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Pain in Extracorporeal Shock-Wave Lithotripsy: A Comparison of Different Lithotripters in Volunteers H. THOMAS SCHNEIDER, THOMAS HUMMEL, PAUL JANOWITZ, ROLAND OTT, HORST NEUHAUS, WERNER SWOBODNIK, ELISABETH PAULI, GERD KOBAL, and CHRISTIAN ELL Departments of Medicine I and Pharmacology and Toxicology, University of Erlangen-Nuremberg, Department of Medicine II, University of Ulm, Ulm; and Department of Medicine II, Technical University of Munich, Munich, Germany

The aim of the present study was to investigate pain sensations experienced during extracorporeal shock-wave application, comparing an electrohydraulic (MPL 9000; Dornier Medizintechnik, Germering, Germany), an electromagnetic (Lithostar Plus; Siemens, Erlangen, Germany), and a piezoelectric (Piezolith 2300; Wolf, Knittlingen, Germany) shock-wave system. In nine healthy volunteers, three therapeutically used intensities were applied in a randomized order with each lithotripter (MPL 9000: 16,20,and 24 kV; Lithostar Plus: settings 5,7,and 9; and Piezolith 2300: settings 2,3, and 4). The subjects received nine series of 20 shock waves amounting to a total of 180 shock waves per session. The treatment was performed under clinical conditions, and no premeditation was given. A visual analog scale and the McGill Pain Questionnaire were used for assessment of pain. In addition, somatosensory evoked potentials caused by shockwave stimulation were recorded. Some of the volunteers were unable to bear the pain caused by the highest shock-wave intensity of the electrohydraulit (n = 3) and the electromagnetic system (n = 4). Estimates using the visual analogue scale showed increased pain sensations with increasing energy settings for each lithotripter. The amplitudes of the somatosensory evoked potentials became larger, and latencies shortened with increasing stimulus intensities (P < 0.05). Subjective estimates by means of the visual analogue scale (P < 0.01) as well as the McGill Pain Questionnaire (NS) and the somatosensory evoked potentials (P < 0.05) showed that stimulation by the piezoelectric lithotripter was less painful than stimulation by the two other generators. he first treatments of patients with biliary calculi using extracorporeal shock waves were performed with a lithotripter that generated shock

T

Erlangen;

waves by means of the electrohydraulic principle, i.e., by spark discharge. Shock-wave lithotripsy using the first-generation electrohydraulic system was extremely painful and therefore as a rule required general or epidural anesthesia.* Today, the electrohydraulic system is more advanced, and shock-wave lithotripsy is currently complemented by electromagnetic and piezoelectric systems, which provide two additional physical principles for generating shock waves. Using second-generation lithotripters of all three types of systems, lithotripsy of biliary calculi can now be performed without anesthesia. In general, IV application of sedatives or analgesics is sufficient for relieving pain. However, publications on clinical biliary lithotripsy indicate that the degree of pain experienced during treatment varies significantly depending on the applied shock-wave principle. Whereas the piezoelectric principle is often described as nearly painless, analgesics and sedatives are required during shock-wave application in substantially more patients when electrohydraulic and electromagnetic systems are used.24 Thus far, no studies have been conducted allowing a comparative assessment of the pain sensations during shock-wave lithotripsy using the various systems. This aspect is, of course, a primary point of concern for the patient. In view of the fact that lithotripsy is gaining more and more momentum in becoming an outpatient treatment method, an evaluation of the pain sensations caused by the different physical systems is of practical importance for operating physicians and system developers. In the present three-center study, the pain sensations observed in healthy volunteers using secondgeneration electrohydraulic, electromagnetic, and piezoelectric shock-wave systems were therefore 0 1992 by

the American Gastroenterological 0016-5085/92/$3.00

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compared on the basis of subjective measurement techniques.

and objective

Methods Study Conditions Nine healthy volunteers participated in the study [two women and 7 men; mean + SD age, 27.2 f 4.2 years (range, 23-36 years)]. The mean weight of the subjects was 68.3 f 8.8 kg, and the mean height was 177 + 7 cm. Before and after completion of the treatments, the health status of all test persons was assessed by checking clinically relevant serum parameters and by an ultrasound investigation of the upper abdomen. The volunteers were aware of the purpose of the study and of the risks of shock-wave treatment in accordance with the declaration of Helsinki/Tokyo/Venice and had given informed consent. The study had been approved by the Ethics Committee at the Department of Medicine of the University of Erlangen-Nuremberg. Lithotripter

