BACKGROUND: Outcome of Extracorporeal Shockwave Lithotripsy (SWL) is determined by physical factors that affect stone fragmentation and clearance.
PURPOSE: To evaluate the predictive value of the Lithotripsy Table Height (LTH) in SWL outcome. Lithotripsy Table Height (LTH) is a variable that represents skin to therapy head distance, and it is proportional to the energy that reaches the stone.
MATERIALS AND METHODS: A prospective study enrolled patients undergoing SWL for radiopaque urinary stones. All procedures were performed using a Modulith SLX (Karl Storz, Germany) Lithotripter. Patient weight, height and age; stone location and size; number of shock waves delivered, and LTH were recorded. One month post-procedure a KUB was obtained. Logistic regression analysis was used to evaluate the effects of these variables on stone-free outcome. A ROC curve was plotted.
RESULTS: Fifty-six patients were enrolled. After one month follow-up, overall success rate (Stone Free) was 83.9% (n = 47). LTH was the only independent predictor of outcome in both univariate and multivariate analysis (p = 0.029). Stone size (p = 0.45) and BMI (p = 0.32) were not significant. In the ROC curve, LTH showed an Area under the Curve = 0.791. Patients with LTH < 218 (n = 8) had relative risk of residual stones = 7.5, odds Ratio: 6.6 (Stone free rate 37.5% vs. 91.5%).
CONCLUSION: LTH appears to be an independent predictor of SWL outcome. High success rates can be expected if LTH > 218. Patients with lower LTH had a less effective therapy, therefore, worse stone fragmentation and clearance. These findings may help improve patient selection for SWL therapy.
Int Braz J Urol. 2011 May-Jun;37(3):355-61; discussion 361
PMID: 21756383 [PubMed - in process]
A very interesting paper.
Lithotripsy Table Height (LTH) was the only independent predictor of outcome in a multivariate analysis Patients with very low LTH 218.
Obviously it is not the SSD or the BMI that have a direct influence on the SWL result but the distance that the shock wave has to travel within the body and the acoustic properties of the tissue that it is passing.