British Journal of Anaesthesia 1992; 69: 399-400


METHOD AND RESULTS was approved by the Hospital Ethics and Drugs committee. Informed written consent was obtained from each patient who agreed to take part in the study. We studied 60 patients of physical status ASA I or


partment of Anaesthetics, Royal Perth Hospital, Wellington Street, Perth, Western Australia WA 6000, Australia. Accepted for Publication: May 13, 1992. •Present address, for correspondence: Department of Anaesthetics, St James's University Hospital, Beckett Street, Leeds L59 7TF.

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II, with uncomplicated renal calculi and undergoing ESWL for the first time. Astra Pharmaceuticals provided 60 identical, 60-g We have investigated 60 patients in a prospective tubes, numbered from 1 to 60. Fifty percent of the double-blind, placebo-controlled study to assess tubes contained EMLA cream and the other 50% the efficacy of EMLA (Eutectic Mixture of Local contained a placebo cream. The order of tubes had Anaesthetics) cream to provide analgesia during been distributed randomly by the company. extracorporeal shock wave lithotripsy (ESWL) with The patients were admitted as outpatients and a second generation lithotriptor. Before operation, numbered consecutively from 1 to 60. A 400-cm2 EMLA or placebo cream was applied to the patient's area was demarcated on the patient's back at the back at the anticipated shock head-skin interface. anticipated site of the shock head coupling. One During the procedure increments of fentanyl 0.5 fig kg'1 were given i. v. on patient demand. There hundred minutes before the expected start of the procedure, 60 g of cream was applied to the area and was no significant difference (P = 0.83) in the dose covered by an occlusive dressing. The cream and of fentanyl given to each group. We cannot occlusive dressing were left in place throughout the recommend, therefore, the use of EMLA cream as procedure. No other premedication was given. an analgesic during ESWL with a second generation The patients were positioned supine on the lithotriptor. lithotripsy machine, and the stone localized by fluoroscopy and ultrasound. The shock head was KEY WORDS positioned such that the shock head-skin interface Anaesthesia: topical. Surgery • extracorporeal shock wave lithowas over the demarcated area. Care was taken to tripsy. ensure that air was not trapped at the interface. An i.v. infusion of compound sodium lactate solution 1 litre was commenced and metoclopramide 10 mg given i.v. Each patient was monitored with pulse Over the past decade, extracorporeal shock wave oximetry, ECG and non-invasive arterial pressure. lithotripsy (ESWL) has been developed and used ESWL was commenced at a generator voltage of extensively in the management of urinary tract 12 kV. The generator voltage was increased to 18 kV stones. With the first generation lithotriptors, it was or 19 kV over the first 250 shocks and maintained at necessary for patients to have general, extradural or these values for the remainder of the procedure. The spinal anaesthesia [1]. The changed physical parapatients were advised to request analgesia if they meters of shock wave generator energy and focusing experienced discomfort or pain. If they requested devices of the more recent second generation analgesia, they were given fentanyl 0.5 ug kg"1 i.v. machines, such as the Storz Modulith SL 20, have and this dose was repeated as required throughout reduced the need for general or regional anaesthesia. the procedure. Supplementary oxygen was given if Patients may be managed now using neuroleptic necessary. techniques or i.v. analgesia alone [1]. As these patients are usually managed as outpatients, it would The EMLA cream was regarded as being effective be advantageous to keep the level of sedation to a if the dose of fentanyl was reduced by 50%. minimum without compromising patient comfort. Statistical significance (P < 0.05) was tested using Student's t test. The aim of this study was to investigate if the The two groups were comparable in age, sex application of the topical anaesthetic cream, Eutectic distribution, weight and height. Two patients were Mixture of Local Anaesthetics (EMLA), to the skin excluded from the placebo group because at oparea exposed to the shock wave, reduced the analgesic eration it was found that their stones had passed into requirement for fentanyl during ESWL. the ureter. There was no significant difference SUMMARY


4-6 6-8 8-10 Fentanyl dose (jig kg"1)


FIG. 1. Dose of fentanyl required to provide analgesia during ESWL in patients receiving cither EMLA ( » or placebo cream


between the two groups in respect of the time the cream had been applied before the procedure, the operation time, the stone size treated, the number of shocks administered and the maximum generator voltage used. The mean dose of fentanyl given to the EMLA group was 3.5 (SD 2.9) ugkg"1,.compared with 3.1 (1.8) |ig kg"1 for the placebo group (fig. 1) (ns: P = 0.49). As the distribution was skewed in both groups, a log transformation was made to the data. The geometric mean value for the EMLA group was 1.82 (1.39) ug kg"1 compared with 1.89 (1.08) ug kg"1 for the placebo group (ns). COMMENT

