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Keywords:

  • Ureteric calculi;
  • lithotripsy;
  • ureteroscopy;
  • ballistic lithotripsy

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and methods
  5. Results
  6. Discussion
  7. References

Objective

To investigate the safety and efficacy of electrokinetic lithotripsy (EKL), a ballistic lithotripter which uses high-energy magnetic fields to propel an impactor to fragment calculi.

Patients and methods

The records and radiographs of 121 patients who underwent ureteroscopy using the EKL for stones in the upper (26), mid (28) or lower (67) ureter were reviewed retrospectively. Ureteroscopy was performed with an 8.5 F semi-rigid ureteroscope, through which a 3 F EKL probe was passed.

Results

A total of 148 stones (mean stone size 11.5 mm, range 6–40) in 121 patients were treated using the EKL. One patient was lost to follow-up. Of 148 stones, 147 (99.3%) were fragmented, including five that had resisted fragmentation with either pulsed-dye laser or electrohydraulic lithotripsy. Despite this, only 45 of 56 patients (80%) with a single stone in the lower ureter were rendered stone-free after a single ureteroscopic procedure. Seven patients in this group (12%) required shock-wave lithotripsy for fragments that had been propelled into the kidney, while four patients (7%) required repeat ureteroscopy for retained ureteric fragments. Complications were limited to minor ureteric perforations in two patients, both of which were treated with a stent.

Conclusion

EKL is an inexpensive and reliable endoscopic method which fragments nearly all urinary calculi. Its limitations include the propulsion of fragments and the need to use an offset, semi-rigid ureteroscope. We recommend the use of a basket or graspers to remove fragments of ≥4 mm after EKL.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and methods
  5. Results
  6. Discussion
  7. References

Advances in ureteroscopic instrumentation and endoscopic expertise have made ureteroscopy a safe and efficient treatment modality for most ureteric calculi. Miniaturization of ureteroscopes, both rigid and flexible, means that the entire upper urinary tract can be accessed with no need for routine dilatation of the ureter [ 1, 2]. A variety of endoscopic lithotrites is available, including electrohydraulic, ultrasonic and ballistic lithotripters, as well as pulsed-dye, Alexandrite and holmium:YAG lasers. While some of these modalities have been accepted as essential parts of the urological armamentarium, others have not stood the test of time. The search continues for the ideal endoscopic lithotrite.

We present our initial experience with a new ballistic method, the electrokinetic lithotripter (EKL, Olympus Keymed, Southend, UK). The EKL uses electromagnetic energy to propel a rigid metal probe through a hollow cylinder to fragment calculi. The goal of the present study was to determine the safety and efficacy of the EKL, and to discuss its limitations.

Patients and methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and methods
  5. Results
  6. Discussion
  7. References

Between July 1995 and December 1997, 121 patients (94 men, 27 women, mean age 55.4 years, range 13–88) underwent ureteroscopy and stone disintegration using the EKL. The stone characteristics for patients with lower ureteric stones are listed in Table 1. An 8.5 F offset semi-rigid ureteroscope (Olympus Keymed, Southend, UK) was used in all cases. The EKL probe was passed through the working channel and placed in contact with the calculus, well away from the ureteric wall. Fragmentation was carried out under direct vision using short bursts of the EKL and continued until further fragmentation was not possible. A basket or graspers were used when the surgeon felt that the fragments were too large to pass spontaneously. A ureteric catheter was placed in most cases and removed the following day. A double-pigtail stent was placed when the surgeon felt that postoperative obstruction was likely.

Table 1.   Patient characteristics and results for treatment of single lower ureteric stones Thumbnail image of

Fragments pushed up to the kidney were treated with shock wave lithotripsy (SWL) on the Wolf 2300 piezoelectric lithotripter (Richard Wolf, Knittlingen, Germany) in the immediate postoperative period. A plain radiograph was taken on the first day after treatment, and further radiographs and/or procedures performed as indicated.

Fragmentation and complication data were recorded prospectively for the entire series. As many of the mid and upper ureteric stones were fragmented and then pushed back into the kidney with no attempt at removal, the analysis of stone-free outcome was limited to lower ureteric stones, with results compared using the separate-variance t-test.

