hitting a tank would have on military personnel leaning against the tank wall [5]. These studies determined that shock waves could be transmitted through living tissue without damage, except for the lung alveoli, a fact attributed to the absorption of the shock wave energy and due to the marked differences in acoustic impedance between pulmonary tissue and water. It was also determined that brittle materials were destroyed by shock waves at the borders of acoustical impedance [6]. The idea that shock waves could be used to break kidney stones germinated as a result of these experiments. Dornier began a collaborative program with urologists at the Institute of Surgical Research, Ludwig Maximilian University, in Munich, West Germany, under the direction of Professor Egbert Schmiedt, to study the use of shock waves for kidney stone treatment. Animal experimentation ensued, until finally, in February 1980, the first kidney stone patient was treated by Dr. Christian Chaussy using the technique of extracorporeal shock-wave lithotripsy [7]. THE PHYSICS OF SHOCK WAVES

Shock waves are high-energy amplitudes of pressure generated in water or air by a sudden release of energy in a small space. They are transmitted through low-attenuation media and propagate according to the physical laws of acoustics. A well-known example of shock waves is the sonic boom, explosive sounds generated by an airplane flying faster than the speed of sound. The pressure wave that makes the boom can shatter windows in its path [8]. The basic principles of shock waves and ultrasound are often confused. Shock waves and ultrasound waves are governed by the same laws of acoustics; however, they are different when compared in terms of their energy content. Ultrasound waves consist of a sinusoidal wave form, whereas a shock wave consists of a single positive pressure front of multiple frequencies with a steep onset and a gradual decline. Shock waves undergo substantially lower attenuation when propagated through body tissue or water and therefore can be transmitted into the body without energy loss [9]. When a shock wave encounters an interface between substances of different acoustic impedance (density), mechanical stress develops in brittle

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EXTRACORPOREAL SHOCK-WAVE LITHOTRIPSY

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materials such as kidney stones. Once the tensile strength of the stone is exceeded, it causes disintegration at the front surface and tears throughout the rest of the stone. The diminished shock wave continues through the stone and is reflected at the posterior surface where the same effect takes place, resulting in further stone fragmentation [IO]. Repeated shock waves result in disintegration of the stone into multiple small fragments, allowing for their spontaneous passage with the urine. Solid materials that are brittle, such as calcium stones, shatter more readily than malleable solids, such as cystine stones, Cystine stones, therefore, require a higher energy shock wave and more exposure for successful disintegration [ 211.

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EQUIPMENT AND TECHNIQUES The Dornier Human Model 3 (HM3)@ Lithotripter, developed and manufactured by Dornier of West Germany, is by far the most widely used equipment for ESWL. The following discussion relates primarily to this apparatus (Figure 1). The lithotripter disintegrates stones with shock waves generated under water by an electrical discharge across a spark gap. The spark gap is located in a hemiellipsoidal reflector within a tub of deionized and degassed warmed water. The patient is strapped into a gantry after the induction of anesthesia and is submerged into the water tub. When the spark gap tires with 18,000 to 24,000 volts, the explosive vaporization of the water initiates a shock wave in the surrounding fluid which propagates spherically from the site of origin (Figure 2). The generated shock wave enters the body and propagates without interference because there is virtually no difference in the acoustic impedance between water and body tissues [ 121. Focusing of the shock wave onto the stone is accomplished in an ellipsoid reflector. Due to its geometric properties, pressure waves originating from the first focal point of the ellipsoid that hit the ellipsoidal wall are reflected to the second focal point. All of the reflected waves have the same path length. Therefore, all of the reflected energy is simultaneously focused on the second focal point, which is the site where the kidney stone has been positioned [ 131. The stone is visualized by biplanar

