Bohris C et al, 2015: Improvement of SWL Efficacy: Reduction of the Respiration-Induced Kidney Motion by Using an Abdominal Compression Plate.
Bohris C, Stief CG, Strittmatter F.
Dornier MedTech Systems , Wessling, Germany .
Department of Urology, University Hospital Grosshadern, Ludwig-Maximilians-University , Munich, Germany.
BACKGROUND AND PURPOSE: In extracorporeal shockwave lithotripsy (SWL), respiratory-induced motion of the upper urinary tract may hamper stone targeting and disintegration. The objective of this study is to analyze the effect of abdominal compression (AC) to kidney motion and to shock wave efficacy.
SUBJECTS AND METHODS: The study included 10 volunteers and 10 kidney stone patients. AC was achieved by a wedge-shaped compression plate. Patients underwent a routine ultrasound-guided SWL. For analgosedation, remifentanil (∼0.1 μg/kg/min) was administered. The respiratory-induced kidney motion, as well as with free breathing and AC, was quantitatively evaluated on basis of recorded ultrasound videos. By definition, shock wave efficacy was 100%, if the stone center was aligned with the shock wave focus. Its decrease depending on off-focus distance was obtained by model stone tests. On this basis, a mean shock wave efficacy value was attributed to the displacement function resulting from each measured kidney motion.
RESULTS: In volunteers, the amplitude of the displacement function with AC (mean: 8 mm; range: 3-11 mm) was significantly lower than with free breathing (mean: 12 mm; range: 5-19 mm) (paired samples t-test, p < 0.001). Correspondingly, the mean efficacy improved to 91% (range: 78%-99%) from 79% (range: 59%-94%) (p < 0.01). In the patient cohort, the amplitudes were similar and the efficacy even higher because of the respiratory depressant effect of remifentanil. By AC, the efficacy improved to 93% (range: 85%-98%) compared with 87% (range: 77%-96%) (p < 0.01).
CONCLUSIONS: AC with a compression plate is easy to perform and well tolerated by patients. It significantly reduces respiratory-induced kidney motion and improves shock wave efficacy.
J Endourol. 2015 Dec 18. [Epub ahead of print]
One of the obstacles for successful disintegration of stones in the kidney, and to some extent also in the proximal ureter, is a low hit-rate for shockwaves depending on respiratory movements.
Clinical experience has shown that movements of the stone and the kidney/ureter vary considerably from one patient to another. The movements are small in patients previously exposed to open or percutaneous surgery, but can in other patients occasionally be quite extensive. Not only does the latter situation result in poor and slow disintegration; large respiratory movements are also certainly associated with increased fluoroscopy time. The usual recommendation to reduce this problem has been to place the stone in focus during maximal expiration.
A more effective method was the broad belt applied over the upper abdomen with the aim of reducing the amplitude of respiratory induced stone movements. As presented in this manuscript the introduction of an abdominal plate is a further improvement in optimizing the efficacy of SWL. The results in this report showed reduced amplitude of stone movement and an associated increased therapeutic efficacy.
Previous attempts with respiratory triggered shockwaves never were a success because of irregular respiration during SWL. The recently suggested method based on US-imaging might be useful provided such a system is easy to use .
When SWL results are published the problem of stone movement is almost never touched and interpretation of the need of a certain number of shockwaves in relation to the actual hit-rate is accordingly not possible. It can, however, be recommended that SWL operators pay increased attention to this important factor. Unfortunately, I have noticed that there is a reluctance even to use a belt, something that is difficult to understand inasmuch every kind of abdominal compression not only results in reduced respiratory movements, it also improves the coupling between the shockwave therapy head and the patient.
It might be a good idea to add facilities for application of an abdominal plate to modern lithotripters and also to incorporate a system for estimates of the stone movement and the hit-rate.
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