Wang CS. et al., 2021: Newly designed solid coupling medium for reducing trapped air pockets during extracorporeal shock wave lithotripsy_ a phantom study
Wang CS, Li CC, Wu WJ, Liou WC, Lin YE, Chen WC.
Department of Urology, School of Medicine, College of Medicine, Kaohsiung Medical University Hospital, No.100, Shiquan 1st Rd., Sanmin Dist., Kaohsiung City 807, Taiwan.
Department of Surgery, St. Joseph Hospital, Kaohsiung City, Taiwan.
Graduate Institute of Human Resource and Knowledge Management, National Kaohsiung Normal University, Kaohsiung City, Taiwan.
CleanWave Medical Co., LTD, Kaohsiung City, Taiwan.
Department of Urology, School of Medicine, College of Medicine, Kaohsiung Medical University Hospital, No.100, Shiquan 1st Rd., Sanmin Dist., Kaohsiung City 807, Taiwan.
6Department of Surgery, St. Joseph Hospital, Kaohsiung City, Taiwan.
Abstract
Introduction: Air pockets between the lithotripter head and body surface are almost inevitably generated when applying a handful of gel onto the contact portion of the treatment head and that on the patient's skin during coupling procedure. These air pockets can compromise the transmission of acoustic energy of shock wave and may significantly affect efficacy of stone disintegration. Comparing to conventional gel, this study aims to investigate efficacy of stone disintegration by using a proprietary isolation-coupling pad ("icPad") as the coupling medium to reduce trapped air pockets during ESWL procedure.
Method: In this phantom study, Dornier lithotripter (Delta-2 RC, Dornier MedTech Europe GmbH Co., Germany) was used with a proprietary gel pads (icPad, Diameter = 150 mm, Thickness = 4 mm and 8 mm). The lithotripter was equipped with inline camera to observe the trapped air pockets between the contact surface of the lithotripter head. A testing and measuring device were used to observe experimental stone disintegration using icPad and semi-liquid gel. The conventional semi-liquid gel was used as control for result comparison.
Results: The stone disintegration rate of icPad 4 mm and 8 mm after 200 shocks of energy at level 2 were significantly higher than that of the semi-liquid gel (disintegration rate 92.3%, 85.0% vs. 45.5%, respectively, p < 0.001). The number of shocks for complete stone disintegration by icPad of 4 mm and 8 mm at the same energy level 2 were significantly lower than that of the semi-liquid gel (the number of shocks 242.0 ± 13.8, 248.7 ± 6.3 vs. 351.0 ± 54.6, respectively, p = 0.011). Furthermore, quantitative comparison of observed air pockets under Optical Coupling Control (OCC) system showed that the area of air pockets in semi-liquid group was significantly larger than that of the group using icPad (8 mm) and that of the group using icPad (8 mm) after sliding (332.7 ± 91.2 vs. 50.3 ± 31.9, 120.3 ± 21.5, respectively, p < 0.05).
Conclusion: The advantages of icPad includes: (1) reduced the numbers of shock wave and increased stone disintegration rate due to icPad's superior efficacy; (2) significantly reduce trapped air pockets in ESWL coupling. Due to the study limitation, more data are needed to confirm our observations before human trials.
BMC Urol. 2021 May 14;21(1):79. doi: 10.1186/s12894-021-00847-y. PMID: 33990213. FREE ARTICLE
Comments 1
As long as the original Dornier HM3 lithotripter was used, optimal transmission of shockwave energy was easily achieved because the shockwaves were generated in the same water compartment as the patient and thus directed into the body without passage of any barriers. Degasified water was a prerequisite for successful transmission.
With modern “dry” lithotripters it is necessary to provide a shockwave path with as little energy loss as possible and different contact transmission media have been used for this purpose. The most popular transmission medium is ultrasound gel, but it has been shown than even small quantities of air bubbles in the gel reduces the shockwave power significantly.
Different tricks have been used to minimize presence of air-bubbles in the gel and recently an optical system with camera was incorporated in the lithotripter to assist in the process of removing air-pockets from the gel. With that device treatment results were improved.
In this report the authors describe a solid coupling pad. This is an interesting innovation by means of which a bridge can be established between the shockwave head and the patient. In a phantom study the absence of air-pockets resulted in significantly better disintegration than with standard semi-liquid gel. The authors also found that the advantage of the pad remained after sliding.
Although the authors conclude that additional in vitro studies are necessary the ic PAD is a very interesting innovation that might be clinically useful.
Hans-Göran Tiselius