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and methods
  5. Results
  6. Discussion
  7. References

Overall, 147 of 148 stones (99.3%) were fragmented. One patient had a 14 mm mid-ureteric stone composed of calcium oxalate monohydrate which resisted fragmentation; he subsequently underwent an uneventful laparoscopic ureterolithotomy. Stones were completely fragmented in five patients who had previously undergone ureteroscopy with failed fragmentation using electrohydraulic lithotripsy (EHL) (four) or pulsed-dye laser (one). In four additional patients, a combination of EHL and EKL was performed for large and/or multiple stones. Stones were fragmented with both devices in each of these patients.

Of 56 patients with single stones in the lower ureter, 45 (80%) were rendered stone-free after one ureteroscopic procedure alone ( Table 1). Four patients (7%) required repeat ureteroscopy for retained ureteric fragments (mean size 4.7 mm, range 4–6). Seven patients (12%) were treated with SWL soon after EKL for fragments (mean size 5.7 mm, range 4–7) which had been propelled into the kidney, six of whom were rendered stone-free. Thus, 51 of 56 patients (91%) were stone-free after ureteroscopy plus one SWL treatment.

No patient required balloon dilatation of the ureter. Three patients (2.5%) required dilatation of the lower ureter with graduated Teflon dilators. Stents were placed in 38% of patients, ureteric catheters in 58% and no drain in 4%. Complications in this series were limited to two cases of small ureteric perforations, one of which occurred in a patient undergoing EHL at the same sitting. Each of these was treated by stenting; renography showed no obstruction after removal of the stents in both cases. No patient to date has been diagnosed with a de novo ureteric stricture.

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and methods
  5. Results
  6. Discussion
  7. References

These results show the safety and efficacy of EKL, especially for the treatment of lower ureteric stones. The safety of ballistic lithotripters in the treatment of ureteric stones has been shown in vitro [ 3] and in several clinical series [ 4, 5]. Complications in the present series were minimal and the fragmentation rate (99.3%) was excellent, including the five patients where other endoscopic lithotrites had failed. Nevertheless, the stone-free rate after ureteroscopy alone for single lower ureteric stones was only 80%.

The EKL has a wide safety margin, as shown by the low rate of complications in the present series. Because follow-up IVU or nuclear renography was not routinely performed, the actual rate of strictures in this series is unknown. It has not been our practice to perform either study because of the low yield in large ureteroscopy series [ 6[7]–8] and the radiation exposure to the patient. Nevertheless, the present excellent rate of follow-up (>99%) clearly shows the low incidence of both perioperative and short-term symptomatic complications.

Limitations of the EKL include its inability to be used through a flexible ureteroscope, its propulsive effect and the size of fragments it produces. The EKL device must be used through an offset ureteroscope, which increases the difficulty of the procedure compared with a straight ureteroscope, especially for trainees. As the EKL cannot be used through a flexible ureteroscope, some fragments which migrated proximally could not be pursued. This may have contributed to the number of patients treated with SWL and to those who required a second ureteroscopic procedure.

The propulsive effect of the EKL is most evident in the number of patients undergoing SWL after ureteroscopy for distal (12%) ureteric stones (efficiency quotient 76%). While this is partly explained by the fact that we have easy access to a lithotripter which involves no anaesthesia, extra hospitalization or charges, the rate of SWL is relatively high compared with ureteroscopic series using holmium or pulsed-dye lasers [ 6[7]–8]. Indeed, the stone-free rate for distal ureteric stones in our pulsed-dye series is 94%, with only 3% of patients requiring SWL and 3% requiring repeat ureteroscopy (efficiency quotient 91%). Most of the failures in the present series occurred early, reflecting accumulating experience for the entire staff. We attribute some of this improvement to our recognition of the propulsive effect of the EKL, and the increased use of helical baskets and graspers to remove fragments of moderate size.

Fragmentation with the EKL is excellent for larger stones, but further fragmentation is difficult for fragments of ≥4 mm. This problem is especially evident when fragmenting very hard stones in a dilated ureter. Teichman et al. [ 9] showed that fragments of ≥4 mm are produced by all types of endoscopic lithotrites, with the exception of the holmium:YAG laser. We have found that patients with fragments of ≥4 mm after ureteroscopy have an unacceptably high requirement for repeat ureteroscopy [ 10]. Therefore, we recommend using baskets or graspers to remove fragments produced by the EKL. Furthermore, a basket may be required to entrap a stone in a dilated ureter before EKL, to prevent proximal migration. These requirements for disposable items, as well as the relatively high need for SWL and repeat ureteroscopy, may offset some of the cost advantages of the EKL.