fluoroscopy. Two independent fluoroscopy image intensifiers are arranged along a nonparallel axis. The patient is moved in the tub of water by a hydraulic positioning device so that the stone lies at the intersection of the two axes and therefore in the focal area of the shock waves. This is confirmed by visualizing the stone at a designated site on each of the two fluoroscopic monitors [ 141. After every 200 shock-wave exposures, the stone is visualized with fluoroscopy to assess fragmentation and to ensure continued alignment. The number of shock waves required for disintegration is related primarily to stone volume, position, and composition. One to 2,000 shock-wave exposures are usually sufficient. The duration of treatment lasts between 20 and 60 minutes depending on how many shock-wave exposures are required to pulverize the stone into sandsized particles. PATIENT SELECI’ION The initial human trials were restricted to patients with single stones less than 1 cm in size. Initial contraindications to ESWL included infected stones, ureteral stones, or radiolucent stones, high-risk patients and patients with obstruction [ 131. However, as more experience was gained, most of these contraindications were dropped. The current absolute contraindications include obstruction distal to the stone, bleeding dyscrasis, and

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pregnancy [15]. Once these conditions are resolved, the patient can be treated with lithotripsy. PHYSICAL LIMITATIONS The distance between the first focal point, the site of the electrode discharge, and the second focal point, where the stone should be located for treatment, is fixed at 23 cm [I2]. It may not be possible to position the calculus at the focus of the shock wave if a patient has a large abdominal girth, an anterior kidney, a pelvic kidney, or a horseshoe kidney. These patients, until the advent of the new-generation lithotripters, had to be managed with the use of the blast-path technique. The path of the center of the shock wave (blast path) generated by the electrode extends up to 10 cm past the focus of the shock wave. The positioning of the patient’s stone along the path of the blast, even if not exactly at the focus of the shock waves, allows for stone disintegration. The blast-path course can be directed against the stone, utilizing the fluoroscopy monitor screens where the blast path extends from its lower outer quadrant on each video screen to the upper inner quadrant [ 14. The Dornier HM3 model will not accommodate patients taller than 6 feet, 6 inches (2 m) or heavier than 297 pounds (135 kg) [17]. PREOPERATIVE PREPARATION Ureteral catheters are often used with ESWL. They can be used to help identify small or radiolucent stones. The ureteral catheter is positioned cystoscopically prior to the procedure and can be removed immediately after the procedure. Double-J stent ureteral catheters are currently being used as a temporizing measure to relieve pain and obstruction until the patient can be brought to an ESWL facility. The double-J stent is increasingly being left in place for a few days or even several weeks. Its presence dilates the ureter and facilitates the passage of stone fragments. A polypropylene suture is usually tied around the distal end of the double-J stent and is allowed to protrude from the urethra so the ureteral catheter can be removed later without cystoscopy [18]. Goldberg [ 191 has described a group of patients with no history of infection, a negative urinalysis, and a negative urine culture who were not given prophylactic antibiotics. Twenty-five percent of these patients had an increase of 5 days in the mean hospital stay due to fever and infection after ESWL. All patients with a history of infection and a positive urinalysis and culture who were given preoperative and postoperative antibiotics remained afebrile with no increase in the mean hospital stay. It is recommended that all patients undergoing ESWL receive prophylactic antibiotics and that patients known to have an infected stone, as in struvite or a urinary tract infection, receive postoperative intravenous antibiotics for at least 48 hours. POSTOPERATIVE CARE Postoperatively, a plain film of the abdomen is obtained to confirm stone fragmentation. Patients are hydrated and given analgesics as needed. Most patients can 352