Systems and Shockwave

Application The investigations were performed using three second-generation shock-wave systems: the electrohydraulic lithotripter MPL 9000 (Dornier Medizintechnik, Germering, Germany), the electromagnetic Lithostar Plus (Siemens, Erlangen, Germany), and the piezoelectric Piezolith 2300 (Wolf, Knittlingen, Germany) equipped with the upgraded generator available since 1989. In the electrohydraulic system, the high-energy pressure pulses are generated by underwater spark discharge. Focusing is achieved by an elliptical reflector. Electromagnetic shock waves are formed by deflection of a thin metal foil following the discharge of an electric coil and are concentrated in the focus of an acoustic lens. In the case of the piezoelectric principle, an electric voltage pulse causes several thousand ceramic elements to instantaneously oscillate. The special hemispherical arrangement of the piezoelements on a spherical calotte automatically focuses the thus generated pressure wave. In all three systems, the shock-wave energy is conducted via a water path. Whereas the patient’s skin is immersed in the water of the transducer, in the case of Piezolith 2300, the shock waves are coupled through a plastic membrane in the electrohydraulic (MPL 9000) and electromagnetic (Lithostar Plus) systems. The selection of the intensity settings tested in this study was adapted to the energy levels mainly used in current therapy of patients with gallbladder stones in the three participating centers. Therefore, using 20 kV with the MPL 9000, setting 9 with the Lithostar Plus, and setting 3 with the Piezolith 2300 as a reference, the following intensities were compared: MPL 9000: 16, 20, and 24 kV; Lithostar Plus: settings 5, 7, and 9; Piezolith 2300: settings 2, 3, and 4. The investigations were performed as a controlled study with a triple-crossover design. Each of the three lithotripters was tested once on each subject in a randomized order. The time interval between sessions was at least 2

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days, In accordance with clinical conditions, test persons were placed in a prone position (MPL 9000 and Piezolith 2300) or either in a supine or left posterior oblique position (Lithostar Plus) while measurements were made. The shock-wave focus was localized sonographically in the lumen of the filled gallbladder (after overnight fasting) by an experienced system operator and, if necessary, repositioned during shock-wave application. No premeditation was administered. During measurements, the subjects were visually and acoustically shielded. In the course of one session, the test persons received three series of 20 shock waves for each of the three intensity settings, i.e., a total of 180 shock waves. At first, three series of pulses were performed with increasing intensities for each generator. The following six series were then applied in a randomized order to minimize habituation. The time interval between the individual pulses ranged between 2 and 3 seconds. In addition, approximately 10 pulses with varying intensities were applied before the actual measurement sequence to accustom the subjects to the treatment conditions. Subjective Reactions

Pain

Assessment

and

General

The volunteers rated the experienced pain level after each applied pulse series (20 shock waves) by means of a visual analogue scale (VAS). The left extreme of the VAS was defined as “no pain” (0 units) and the right extreme as “unbearable pain” (100 units). In case a subject estimated the highest intensity > 75 units, this rating was interpreted as unbearable pain, and further application of shock waves at this intensity level was discontinued. If subjects rated the medium intensity as >75 units, a similar procedure was adopted; the highest intensity was expected to certainly cause unbearable pain, and shockwave applications of highest intensity were therefore skipped. In both cases, the highest intensity was replaced by a lower energy setting (MPL 9000,14 kV; Lithostar Plus, setting 3; Piezolith 2300, setting 1) to still allow the randomized application of three different intensity settings during the remainder of the session. After each session, the test persons were requested to describe the most painful sensation by means of the McGill Pain Questionnaire (MPQ).’ Of 78 descriptors, any number (number of words chosen) could be selected to characterize the experienced pain. Additionally, the average pain rating index was determined. This was done by calculating numbers ranging from 1 to 5, which had been assigned to the individual descriptors. Circulatory disturbances were monitored, and the test persons were questioned as to adverse effects, such as nausea and vertigo, experienced during shock-wave application as well as the location of the pain sensations, which they were requested to indicate in a skeleton sketch of the body. Somatosensory

Evoked

Potentials

The electroencephalogram (EEG) was recorded from five recording sites of the international lo/20 system (Cz, Pz, Fz, C3, and C4) referenced to linked earlobes (Al +

