Một số kỹ thuật tồn tại để giúp ngăn chặn di cư mảnh ngược. Mặc dù xuất sắc trực quan là cần thiết để cả hai cho phép lithotripsy và ngăn ngừa chấn thương vô ý niệu quản, giảm lực lượng irrigant trong quá trình phân mảnh đá | Chapter 6 Ureteroscopy 99 Several techniques exist to help prevent retrograde fragment migration. Although excellent visualization is necessary to both allow for lithotripsy and prevent inadvertent ureteral injury decreasing the irrigant force during stone fragmentation may help prevent migration. Positioning the operating table in reverse trendelenberg can also be helpful in some cases. Alternatively the lithotriptor probe may be positioned at the anterior aspect of the calculus and a mild amount of posterior pressure may be applied to hold the stone against the posterior ureteral wall during the lithotripsy. If retrograde migration is observed during lithotripsy the stone may be pulled distally in the ureter using ureteroscopic graspers prior to continuing with lithotripsy. The choice of lithotriptor is an important consideration in minimizing the risk of proximal migration. Pneumatic lithotriptors for example are accompanied by a high rate of stone propulsion and subsequent migration. Migration rates during PL range from 2 to 17 37 . Stone migration rates during EHL have also been significant with one series reporting proximal migration rates of 14 38 . In contrast significant proximal migration during Ho YAG laser lithotripsy appears to be less of a problem 39 . The Dretler stone cone Medsource Norwell MA offers a new technique to prevent retrograde migration. The device functions also as a guidewire and may be passed proximally into the renal pelvis. A radio-opaque marker delineates the location of the stone cone. The marker is introduced past the site of the calculus at which point the stone cone is deployed. In one series utilizing the Dretler stone cone only 6 of 50 patients had residual stone fragments and no patients required auxiliary procedures 40 . Finally ureteral caliber in an important risk factor for stone migration. If ureteral stents have been placed prior to attempting lithotripsy the dilated ureter may increase the risk of migration. In this .