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be discharged from the hospital the next day, and they continuously pass stone fragments in their voided urine for the next several days to several weeks [20]. Over 90 percent of patients can resume their normal level of activity after discharge. Post-ESWL patient disability time is markedly reduced, in comparison with the patient who requires an open surgical procedure [21]. Close follow-up is necessary as only a few patients are free of stones when discharged from the hospital. RESULTS OF ESWL Successful ESWL treatment requires complete disintegration of the targeted calculus as well as complete discharge of all stone fragments with the urine. These two factors are dependent on stone size, stone location and composition, previous renal or ureteral surgery, individual anatomy (ureter size and pathway), renal function, and patient ambulation and hydration potential [22]. Stone-free rates 3 months after ESWL vary from 44 to 90 percent [23-301. This wide range reflects a different stone population either by site, with kidney stones having a higher success rate of treatment than ureteral stones, or by size. Most studies suggest an inverse relationship between stone size and post-ESWL stone-free rates. Stones smaller than 1 cm have a much higher success rate than stones larger than 2 cm [24,26]. The severity of posttreatment pain, the length of hospital stay, the likelihood of post-ESWL obstruction, and the number of adjuvant procedures are all related directly to the size of the stone treated [24]. Overall, among 5,760 patients described in several studies and combined, 4,347 (76 percent) were free of stones 3 months after ESWL treatment. The incidence of stone disease requiring open surgery varied between 0 and 1.l percent overall for both kidney and ureteral stones [23-301. Upper ureteral stones: Chaussy et al [31] reported their first trial in treating two patients with ureteral stones in 198 1. These stones had been lodged in the ureter over 6 months. Both patients failed to pass any fragments after ESWL and required ureterolithotomy. During surgery, it was noted that the stones had been completely fragmented but were compressed by the ureteral wall, so their contour underwent no change [3I]. In vitro studies have shown that after initial fragmentation of the outer shell of impacted stones during the first series of shockwave applications, the stone fragments are kept in place by the external ureteral mucosal contact [32]. The first small fragments of the outer shell do not fall away, so the new interfaces have an influence on transmission of shock-wave energy being reflected or absorbed. The efficacy of the subsequent shock waves to fragment the remaining stone is markedly reduced. Creation of a suflicient expansion chamber for stones in the ureteral wall is necessary for successful fragmentation, and this can be accomplished with a ureteral catheter [33]. The treatment success rate is significantly greater if the stone is manipulated into the kidney before ESWL. Mueller et al [32] treated 148 patients with high ureteral stones in situ with a success rate of 62 percent. Lingeman et al [34] treated 30 patients with upper ureteral stones 157

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which were manipulated into the renal pelvis prior to ESWL with a success rate of over 99 percent. One hundred twenty-three patients with ureteral stones were treated in situ with a success rate of 87 percent. Upper ureteral stones manipulated into the kidney require less energy for successful fragmentation. Also, the need for subsequent procedures is reduced [32-34. If the ureteral stent cannot push the calculus up or bypass the calculus, an injection of 2 percent lidocaine viscous solution, dilute surgical lubricant, or saline solution is instilled in the area of the stone through the ureteral catheter. This may lubricate or relax the ureter [37]. Another technique with a high rate of success is the ureteral occlusion catheter push technique. A steel guide wire is placed to pass the area of the stone, a ureteral occlusion balloon catheter is passed through the wire close to the calculus, the balloon is then inflated with enough contrast media to fill the ureteral lumen, and finally the occlusion catheter is advanced over the wire, pushing the stone proximally into the renal pelvis [38]. If this also fails, a ureteral catheter can be placed just below the stone and ESWL treatment initiated [36]. Ureteral stones are treated between 21 and 24 kV, with a maximum dosage of 3,000 shock waves when fragmentation is unclear on the x-ray monitor. Unlike stones in the renal pelvis, which fragment and separate, ureteral calculi fragment but the pieces remain together for 24 to 72 hours [39]. Complications are infrequent, with the most common being ureteral perforation in up to 5 percent of cases. These perforations are managed conservatively with a ureteral catheter [40]. Lower ureteral calculi: Stones in the middle and distal ureter that lie at or below the level of the pelvic bone require special positioning. The shock waves are attenuated by their passage through bone and may not effectively fragment the calculi. Rassweiler and Sisenberger [41] have recommended that patients be positioned in a more upright position to provide unhindered passage of the shock waves into the pelvis from below. Rotation of the patient to the side of the stone is helpful if the stone lies close to the sacrum; however, this technique is contraindicated in women of childbearing age due to the unknown effects of shock waves on ovarian function [42]. There is a possibility of poor visualization of the lower ureteral calculi. The use of retrograde urography and intravenous urography may facilitate the visualization of these calculi. Jenkins, at the University of Virginia, treated 24 patients. Seven of the 24 patients (30 percent) passed the fragments after ESWL treatment, 2 (9 percent) required 2 ESWL treatments, and the rest either failed treatment, required further manipulation, or were lost to follow-up [39]. Miller et al [43] were successful in treating 39 of 43 patients (90 percent) without complications or adverse effects. Two patients required a second ESWL treatment. In the four patients who failed treatment (10 percent), stone removal was accomplished using open surgery in two patients and ureteroscopy in two patients. Chaussy and Fuchs [42] treated 44 patients with distal ureteral stones. They were able to localize the stones in 18