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AZ). Eye movements were recorded from the Fp2 lead. To minimize blink artifacts, subjects were asked to gaze at a black spot placed in front of them during measurements. Late-nearfield evoked potential? were obtained, which are to date the only type of cortically evoked potentials recorded in the nociceptive system.’ The passband of the system was between 0.02 and 30 Hz. Data were continuously recorded on magnetic tape (TEAC R-71). They were digitized off-line with a sampling frequency of 500 Hz (CED 1401; Cambridge Electronic Devices), and stimuluslinked EEG segments of 1024-millisecond duration were stored on disk cartridges of a computer (PDP 11/23, DEC).’ Single responses contaminated by eye blinks > 40 pV were discarded from the average, and averaged responses with a blink artifact > 40 yV in the Fp2 lead were excluded from further analysis. Because of the stimulation procedure, a maximum of 60 records were available for obtaining a single averaged response. Latencies of the somatosensory evoked potentials (SSEPs) were measured in relation to stimulus onset (T-Pl, T-Nl, and T42). Furthermore, two peak-to-peak amplitudes (.4PlNl and A-NlP2) were obtained.g Statistical

Analysis

To compare the different lithotripters, the results of pain estimates (VAS) were subjected to a two-way multivariate analysis of variance (MANOVA), repeated measurements design, with the within-subject factors “lithotripter” and “intensity” (df, IO/~). Additionally, trend analyses were performed for each lithotripter (within-subject factor intensity; MPL 9000: df, 12/2; Lithostar Plus: df, 14/2; Piezolith 2300: df, 16/2). The results of the MPQ (pain rating index and number of words chosen) were also analyzed by means of MANOVA (within-subject factor lithotripter: df, 16/2). After testing SSEP data for a gaussian distribution (KomolgorovSmirnov test), data were submitted to MANOVA, repeated measurements design (within-subject factor lithotripter; df, IO/~). Somatosensory evoked potential parameters were thus treated as independent variables. To establish dose-response relationships of the SSEP parameters, trend analyses were computed separately for each lithotripter [within-subject factor intensity) MPL 9000 and Lithostar Plus: df, 12/2; Piezolith 2300: df, 10/2).

Results Pain

Localization

and Pain

pain sensations caused by the shock waves as sharp and pricking at the superficial entry zone and as dull and stabbing deep inside the body. However, no major differences in the quality of pain were reported for the three lithotripters tested. Subjective Reactions

Pain Assessment

and General

The general reactions to shock-wave treatment and the degree of tolerability of the application are presented in Table 1. The evaluation of the MPQ showed no significant differences between the three tested generators. However, the piezoelectric system was generally rated as causing less pain according to the mean values in the pain rating index and the number of words chosen (Table 2). Data from the VAS showed a linear increase in pain intensity (Piezolith 2300: t = 5.20, P < 0.001; MPL 9000: t = 4.41, P < 0.01; and Lithostar Plus: t = 25.1, P < 0.001) with increasing shock-wave intensity for all three systems (Figure 1). Shock-wave application by the piezoelectric generator was less painful than by the electrohydraulic and electromagnetic systems (F = 9.25, P < 0.01). Subjects rated the highest intensity level of the Piezolith 2300 as less painful than the medium intensity levels delivered by the MPL 9000 or the Lithostar Plus at comparable intensity settings. Somatosensory

Evoked Potentials

For technical reasons, it was not possible to evaluate the SSEPs recorded in three sessions using the piezoelectric generator. Nonetheless, analysis of the SSEP trends showed a positive linear relationship between shock-wave intensities and amplitudes recorded at nearly all recording positions, when the piezoelectric system was used (A41Nl: Cz: t = 3.43, P < 0.05; C4: t = 8.61, P < 0.01; AJJlP2: Fz: t = 3.20, P < 0.05; cz: t = 4.04, P < 0.01; c4: t = 3.93, P < 0.05; Pz: t = 2.64, P < 0.05). Using the electromagnetic principle, the same significant relationship was

Characteristics

The subjects localized the pain caused by shock-wave application mainly in the region of the abdominal wall and/or in the extension of the shock-wave axis located paravertebrally in the back. This was the case for all three tested systems. Pain sensations were thus located in the approximate region of the head zone of the liver and gallbladder (Th7-Th8). Pain that radiated into the right shoulder, corresponding to the head zone of the diaphragm, as observed for biliary colics, was not reported by any of the subjects. Two thirds of the subjects described the

