The efficacy of a range of contact media as coupling agents in extracorporeal shockwave lithotripsy

Objective To determine if the nature of the coupling agent normally used be tween the lithotripter and the patient affects the stone fragmentation rate during extracorporeal shock wave lithotripsy. Materials and methods A jig designed to hold 'phantom' 10-mm stones at the focal point was fixed against the shock wave delivery point of an electroma gnetic lithotripter (Dornier Compact, Germany). A layer of either petroleum jelly (Vaseline(TM), Cheeseborough-Ponds Ltd, London, UK) ultrasonography jelly, a eutectic mixture of local anaesthetic (EMLA) cream, Instillagel (F arco-Pharma, Cologne. Germany) or a commercial water-soluble lubricating je lly was placed between the jig and shockwave head, and the number of shock waves required to fragment the stones was recorded. Results Significantly more shock waves were required to fragment stones whe n petroleum jelly was used as the coupling agent than with all the other ag ents under test. whereas significantly fewer shock waves were required when using Instillagel or lubricating jelly than for all other agents. Conclusion The coupling agent used in water-free lithotripsy can affect the stone fragmentation rate and should not be considered inert. Ultrasonograp hy jelly is probably the optimum agent available for use as a lithotripsy c oupling agent.