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Harrogate S et al, 2016: Quantification of the range of motion of kidney and ureteric stones during shockwave lithotripsy in conscious patients.

Harrogate S, Yick S, Williams JC, Cleveland R, Turney BW.
Oxford University Medical School, John Radcliffe Hospital, Oxford, United Kingdom.
Department of Anatomy and Cell Biology, Indiana University School of Medicine, Indianapolis, Indiana.
Department of Engineering, Institute of Biomedical Engineering, University of Oxford, Oxford, United Kingdom.
Oxford Stone Group, Nuffield Department of Surgical Sciences, Department of Urology, University of Oxford, United Kingdom.

Abstract

Effective shockwave lithotripsy requires accurate targeting of the stone throughout the course of treatment. Stone movement secondary to respiratory movement can make this more difficult. In vitro work has shown that stone motion outside the focal region reduces the efficacy of stone fragmentation; however, there is little clinical data on the degree of stone movement in patients during treatment. To investigate this, X-ray fluoroscopic images of kidney and ureteric stones at the upper and lower limits of the normal respiratory cycle were acquired during SWL of 54 conscious patients, and stone excursion was calculated from these images. In addition, respiration rate and patient perceived pain were recorded during the course of the treatment. It was founds that stone motion secondary to respiration was 7.7±2.9mm for kidney stones and 3.6±2.1mm for ureteric stones-less than has been reported in studies with anaesthetised patients. There was no significant change of motion over the course of a treatment although pain was found to increase. These data suggest that stone motion in conscious patients is less than in anaesthetised patients. Further it suggests that lithotripters with focal regions of 8 mm or greater should not suffer from a marked drop in fragmentation efficiency due to stone motion.

J Endourol. 2016 Jan 12. [Epub ahead of print]

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Hans-Göran Tiselius on Monday, 20 June 2016 08:52

This report is highly interesting inasmuch as the hit-rate of shockwaves to a large extent is determined by the respiratory induced movement of the renal collecting system and stones. Stone movement has been recognized as a problem of SWL treatment ever since this treatment modality was introduced more than 30 years ago. Despite the importance of this factor it is seldom mentioned in reports of SWL [1]. To overcome the problem of stone movement, it has been a rule always to place the stone in focus during the expiratory phase. Additional assisting steps have been to use a belt or a plate with the aim of reducing this kind of movement [2]. Other tricks that have been used are high frequency ventilation (only possible with general anaesthesia) [3,4] and respiratory triggered shockwaves. None of the latter two methods have been met with desired success.

Stones located in the kidneys and ureters were included in this study. As expected the distance that stones in the ureter moved was much smaller than that of stones in the kidney. It is not mentioned, however, in which part of the ureter that the stones were located. In my own experience only stones in the proximal ureter move in a way that causes any problem.

It is understood (or at least assumed) that the patients in this study were recruited consecutively. Therefore the authors can be congratulated to extremely cooperative patients because in my own experience some patients demonstrate much more pronounced stone movement than recorded in this group of patients.

The authors compare the results with those during anaesthesia, but that difference can probably to some extent be explained by the artificially supported respiration during anaesthesia. In other words the stone movement during general anaesthesia is determined by the anaesthetist.

It is not mentioned if the authors applied a belt or not to reduce stone movement, but nevertheless the range of stone movement was apparently relatively small and if this finding represents the average situation in a larger group of patients, respiratory stone movement should not be of major concern in the clinical routine.

The authors’ recommendation that the large focus should be used for stones in the kidney and the small focus for stones in the ureter is worthwhile to note.

That almost half of the 29 patients in whom follow-up data were available had stones that after 2 weeks appeared without change is disappointing, particularly since the mean stone diameter was only 8-9 mm.

The lesson learnt from this study is that in general stone movements are small, at least horizontally, but despite this finding it seems desirable to include an estimate of the percentage or number of shockwaves that really hits the stone during SWL treatment. That information advantageously should be presented together with the total number of shockwaves delivered.