During ESWL, a shock wave is generated from within a water cushion. The shock wave is then focused by reflectors, onto the renal calculi. In order to reach the stone, the shock wave has to pass through the water cushion, the water cushion—skin interface and the body tissues. When the shock wave passes through substances of different acoustic impedances, some energy is reflected and dissipated. The greater the difference in acoustic impedance, the greater the dissipation of energy. Other than when the shock wave passes through the stone, the greatest difference in acoustic impedance probably occurs at the water cushion-skin interface [1]. The sensation experienced by patients undergoing ESWL is described initially as a sharp stinging pain at the skin, which intensifies to a "thumping" sensation as the energy increases. On examining the patients after operation, there is almost invariably an area of erythema, sometimes petechiae and occasionally bleeding over the area of skin through which the shock wave passes. We speculated, therefore, that a large element of the pain experienced during ESWL was from the skin surface. This is supported by other workers who have successfully used local

ACKNOWLEDGEMENTS We thank Astra Pharmaceuticals for providing the EMLA and placebo cream and Mr M. K. Bulsara, of the University of Western Australia, for statistical analysis of the data. REFERENCES 1. Chaussy GC, Fuchs GJ. Current state and future developments of noninvasive treatment of urinary stones with extracorporeal shock wave lithotripsy. Journal of Urology 1989; 141: 782-789. 2. Loening S, Kramolowsky EV, Willoughby B. Use of local anesthesia for extracorporeal shock wave lithotripsy. Journal of Urology 1987; 137: 626-628. 3. Bjerring P, Arendt-Nielsen L. Depth and duration of skin analgesia to needle insertion after topical application of EMLA cream. British Journal of Anaesthesia 1990; 64: 173-177. 4. Arendt-Nielsen L, Bjerring P, Nielsen J. Regional variations in analgesic efficacy of EMLA cream. Acta Dermatologica Scandinavica 1990; 70: 314-318. 5. Fornage BD, Deshayes JL.. Ultrasound of normal skin. Journal of Clinical Ultrasound 1986; 14: 619-622. 6. Bierkens AF, Maes RM, Hendriks AJM, Erdos AF, De Vries JDM, Debruyne FMJ. The use of local anesthesia in second generation extracorporeal shock wave lithotripsy: Eutectic Mixture of Local Anesthestics. Journal of Urology 1991; 146: 287-289.

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infiltration of the skin to reduce the amount of systemic analgesia needed during ESWL [2]. The topical anaesthetic, EMLA cream, has been used successfully for painless venepuncture, removal of condylomata acuminata and harvesting of split skin grafts. It has been shown that, after an application time of 90 min, skin analgesia to a depth of greater than 4 mm can be achieved [3, 4]. Using ultrasound, Fornage and Deshayes determined the mean dermal thickness over the back to be 3.6 (0.5) mm [5]. Hence, if a large element of the pain experienced during ESWL is at the skin surface, we postulated that EMLA cream should reduce the amount of systemic analgesia required during the procedure. Our study has shown that, when compared with placebo, EMLA cream did not reduce the amount of systemic analgesia required during ESWL with the Store Modulith SL 20. This is in contrast with a similar study by Bierkens and colleagues [6], who showed that EMLA cream reduced fentanyl requirements during ESWL, but not significantly. However, they used a Siemens Lithostar, and even in their placebo group only 53 % of patients required fentanyl, in a mean dose of 0.98 ugkg"1. In comparison, 96 % of our placebo group required fentanyl in a mean dose of 3.1 ug kg"1. This highlights the variable anaesthetic requirements for ESWL with the different second generation machines. We conclude that the pain experienced during ESWL with the Storz Modulith SL 20 is at a level deeper than the skin surface. The pain may be caused by stone movement, impingement of the shock wave on the peritoneum or renal pelvic tissues or, in occasional patients, from the shock wave accidentally hitting the 12th rib. Thus we cannot recommend topical anaesthesia for lithotripsy with the Storz Modulith SL 20.

Topical anaesthesia for extracorporeal shock wave lithotripsy.

We have investigated 60 patients in a prospective double-blind, placebo-controlled study to assess the efficacy of EMLA (Eutectic Mixture of Local Ana...
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