Body Mass Index Predicts Outcome of Ureteroscopy-Assisted Retrograde Nephrostomy for Percutaneous Nephrolithotomy

Introduction: Several clinical series of retrograde nephrostomy for percutaneous nephrolithotomy (PCNL) have been published over the past 30 years demonstrating good outcomes and safety. We previously reported our adaptation of the Lawson technique, wherein we deploy the puncture wire through a flexible ureteroscope. We herein aim to clarify the performance characteristics of this nephrostomy creation technique. Materials and Methods: Institutional Review Board approval and informed consent were obtained. A ureteroscopy-assisted retrograde nephrostomy (UARN) procedure was performed as described previously. Data were collected prospectively. Multiple patient and operative factors were evaluated for association with UARN success and nephrostomy creation time: body mass index (BMI), skin-to-stone distance, Guy's score, Clinical Research of the Endourological Society nephrolithometric score, hydronephrosis, stone burden, location of nephrostomy, exit from a stone-bearing calix, and use of holmium laser to access calix. Results: Nephrostomy was successful in 49/52 UARN procedures (94%). Only single access was placed: upper-18, mid-27, and lower-7. Median BMI was 29 kg/m(2) and median time for nephrostomy creation was 39 minutes. Fluoroscopy time for the entire PCNL including nephrostomy creation was 84 and 16 seconds for case numbers 1-25 and 26-52, respectively. By stepwise linear regression, variables correlating with nephrostomy creation time were BMI (r(2) = 0.219), stone burden (r(2) = 0.094), use of holmium laser to access calix (r(2) = 0.104), and total r(2) linear = 0.416. Conclusions: UARN is an intuitive safe procedure that offers dramatic reductions in fluoroscopy times. UARN is best suited to cases requiring only one nephrostomy tract. Upper pole access is commonly performed with a subcostal technique to navigate the puncture wire below the ribs. Increasing BMI best predicts longer nephrostomy creation times; procedure failure was associated with BMI exceeding 40 kg/m(2). UARN is a robust technique for nephrostomy creation in appropriately selected patients.