January 1990, Volume 40, Issue 1

Special Communication

EXTRACORPOREAL SHOCK WAVE LITHOTRIPSY

J. Talati  ( Departments of Urology , The Aga Khan University, Karachi. )

After circumcision the first operations done on man were for bladder stone. Done by charlatans the operation often resulted in loss of life and caused the early lithotomists to maintain a peri­patetic existence, vanishing from the town the night after surgery was performed. About two centuries ago stones became a common disease amongst kings: surgeons took over from the charlatans and commenced blind skilful mechanical lithotripsy where a curved instrument was introduced per urethram, its jaws opened to engage the stone which was then crushed by a mechanical (screw driven) closure of the jaws. Now-a-days urinary bladder lithotripsy is done under vision and aided by ultrasound drilling, or electrohydraulic shock wave produced by a direct contact probe. Renal stones can be safely operated on or removed percutaneously.
Non-invasive lithotripsy
Aforementioned invasive methods are being gradually superseded by extracorporeal lithotrip­sy, available in Pakistan since August 1988, in which externally produced shock waves are focus­sed onto the stone. Repeated shocks act by alter­nately compressing the stone as the wave proceeds towards it and expanding it as the wave reflected from the far surface of the stone returns back as a tensile force. The shocks loosen up the texture of the stone, produce cracks in it and chip off minute particles from the surface..
To do this effectively a shock wave source, a stone locating device and motors to move the table on which the patient lies have been put together by various manufacturers to produce the extracor­poreal lithotriptor.
Shock wave source
Shock waves may be produced from a point source electrohydraulically (as in the Dornier, Medstone and Technomed machines) or from an extended source electromagnetically (as in Sie­mens lithostar1), piezoelectrically (as in Edap and Wolff machines). The Japanese areat present developing their lithotriptor which uses micro-ex­plosions to generate the shockwaves. Others are developing lasers2. Shock waves need to enter the body in such away that they are focussed onto a fine point. The smallest focus point according to manu­facturers data is seen in the Wolff machine (focus point under 1 cm.) and the Dornier’s MPL 9000 (focus point a spindle 2cm long 0.3 wide with 50% of shock wave energy for another 0.3cm). Focuss­ing can be done by lens systems (Siemens) or by parabolic reflectors (Technomed, Dornier) or may be a function of the way in which an array of piezoelectric cells is arranged in a dish (Wolf and Edap). The finer the focus the more accurately can shockwaves be focussed onto the stone, avoiding renal substance and minimising damage. Distor­tion of the focus can occur as varying thicknesses of fat in obese patients refract the waves reducing their efficacy. Skin to focus distance is also impor­tant and it is at times virtually impossible to “reach” the stone in obese patients weighing 100 kilograms.
Piezoelectric lithotripsy is said to offer the advantage of being painless. However, Marberger3 from Austria reports that even piezoelectric waves can be painful at repetition rates of 20/second or more. The pressure developed at the focus point varies from 310-1200 bar and children need to be treated at the lower pressures.
Valencien et al4 using the Edap LTO1 piezoelectric lithotriptor, have performed anal­gesia free lithotripsy with 1.25 shocks/sec. How­ever their success rate is 74% :26% failed therapy. Higher success rates need more shocks.
In the Japanese lithotriptor described by Kuwahara5 explosive pellets peadiazide are cle­tonated electrically by a platinum igniting bridge connected to a 18V battery.
Stone locating device
Stones may be visualised by x-rays as in Siemens lithostar, Dornier HM3 and 4 or by ultrasound as in Dornier MPL 9000, Edap LTO1, Wolf Piezolith and Technorned Sonolith2. The ultrasound monitored machines can demonstrate opaque as well as non opaque stones in the kidney, gallbladder and urinary bladder. As 11% of our stones contain 30% of more uric acid, ultrasound imaging has definite advantages. However ureteric stones cannot belocalised with ease by this method except in the upper or lower 1/6. This disadvantage is offset by the fact that gall stones can be easily visualised. One has, however, to remember that in Pakistan less than 5% of stones in the gall bladder are treatable by ESWL keeping strict selection criteria.
A special advantage of ultrasound is that there is no harmfu! irradiation and lithotripsy staff can move about freely within the room. This allows close contact to be maintained with the patient and is comforting and reassuring to them. Continuous monitoring allows the operator to “shoot” shock­waves only when the stone is in the target zone thus during coughing, sighing, deep breathing or rest­lessness the patient’s kidney is spared the splatter­ing of shocks that would occur if targeting were by intermittent radiological control. The value of continuous ultrasound monitoring is better under­stood when one realises that renal excursions of 50mm and over can occur during a deep sigh or cough and that mean movement of the kidney due to ventilation during anaesthesia is 34.3±4.3mm. High frequency jet ventilation reduces the move­ment to 4.1±1.9mm and would be useful when using radiological methods of stone localisation6.
