Study Type – Therapy (case series)
Level of Evidence 4
What's known on the subject? and What does the study add?
Animal studies have shown that one approach to reduce SWL-induced renal injury is to pause treatment for 3–4 min early in the SWL-treatment protocol. However, there is typically no pause in treatment during clinical lithotripsy.
We show in a porcine model that a pause in SWL treatment is unnecessary to achieve a reduction in renal injury if treatment is begun at a low power setting that generates low-amplitude SWs, and given continuously for ≈4 min before applying higher-amplitude SWs.
- • To test the idea that a pause (≈3 min) in the delivery of shockwaves (SWs) soon after the initiation of SW lithotripsy (SWL) is unnecessary for achieving a reduction in renal injury, if treatment is begun at a low power setting that generates low-amplitude SWs.
MATERIALS AND METHODS
- • Anaesthetised female pigs were assigned to one of three SWL treatment protocols that did not involve a pause in SW delivery of >10 s (2000 SWs at 24 kV; 100 SWs at 12 kV +≈10-s pause + 2000 SWs at 24 kV; 500 SWs at 12 kV +≈10-s pause + 2000 SWs at 24 kV).
- • All SWs were delivered at 120 SWs/min using an unmodified Dornier HM3 lithotripter.
- • Renal function was measured before and after SWL.
- • The kidneys were then processed for quantification of the SWL-induced haemorrhagic lesion. Values for lesion size were compared to previous data collected from pigs in which treatment included a 3-min pause in SW delivery.
- • All SWL treatment protocols produced a similar degree of vasoconstriction (23–41% reduction in glomerular filtration rate and effective renal plasma flow) in the SW-treated kidney.
- • The mean renal lesion in pigs treated with 100 low-amplitude SWs delivered before the main dose of 2000 high-amplitude SWs (2.27% functional renal volume [FRV]) was statistically similar to that measured for pigs treated with 2000 SWs all at high-amplitude (3.29% FRV).
- • However, pigs treated with 500 low-amplitude SWs before the main SW dose had a significantly smaller lesion (0.44% FRV) that was comparable with the lesion in pigs from a previous study in which there was a 3-min pause in treatment separating a smaller initial dose of 100 low-amplitude SWs from the main dose of 2000 high-amplitude SWs (0.46% FRV). The time between the initiation of the low – and high-amplitude SWs was ≈4 min for these latter two groups compared with ≈1 min when there was negligible pause after the initial 100 low-amplitude SWs in the protocol.
- • Pig kidneys treated by SWL using a two-step low-to-high power ramping protocol were protected from injury with negligible pause between steps, provided the time between the initiation of low-amplitude SWs and switching to high-amplitude SWs was ≈4 min.
- • Comparison with results from previous studies shows that protection can be achieved using various step-wise treatment scenarios in which either the initial dose of SWs is delivered at low-amplitude for ≈4 min, or there is a definitive pause before resuming SW treatment at higher amplitude.
- • Thus, we conclude that renal protection can be achieved without instituting a pause in SWL treatment. It remains prudent to consider that renal protection depends on the acoustic and temporal properties of SWs administered at the beginning stages of a SWL ramping protocol, and that this may differ according to the lithotripter being used.