Table 1. Number of General Reactions During Extracorporeal Shock-Wave Application With Different Lithotripters in Nine Volunteers Shock-wave principle lithotripter

Electrohydraulic MPL 9000

Electromagnetic Lithostar Plus

Piezoelectric Piezolith 2300

Nausea Vertigo Orthostatic dysregulation Intolerable nain

4 2

4 1

1 0

0 3

1 4

0 0

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Table 2. McGill Pain Questionnaire: Pain Rating Index and Number of Words Chosen After 180 Shock Waves Shock-Wave principle lithotripter

Electrohydraulic MPL 9000

Piezoelectric Piezolith 2300

Electromagnetic Lithostar Plus

MPQ 3.3 * 0.2 7.0 2 4.7

PRI NWC

3.4 + 0.2 8.6 f 4.4

3.2 f 0.4 6.0 f 3.9

100

[EUI

16 kV n=9

20 kV n=9

24 kV n=7

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Discussion

found for amplitude A_PlNl at position Cz (t = 3.60, P < 0.05) and using the electrohydraulic principle for amplitude A_NlPZ at position Pz (t = 2.74, P < 0.05). Latencies shortened in relation to increasing shockwave intensities for all three generators: piezoelectric at T41 (C4: t = 2.60, P < 0.05; Pz: t = 4.46, P < 0.01) and at T-N1 (C4:t = 2.78,P < 0.05); electromagnetic at T-P1 (Pz: t = 2.46, P < 0.05); electrohydraulic at T-P1 (Cz: t = 3.08,P < 0.05). A comparison between the three shock-wave systems (Figure 2) showed that significantly lower SSEP amplitudes A-NlP2 were recorded when the piezoelectric lithotripter was used (low intensity: Fz: F = 4.27, P < 0.05; C3: F = 11.02, P < 0.01; Cz: F = 7.09, P < 0.05; C4: F = 9.77, P < 0.01; Pz: F = 5.82, P < 0.05; medium intensity: Cz: F = 5.20, P < 0.05;C4: F = 6.78, P < 0.05;high intensity: C4: F = 12.49, P < 0.01) (Figure 2). Correspondingly, latencies T_Pl (C3:high intensity: F = 10.88, P < 0.01; low intensity: F = 7.78, P < 0.01)and T-N1 (C3:high intensity: F = 5.83, P < 0.05; low intensity: F = 8.30,P < 0.01;C4: 100

LITHOTRIPSY

medium intensity: F = 6.32, P < 0.05) were longer in treatments with the piezoelectric system. The largest amplitudes and shortest latencies were found after application of electromagnetically generated shock waves. Considering the relationships between stimulus intensity and SSEP parameters as well as the associated changes of pain estimates, SSEP indicated the electromagnetic generator to be more painful than the other two lithotripters.

NOTE. Results are expressed as means + SD; n = 9. PRI, pain rating index; NWC, number of words chosen.

VJI

SHOCK-WAVE

Three different physical principles are currently applied in extracorporeal shock-wave lithotripsy of biliary calculi. The lithotripters tested in the present study represent the current state of the art in electrohydraulic, electromagnetic, and piezoelectric shock wave techniques. A number of reports on all three types of systems have been published, confirming the clinical capabilities of these lithotripters.lm4 During the initial phase of shockwave therapy, emphasis was placed primarily on the shock-wave power, i.e., the fragmentation efficiency of the lithotripter. In view of the existing surgical alternatives, the pain associated with the shock-wave technique and, therefore, the need for anesthesia were considered to be acceptable, as was the risk of tissue traumatization resulting from shock-wave application.“-l3 Nowadays, the degree of stress imposed on tissue, and especially the aspect of patient comfort, play an increasingly important role in the choice of suitable lithotripters. This is emphasized by the fact that biliary lithotripsy is increasingly performed in an outpatient manner.

-

100

B

setting 5 n=9

setting 7 n=9

setting 9 t-t=8

C

[EUI

setting 2

setting 3

setting 4

n=9

n=9

n=9

Figure 1. Visual analogue scale [O-100 mean intensity estimates (EUs)]. Mean intensity estimates using (A) the electrohydraulic MPL 9000 at 16,20, and 24 kV; (B) the electromagnetic Lithostar Plus at settings 5,7, and 9; and(C) the piezoelectric Piezolith 2300 at settings 2,3, and 4 are shown. With each lithotripter, the three intensity settings were applied in a pseudorandomized order. Estimates were obtained after a series of 20 shock waves each. Statistical analysis (MANOVA) showed significant differences between intensity estimates obtained with the Piezolith 2300 as well as the other lithotripters at all tested energy settings (P < 0.01).

