What is Extracorporeal Shock Wave Lithotripsy or ESWL?
Research done in the late 1970s showed that shock waves generated outside the body can pulverize urinary stones inside the body. The pulverization resulted in sand-like particles which could be passed easily. Such treatment has become the standard therapy for stones of the upper urinary tract (kidney and upper ureter).
Shock waves are high energy pressure waves and may be generated in air or water. In this medical application, shock waves are generated underwater by a “spark plug” electrode. Ignition of the electrode generates a spark, which in turn, generates a shock wave that is transmitted through water and any adjacent living tissue. The shock wave may be focused with mechanical devices so that its energy can be concentrated on a urinary stone. Multiple shock waves fragment or pulverize the stone. The resilient or movable nature of nearby living tissue results in little or no tissue damage from the passing shock wave.
Candidates for ESWL
Any patient with a stone of the kidney or upper ureter is a candidate. But there are reasons for NOT doing ESWL. Patients may not be good candidates for ESWL treatment if:
weight exceeds 300 lbs. (140 kg) height exceeds 6 feet, 8 inches the stone-containing kidney has little or no function, life-threatening cardiac (heart) problems exist, the ureteral stone is below the hip bone (iliac crest) (depending of machine type), bleeding disorders, pregnancy, some cardiac pacemakers, in the opinion of the attending physician the risks of anesthesia and ESWL treatment outweigh the potential benefits, or some other form of stone treatment is more appropriate.
Furthermore, the size, location and number of stones and/or the presence of unusual or abnormal structural abnormalities of the kidneys or ureters may make other forms of treatment preferable. In some instances, combination treatment using ESWL may be needed This would include surgical removal of stones from the kidney or ureter with telescopes after pretreatment with ESWL.
Patients who on preliminary review seem to be candidates for ESWL treatment will undergo tests consisting of blood and urine tests, studies to determine the presence of urinary infection, X-rays, and, if necessary, an electrocardiogram and isotope studies of kidney function.
Alternative methods for stone removal (i.e. the traditional open surgical techniques and percutaneous lithotripsy (telescopic removal from the kidney through a small incision) will also be considered and explained.
Most candidates are admitted to the hospital the morning of treatment. An anesthetic will be administered. Selection of the anesthetic is up to the patient and anesthesiologist. Sedatives are routinely given intravenously during the procedure to make the patient relaxed and comfortable. The anesthetized patient is placed on a support platform, which is suspended overhead. A catheter is sometimes placed into the patient’s urinary bladder after the patient has been anesthetized.
The patient is then precisely positioned in the water bath with the head and shoulders out of the water, so that the kidney stones are positioned at the highest energy point of the shock waves. Positioning is assisted with two x-ray monitors. When positioning is complete, shock wave treatment will be initiated. Approximately 300-2500 shock waves from the electrode will be utilized. The treatment procedure will last approximately one hour. The urologist conducting the treatment monitors stone fragmentation using the fluoroscopes. Every few minutes the patient will be re-positioned using fluoroscopes and the hydraulic suspension system.
Follow-Up After ESWL
Typically patients will usually be discharged on the day of treatment. Blood-tinged urine is to be expected for a few days. Stone particles typically begin to pass during treatment and may continue to pass intermittently for several weeks. Most patients have remarkably little discomfort. Pain will be treated with appropriate painkilling drugs.
Patients will be discharged from the hospital when their symptoms and medical condition warrant. Laboratory and radiographic studies similar to those made before ESWL treatment will be made at periodic intervals after treatment to assess the patient’s response. Follow-up after treatment is usually done within a few weeks in the office.
What are the Limitations of ESWL?
1. Visualization of Stones: In most cases only stones that are visible on radiographs and the fluoroscope may be treated. Some stones may be too small and/or too faint to be reliably treated with ESWL.
2. Non-fragmentable Stones: The location and/or crystalline type of stone may affect its pulverization. For example, cystine stones are more resistant to ESWL than other crystalline types. Stones located in the ureter pulverize to a lesser extent than if they were located in the kidney.
3. Very Large Stones: Patients with very large stones may not be good candidates for ESWL because the volume of particles may be too much for the urinary system to pass conveniently. In such cases tubes placed through the flank into the kidney or from the bladder into the kidney (stents) may be of assistance in facilitating passage of stone debris.
4. Patient Size: The Lithotripter is designed for average size adults. Children and/or persons of exceptionally large or small statures may not fit into the apparatus.