Low-frequency extracorporeal shock wave lithotripsy improves renal pelvic stone disintegration in a pig model

To compare disintegration rates for renal stones treated by 60 vs 120 shock waves (SW)/min at the same energy settings, using standardized validated artificial stones in a pig model.

Gypsum artificial stones (13 x 6 mm) were inserted into the renal pelvis on either side of 12 anaesthetized pigs by open surgery. Extracorporeal SW lithotripsy (ESWL) was applied using a new electromagnetic lithotripter (Lithoskop, Siemens AG Healthcare, Munich, Germany) at 60 and 120 SW/min; 3000 SW were applied to each kidney with the same energy settings. Stone fragments were collected after nephrectomy, passed through calibrated test sieves, and weighed. Fragment size categories were stratified according to the sieve hole size as set by the manufacturer. Fragments of < or =4.75 mm were defined as capable of spontaneous passage. For each pig the number of stone fragments of the respective size categories was counted and weighed. The results were analysed statistically using the Mann-Whitney U-test.

For fragments of >4.75 mm, the median (range) fragment counts were 0 (0-1) for 60 and 1 (0-3) for 120 SW/min (P = 0.006). For small fragments of 2.0-2.8 mm, the median fragment counts were 15 (4-24) for 60 and 10 (2-25) for 120 SW/min (P = 0.033); for fragments of 1.0-2.0 mm the respective values were 42.5 (9-81) and 21.5 (6-56) (P = 0.004). Of the total stone fragment mass in the 60 and 120 SW/min groups, 4.34% and 31.31% were >4.75 mm. There was complete disintegration yielding fragments capable of spontaneous passage in 10 of 12 renal units at 60 and in three of 12 renal units at 120 SW/min. The mean treatment time was 55.4 min for therapy at 60 and 34.3 min for therapy at 120 SW/min (P = 0.001). One parenchymal haematoma of 15 x 10 mm developed in the 60 SW/min group and another of 20 x 10 mm developed in the 120 SW/min group.

ESWL fragmentation with equal energy application yields significantly smaller fragments at 60 than at 120 SW/min. The theoretical stone passage rate could therefore be approximately 80% for 60 vs 25% for 120 SW/min ESWL. Renal haematoma formation was comparable in both groups.