BERKELEY, CA (UroToday.com) - The increasing tendency to repeat SWL sessions, especially with the new-generation machines, calls for knowledge of any side effects of clinical importance. SWL studies in animals and humans showed dose dependent, short-term and long-term adverse effects. These changes are secondary to the cellular and microvascular effects of trauma, hemorrhage, ischemia, free radical formation, and impairment of renal hemodynamics.
This study examined the acute post-SWL morphological and hemodynamic renal changes as evaluated by dynamic contrast enhanced magnetic resonance imaging (DCE-MRI). Each patient received one SWL session with application of 3000 shock waves at a rate of 80/min. The lithotripter used was the electromagnetic Dornier Lithotripter S (DoLi S) (Dornier Med Tech, Germering, Germany) with EMSE 220F-XXP. Treatment was started at first step of the machine power (that delivered 49 MPa focal pressure, 0.35 mJ/mm2) then increased gradually by one step every 200 shocks up to step 4 (77 MPa, 0.7 mJ/mm2). Before, within 4 hours after SWL and one week post-SWL, magnetic resonance imaging with dynamic studies was done for all patients to assess the renal perfusion by generating MR dynamic signal intensity-time curves representing region of interest (ROI) all over the kidney, excluding the pelvicalyceal system, to obtain the relative maximum intensity (RMI) units of enhancement (total enhancement intensity units – total intensity units at non-enhanced scan) that represents renal blood flow. Structural renal changes were assessed at the same time (obstruction and parenchymal injuries).
In the present study we could not detect any renal perfusion changes 2-4 hours post-SWL. On the contrary, In a previous study[1] we used DCE-MRI to assess the acute renal perfusion changes 2-4 hours post-SWL to compare the effects of 2 lithotripters, and we found that for the patients treated by DoLi S, there was a significant decrease in renal perfusion in both kidneys after SWL. This is most probably induced via a systemic mechanism and not only an effect of SWL. Strohmaier et al.[2] determined that the active renin concentration was increased immediately and sustained at one day after SWL. These findings explain the decrease in renal perfusion in the contralateral kidney not exposed to SWs.
This contradiction in the findings of both studies could be explained by the difference in the energy level delivered at the kidney. In the previous study, DoLi S was equipped with EMSE 220F with focal diameter of 2.5 mm at 80% power setting that delivers 82.8 MPa (1.22 mJ/mm2) at the kidney, while in the present study DoLi S was equipped with EMSE 220F-XXP with focal diameter 3.5 mm at the used power setting of 4 that delivers 77 MPa (0.7 mJ/mm2) at the kidney which means a wider focal size and much lower energy. Mitterberger et al.[3] observed the same findings as our previous study[1] but they used a different lithotripter and higher energy levels than we used in the present study. This discrepancy of the findings of our present study and the other 2 studies leads to the assumption that in the clinical situation the higher energy causes activation of the systemic mechanism of renin angiotensin system while the lower energy doesn’t activate this systemic mechanism.
Thus, we could assume that the application of low energy level is safe and effective with good success rate but this issue needs further prospective clinical studies with longer follow up period of the patients.
In the present study, on 2-4 hours post-SWL MRI there was no generalized loss of corticomedullary differentiation, while at one week, 8.3% of patients had generalized loss combined with ureteral obstruction by steinstrasse in all of them. Furthermore, when we stratified the results of renal perfusion according to obstruction of the treated kidney on one week post-SWL we found that the treated kidneys that were obstructed at one week showed significant decrease of renal perfusion in comparison to both pre- and early post-SWL estimates. Furthermore, in a previous study, dynamic renal scintigraphic scanning with technetium-99m mercaptotriglycine (99mTc-MAG-3) revealed that post-SWL obstruction causes deterioration in renal function early after SWL and may cause chronic effects.[4]
Thus, the generalized loss of corticomedullary differentiation and the decrease in renal perfusion of the treated kidney are caused by obstruction, not by shock waves, as it was not present immediately post-SWL. Therefore post-SWL obstruction must be managed urgently. These findings need further prospective studies to evaluate the role of obstruction.
We concluded that:
- With proper energy level and prudent selection of patient, SWL by itself has no major effects on bilateral renal perfusion and induces minimal and reversible acute renal morphologic changes.
- Post-SWL obstruction has major effects on the renal perfusion of the treated kidney and must be managed urgently.
References:
- Sheir KZ, Elhalwagy SM, Abo-Elghar ME et al. Evaluation of a synchronous twin-pulse technique for shock wave lithotripsy: a prospective randomized study of effectiveness and safety in comparison to standard single-pulse technique. BJU International 2008; 101: 1420.
- Strohmaier WL, Carl AM, Wilbert DM et al. Effects of extracorporeal shock wave lithotripsy on plasma concentrations of endothelin and renin in humans. J Urol 1996; 155: 48.
- Mitterberger M, Pinggera GM, Neururer R et al. Multimodal evaluation of renal perfusional changes due to extracorporeal shock wave lithotripsy. BJU International 2008; 101: 731.
- Sheir KZ and Gad HM: Prospective study of the effects of shock wave lithotripsy on renal function: Role of post-shock wave lithotripsy obstruction. Urology 2003; 61: 1102.
Written by:
Khaled Z. Sheir, MD as part of Beyond the Abstract on UroToday.com. This initiative offers a method of publishing for the professional urology community. Authors are given an opportunity to expand on the circumstances, limitations etc... of their research by referencing the published abstract.
Department of Urology, Urology and Nephrology Center, Mansoura University, Mansoura, Egypt