The disadvantage of not being able to visua­lise ureteric calculi can be overcome. Ureteric calculi can be pushed back into the kidney and blasted by ultrasound monitored machines by a push bang technique7. Marberger et al3 mention that 60% of ureteric calculi proximal to the pelvic brim can be manipulated into the pelvis of the kidney. Graff8 was also able to push back 57% of the stones causing ureteral obstruction. Our ex­perience is otherwise as in Pakistan stones often have been impacted in the ureter for many months.
Vallencien4 has reported on difficulty in visualising stones in 10% and inability in 3% of patients, using ultrasound monitoring. He also noted that the rib interfered with localisation in7% of patients. Third generation lithotriptor have more powerful ultrasounds and the ability to move the in line scanner obliquely and radially to over­come these problems. All stones larger than 3mm can be easily visualised.
Radiological visualisation has an edge over ultrasound in that ureteric stones are easily visua­lised and treated. Graff et al8 treat non obstructing ureteral stones in situ with a 13% second treatment rate and 5.9% ancillary procedure rate. In situ fragmentation of ureteral stones, however, gives a 60-90% successful fragmentation rate as against 98-99% successful fragmentation of renal cal­culi9,10. Stones impacted in the ureter are more resistant to shock wave fragmentation11. This is because of lack of fluid filled space surrounding the stone which therefore has little room to expand11. Urine does not permeate the stone and the thick muscle near the ureter absorbs sound. Non opaque stones can be identified by continuous irrigation of the pelvis with dye introduced through a ureteric catheter.
Radiation exposure with radiologically monitored machines
Radiation exposure has been variously quo­ted as less than that of an IVP to 5times that of an IVP. A patient is likely to receive a total of 26
Roentgen. A total time of 3-4 minutes of fluoros­copy would deliver 21 roentgens and 8 frames of video spot filming an additional 5. The scattered radiation has been found to be approximately 0.5m R per hour at 3 feet or 91cm from the center12. Surface radiation dose to the back of a patient from the X-ray unit on the side of the kidney averaged 10 rem (lOOm Sv) per treatment although the range was wide (1-30 rem). The opposing X-ray machine gave 5.5 rem (55m Sv) (range 01-21 rem). The estimated female gonad done averaged lOOm rem (1.2mSv). Radiationexposureto personnelwas2m rem (0.02m Sv).
The most advantageous situation wouldbe to have an X-ray monitored lithotriptor available for ureteric stones and an ultrasound machine for renal, upper and lower 1/6th ureteric stones.
Mechanism to move the patients stone onto the focus point of the machine
Approximate surface marking of the stone allows placement of the patient so that the focus point is near the stone. Finer adjustments can then be done by mechanical movement of the table. Complex computerised motors which move the table in relation to the ultrasound scan are avail­able in Dornier MPL 9000. These facilitate the not-so-expert in locating the stone.
Contraindications to Extracorporeal Shock-wave Lithotripsy
Patients with heartblock and pregnant pat­ients should not be treated by ESWL. Patients with cardiac and respiratory problems need to be brought into the best possible situation and require intensive monitoring during the procedure. Coa­gulopathies should be corrected. We have treated a thrombocytopenic patient after platelet trans­fusion. Others have treated haemophiliacs14. Pa­tients with solitary kidneys need to be treated with care.
Tissue damage in lithotripsy
A shock wave blast travelling through tissues would be expected to produce some cellular damage. This is minimised by (a) enlarging the area through which the shock wave enters the body so that the shockwave strength per unit skin area is. reduced and (b) by htving a very small focus. Mitochondral damage at cellular level is expected and animal experiments have shown oedema and capillary damage manifest as hematuria (14a). Pen-capsular and subcapsular hematomas were seen frequently with the older machines with greater power and larger focus. We have en­countered only one perirenal hematoma in the series of our initial consecutive 350 treatments (0.28%).
Molley15 has cautioned about possible soft tissue damage and has suggested a 25-75% pos­ sible incidence of perinephric, subcapsular and parenchymal hemorrhage. Sofras16 has quoted a 0.2% hematoma rate.
An Indiana university study by Knapp17 detected hematoma in 0.66% of 3620 patients. Coagulation studies were normal in these patients and the formation of the hematoma was not related to the number of shockwaves or voltage used. However, if the patient was hypertensive, then 2.5% formed a hematoma and if the hypertension was uncontrolled 3.8% did so. Whilst these were seen with the older machines with radiological control, powerful punch and large focus, it will be worthwhile carefully looking for a hematoma in patients who have had a drop of 2G hemoglobin, or persisting flank pain.
Careful study of lithotripsy patients has shown elevation of enzyme levels in some cases. In a small study Gilbert18 have shown that 12 of 26 patients had post ESWL protein excretion exceed­ing 1.5G. This is above what would be expected from simple hematuria and it is suggested that proteinuria is the result of shockwaves on the fixed negative charge of glomerular capillaries. This proteinuria was seen at mean operating voltage of 20KV and an average of 1600 shockwaves.
Ureteric obstruction