patients (40 percent) with the Dornier HM3 Lithotripter. Of the 18 patients, 16 (89 percent) had successful fragmentation. More recently, Jenkins and Gillenwater [44] started treating patients who had distal ureteral calculi with ESWL in the prone position. This prevents the blockage of shock waves by the bony pelvis, allowing the shock waves to enter anteriorly and exit posteriorly. Fifteen patients were treated in the prone position, including two patients with horseshoe kidneys and one patient with a pelvic kidney. Successful fragmentation was achieved in all patients after a single ESWL treatment of 3,000 shock waves. Transplanted kidneys: Renal allograft calculi formation occurs in less than 1 percent of all transplanted kidneys [45]. This may be associated with significant morbidity in this immunosuppressed population with a single kidney. Stones lying in kidneys in a low lumbar area or in the iliac fossa present similar problems with positioning as stones lying in the distal ureter. Therefore, a similar treatment approach is necessary [46]. Several centers have had experience with a limited number of patients with calculi in a transplanted kidney. One patient at the University of Florida required adjunctive percutaneous nephrolithotomy, whereas one patient at the University of Louisville was treated successfully with ESWL alone [45,47]. Solitary kidneys: Kulb et al [48] have demonstrated that ESWL is effective and safe in patients with a solitary kidney. They treated 60 patients with renal calculi. Of 59 patients evaluated after ESWL, 98 percent had successful results, that is, they were free of stones but had clinically insignificant residual fragments. Six patients required stone manipulation after therapy for steinstrusse (stone street), which denotes the accumulation of stone fragments along the course of the water after lithotripsy. Postoperative follow-up was found to be essential in this patient population. SPECIAL CONSIDERATIONS Patient age: Urinary calculi in the pediatric age

group is a rare occurrence. In the neonatal age group, urinary calculi occur secondary to the use of intravenous hyperalimentation or furosemide in an intensive care unit setting [49,50]. Most other pediatric calculi are secondary to a metabolic disorder. These patients tend to have a high recurrence rate of stone formation; therefore, ESWL, as a noninvasive procedure, is very advantageous. Use of lithotripsy in the pediatric population has been limited due to technical limitations including patient size and concerns over posttreatment fragment passage. With modifications in the gantry, size is no longer a contraindication for ESWL. In small children, the distance between the kidneys and the lungs is less than in the adult. The 1.5 cm focus of the shock wave cannot be adjusted and may encompass the lung fields. Since shock waves do not penetrate solid-air interfaces well, a polystyrene plastic (Styrofoam@) sheet, which consists of many solid-air interfaces, is used to protect the lungs from injury [51]. Special measures, such as the use of a lead shield, are also needed to protect the gonads from radiation exposure.

