BACKGROUND AND PURPOSE: Studies have suggested that shockwave lithotripsy (SWL) stone fragmentation rates can be affected by characteristics of the fluid media surrounding the stone, although evidence to implicate the impact of urine specific gravity (SG) is limited and inconclusive. Our aim is to further explore the impact fluid media and SGs have on stone fragmentation using a variable focus lithotripter.
MATERIALS AND METHODS: Artificial stones were presoaked for 24 hours in urine and then shocked in various fluid media including artificial urine (SG 1.010 control, 1.020, and 1.07), human pooled urine (HPU), degassed HPU, Pentastarch, 100% and 30% contrast, degassed 30% contrast, 100% ethanol, deionized water (dH(2)O), degassed dH(2)O, 5% glucose, Ringer lactate, 0.9% saline, glycerol, whole blood, and lubricating gel. After soaking, SWL using the Modulith SLX-F2 electromagnetic lithotripter was performed. Fragments were dried and sieved using a 4-mm diameter opening grid. Fragments >4 mm were weighed and fragmentation coefficients (FCs) calculated (pre-SWL weight - post-SWL weight)/(pre-SWL weight) × 100. Fifteen stones were shocked for each fluid group.
RESULTS: Fluid type, viscosity, and degassing all significantly impacted stone fragmentation. While the solutions' SG, per se, did not appear to affect stone fragmentation, the use of degassed 30% contrast significantly improved stone destruction over the SG 1.010 artificial urine control (95.3% vs 71.4, P < 0.01). Furthermore, degassing improved comminution rates by increasing the number of completely fragmented stones (FC = 100%). Using degassed 30% contrast, 12/15 stones were completely fragmented, compared with only 2/15 in the control group (P = 0.007). Among the whole blood, glycerol, and lubricating gel groups, only 1/15, 0/15, and 1/15 stones reached 100% FC respectively in the narrow focus, possibly because of the detrimental impact of increased viscosity.
CONCLUSIONS: Different fluid media can significantly affect FC in vitro. Among the various fluids tested, degassed 30% contrast significantly increased the FC and total number of completely fragmented stones.
J Endourol. 2011 Mar;25(3):397-401. doi: 10.1089/end.2010.0242
PMID: 21401394 [PubMed - in process]
This report on in vitro disintegration of artificial stones in different fluid media is indeed very interesting and the results might be clinically important. The experiments were carried out with a Storz Modulith SLX-F2 lithotripter. It is noteworthy that that the best fragmentation was recorded with contrast media and with degasified de-ionized water. In contrast lubricating jelly and glycerol apparently counteracted stone disintegration.
From a clinical point of view and based on these observations, lubricants installed in the ureter in order to facilitate stone passage probably should be avoided if ESWL treatment is planned in association with such a procedure. It also might be of value to make an attempt to enhance disintegration of stones by contrast administration in patients who have either a percutaneous nephrostomy catheter or a ureteral catheter in place.
It would be of interest to learn if these results also can be translated to the properties of real stones with known composition.
One of the drawbacks of the study is that a shockwave frequency of 120 per minute (2 Hz) was used, since it is today reasonably well established that a better disintegration can be obtained with a low shock wave frequency. Nevertheless the findings are highly interesting an we can look forward to further experiments in this field.