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Urological Surgery

Principles of Extracorporeal Shock Wave Lithotripsy

a report by

Kai Uwe Köhrmann

Professor of Urology, Ruprecht-Karls Universität Heidelberg

Extracorporeal shock wave lithotripsy (ESWL) is one of the most frequently applied procedures for the treatment of urolithiasis.1 Since the mid 1980s ESWL has been established as a minimally invasive procedure for a wide indication of urinary stones. Since the first generation of shock wave lithotripters, the efficacy of these devices has been almost constant. Technical development mainly improved patient comfort and safety, optimised handling, reduced primary and maintenance costs and provided multiple (e.g. endourological procedures) and inter-disciplinary (e.g. for induratio penis plastica (IPP), tendinosis calcarea and bile duct stone) uses. In contrast to extracorporeal lithotripsy, the efficacy of the endourological procedures (ureterorenoscopy and percutaneous nephrolithotomy) was increased by the development of smaller and flexible endoscopes in combination with effective lithotripsy (laser) and retrieval (nitinol basket) tools. The disadvantage of these procedures is the routine need for anaesthesia and the higher rate of significant complication. Meanwhile, these more invasive, but also more effective, treatments are increasingly preferred by patients, who do not accept the longer time period to become stone-free, and by urologists who are involved in a diagnosis-related group (DRG) system. The increasing number of lithotripters in Germany and Europe, together with the upcoming endourological procedures, means that the number of treatments per unit more frequently decreases. For lithotripter manufacturers, the market increase is due to replacement purchase ­ necessary for the first lithotripters installed more than 15 years ago and the installations in developing countries. Decreasing treatment numbers and installation in smaller or developing institutions create demands for more economic, and even low-budget,

lithotripters. This development, together with the different technical principles and equipment of the lithotripter, complicates the selection of a lithotripter once the decision for such an investment has been made. An acoustic wave is generated under water (see Figure 1) and is focused to a high pressure density onto a focal point. The patient is positioned on a treatment table, where the stone is localised by means of an imaging system, and the focal point of the shock wave source is positioned by moving the patient or the shock wave source. Two thousand shock waves are applied with a frequency of 60 to 120 shots per minute resulting in a treatment time of nearly one hour. Stone position and disintegration is checked routinely using the imaging system. The need for anaesthesia depends on the lithotripter and the patient. In case of insufficient success, retreatment can be performed within a few days after the first treatment. Sometimes, auxiliary procedures are necessary to treat complications (ureter stent or nephrostomy tube for severe colic or hydronephrosis) or to achieve complete stone disintegration (contact lithotripsy by ureteroscopy or percutaneous lithotomy). Lithotripters are therefore composed of four essential parts, which differ significantly between the devices ­ shock wave generator, localisation system, shock wave coupling and auxiliary equipment. Shock wave generation is based on electro-hydraulic, electromagnetic or piezoelectric sources. This principle of shock wave generation reaches high disintegrative capacity, but also causes pain. Deep analgosedation or anaesthesia is therefore necessary for highly effective stone disintegration. A localisation system identifies the stones and guides the positioning of the stone within the focal point; fluoroscopy or sonography can be used for this.

Dr Kai Uwe Köhrmann has been Professor of Urology at the Ruprecht-Karls Universität Heidelberg since March 2002 and Head of the Department of Urology at the Theresienkrankenhaus Hospital in Mannheim since 2003. Dr Köhrmann has been Chairman of the working party Urolithiasis of the German Urological Society since November 2002 and has been Co-Chairman of the German Society of Shock Wave Lithotripsy since September 2004. He undertook practical training in nursing in 1979, and was a student of human medicine at the Johannes-Gutenberg University, obtaining a medical degree in 1987 and a further speciality degree in urology in March 1993. In November 1994, Dr Köhrmann qualified as Associate Professor of Urology at the University of Heidelberg.

1. Rao N, "Surgical Treatment of Renal and Ureteric Stones", Business Briefing: Global Surgery (2003), Reference Section www.touchbriefings.com pp. 1­3.