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Newman et al [52] treated 17 children between 3 and 17 years of age with ESWL. None required treatment. Seventy-two percent were stone free and 21 percent had insignificant fragments. Seven percent had stone fragments larger than 2 mm. Kramalowsky et al [53] treated 16 kidneys in 14 patients 17 years of age or younger. One patient required a second ESWL treatment. At 3-month follow-up, 11 of 13 treated kidneys were free of stones, whereas 2 patients had only residual fragments. Mininberg et al [54] treated 19 kidneys with ESWL in 17 children. Two patients were retreated. At 3-month follow-up, 9 of 19 treatments (47 percent) resulted in kidneys that were free of stones. In 8 of 19 treatments (40 percent), many stone fragments were present and 1 patient had no response to treatment. Sigman et al [55] treated 38 children with a 97 percent successful fragmentation rate. Five patients (13 percent) required retreatment. At l-month follow-up, 14 patients (70 percent) were free of stones. Complication rates in these series ranged from 0 to 5 percent, with an overall complication rate of 5 percent. Postoperatively, two children had pulmonary edema. One had sepsis and one patient, in whom a polystyrene sheet was not used, developed a pulmonary contusion. All of these complications resolved promptly without sequelae. Overall, the effectiveness and safety of ESWL in the pediatric population is the same as that in the adult population [52-561. Patients over 70 years of age who undergo ESWL have no increased morbidity in comparison to all treated patients, despite the associated medical problems of this patient population [57]. Anesthesia: Most lithotripters in use today require anesthesia. The shock wave causes considerable pain as it traverses the body wall [58]. The choice of anesthesia varies between lithotripter centers. Five types of anesthesia are available: general, spinal, epidural, local, and high-frequency jet ventilation. When compared with mechanical ventilation during general anesthesia, high-frequency jet ventilation reduces stone movement. This results in a decreased shock and energy requirement for stone fragmentation [59]. General anesthesia is the preferred method at most centers. Attempts at using a local field block injected subcutaneously at the skin entry site of the shock waves is applicable in selected patients [60]. Quadriplegic patients can be treated without anesthesia. Patients who are incompletely quadriplegic and have intact flank sensation require a local field block. These patients may undergo ESWL safely and successfully without the morbidity associated with anesthesia [61,62]. New-generation lithotripters are now available that provide anesthesia-free treatments. A lower level of energy is utilized and more shock waves are delivered, making the whole process pain-free [63]. Radiation exposure: Initially, Chaussy and Schmiedt [13,14] reported an average fluoroscopy time of 30 to 90 seconds with approximately 900 shock-wave treatments, for a total exposure of approximately 4 rads. The average patient’s radiation exposure with ESWL in the FDA study was measured to be between 10 and 15 rads, with an average fluoroscopy time of 3 to 5 minutes [17]. Neither of these studies measured the number of 354

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spot images (quick picks). McCullough [64] reported a combined spot and fluoroscopy time exposure of about 26 rads earlier in his series, with a reduction to approximately 17 rads later in the series, and correlated this with an increased operator skill. Lin and Hrejsa [65] estimated that the average patient received 3.5 minutes of fluoroscopy and eight spot films for a calculated exposure of 21 and 5 rads, respectively, for a total of 26 rads. Bush et al [66] calculated an average exposure of 10 to 20 rads per ESWL treatment. A number of variables affect total patient radiation exposure, such as stone opacity, size, composition, number of stones, and operator skill [67]. Also, differences in radiation monitors, measurement techniques, and calculations may account for the varied radiation exposure doses reported [68]. The scattered radiation exposure to ESWL personnel is in the range of 0.5 millirads per treatment. This minimal exposure is due to the attenuation provided by the water bath and the steel tank itself. This is well within the safety standards set by the National Council of Radiation Protection, which recommends that the maximum permissible exposure for radiation workers be limited to less than 100 millirads per week [651. Renal posttreatment function: Transient nephrotic range proteinuria occurs after treatment, returning to normal values within 6 months. The glomerular filtration rate increases after successful treatment in patients with an obstructed kidney secondary to stones prior to ESWL. The kidney maintains its ability to dilute urine and conserve sodium [69,70]. The effective renal plasma flow was found to be increased by Chaussy et al [71] when a renal scan was performed after ESWL. Lingeman et al [72] found no difference in the estimated renal perfusion flow when correcting for pre-ESWL kidney obstruction. Kaude et al [73] showed that the total effective renal plasma flow was not changed after treatment, but the effective renal plasma flow percentage of the treated kidney decreased by about 5 percent. Long-term studies will be needed to determine the exact effect of ESWL on effective renal plasma flow and renal concentrating ability. COMPLICATIONS Ureteral obstruction:

Chaussy and Schmiedt [74] reported the major complication in their first 1,000 patients as being ureteral obstruction by steinstrasse, necessitating ureteral instrumentation or percutaneous drainage in 8 percent of 896 cases. As already mentioned earlier in this review, steinstrasse denotes the accumulation of stone fragments along the course of the ureter after lithotripsy. If asymptomatic and not obstructing, no treatment is needed. Most patients are expected to pass these stone fragments without obstruction or pain; however, in up to 4 percent of patients in recent series, ureteral obstruction occurs due to tight impaction of stone fragments [39]. If pain is present, the placement of a percutaneous nephrostomy tube would relieve the pressure and allow time for the fragments to pass spontaneously. Further endoscopic intervention with stone frag157

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ment extraction and ureteroscopy may be needed if the obstruction persists [ 7.51.The likelihood of posttreatment obstruction is related directly to the size of the stone treated [24]. Placement of a ureteral catheter prior to treatment dilates the ureter and facilitates the passage of these stone fragments after ESWL. With the current widespread use of ureteral stenting, this complication has been markedly reduced. Grable and Drylie [ 761 noted no incidence of ureteral obstruction in 48 patients managed with ureteral stents as opposed to 13 percent of 201 nonstented patients who developed ureteral obstruction and required intervention with either ureteral catheterization, basketing, ureteroscopy or percutaneous nephrostomy. Gibbons [77] treated over 200 patients with a double-J stent, and less than 3 percent required post-ESWL fragment manipulation. All patients do not manifest renal obstruction with pain. Therefore, all patients require careful follow-up to monitor for the presence of silent hydronephrosis. Hardy and McLeod [ 781 reported two cases of irreversible renal damage secondary to silent ureteral obstruction. These patients waited for up to 5 months to be seen. This further stresses the importance of a close follow-up for all patients after ESWL. Hemorrhage: Virtually all patients manifest gross hematuria after several hundred shock waves due to intrarenal hemorrhage. Although the first ESWL studies indicated a low incidence of renal hemorrhage (0.34 percent to 0.6 percent), later studies, which examined kidneys with magnetic resonance imaging after lithotripsy, have indicated a much higher incidence of renal and perirenal hemorrhage (Figure 3) [23,24,79,80]. Kaude et al [73] examined the kidneys with magnetic resonance imaging after ESWL and reported a 29 percent incidence of renal hemorrhage. Rubin et al [81] studied 50 patients before and after ESWL with magnetic resonance imaging and found a 15 percent incidence of subcapsular hematoma and a 4 percent incidence of intrarenal hematoma after ESWL. Patients with preexisting hypertension, pretreatment urinary tract infection, and those who undergo simultaneous bilateral treatment have an increased incidence of perinephric hematoma [82]. The number and kilovolt power of shock waves do not correlate with the development of renal hemorrhage [80-821. Management is conservative although up to one-third of the patients require transfusion [83]. Hypertension: Lingeman and Kulb [84] evaluated 295 patients before and at least 1 year after ESWL and found a new onset of hypertension requiring pharmacologic therapy in 8 percent of patients. An additional 15 percent of the patients had an increase in diastolic blood pressure, averaging 16 ml Hg but did not require pharmacologic treatment. Williams et al [85] evaluated 91 patients before and up to 21 months after ESWL. Eight percent developed hypertension severe enough to require treatment. Peterson and Finlayson [86] reported sustained hypertension occurring immediately after ESWL in 3 of 79 patients (4 percent). A causal relationship was suggested at least for those patients who developed hypertension within 2 months after ESWL. It has been sugTHE AMERICAN