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a

n=6

Intensity Low

Medium

High

The aim of the present study was to evaluate discomfort and pain sensations caused by extracorporeal shock-wave application and to compare three lithotripters based on different physical shock-wave principles with respect to their pain induction. Pain, however, is only one aspect in performing biliary lithotripsy. A precondition for a comparison of pain sensations arising during extracorporeal shock-wave application is that there are no significant differences concerning the fragmentation efficacy, which was shown to be the case when using all three lithotripters at maximum intensity settings.14 Undoubtedly, this study conducted on pain sensations in volunteers does not completely reflect the clinical situation of shock-wave application in biliary lithotripsy. In the present study, the subjects were young and healthy students, the number of pulses applied was limited (180 shock waves per session), and, for technical reasons, the frequency of the shock-wave application was restricted to 0.3 Hz. However, a study design in which each test person underwent treatment by each of the different lithotripters in a randomized order, in our view, seemed to be the only suitable approach to compare different lithotripter systems on an objective basis and to review the published clinical experiences, including a heroic self-trial,15 and the information provided by the manufacturers. For evaluating the discomfort and the pain sensations during extracorporeal shock-wave application, we monitored general reactions of the volunteers and noted if the treatment was not tolerated by the subject. Furthermore, the volunteers were asked to estimate and describe the pain sensations by means of the VAS and the MPQ. Both MPQ and VAS are

Vol. 102,No. 2

Figure 2. Grand means of the SSEPs at recording position Cz. The scheme shows the recording location at the head and a schematic presentation of the peaks Nl and P2. Using the Piezolith 2300 (C) (low intensity, setting 2; medium intensity, setting 3; and high intensity, setting 4), amplitudes are reduced and latencies prolonged compared with the MPL 9000 (A)(low intensity, 16 kV; medium intensity, 20 kV; and high intensity, 24 kV) and the Lithostar Plus (B)(low intensity, setting 5; medium intensity, setting 7; and high intensity, setting 9).

well established and most widely used to assess pain. The MPQ, however, is more specifically designed for assessing chronic pain sensations.16 This might explain why significant differences between the three tested lithotripters were detected when using the VAS, and only slight differences were found when using the MPQ. In pain research, evoked potentials are used to quantitatively assess pain sensations subsequent to more specific’ or unspecific stimuli.17 In the current study, positive correlations between the amplitudes and latencies of the SSEP and stimulus intensities were found, i.e., amplitudes became larger and latencies shortened when stimulus intensities increased. Because the stimulus durations (approximately 5 microseconds) of the three tested shock-wave generators were nearly equivalent, differences in the SSEP are not based on such specific technical properties of the lithotripters. Findings reported in other studies, in which pain-related evoked potentials were monitored subsequent to thermall’ stimulation of the skin or after chemical stimulation of the nasal mucosa,lg uniformly indicated shortened latencies in conjunction with an increase of the amplitudes of the pain-related evoked potentials. In view of these investigations, and especially in the light of the subjective pain intensity ratings reported by the volunteers, the decrease of amplitudes as well as the prolongation of latencies of the SSEP can serve as an additional criterion for assessing the pain intensity induced by the respective lithotripter. Shock waves, however, do not only trigger intracutaneous or visceral nocisensors but also intracutaneous mechanosensors or thermosensors. Given the range of intensities used in these experiments,

