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  1. 1. Extracorporeal Shockwave Lithotripsy Dr.3amer 3alwan 3rd year board in urology
  2. 2. HISTORICAL OVERVIEW  High-energy shockwaves have been recognized for many years. Example of high- energy shockwaves is the potentially window shattering sonic boom created when aircraft pass beyond the speed of sound.  Engineers at Dornier Medical Systems during research on the effects of shockwaves on military hardware to determine if the shockwaves striking the wall of a military tank would damage the lungs of enemy member,discovered the possibility of safely applying shockwave energy to human tissue when an engineer touched a target body by chance. The engineer felt a sensation similar to an electric shock, although the contact point at the skin showed no damage at all. In the course of this effort the engineers discovered that shockwaves generated in water could pass through living tissue (except for the lung) without damage but that brittle materials in the path of the shockwaves would be fragmented.
  3. 3. Methods and Physical Principles
  4. 4. 1-Electrohydraulic Generator: • shockwave is generated by an underwater spark discharge. • For the shockwave to be focused onto a calculus the electrode is placed at one focus (termed F1) of an ellipsoid, and the target (the kidney stone) is placed at the other focus (termed F2). • Disadvantages are the substantial pressure fluctuations from shock to shock and a relatively short electrode life.
  5. 5. 2.Electromagnetic Generator:  An electrical current pass through conductors producing strong magnetic field moving the plate against the water and thereby generating a pressure wave.  The energy in the shockwave is concentrated onto the target by focusing it with an acoustic lens.  Advantage: Introduction of energy into the patient’s body over a large skin area, which may cause less pain.
  6. 6. 3.Piezoelectric Generator:  These generators are made of a ceramic elements each of which can be induced to rapidly expand by the application of a high-voltage pulse.The piezoelectric elements are usually placed inside of a spherical dish to permit convergence of the shockfront.  The advantages include the focusing accuracy, a long service life, and the possibility of an anesthetic-free treatment because of the relatively low energy density at the skin entry point of the shockwave.
  7. 7. Imaging Systems
  8. 8. 1.Fluoroscopy Alone :  Advantages of fluoroscopy include its familiarity to most urologists, the ability to visualize radiopaque calculi throughout the urinary tract, the ability to use iodinated contrast agents to aid in stone localization, and the ability to display anatomic detail.  The disadvantages include the exposure of the staff and patient to ionizing radiation, the high maintenance demands of the equipment, and the inability to visualize radiolucent calculi without the use of radiographic contrast agents.
  9. 9. 2. Ultrasonography Alone  Advantages: is inexpensive to manufacture and to maintain compared with fluoroscopic systems. Another advantage is in the treatment of children and infants when one is concerned about the dose of ionizing radiation. In addition, ultrasonography can localize slightly opaque or nonopaque calculi.  Disadvantages: requires a highly trained operator. It is almost impossible to view a stone in areas such as the middle third of the ureter or when there is an indwelling ureteral catheter. Once a stone is fragmented, it is difficult to identify each individual stone piece.
  10. 10. 3. Combination of Ultrasonography and Fluoroscopy  In some cases combining ultrasonography and fluoroscopy for stone localization are clearly advantageous but each system has a drawback that limits one of the functions of the system.
  11. 11. Mechanisms of Stone Comminution
  12. 12.  A typical shockwave involves an initial short compressive front with pressures of about 40 MPa that is followed by a longer, lower-amplitude negative (tensile) pressure of 10 MPa, with the entire pulse lasting for a duration of 4 µsec.The ratio of the positive to negative peak pressures is approximately 5:1.
  13. 13. 1-spall fracture  Once the shockwave enters the stone it will be reflected at sites of impedance mismatch. One such location is at the distal surface of the stone at the stone- fluid (urine) interface. As the shockwave is reflected, it is inverted in phase to a tensile (negative) wave. If the tensile wave exceeds the tensile strength of the stone, there is an induction of microcracks that eventually coalesce, resulting in stone fragmentation, which is termed spallation
  14. 14. 2- Squeezing-splitting or circumferential compression  The shockwave advances faster through the stone than in the fluid outside the stone. The shockwave that propagates in the fluid outside the stone produces a circumferential force on the stone, resulting in a tensile stress in the stone that is at its maximum at the proximal and distal ends of the stone
  15. 15. 3- shear stress  The shock waves propagate through the stone and will result in regions of high shear stress inside the stone. Many materials are weak in shear, particularly if they consist of layers, because the bonding strength of the matrix between layers often has a low ultimate shear stress.
  16. 16. 4- Superfocusing  The shockwave that is reflected at the distal surface of the stone can be focused either by refraction or by diffraction from the corners of the stone.
  17. 17. 5- Cavitation  During the negative pressure wave, the pressure inside the bubble falls below the vapor pressure of the fluid, and the bubble fills with vapor and grows rapidly in size (almost three orders of magnitude)and then collapse violently, giving rise to high pressures and temperatures.
  18. 18. 6- Dynamic fracture  the damage induced by SWL accumulates during the course of the treatment, leading to the eventual destruction of the stone.
