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

To determine if the nature of the coupling agent normally used between the lithotripter and the patient affects the stone fragmentation rate during extracorporeal shock wave lithotripsy.

A jig designed to hold 'phantom' 10-mm stones at the focal point was fixed against the shock wave delivery point of an electromagnetic lithotripter (Dornier Compact, Germany). A layer of either petroleum jelly (Vaseline, Cheeseborough-Ponds Ltd, London, UK) ultrasonography jelly, a eutectic mixture of local anaesthetic (EMLA) cream, Instillagel (Farco-Pharma, Cologne, Germany) or a commercial water-soluble lubricating jelly was placed between the jig and shockwave head, and the number of shock waves required to fragment the stones was recorded.

Significantly more shock waves were required to fragment stones when petroleum jelly was used as the coupling agent than with all the other agents under test, whereas significantly fewer shock waves were required when using Instillagel or lubricating jelly than for all other agents.

The coupling agent used in water-free lithotripsy can affect the stone fragmentation rate and should not be considered inert. Ultrasonography jelly is probably the optimum agent available for use as a lithotripsy coupling agent.