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excitation of sensory systems other than pain seemingly does not contaminate the signal to a degree that SSEPs can no longer function as tools for pain measurement.17~‘g The question whether discomfort and pain may be partially influenced by the position of the patient on the machine remains unresolved. In the case of the tested piezoelectric and electrohydraulic systems, lithotripsy is performed with the patient in the prone position, whereas with the overtable generator of the Lithostar Plus the patient is usually lying on his back or in a left posterior oblique position. Therefore, the ventral gallbladder wall is located closer to the focus area in the electrohydraulic and piezoelectric lithotripters than in the case of shock-wave application with the electromagnetic overtable generator. From clinical experience it is known that many patients consider direct shock-wave impact on the gallbladder wall especially painful. Therefore, in clinical applications, the shock-wave focus should never be positioned directly in the region of the ventral gallbladder wall but rather 5-15 mm within the gallbladder lumen, Therefore, and in view of the potential risk of damage to tissue in the gallbladder wa11,13the same procedure was adopted in treating the volunteers in the present study. Although all subjects were able to bear the shockwave application at maximum intensity levels with the piezoelectric lithotripter (Piezolith 2300),as opposed to the electrohydraulic (MPL 9000) and electromagnetic (Lithostar Plus) systems, our results show that piezoelectric lithotripsy is not free of pain sensations. On the other hand, it was shown that the application of shock waves using the piezoelectric lithotripter causes less pain than the electrohydraulic and electromagnetic systems. These differences are underlined by the fact that the pain sensations experienced at maximum energies of the piezoelectric lithotripter, as indicated by the VAS, were rated significantly less severe than in the case of the electrohydraulic and electromagnetic generators at the submaximum intensity levels used for this comparison Furthermore, in clinical biliary lithotripsy in most of the patients treated with the piezoelectric system, it is not necessary to apply the highest available shock-wave intensity to achieve a successful disintegration of the calculi. This explains why anesthesia and the IV application of analgesics and sedatives may generally be avoided when using the piezoelectric lithotripter.’ However, analgesic and sedative drugs have to be administered in a substantially higher percentage of patients treated with the tested electrohydraulic (MPL 9000)3 and electromagnetic (Lithostar PIus)~ systems at clinically used shock-wave intensity levels to achieve a fragmenta-

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tion efficiency comparable with that of the piezoelectric generator. Pain sensations arising during shock-wave lithotripsy can be explained in two ways: first, by stimulation of intracutaneous nociceptors, and second, visceral pain sensations might be of importance, especially in the vicinity of the highest shock-wave pressure zone. In vitro measurements of the physicotechnical parameters of the three tested lithotripters showed that the piezoelectric system has the smallest focus volume but the highest pressure in the focus area.” However, reliable measurement techniques capable of intracorporeally determining the duration of the stimulus, the shock-wave path, focus size, and the maximum focus pressure are to date not available. Our results indicate that the magnitude of the maximum pressure developed in the shockwave focus appears to be of little consequence for the observed pain sensations. The total volume of the focus zone, however, which is similar for the electromagnetic and the electrohydraulic generators and larger than the piezoelectric focus, might influence the experienced pain, Furthermore, in the application of different shock wave sources, the so-called aperture is an essential factor in causing pain, The aperture determines the magnitude of the skin area that is effective in coupling the shock waves to the body. The smaller the aperture angle, the higher the shock-wave density; the larger the aperture angle, the more the total energy is distributed over a larger area, i.e., the energy density decreases. The aperture angle is 88" for Piezolith 2300,81’ for MPL 9000, and 74"for Lithostar Plus. The straightforward results of this study favoring the piezoelectric system lead to the conclusion that, beside the origination of pain in the focus area, the pain experienced in the skin region is of importance in shock-wave therapy. This conclusion is supported by another study showing that the application of a local anesthetic cream to the ventral skin before shock-wave exposure led to a significant reduction of pain sensationszl In summary, our study investigating three secondgeneration lithotripters gives the following results, Discomfort and pain sensations occur during application of extracorporeal shock waves and increase with increasing shock-wave intensity, irrespective of the physical principle of shock-wave generation. No relevant differences were noted between the pain sensations caused by the electrohydraulic and electromagnetic lithotripters. The piezoelectric generator, however, seemingly causes less pain than the two other systems. References 1. Sackmann M, Delius M, Sauerbruch T, Ho11 J, Ippisch E, Hagelauer U, Wess W, Brendel W. Paumgartner G. Shock-wave

