1575Vol. 11 | No. 03 | May - June 2014 |U R O LO G Y J O U R N A L Department of Urology, Military Hospital Avicenna, Marrakech, Morocco. Youness El Harrech, Najib Abakka, Jihad El Anzaoui, Omar Goundale, Driss Touiti One-Shot Dilation in Modified Supine Position for Percutaneous Nephrolithot- omy: Experience From Over 300 Cases Corresponding Author: Youness EL Harrech, MD Service d’urologie, Hôpital Militaire Avicenne, Marrakech, Maroc. Tel: +212 661 32 6160 E-mail: youness.elharrech@ gmail.com Received May 2013 Accepted April 2014 Purpose: To evaluate the feasibility, safety and efficacy of one-shot dilation (OSD) in modified supine position percutaneous nephrolithotomy (PCNL). Materials and Methods: A total of 320 PCNL in a total of 291 patients were performed be- tween October 2008 and July 2011. There were no specific exclusion criteria. Patients with kidney anomalies or solitary kidney, with history of renal surgery or extracorporeal shockwave lithotripsy (SWL), those with staghorn calculi or needing more than one access, were eligible for inclusion. Data collected included patient demographics and stone characteristics, access time, radiation exposure, total operating time, preoperative and postoperative hemoglobin concentrations, tract dilatation failures, complications and transfusions. Results: Mean stone size was 38 mm (16-110 mm). The mean time access was 2.1 min (range 0.7-6.2 min). Tract dilatation fluoroscopy time was 25 ± 17 sec. The targeted calix could be en- tered with a success rate of 97.81%. The mean hemoglobin decrease was –1.17 g/dL ± 0.84. There were no visceral, pleural, collecting systems or vascular injuries. Major complications in- cluded, transfusion in 4 (1.25%) patients, pseudoaneurysm with persistent bleeding necessitating nephrectomy in 1 (0.3%) patient and two deaths (0.62%) after surgery. There was no significant difference in successful access and complications between patients with and without previous open surgery and in those with or without staghorn stones (P > .05). Conclusion: The use of one shot and modified supine position combines the advantages of these both methods including less radiation exposure and shorter access and operative time. The one shot dilation is safe, easy to learn, cost effective and offers a potential alternative to the standard devices particularly in developing countries. Keywords: dilatation; nephrostomy; percutaneous; methods; punctures; feasibility studies; uri- nary calculi; surgery; postoperative complications. ENDOUROLOGY AND STONE DISEASE 1576 | INTRODUCTION One of the most fundamental steps of percutaneous nephrolithotomy (PCNL) is the creation of the ne-phrostomy access. It can be done with serial polyu- rethane co-axial dilators (Amplatz dilators), balloon dilators and telescoping metallic co-axial dilators (Alken dilators). Use of an Amplatz dilator set or metal incremental dilators is time consuming and requires longer exposure to fluoroscopy. (1) More recently, to reduce access time and radiation expo- sure during access, and to reduce cost, a single-step tech- nique involving the use of an Amplatz serial dilator over a metallic telescopic dilator (‘‘one-shot’’) has become accepted as a safe and effective technique.(1-3) Starting in 2004, we routinely adopted the modified supine position to perform PCNL in patients affected by large and/ or complex urolithiasis.(4) This position has been considered by the second consultation on urolithiasis in 2007 as safe and effective.(5) We designed a prospective study in two different centers to evaluate the feasibility, safety and efficacy of one-stage dila- tion (OSD) in modified supine position. To our knowledge, no published clinical trials have used this dilation technique in supine position. MATERIALS AND METHODS A prospective chart and database was done of all patients undergoing PCNL using one shot dilation between October 2008 and July 2011 in one center. During this period, we per- formed 320 procedures in a total of 291 patients. There were no specific exclusion criteria. All adult candidates for PCNL were considered for enrollment consecutively. Patients with kidney anomalies or solitary kidney, with history of renal sur- gery or extracorporeal shockwave lithotripsy (SWL), those with staghorn calculi or needing more than one access, were eligible for inclusion. The purpose of the study was explained to all patients, and their informed consent was obtained. The parameters collected were patient demographics and stone (size, location and type) characteristics, total operat- ing time, preoperative and postoperative hemoglobin con- centrations, the number of transfusions, the number of tracts required, tract dilatation failures (inability to visualize the targeted calix by nephroscope) and injury of neighboring or- gans. The main study endpoints included access time (from needle puncture to the start of nephroscopy), radiation expo- sure during access (the number of seconds of X-ray exposure elapsed from the access needle to the placement of the Am- platz sheath). Operations were performed by eight different urologists with vast experience in the field of endourology. Statistical Analysis The continuous variables were analyzed using parametric (student’s t-test) and nonparametric (Mann-Whitney U test) statistical methods. Categorical variables were analyzed us- ing the Pearson chi square test. A logistic model was used to determine the odds ratios for statistically significant param- eters affecting complications. Data were expressed as mean ± standard deviation. A P value of < .05 was considered sig- nificant. Data were analyzed with the statistical package for the social science (SPSS Inc, Chicago, Illinois, USA) version 15.0. Technique PCNL was performed in the modified supine position ac- cording to techniques previously described.