Fragments of stone passing down the ureter will cause temporary obstruction. This is often partial when the fragments are 2-3mm in size as they allow urine to trickle past the loosely arranged pieces. Finer dust is more likely to impact, but the fmer powder is more likely to pass spontaneously. Ureteric obstruction has been noted in upto 6.3% and aneuria in 1.3%16. One should be alert to the possibility of silent renal destruction19. Fedullo et al20 have noted a stein strasse (literally stone street), a collection of particles in the ureter in 20% of 1000 patients studied. 65% of these passed spontaneously but 35% needed ureteroscopy (in 3/4th of these patients)PCN or fluoroscopically inserted retrograde double J stent. If the leading stone is small, stein strasse will pass: but if the lead stone or the fragments are large then ancillary .procedures are needed. Keeping this in mind it is beneficial to (a) deliver shock waves that produce a finer powder by using a lower KV and (b) pulverise any large residual fragments by a second sitting before it has a chance of working its way into the ureter. It is. wise to preempt obstruction by plading a double J stent and we agree with Libby21 and Shabsigh22 that stenting provides extra safety in lithotripsy. The incidence of colic and urosepsis are reduced. Hospital stay is shortened and there are fewer episodes of readmission22. Using a stent, Libby21, reduced the incidence of auxiliary proce­dures from 15 to 6% and Shabsigh22 from 17 to 10%. Libby21 used a stent for stone size above
25mm. We recommend it for stones over 2cm in size in agreement with Riehle23 except when a calcium oxalate dehydrate stone is seen on x-ray and one can predict its easy fragmentation into fine dust. Libby’s21 stone population of 1645 kidneys (seen in one year of operations) had 646 kidneys with stones > 14mm and 283 > 25mm. Stent insertion at cystoscopy is a simple procedure, but adds to time and costs. A stent alone costs Rs.900-1800 plus consultant and O.R. time. Stents need to be removed after all fragments have been passed. Normally another cystoscopy is necessary but if stents with a pull through nylon thread are used then the stent can be removed by traction on this suture in the outpatient department. Because of safety factor, 30-70% of ESWL patients in Ame­rica have pretreatment insertion of stents23. Com­plications and stent materials are well discussed in Saltzman’s24 reviews.
Recurrence and Stone clearance
Stones will recur at an expected rate of 5% per annum. Recurrence after lithotripsy will be expected to have the same frequency. However, if radiologically visible fragments are left in situ and do not clear out, recurrence would likely become more frequent. Molley15 suggests that there will be a 15% recurrence rate in the first year and 50% overall recurrence rate. Chaussly and Schmiedt have reported (quoted in Miles28) a90% clearance of stones at 3 months. Fuchs, G. (also quoted in same article) mentions a 85% clearance rate. Miles et al25 from Gainsville Florida found that 50% of their patients had residual stones 3-21 months after ESWL. This is a rather low figure for stone clearance and even the centers in US report 65-77% stone free status26,26a Diligent follow up and if necessary retreatment are a sine qua non of any lithotripsy programme if it is to be successful.
Good clearance of the stone is essential and is aided by a high water intake. Double J stents should not be removed until radiological and ultrasound evidence of complete stone clearance has been obtained.
Ancillary procedures
Combination percutaneous nephrolitho­tomy or operation and lithotrips,y is recommended for stones in excess of 40mm21. Much however depends upon stone fragility and availability of ancillary procedures. Uric acid stones may frag­ment with difficulty but they can be dissolved by allopurinal and alkalinasation of urine. Struvite stones fragment easily and citrates help their dissolution27. Acetylcysteine irrigation of the pel­vis will assist cysteine stone fragmentation28. Cal­cium (Ca) oxalate dihydrate a loose textured stone often easily detectable as such on x-ray KUB, will shatter with ease. We have treated large Caoxalate dihydrate stones upto 5cms in size with ESWL monotherapy. Treatment needs to be spread out so that fragments have time to be washed out and the total fragment burden presented to the ureter is not excessive at any one time.
Occasionallyuric acid calculi fail to fragment easily. Calcium oxalate monohydrate stones ap­pearing as dense white uniform opacities on KUB are notoriously difficult to fragment. In such cases and in patients with large stone burdens or burdens distributed over a large area as multiple stones, it is beneficial to debulk the stone by percutaneous nephrolithotomy(PCNL).
The lithotriptist has to be ready to detect downward migration of large fragments into the ureter. These need to be blown back into the pelvis and blasted again. This is possible with the stone in the upper ureter. In the lower ureter, Dormia basketing or ureterorenoscopy will, at times, be necessary.
Hazards to Personnel
In addition to radiation hazards, sound levels upto 110 dB were common with the first generation lithotriptors29. We have found that levels do not exceed 90 dB at 20 KV output on the MPL 9000 Donier lithotriptor.
Ureteric Stones: ESWL or Ureterorenoscopy?
Ureterorenoscopy (URS) has a 17% per­foration rate30, 17% major complication rate31, 35% of failure rate32. Some ureteric stones are best tackled by ureterolithotomy33 which even in 1989 gives avery satisfactory cost effective short hospital stay result. Distal stones are better treated by ESWL with an expected 94% stone free rate of 90% at six weeks and mean procedure time one third that of URS34.. High power and large number of shocks are needed35 for ureteric stones.

