Impact of body mass index on success, complications and failure of extracorporeal shock wave lithotripsy

Introduction: Extracorporeal shock wave lithotripsy (ESWL) is known as the most common method in treating urinary stones (70%) and is a selective method to treat small urinary stones (<2-2.5 cm). General opinion is that the success rate of ESWL in obese patients is low and risk of complications is high. Objectives: The aim of this study was to evaluate the impact of body mass index (BMI) and the stone-to-skin distance on success, complications and failure of ESWL. Patients and Methods: In this study, 222 patients who referred to lithotripsy clinic of Kashani hospital of Shahrekord to break stones with diameters of 5 to 20 mm participated in the study. Their urinary stones were in kidneys, lower calyces, upper calyces, pelvis or proximal ureter and were divided into two equal groups of BMI >25 kg/m2 and BMI <25 kg/m2. Assessing the position and diameter of the stones was based on radiographic findings such as sonography and CT scan. Regarding success, failure and complications of lithotripsy, two groups were compared. Results: Around 105 and 117 patients out of 222 subjects, were respectively assigned in BMI>25 kg/m2 and BMI <25 kg/m2 groups. The failure and success of both groups were statistically significant (P = 0.023). In terms of treatment outcomes, difference between two groups was high in low skin-to-stone distance (SSD). Logistic regression showed that both BMI and SSD are effective factors in treating the stone while SSD was more effective (P = 0.004) than BMI (P = 0.023) since SSD>7.5 cm predicts treatment failure. Conclusion: BMI and SSD are effective factors on the outcome of ESWL. Higher BMI and SSD> 7.5 cm are effective factors on treatment failure.