References
1. Bohris C, Bayer T, Lechner C.
Hit/Miss monitoring of ESWL by spectral Doppler ultrasound.
Ultrasound Med Biol. 2003 May;29(5):705-12.
2. Bohris C, Stief CG, Strittmatter F.
Improvement of SWL Efficacy: Reduction of the Respiration-Induced Kidney Motion by Using an Abdominal Compression Plate.
J Endourol. 2015 Dec 18. [Epub ahead of print]
3. Schulte am Esch J, Kochs E, Meyer WH.
Use of high frequency jet ventilation in extracorporeal shockwave lithotripsy.
Anaesthesist. 1985 Jun;34(6):294-8. German.
4. Mucksavage P, Mayer WA, Mandel JE, Van Arsdalen KN.
High-frequency jet ventilation is beneficial during shock wave lithotripsy utilizing a newer unit with a narrower focal zone.
Can Urol Assoc J. 2010 Oct;4(5):333-5.

This report is highly interesting inasmuch as the hit-rate of shockwaves to a large extent is determined by the respiratory induced movement of the renal collecting system and stones. Stone movement has been recognized as a problem of SWL treatment ever since this treatment modality was introduced more than 30 years ago. Despite the importance of this factor it is seldom mentioned in reports of SWL [1]. To overcome the problem of stone movement, it has been a rule always to place the stone in focus during the expiratory phase. Additional assisting steps have been to use a belt or a plate with the aim of reducing this kind of movement [2]. Other tricks that have been used are high frequency ventilation (only possible with general anaesthesia) [3,4] and respiratory triggered shockwaves. None of the latter two methods have been met with desired success. Stones located in the kidneys and ureters were included in this study. As expected the distance that stones in the ureter moved was much smaller than that of stones in the kidney. It is not mentioned, however, in which part of the ureter that the stones were located. In my own experience only stones in the proximal ureter move in a way that causes any problem. It is understood (or at least assumed) that the patients in this study were recruited consecutively. Therefore the authors can be congratulated to extremely cooperative patients because in my own experience some patients demonstrate much more pronounced stone movement than recorded in this group of patients. The authors compare the results with those during anaesthesia, but that difference can probably to some extent be explained by the artificially supported respiration during anaesthesia. In other words the stone movement during general anaesthesia is determined by the anaesthetist. It is not mentioned if the authors applied a belt or not to reduce stone movement, but nevertheless the range of stone movement was apparently relatively small and if this finding represents the average situation in a larger group of patients, respiratory stone movement should not be of major concern in the clinical routine. The authors’ recommendation that the large focus should be used for stones in the kidney and the small focus for stones in the ureter is worthwhile to note. That almost half of the 29 patients in whom follow-up data were available had stones that after 2 weeks appeared without change is disappointing, particularly since the mean stone diameter was only 8-9 mm. The lesson learnt from this study is that in general stone movements are small, at least horizontally, but despite this finding it seems desirable to include an estimate of the percentage or number of shockwaves that really hits the stone during SWL treatment. That information advantageously should be presented together with the total number of shockwaves delivered. References 1. Bohris C, Bayer T, Lechner C. Hit/Miss monitoring of ESWL by spectral Doppler ultrasound. Ultrasound Med Biol. 2003 May;29(5):705-12. 2. Bohris C, Stief CG, Strittmatter F. Improvement of SWL Efficacy: Reduction of the Respiration-Induced Kidney Motion by Using an Abdominal Compression Plate. J Endourol. 2015 Dec 18. [Epub ahead of print] 3. Schulte am Esch J, Kochs E, Meyer WH. Use of high frequency jet ventilation in extracorporeal shockwave lithotripsy. Anaesthesist. 1985 Jun;34(6):294-8. German. 4. Mucksavage P, Mayer WA, Mandel JE, Van Arsdalen KN. High-frequency jet ventilation is beneficial during shock wave lithotripsy utilizing a newer unit with a narrower focal zone. Can Urol Assoc J. 2010 Oct;4(5):333-5.
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