Figure 3. Magnetk resonance imagbg showb~ subcapular hematoma after extrauxporeal shock-wave I-. ReprInted from [SS] with permisskn ot the pubtisher. gested that renal trauma caused by ESWL may cause hypertension as a result of a perirenal hematoma by way of the well known Page kidney effect: trauma - perirenal hemorrhage - fibrosis - compression of renal parenchyma - increased interstitial pressure - decreased renal perfusion - renin-release - generation of angiotensin II - hypertension [85]. Brewer et al [87] delivered 3,000 to 10,000 shock waves to perfused cadaver kidneys and compared these to control kidneys. Macrovascular damage was demonstrated in each ESWL-treated kidney, and a link to hypertension was suggested. A longterm correlation between decreased renal function of the treated kidney and hypertension in patients treated with ESWL has also been suggested [SS]. Several factors could account for the 8 percent incidence of hypertension after ESWL in these studies, including a difference in blood pressure measurement techniques and a selective follow-up. Also, the active incidence of previously normotensive patients who would have been hypertensive regardless of ESWL is unknown [88]. A prospective, controlled study with a large number of patients will be necessary to answer these questions. Cardiac dysrhythmias: In Chaussy’s [I21 early experiments, dysrhythmias occurred in 80 percent of patients when the spark gap generating the shock wave was hand triggered. This led to the discharge of the shock wave on the R wave in the refractory face of the cardiac cycle. Up to 0.8 percent of patients have been reported to develop cardiac arrhythmias with the R-wave shock trigger mechanism [39]. Most are treated pharmacologically with no sequela [89]. Cardiac enzymes and isoenzymes have also been measured. Increased CPKmm bands are present immediately after ESWL with no increase of MB bands [ 901. SECOND-GENERATION

LITHOTRII’TERS

The wide success of ESWL has prompted the development of new lithotripters (Table I). Several major changes are present in the new machines. The energy generation mode, which is a spark-gap in the HM3, has also been accomplished with a piezo-electric discharge, JOURNAL

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TABLE I Characterlstlcs of Various Llihotrlpters Manufacturer’

Generation

Focusing

Coupling

Cornier HM3

Spark gap

Ellipsoid

Bath

Dormer HM4

Spark gap

Ellipsoid

Membrane

Wolf Plezollth 2200 EDAP LT-0 1

Plezo electric Piezoelectric 2 electr* magnets

Spherical

Localization

Positioning

Anesthesia

Capability

Move patient

Pool

Biplane fluoroscope Biplane fluoroscope Ultrasound

General or regional General or regional None

Renal & ureteral Renal 8 ureteral Renal only

Spherical

Membrane

Ultrasound

Move generator

Renal only

Membrane

2 fluoroscopes

Move generator

Membrane

Fluoroscope

Move patient Move patient

Move generator

Analgesia or none General or regional General or regional General or regional General or regional General or regional

Slemens Llthostar lnternatlonal Biomedlcs Medstone

Spark BP

Acoustic lens Ellipsoid

Spark geP

Ellipsoid

Membrane

Northgate

SPam gap

Elllpsold

Membrane

Plain x-ray films Ultrasound

Technomed

Spark gap

Ellipsoid

Pool

Ultrasound

* Lo&Ions:

Move generator

Move reflector

Renal & ureteral Renal 8. ureteral Renal & ureteral Renal 8 ureteral Renal & ureteral

West Germany (Dornier. Wolf, Siemans); France (EDAP, Technomed); United States (International Biomedics, Medstone, Northgate).

