Review for 10.1186/1471-230X-2-15 (2002)

Reviewer's report
 Bouveret's Syndrome Complicated by Distal Gallstone Ileus after Laser Lithotropsy Using Title:
Holmium: YAG Laser
Authors:
Mohammad M. Alsolaiman (modar9@hotmail.com )
Christoph Reitz (luckyluko@mindspring.com )
Ali T. Nawras (nawrasa@mail.amc.edu )
John B Rodgers (RodgerJ@mail.amc.edu )
Benedict J Maliakkal (MaliaKB@mail.amc.edu )
 2  12 Jun 2002 Version: Date:
 Dr Joel Teichman Reviewer:
 A paper of considerable general medical or scientific interest Level of interest:
 Accept without revision Advice on publication:
The authors describe a case report in which the holmium:YAG laser was not useful in fragmenting a 
large gallstone in the duodenum. Some technical issues bear mention. The holmium:YAG laser (pulse 
duration 250 usec) fragments all stone compositions by a photothermal mechanism (Vassar et al: 
Holmium:YAG lithotripsy: Photothermal mechanism. J Endourol 1999; 13: 181-90). As a result, it does 
not produce "large cracks", as the authors indicate. In contrast, lasers with short pulse durations (1 
usec) fragment stones through photoacoustic effects, which create "large cracks" (Rink et al: 
Fragmentation process of current laser lithotriptors. Lasers Surg Med 1995; 16: 134). The fact that the 
holmium:YAG laser fragments all compositions and produces tiny craters and small fragments makes it 
more advantageous than other intracorporeal lithotripsy devices (Teichman et al: Holmium:YAG 
lithotripsy yields smaller fragments than Lithoclast, pulsed dye or electrohydraulic lithotripsy. J Urol 
1998; 159: 17-28). The small fragments are particularly advantageous as they are mostly less than 1 
mm in size, and will pass harmlessly in the gastrointestinal tract (or urinary tract for urological 
applications). These small fragments produce an endoscopic appearance of a "snow storm", and may obscure vision, so that we use a hand irrigation device to lavage the fragments away from the stone 
surface and maintain endoscopic visualization. 
The authors used a 550 um fiber and then a 1000 um fiber at 0.5 J and 5 Hz. They did not use higher 
settings due to fear of perforation. First, these low power settings for the 1000 um fiber produce low 
laser fluence and diminish ablation efficiency (Vassar et al: Holmium:YAG lithotripsy efficiency varies 
with energy density. J Urol 1998; 160: 471-6.) Had they increased their power, or maintained their power
setting but used the smaller 365 um fiber, their ablation efficiency would have increased. The concern 
over perforation was moot, since photoacoustic effects from the holmium:YAG laser are minimal, as 
opposed to the lasers with short pulse durations. The most efficient settings for holmium:YAG lithotripsy
appear to be 1 J at 10 Hz for most stone compositions (Spore et al: Holmium:YAG lithotripsy: optimal power setting. J Endourol 1999; 13: 559-566). For most urologic applications, the proper use of holmium:YAG power settings and optical fibers should yield stone-free results in >85% of cases in one 
setting, including stones as large as 6 cm (Teichman et al: Holmium:YAG cystolithotripsy of large 
bladder calculi. Urology 1997; 50: 44, Sofer et al: Holmium:YAG laser lithotripsy for upper urinary tract 
calculi in 598 patients. J Urol 2002; 167: 31-4.) Quite simply, if you can access the stone, the laser will 
fragment it successfully. I would expect gastrointestinal applications should yield equivalent results. 
Competing interests:
None declared.