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lithotripsy of gallbladder stones. The first 175patients. N Engl J Med 1988:318:393-397. 2. El1 C, Kerzel W, Schneider HT, Benninger J, Wirtz P, Domschke W, Hahn EG. Piezoelectric lithotripsy: stone disintegration and follow-up results in the first 100 patients with symptomatic gallbladder stones. Gastroenterology 1990; 99:1439-1444. 3 Schoenfield LJ, Berci G, Carnovale RL, Casarella W, Caslowitz P, Chumley D, Davis RC, Gillenwater JY, Johnson AC, Jones RS, Jordan RG, Kafonek DR, Laufer I, Lillemoe KD, Lu S, Maglinte D, Maher JW, Malet PF, Malt RA, Marks JW, McCallum RW, Nahrwold DL, Nemcek A, Pambianco DJ, Pitt HA, Reinhold RB, Rosenthal A, Rothschild JG, Saba G, Schirmer BD, Steinberg HV, Summers RW, Torres WE. The effect of ursodiol on the efficacy and safety of extracorporeal shock-wave lithotripsy of gallstones. The Dornier National Biliary Lithotripsy Study. N Engl J Med 1990;323:1239-1245. 4. Fache JS, Rawat BR, Burhenne HJ. Extracorporeal cholecystolithotripsy without oral chemolitholysis. Radiology 1990; 177:719-721. 5. Stein CH, Mend1 G. The German counterpart to McGill Pain Questionnaire. Pain 1988;32:251-255. 6. Picton TW, Hillyard SA. Endogenous event-related potentials. In: TW Picton, ed. EEG Handbook. Volume 3. Amsterdam, The Netherlands: Elsevier, 1988:361-426. 7. Regan D. Human brain electrophysiology. New York: Elsevier, 1989:280. 8. Kobal G. Pain-related electrical potentials of the human nasal mucosa elicited by chemical stimulation. Pain 1985;22:151163. 9. Kobal G, Hummel C, Ntirnberg B, Brune K. Effects of pentazotine and acetylsalicylic acid on pain-related evoked potentials and vigilance in relationship to pharmacokinetic parameters. Agents Actions 1990;29:342-359. 10. White C, Sweet WH. Pain, its mechanisms and neurosurgical control. Springfield, IL: Thomas, 1955. 11.Delius M, Enders G, Heine G, Stork J, Remberger K, Brendel W. Biological effects of shockwaves: lung hemorrhage by shockwaves in dogs-pressure dependence. Ultrasound Med Biol 1987;13:61-71. 12.Delius M, Enders G, Xuan Z, Liebich HG, Brendel W. Biologi-

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cal effects of shockwaves: kidney damage by shockwaves in dogs-dose dependence. Ultrasound Med Biol 1988;14:117122. 13. El1 C, Kerzel W, Heyder N, Langer H, Mischke U, Giedl J, Domschke W. Tissue reactions under piezoelectric shockwave application for the fragmentation of biliary calculi. Gut 1989;30:680-685. 14. Schneider HT, Fromm M, Ott R, Janowitz P, Swobodnik W, Neuhaus H, El1 C. In vitro fragmentation of gallstones: comparison of electrohydraulic, electromagnetic, and piezoelectric shockwave lithotripters. Hepatology 1991;14:301-305. 15. Staritz M. Is extracorporeal biliary lithotripsy painless? My experience with three shock-wave sources (letter). N Engl J Med 1989;320:811. 16. Melzack R. The McGill Pain Questionnaire: major properties and scoring methods. Pain 1975;1:277-299. 17. Bromm B, Meier W. The intracutaneous stimulus: a new pain model for algesimetric studies. Methods Find Exp Clin Pharmacol 1984;6:405-410. 18. Arendt-Nielsen L. First pain event related potentials to argon laser stimuli: recording and quantification. J Neurol Neurosurgpsychiatr 1990;53:398-404. 19.Hummel T, Friedmann T, Pauli E, Niebch G, Borbe HO, Kobal G. Dose-related analgesic effects of flupirtine. Br J Clin Pharmacol 1991;32:69-76. 20. Coleman AJ, Saunders JE. A survey of the acoustic output of commercial extracorporeal shockwave lithotripters. Ultrasound Med Biol 1989;15:213-227. 21. Schneider HT, Hummel T, Pauli E, Kobal G, Hahn EG, El1 C. Local anaesthetic cream for pain reduction during extracorporeal shockwave application (abstr). Hepatology 1990; 12:A1022.

Received August 14, 1990. Accepted July 3, 1991. Address requests for reprints to: Priv.-Doz. Dr. Med. Christian Ell, Department of Medicine I, University of Erlangen-Nurem12,W-8520,Erlangen, Germany. berg, KraukenhausstraBe The authors thank Dr. Michael Grade for translating and revising the manuscript. A preliminary report of this study was presented at the Annual Meeting of the American Gastroenterological Association, San Antonio, Texas, May 14-17,1990.