Nussberger F et al, 2016: A low or high BMI is a risk factor for renal hematoma after extracorporeal shock wave lithotripsy for kidney stones.
Nussberger F, Roth B, Metzger T, Kiss B, Thalmann GN, Seiler R.
Department of Urology, University of Bern, Freiburgstrasse, 3010, Bern, Switzerland.
The purpose of this study was to evaluate risk factors for renal hematoma after extracorporeal shock wave lithotripsy (SWL) for kidney stones in a matched case-control analysis of a subgroup of patients recruited from a prospective randomized cohort. Between 06/2010 and 03/2013, 418 patients underwent SWL with the MODULITH®-SLX-F2-lithotripter for kidney stones. In 39/418 patients (9 %), ultrasound at post-treatment day 1 revealed renal hematomas. For 37 of these patients, a matched group without hematoma could be selected according to the following matching criteria: age, gender, number and energy of shock waves, stone burden and localization. Risk factors for renal hematoma after SWL were compared between the two groups. The rates of diabetes, stopped anticoagulant/antiplatelet medications and arterial hypertension were not different between the two groups (p > 0.2). The skin-kidney distance was virtually the same in both groups (p = 0.5). In the hematoma group, significantly more patients had a high (>30: n = 16) as well as a low (<21.5: n = 4) BMI when compared to the control group (n = 4; n = 0; p < 0.001). Importantly, all patients with BMI <21.5 developed renal hematomas after SWL. Patients with a high (>30) or low (<21.5) BMI had a higher risk for renal damage after SWL. Therefore, alternative endoscopic treatment options should be considered in these patients.
Urolithiasis. 2016 Aug 30. [Epub ahead of print]
This is an interesting matched pair analysis of a patient’s subgroup of a larger study on the effects of ramping on ESWL effects and side effects (1). The contemporary literature shows a large discrepancy in the frequency of post ESWL hematomas like 7 in 1324 (2) or 39 in 418 (1). The studies usually fail to give a valid explanation for these differences and frequently offer only speculations on the causality of the relations they describe. The present paper is no exception. In a recent review on effects and side effects of ESWL (3) one of the authors conclusion was: “At present, there is a debate on the fragmentation and tissue injury processes, and no clear metric indicates how well a stone will break or how damaged tissue will suffer.”
What is important? BMI, hypertension, skin-kidney distance? In the present study the findings were
“ … more patients with renal hematomas had hypertension when compared to the control group. However, this trend was not significant, most likely due to a too small cohort scale.”
“… the low number of patients with BMI 30) or low (e at increased risk for renal damage post-SWL. Therefore, alternative endoscopic treatment options should be considered in these patients.”
At present the only recommendation seems to be to do a precise targeting and to adapt the voltage and number of shots to a necessary minimum.
1 Does Stepwise Voltage Ramping Protect the Kidney from Injury During Extracorporeal Shockwave Lithotripsy? Results of a Prospective Randomized Trial. Skuginna V et al. Eur Urol. 2016 Feb; 69(2):267-73
2 Incidence and risk factors of renal hematoma: a prospective study of 1,300 SWL treatments. Schnabel MJ et al. Urolithiasis. 2014 Jun;42(3):247-53)
3 Shock wave technology and application: an update. Rassweiler JJ et al. Eur Urol. 2011 May;59(5):784-96.