Improvement of SWL Efficacy: Reduction of the Respiration-Induced Kidney Motion by Using an Abdominal Compression Plate.

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.