CONCLUSION

In a controlled environment with diligent follow up extracorporeal shockwave lithotripsy is safe and effective. For complex “hard” stones it is best used in combination with PCNL and open surgery. Major lithotripsy centers need to be established within Pakistan with both ultrasound and radiologically controlled machines. Intensive research is needed to eliminate unnecessary “frills” from these complex first to third generation machi­nes and develop a simple lithotriptor accessible to the common man in Pakistan.

REFERENCES

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2. Saltzman, B. Second-generation shock-wave lithotripters, variations, indications, and efficacy in the treatment of ureteral calculi. Urol. Clin, North Am., 1988; 15:385.
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4. Vallencien, G., Aviles, J., Minoz, R., Veillon, B., Charton, M.and Brisset,J.M.Piezoelectricextracorporeallithotrip­ sy by ultrashort waves with the EDAP LT 01 Device. J. Urol., 1988; 139: 689.
5. Kuwahara, M., Kambe, K., Kurosu, S., Kageyama, S., loritani, N., Orikasa, M. and Takayama, K Clinical application of extracbrporeal shock wave lithotripsy using microexplosions. J. Urol., 1987; 137:837.
6. Warner, M.A., Warner, M.E., Buck, C. F. and Segura, J. W. Clinical efficacy of high frequency jet ventilation during extracorporeal shock wave lithotripsy of renal and ureteral calculi. A comparison with conventional mechanical yen­ tilation.J. Urol., 1988; 139:486.
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