Shockwave Lithotripsy Program Project

Kidney stone disease (nephrolithiasis) is a significant health problem in the United States and world-wide. Between 5% to 15% of the general population will develop a urinary calculus during their lifetime (1) and will account for about 7 to 10 of every 1000-hospital admissions in the United States (2).  The prevalence of kidney stones in the United States varies dependent on race, sex, and geographic location (3). Four of every five patients with stones are men, and in both sexes, the peak age of onset is during the third to fourth decade of life.  Caucasians are at highest risk for stones, while African Americans at lowest risk.  The disease is relatively uncommon in patients younger than the age of 15.  The age-adjusted prevalence increases from north to south and from west to east.  The rate of stone disease appears to increase during the summer months in the south.  The economic impact of urolithiasis is enormous.  In 1993, the total annual cost for urolithiasis treatment in the United States was estimated to be $1.8 billion (4).

Advances in endourological techniques have so dramatically altered the management of patients with symptomatic stone disease that the need for open surgical lithotomy has essentially been eliminated. Four minimally invasive treatments, retrograde ureteroscopic intrarenal surgery (RIRS), percutaneous nephrolithotomy (PNL), laparoscopic surgery and extracorporeal shock wave lithotripsy (ESWL) allow virtually any stone to be removed from the upper urinary tract without resorting to open surgery. There is controversy regarding which of these techniques is the most efficacious. However, at the current time SWL is the preferred initial treatment for approximately 80- 85% of non-staghorn renal stones (5).

  Extracorporeal shock wave lithotripsy (ESWL) is a non-invasive method in which high intensity sound waves (shock waves) are generated outside of the patient and then focused on the stone within the kidney or ureter. The focal point of the shock wave is fixed, and the patient is moved so that the stone (imaged by fluoroscopy or ultrasound) rests at the focal point (F2 for electrohydraulic machines). The urologist controls three parameters; number of shock waves administered, the repetition rate, and the voltage (or energy) of the shock wave generator. The process of stone comminution is monitored by imaging, and treatment is terminated when it is judged that residual fragments are small enough to be voided in the urine or grasped and removed using transurethral or percutaneous probes. A variety of factors are weighed in determining a treatment protocol, including the number, size, location and suspected composition of the stones, the age and health of the patient, and the type of lithotripter being used. Most ESWL patients are treated as outpatients in a single session with or without anesthesia.  As a rule stones <10mm are best treated with ESWL.  For stones between 10-20mm, ESWL is still the first line treatment unless factors of stone composition, location, or renal anatomy shift the balance toward invasive but definite treatment modalities (PNL or RIRS).  Stones grater than 20mm should be primarily treated by PNL, unless specific indications for RIRS are present (i.e. bleeding diathesis, obesity, etc). 

  The lithotripter is a very important factor in the treatment equation. The first lithotripter that was introduced into the United States (in 1984) was the unmodified Dornier HM3. This is an electrohydraulic device that generates shock waves by underwater spark discharge (other modes include electromagnetic and piezoelectric generators). The shock waves are focused by a brass ellipsoidal reflector to a geometric focal point (F2) approximately 13.5 cm above the rim of the reflector. Investigators have used ultrasonic hydrophones to map the pressure field in the water tank of the HM3 and have determined that the pressure, in F2 is a zone roughly cylindrical in shape (i.e. tapered cylinder) approximately 15 mm in diameter by 80 mm long. Peak pressures at F2 approach 100 MPa (1 MPa=1 atm). Lithotripter shock waves exhibit a signature pattern characterized by a narrow positive pressure spike with short rise time (<200 mS) and rapid fall followed by a blunt negative pressure trough (p-=-10MPa). These characteristics of the SW determine its acoustic effects and can be manipulated by changing various elements of the SW generator or the SW reflector.