Several studies have compared the EKL with the Swiss Lithoclast (Electro Medical Systems, Lausanne, Switzerland), both in vitro and in clinical studies. The in vitro studies report conflicting results for the velocity and excursion of the two devices [ 11, 12]. These findings can be explained by the Swiss Lithoclast having a higher peak velocity, but the EKL maintaining a high velocity throughout more of the pulse cycle. Both clinical comparison studies reported no difference between EKL and the Swiss Lithoclast, but the sample sizes were small [ 11, 13]. As the two devices have similar mechanisms of action and rely on similar endoscopic techniques, any clinical differences between them are likely to be small. The advantages and limitations described in this series are broadly applicable to the Swiss Lithoclast.

Before the present series, we had been using a pulsed-dye laser, which has less of a propulsive effect than the EKL. There are other important distinctions between them. First, we and others [ 4] have found the pulsed-dye laser to be unreliable and expensive in terms of the initial capital outlay and running costs; in contrast, the EKL unit has required no major repairs and the running costs are negligible. Second, we and others [ 14] have noted reduced visibility through the ureteroscopes, presumably from vibrational damage, after repeated use of the EKL. Third, the distinct advantage of the pulsed-dye and holmium lasers is that they can be used with both semi-rigid and flexible ureteroscopes, and therefore can be more effectively applied to proximal ureteric stones [ 7].

In summary, EKL is safe, inexpensive and reliable. Caution is needed to avoid propelling stones into the proximal ureter or kidney. We recommend the use of baskets or graspers to remove fragments of ≥4 mm, as these fragments pose a risk for further ureteroscopy.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and methods
  5. Results
  6. Discussion
  7. References
  • 1
    Abdel-Razzak OM & Bagley DH The 6.9F semi-rigid ureteroscope in clinical use. Urology 1993;41 45 7
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    Grasso M & Bagley DH A 7.5/8.2F actively deflectable, flexible ureteroscope: a new device for both diagnostic and therapeutic upper urinary tract endoscopy. Urology 1994;43 435 8
  • 3
    Denstedt JD, Razvi HA, Rowe E et al. Investigation of the tissue effects of a new device for intracorporeal lithotripsy— the Swiss Lithoclast. J Urol 1995;153 535 7
  • 4
    Naqvi SAA, Khaliq M, Zafar MN, Rizvi SAH Treatment of ureteric stones: comparison of laser and pneumatic lithotripsy. Br J Urol 1994;74 694 8
  • 5
    Schultze H, Haupt G, Piergiovanni M et al. The Swiss Lithoclast: a new device for endoscopic stone disintegration. J Urol 1993;149 15 8
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    Razvi HA, Denstedt JD, Chun SS, Sales JL Intracorporeal lithotripsy with the holmium: YAG laser. J Urol 1996;156 912 4
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    Erhard M, Salwen J, Bagley DH Ureteroscopic removal of mid and proximal ureteral calculi. J Urol 1996;155 38 42
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    Teichman JMH, Rao RD, Rogenes VJ, Harris JM Ureteroscopic management of ureteral calculi: electrohydraulic versus holmium: YAG lithotripsy. J Urol 1997;158 1357 61
  • 9
    Teichman JMH, Vassar GJ, Bishoff JT, Bellman GC Holmium:YAG lithotripsy yields smaller fragments than Lithoclast, pulsed dye laser or electrohydraulic lithotripsy. J Urol 1998;159 17 23
  • 10
    Keeley Fx Jr, Smith G, Chrisofos M, Tolley DA Fate of residual fragments following ureteroscopic lithotripsy (abstract). J Endourol 1998;12 (Suppl): S216
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    Vorreuther R, Klotz T, Heidenreich A, Nayal W, Engelmann U Pneumatic v electrokinetic lithotripsy in treatment of ureteral stones. J Endourol 1998;12 233 6
  • 12
    Haupt G, Van Ophoven A, Pannek J, Herde T, Senge T In vitro coparison of two ballistic systems for endoscopic stone disintegration. J Endourol 1996;10 417 20
  • 13
    Menezes P, Dickinson A, Timoney A Results of a prospective randomized study comparing Lithoclast and EKL for ureteric stones. BJU Int 1999;84: in press
  • 14
    Shroff S Letter to the editor. Br J Urol 1995;75 810