BUSINESS BRIEFING: GLOBAL SURGERY ­ FUTURE DIRECTIONS 2005

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Urological Surgery

Figure 1: The Electrohydraulic Electrode Generating Acoustic Pressure on the Focal Point

For these the patient has to be in a stable position on the table. The table has to be movable in all three dimensions and be able to be tilted into the Trendelenburg position. Comfortable access for the surgeon to perform transurethral or percutaneous procedures should be enabled. For a smooth work flow, a narrow arrangement is used with fixed integrated lithotripter components optimally integrated in the high-end lithotripter for a urological workstation (see Figure 2) with capital costs of approximately 300,000 to 350,000. In a modular system the components, e.g. localisation system (most frequently fluoroscopic C-arc) and operating table, can be used separately from the shock wave source. Usually, these systems, with capital costs of 250,000 to 300,000, need more space and time to be composed and adjusted for the ESWL session. The low-budget lithotripter consists of a mobile shock wave source with limited efficacy and an integrated ultrasound localisation system that is coupled by a water cushion to a patient who is positioned on a common stretcher. The capital cost of this `economy class' is 150,000 to 250,000. Efficacy of stone disintegration is the most important characteristic of the lithotripter. Numerous efforts have been performed to define and compare efficacy of the different devices by physical characterisation, experimental studies and clinical evaluations; however, at the time of press no standards exist for these issues. It should be mentioned that studies with the highest scientific evidence, such as multicentre prospective randomised studies, are missing. Other retrospective evaluations show a wide range of efficacy for particular lithotripters and sometimes produce conflicting results. Nevertheless, the following tendency can be drawn from the literature.

Clinical Evaluation

The urinary stone is positioned on the focal point and disintegrates after multiple shots.

Figure 2: Example of a Urologic Workstation

The highly effective shock wave source is integrated in a multipurpose table with a fluoroscopic and ultrasound imaging system.

The ideal, but expensive, solution is the integration of both fluoroscopic and sonographic localisation systems in a particular lithotripter, to be used alternatively. This enables the localisation of all stones independent of their composition and position in the urinary tract. The optimal coupling of the shock wave is a water bath, in which the patient is completely or partially positioned. The use of a water cushion increases comfort for both the patient and medical assistants. The disadvantage is that each layer incorporated in the shock wave path can reduce shock wave efficacy. Additional facilities of the lithotripter define treatment comfort for the patient and the medical staff as well as offering the possibility for multiple and interdisciplinary use. The valuable equipment of a fluoroscopic and sonographic imaging system and treatment table can be designed to be used for general diagnostic procedures as well as endourological, amongst other, interventional measures.

For clinical comparison, the essential parameters of efficacy were calculated by the efficacy quotient (EQ):

EQ% = rate_of_stonefree_patients_after3months 100%+rate_of_re-ESWL+rate_of_auxiliary_procedures

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whereby the highest efficacy provides the lithotripter that reached the highest rate of stonefree patents with the lowest number of re-treatments and lowest rate of auxiliary procedures (to treat complications or to complete disintegration).

BUSINESS BRIEFING: GLOBAL SURGERY ­ FUTURE DIRECTIONS 2005

Principles of Extracorporeal Shock Wave Lithotripsy

The highest EQ was calculated for the very first commercial lithotripter, the unmodified Dornier HM3. Few other generators reached this high efficacy level (see Table 1). Due to the higher re-treatment rate, piezoelectric lithotripters usually had a tendency to produce a lower EQ. For comprehensive clinical classification, additional parameters (e.g. adverse side effects) should be considered. With this respect, the most effective device, HM3, usually requires general anaesthesia, but ­ in contrast to the less effective piezoelectric lithotripters ­ can be applied without any analgesia. In most institutions, preferred lithotripters are those that can be used in analgosedation (modified HM3, other electrohydraulic and electromagnetic lithotripters and high-energy piezoelectric lithotripters). A correlation of disintegrative efficacy and pain/need for anaesthesia can therefore be assumed. Direct side effects of shock waves, especially renal haematomas, are rare. They occur with a rate of less than 1% with all common lithotripters.

Table 1: Efficacy Quotient (EQ) for Different Lithotripters According to Teichman et al. 2

Generator system No. of Patients EQ

Dornier HM3 Modulith SLX Lithostar C Medstone STS Econolith Dornier Doli

electrohydraulic electromagnetic electromagnetic electrohydraulic electrohydraulic electromagnetic

4,242 1,049 23,559 3,015 500 103

0.64­0.67 0.57­0.67 0.56­0.64 0.60­0.67 0.56 0.36

Conclusion

Each urological institution involved in stone treatment needs access to a shock wave lithotripter. The three different systems of shock wave generators (electrohydraulic, electromagnetic and piezoelectric) can destroy urinary stones effectively. However, significant differences exist between and within these systems and standardised comparison of lithotripter efficiency does not exist. Besides the shock wave source, lithotripters are characterised by the localisation system and additional facilities for multiple or interdisciplinary use. The demands of the institution and its budget will decide the choice.

2. Teichman J M, Portis A J, Cecconi P P et al., "In vitro comparison of shock wave lithotripsy machines", J Urol. (October 2000);164(4): pp. 1,259­1,264.

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