  Since the introduction of SWL in the early 1980's, some 40 different lithotripters have been marketed world-wide (6). Advancements in SWL technology have centered on improvements in imaging systems, the development of devices that can serve both as lithotripters and as endourological treatment tables, and attempts to reduce SW pressures so that patients feel less discomfort and can have the option of being treated without general anesthesia. These lithotripters have been resoundingly unsuccessful. Lithotripters have also been developed which focus the SW to a smaller focal point with the idea of reducing the number of SWs necessary for stone comminution and, thereby, reducing the risk of adverse side effects. This design, too, has proven to be less effective in clinical practice than existing technology. In general, the less powerful lithotripters with smaller focal points result in lower stone-free rates and/or higher retreatment rates (6,7,8).  The stone free rate can be improved for these machines if the patient is anesthetized, suggesting that there is a reduction in body movements which permits more direct hits of the shock wave on the stone (9).  A more critical issues appears to be developing for these devices, in that is an increased rate of bioeffects like subcapsular hematomas, colon perforations, and ruptured spleens (10-13),.

  No lithotripsy system has convincingly equaled the results produced by the unmodified Dornier HM3. Thus, in the past several years many lithotripsy centers have abandoned these lithotripters to return to the device that has been proven by clinical experience to be most efficacious, the for SWL, the Dornier HM3.  However, fewer of these used machines (the HM3 is no longer manufactured) are available so eventually the HM3 users will be required to purchase a different lithotripter.  What makes the HM3 so effective at breaking stones is probably its considerable variability, shot-to-shot, in peak pressure and volume of focal point, (F2). As a result, the shock waves hit the stone at many adjacent spots instead of only one. The analogy of the stone cutter may help explain the phenomenon, where hits along the length of a scored line tend to be more effective in creating and expanding a crack, than hits all at one point. However, stone comminution is no longer the only end point. Kidney injuries must now be factored into the stone treatment equation. At present this cannot be done because we do not have a physically-based quantitative definition of SWL that is based on the properties of shock waves (pressure wave rise time, peak pressure, etc), renal tissue and stones.

1.                  Consensus conference.  Prevention and treatment of kidney stones.  JAMA 1988;260:977.

2.                  Levy FL, Adams-Huet, Pak CVC.  Ambulatory evaluation of nephrolithiasis: An update of a 1980 protocol. Am J Med 1995;98:51.

3.                  Soucie JM, Thun MJ, Coates RJ et al.  Demographic and geographic variability of kidney stones in the United States.  Kidney Int 1994;46:893.

4.                  Clark JY, Thompson IM, Optenberg SA.  Economic impact of urolithiasis in the United States.  J Urol 1995;154:2020.

5.                  Wickham JEA  Treatment of urinary tract stones.  BMJ 1993;53:297.

6.                  Lingeman JE, Safar FS  Lithotripsy systems: In Smith AD, Badlani GH, Bagley DH, Clayman RV, Jordan GH, Kavoussi LR, Lingeman JE, Preminger GM, Segura JW (eds); Smith’s Textbook of Endourology.  St Louis, Quality Medical Publishers, 1996;40:553.

7.                  Lingeman JE  Extracorporeal shock wave lithotripsy devices: Are we making progress.  In Lingeman JE, Preminger GM (eds); New Developments in the Mangement of Urolithiasis.  New York, Igaku-Shoin, 1996;79.

8.                  Grenabo L, Lindqvist K, Adami HO, et al Extracorporeal shock wave lithotripsy for the treatment of renal stones: Treatment policy is as important for success as type of lithotripter and patient selection. Arch Surg 1997;132:20.

9.                  Eichel L, Batzold P, Erturk E.  Operator experience and adequate anesthesia improve treatment outcome with third-generation lithotripters.  J Endourol 2001;15:671.

10.              Kohrmann KU, Rassweiler JJ, Manning M, et al.  The clinical introduction of a third generation lithotripter Modulith SL 20.  J Urol 1995;153:1379.

11.              Piper NY, Dalrymple N, Bishoff JT.  Incidence of renal hematoma formation after ESWL using the new Dornier Doli-S lithotripter.  J Urol 2001;165:S377.

12.              Thuroff S, Thorsten B, Chaussy C.  Anatomy related shockwave (SW) power using Siemens Lithostar multline.  J Urol 1998;159S34.

13.              Ueda S, Matsuko K, Yamashita K, et al.  Perirenal hematomas caused by SWL with EDAP LT-01 lithotripter.  J Endourol 1993;7:11.