Effect of urine specific gravity on effectiveness of shockwave lithotripsy.
OBJECTIVE
To determine the effect of urine specific gravity (SG) and radiographic contrast medium on the efficiency of extracorporeal shockwave lithotripsy (SWL) fragmentation using a previously published in vitro model.


METHODS
Artificial kidney stones (BegoStone [BEGO USA, Smithfield, RI]) of a standard size (10 x 10 mm) and weight (mean 1.90 g; range 1.89-1.91 g) were randomly allotted to one of four test media with differing SG: group 1: synthetic urine, SG 1.003; group 2: synthetic urine, SG 1.040; group 3: 50% radiographic contrast (Cysto-Conray II, Mallinckrodt Inc., Hazelwood, MO), 50% synthetic urine, SG 1.069; and group 4: 100% contrast, SG 1.121. The stones were placed in cups made of 2.2-mm screen mesh and exposed to 500 shockwaves at 20 KV from a spark-gap lithotripter (Econolith 2000; Medispec, Germantown, MD). The stone fragmentation rate (i.e., percent fragmentation) was determined by dividing the dry residual stone weight by the prelithotripsy dry weight (X 100).


RESULTS
The mean fragmentation rate for the four groups was 31.7%, 37.6%, 31.8%, and 27.2%, respectively. Statistical significance was not achieved (P = 0.1).


CONCLUSIONS
Stone breakage tends to be more effective when urine SG is about 1.040 than at higher or lower values. Hence, the recommendation for an overnight fast prior to SWL is well founded. Introduction of contrast medium may inhibit stone breakage because it increases the specific gravity.
Li
Ching-Chia
CC
Department of Urology, University of California, Irvine, CA, USA.
Finley
David S
DS
Uribe
Carlos
C
Eichel
Louis
L
Lee
David I
DI
McDougall
Elspeth M
EM
Clayman
Ralph V
RV
D006801:Humans; D007669:Kidney Calculi / Q000473:pathology / Q000628:therapy*; D008096:Lithotripsy; D008954:Models, Biological; D009997:Osmotic Pressure; D013046:Specific Gravity; D016482:Urinalysis