electromagnet, or pulsed laser. Stone localization is being performed with ultrasound and plain x-ray films in addition to fluoroscopy. Most of the newly developed machines have also eliminated the water bath. Probably the largest change has been the use of a lower energy shock wave, allowing for anesthesia-free treatment [91]. However, a larger number of shock waves need to be delivered to fragment the stone, and the incidence of retreatment is also increased [92]. Experimental centers utilizing the new-generation lithotripters are currently being established throughout the world and several are now in operation. Large patient series will be necessary to assess the results and efficacy of each second-generation lithotripter. REFERENCES 1. Sierkakowski R, Finlayson B, Landes RR, Finlayson CD, Sierakowski N. The frequency of urolithiasis in hospital discharge diagnosis in the United States. Invest Urol 1978; 15: 438-41. 2. Johnson CM, Wilson DM, G’Fallon WM, Malek RS, Kurland CT. Renal stone epidemiology: a 25year study in Rochester, Minnesota. Kidney Int 1979; 16: 624-31. 3. Coe FL, Keck G, Norton ER. The natural history of calcium urolithiasis. JAMA 1977; 238: 15 19-28. 4. Marshall V, White RH, DeSaintonge MC, Tresidder GC. The natural history of renal and ureteric calculi. Br J Urol 1975; 47: 117-24. 5. Anonymous. Chaussy recounts shock wave research, development. J Stone Treat 1986; 1: l-4. 6. Chaussy C, Brendel W, Schmiedt E. Extracorporeally induced destruction of kidney stones by shock waves. Lancet 1980; 6: 12658. 7. Finlayson B, Thomas WC Jr. Editorial: extracorporeal shockwave lithotripsy. Ann Intern Med 1984; 101: 387-9. 8. Wilson HA Jr. Sonic boom. Sci Am 1962; 206: 36-43. 9. Chaussy CG, Fuchs GJ. Extracorporeal shock wave lithotripsy. Monogr Urol 1987; 8: 80-99. 10. Mulley AG Jr, Carlson KJ. Lithotripsy. Ann Intern Med 1985; 103: 626-9. 11. Dretler SP. Stone fragility: a new therapeutic distinction. J Urol 1988; 139: 1124-7. 12. Chaussy C, Schmiedt E, Jocham D, Walther V, Brendel W. 356

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84. Lingeman JE, Kulb TB. Hypertension following extracorporeal shock wave lithotripsy. J Urol 1987; 137: 142A. 85. Williams CM, Kaude JV, Newman RC, Peterson JC, Thomas WC. Extracorporeal shock-wave lithotripsy: long-term complications. AJR 1988; 150: 31 l-5. 86. Peterson JC, Finlayson B. Effects of ESWL on blood pressure. In: Gravenstein J, Peter K eds. Extracorporeal shock wave lithotripsy for renal stone disease. Boston: Butterworth, 1986: 145-50. 87. Brewer SL, Atala A, Ackerman DM, Steinbock GS. Shock wave lithotripsy damage in human cadaver kidneys. Proceedings Southeastern Section AUA, Boca Raton, FL, 1988: 50. 88. Mulley AG Jr, Carlson KJ, Dretler SP. ExtracorporealShockwave lithotripsy: Slam-bang effects, silent side effects? AJR 1988; 150: 316-8. 89. Coptcoat MJ, Webb DR, Kellett MJ, et al. The complications of extracorporeal shockwave lithotripsy: management and prevention. Br J Urol 1986; 58: 578-80. 90. Marberger M, Turk C, Steinkogler I. Painless piezoelectric extracorporeal lithotripsy. J Ural 1988; 139: 695-8. 91. Coptcoat MJ, Miller RA, Wickham JEA eds. Lithotripsy II: textbook of second generation extracorporeal lithotripsy. London: BDI, 1987. 92. Graff J, Schmidt A, Pastor J, Herberhold D, Rassweiler J, Hankemeier U. New generator for low pressure lithotripsy with the Dornier HM3: preliminary experience of 2 centers. J Urol 1988; 139: 904-7.

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