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Does laser lithotripsy hit the target?
  1. M L WILKINSON
  1. Gastroenterology Unit,
  2. 5th Floor,
  3. Thomas Guy House,
  4. Guy’s Hospital, London SE1 9RT, UK

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    Ever since it was generally concluded that endoscopic retrograde cholangiopancreatography (ERCP) and sphincterotomy was the treatment of choice for choledocholithiasis, big bile duct stones have remained a major challenge for the endoscopist. Extending a sphincterotomy increases risk of bleeding and perforation, mechanical lithotripters are generally expensive, cumbersome to use, fragile, and fail to grasp the stones effectively in a significant proportion of cases. Intraduct solvents such as mono octanoin or methyl tert butyl ether are ineffectual or dangerous, or both. The somewhat defeatist approach of placing stents in elderly patients can lead to stent migration with occasional serious consequences or the formation of multiple stones above the stent, with the consequent risk of further cholangitis. There is probably a place at a few referral centres for extracorporeal shock wave lithotripsy (ESWL) but this requires some sort of biliary catheter to deliver x ray contrast medium to facilitate targeting, which usually means at least two ERCPs in addition to the lithotripsy sessions. Furthermore, not all stones fragment easily and the capital costs and low usage mean that endoscopists must borrow sessions from their urological colleagues in most instances. One must not forget that surgery, despite its risks, may sometimes be the best option, but this is the ultimate admission of defeat by the endoscopist.

    One approach which has spawned several publications but has not achieved much “market penetration” is contact lithotripsy. The initial, cheaper, electrohydraulic shock wave machines were rapidly shown to be very effective not only at fragmenting stones but also at punching holes through the bile duct wall unless every shot was clearly on target.1 2 Targeting is anything but easy when vision is obscured by clouds of gallstone fragments.

    Subsequently a variety of laser techniques have been used. The coumadin pulsed-dye laser was intended, by choice of wavelength, to avoid damage to soft tissues through the elimination of absorption by haemoglobin but this was only partially successful and perforation can still occur, at least in animal models.3 Many ingenious mechanical devices, such as balloon catheters and wire guided Dormia baskets were developed in an attempt to improve targeting by x ray monitors but in a three dimensional system such methods were always open to error and the use of miniscopes, delivered either percutaneously or via a “mother and baby” per oral system became more popular. Popular is only a relative term, however, for the difficulty of two skilled endoscopists, preferably close friends, manipulating one scope through the other in the deep recesses of the intrahepatic biliary tree while listening with a long stethoscope to check for good stone contact as one of them depresses the laser foot pedal while simultaneously observing both x ray and endoscopy monitors and keeping the field of view constantly flushed of fragments, should not be underestimated. For these reasons the percutaneous approach gained ascendancy but both continue to suffer from the targeting problem which makes them very user unfriendly.4 5

    The alternative approach, to develop a laser system which “knew” when it was aimed at a stone and only fired then was followed chiefly in Austria6 and Germany7 8 where at least three units have used the Rhodamine 6G pulsed dye laser with optical stone detection system produced by Telemit of Munich, including Hochberger et al who have published their latest results in this issue (see page 823). This technical advance means that it is no longer crucial to check that every shot of the laser is aimed correctly, as the power is extinguished after 5–8% of a shot is delivered, unless the returning reflected light indicates a hard target. Thus, radiologically assisted targeting, as in conventional ERCP, is all that is necessary and in their series of 60 patients accumulated over five and a half years, 87% fragmentation and duct clearance was achieved, albeit with five serious complications. In the three published series on this laser so far, 114 patients have been treated, 103 (90%) successfully. The biggest news for endoscopists, however, is that 47 of the 60 patients in the present study were treated by conventional ERCP with x ray fluoroscopic targeting alone. This blind firing does seem to increase the time required for fragmentation, however, as three times as many pulses are cut off on the grounds of bad targeting despite the use of balloons and wire guided baskets to improve aim. In their earlier study the authors admitted that one third of the patients required additional ESWL to achieve sufficient fragmentation for complete stone clearance. A corresponding figure is not available in the present study. Since sessions could incorporate up to one hour of laser firing and a mean of 1.8 sessions per patient, the procedure remains something of a test of endurance for both patient and staff.

    However, according to Hochberger et al this paper is something of an historical document as they are currently using a piezo-acoustic stone detection system coupled to a Q switched NdYAG laser at only one third of the cost of the laser detailed in the present study and with greater effectiveness.9 Time will tell. In the meantime, why have so few centres purchased Rhodamine 6G lasers? I think at present that most people rely on the methods outlined in the first paragraph and until the “best buy” laser is built it would be better to wait a little longer. However, at least one or two centres in the UK should be investigating this additional method of managing large bile duct stones rather than leaving it all to our continental colleagues.

    See article on page 823

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