  19. 19. Bioeffects of SWL
  20. 20. 1. Acute Extrarenal Damage  visceral injuries, such as perforation of the colon, hepatic hematoma, splenic rupture, pancreatitis, and abdominal wall abscess.  Extrarenal vascular complications such as rupture of the hepatic artery, rupture of the abdominal aorta, and iliac vein thrombosis.  Thoracic events, such as pneumothorax and urinothorax.  shockwaves could induce cardiac arrhythmia, an observation that led to electrocardiographic synchronization with R-wave triggering on the Dornier HM3 device.  The development of diabetes was related to the total number of shockwaves and the power level of the lithotripter.
  21. 21. 2. Acute Renal Injury  Hematuria is so common that it may be considered an incidental finding, and its severity is rarely of concern. Although hematuria was initially considered to be a consequence of irritation of the urothelium as stones were fragmented by shockwaves, it is now known that shockwaves rupture blood vessels and can damage surrounding renal tubules .  risk factors: • unsatisfactory control of their hypertension at the time of SWL • diabetes mellitus • coronary artery disease • Obesity.
  22. 22. 3. Chronic Renal Injury  accelerated rise in systemic blood pressure because 1. subcapsular hematomas can induce hypertension, such changes are generally transient. 2. Mesangial proliferation after SWL could induce hypertensive changes  decrease in renal function  increase in the rate of stone recurrence (Stone recurrence rates may be higher after SWL because of residual stone debris)  induction of brushite stone disease.
  23. 23. Techniques to Optimize SWL Outcome
  24. 24.  wider focal width increase the likelihood of stone breakage because the kidney tends to move, as a consequence of respiratory motion, the stone may move in and out of a narrow focal zone.  Optimal coupling permits the efficient transfer of energy from the lithotripter to the patient; poor coupling will reduce stone breakage. Most commonly, energy transfer through a coupling medium is attenuated by air pockets in the coupling interface itself.  Decrease the rate of shockwaves because the dynamic bubbles are given a longer time interval to dissipate with a slower rate and therefore have less of a shielding effect and energy draw from subsequent shocks.  Decrease the energy setting on the machine. Increasing the power setting on most electromagnetic lithotripters actually narrows the focal zone which decreases stone breakage and may also increase the risk of renal injury.  To reduce stone motion, urologists can perform SWL with general anesthesia, which will control the patient’s respiratory rate and volume.
  25. 25. Anesthesia
  26. 26. 1. in 1980s regional or general anesthesia was used in all instances because the unmodified HM3 device produced a powerful shockwave and treatment at recommended energy levels caused intolerable pain. 2. Short-acting agents, such as the narcotic alfentanil and the sedative- hypnotics midazolam and propofol can be used in various combinations to allow most SWL treatments with any lithotripter. 3. topical agents e.g.EMLA cream, a mixture of lidocaine and prilocaine, has been shown to reduce anesthesia requirements during SWL . EMLA cream should be applied at least 45 minutes before SWL. 4. Children and extremely anxious individuals may be served best by general anesthesia. Patients who received general anesthesia experienced a significantly greater stone-free rate than did those patients who underwent intravenous sedation. Possible explanation for this is the more controlled respiratory excursion that is conferred by the general anesthetic.
  27. 27. Fragmentation
  28. 28.  Safe shock wave dosage is unknown. Shock waves induce trauma, including intrarenal and perirenal hemorrhage and edema, and thus the minimal shocks needed to achieve fragmentation should be given.  Determination of adequate fragmentation during treatment may be difficult. Initial sharp edges become fuzzy or blurred .Stones that were initially visualized may disappear after successful fragmentation.  Intermittent visualization ensures accurate focusing and assessment of progress and eventual termination of the procedure.
  29. 29. Preoperative antibiotic prophylaxis
  30. 30. Indications The American Urological Association Stone Guidelines Panel has classified ESWL as a potential first-line treatment for ureteral and renal stones smaller than 2 cm.
  31. 31. Indications
  32. 32.  The reasons for poor clearance of fragments from the lower pole after SWL are unclear. The gravity-dependent position of the lower pole calyx may impede the passage of stone fragments,The examination of the angle formed between the lower infundibulum and the renal pelvis and if the angle greater than 90 degrees it should facilitate drainage of fragments from the lower pole.
  33. 33. Contraindications  Absolute 1. Pregnancy 2. uncorrected blood clotting disorders (including anticoagulation) 3. known renal artery stenosis 4. Acute UTI or urosepsis 5. Uncorrected obstruction distal to the stone 6. Abdominal aortic aneurysm  Relative 1. Uncontrolled HT 2. Morbid obesity 3. Renal ectopy or malformation 4. Renal insuficiency 5. Cardiac pacemaker
  34. 34. New applications
  35. 35. 1. Heel spur 2. Pancreatic stone 3. Gall stone 4. Peyronie disease 5. Erectile dysfunction
  36. 36. Postoperative care
  37. 37.  Patients should be encouraged to maintain an active ambulatory status to facilitate stone passage.  Fluid intake should be encouraged.  Severe pain unresponsive to routine intravenous or oral medications should alert the physician for perirenal hematomas. In such a situation, CT scan should then be undertaken to stage the injury.  Steinstrasse (stone street) Asymptomatic individuals can be followed up with serial KUBs and ultrasonography. Severe pain or fever requires intervention. Percutaneous nephrostomy drainage is usually uncomplicated owing to the associated hydronephrosis. Decompressing the collecting system allows for effective coaptation of the ureteral walls and encourages resolution of the problem. If steinstrasse does not resolve ,retrograde endoscopic manipulations is required.