(4) In brief, the patient received general anesthesia and a single dose of an- tibiotic was administered intravenously. With the patient in the lithotomy position, a 5 French (F) ureteral catheter was inserted transurethrally. The patient was then placed in the modified supine position with the legs extended and the ipsilateral leg crossed over the contralateral leg. A cushion was placed below the ipsilateral flank to provide a 45-degree inclination. For patients with concomitant ureteral stones or depending on the surgeon preference, the split-leg modified lateral position was used. The patient was maintained in the lithotomy position with a 30-degree flank inclination.(6) The ipsilateral arm was over the thorax and the contralateral arm was used for intravenous infusion. An 18 gauge needle was horizontally introduced through the flank in the posterior axillary line into the collecting system. Renal access was achieved under fluoroscopic guidance after visualization of the pelvicaliceal system by retrograde injec- tion of diluted contrast through the ureteral catheter. An attempt, even if not always successful, was made to intro- duce the wire down the ureter. The skin over the puncture site and the fascial layers were in- cised. After the needle was removed, the Alken guide was re- placed under fluoroscopic guidance (Figures 1 and 2). Then, a single 25F Amplatz dilator was pulled in on the Alken Endourology And Stone Disease 1577Vol. 11 | No. 03 | May - June 2014 |U R O LO G Y J O U R N A L One Shot Dilatation in PCNL | Harrech et al guide (Figure 3). This single passage allowed the insertion of the 30F Amplatz sheath over the Amplatz dilator (Figure 4). Fluoroscopy was used in all steps of tract dilation and sheath placement. After the correct position of the Amplatz sheath was verified, the complex of Amplatz dilator and Alken guide were removed keeping the Amplatz sheath and work- ing guidewire in situ. In patients with horseshoe or pelvic kidney a nephrostomy tube was placed pre operatively under scan guidance or we used laparoscopy to guide puncture. RESULTS The preoperative patient and stone characteristics are sum- marized in Table 1. Mean age was 50.4 years (range 11 to 81 years). Mean stone size was 38 mm (16-110 mm). Of study subjects 28 patients had anatomical or functional solitary kid- ney. Two patients had horseshoe kidneys, 5 patients had pel- vic kidney, 31 patients had a history of ipsilateral open neph- rolithotomy and 57 patients had staghorn stones. Calyceal diverticula have been noted in 6 cases. In 76 procedures, access was obtained via an upper pole access, while in the other access was achieved through a middle or lower pole. Totally tubeless surgery was performed in the 41 last pro- cedures. Intraoperative data, postoperative values and proce- dural outcomes are shown in Table 2. Mean operative time was 54.8 min (range 25 to 137 min). The mean time required for the access was 2.1 min (range 0.7-6.2 min). Tract dilata- tion fluoroscopy time was available for 190 procedures and was 25 ± 17 seconds. The total X-ray exposure was 142 ± 54 seconds. Mean postoperative hospital stay was 3.67 days (range 2 to 12 days). By applying a one-stage technique, the targeted calix could be entered with a success rate of 97.81%. Conversion to Alken dilation method was not needed in any instance. There was no significant difference in successful calix entrance in those with and without previous open sur- gery (success rate of 96.6% and 98.1%, respectively) and in those with or without staghorn stones (success rate of 97.2% and 98.6%, respectively). In three patients (two with a his- tory of open surgery), renal access dilatation failed because heavy resistance of the fascial prevented the Amplatz dilator from advancing over the guidewire. Kidney hypermobility caused the failure of four dilatation procedures. Visual clar- ity during PCNL was quantified as bad and surgery had to be abandoned in nine cases (2.81%). The procedure was de- ferred in all these patients. A comparison of the preoperative and postoperative hemoglobin was available for 148 proce- dures. The mean hemoglobin decrease was 1.17 g/dL ± 0.84. Four patients required blood transfusions (1.25%). In regard to staghorn stones, no significant difference was noted in the Hb drop (1.38 g/dL for staghorn stones vs. 1.08 g/dL for pa- tient without staghorn stones, P = .13). No major complica- tions, such as visceral, pleural, or vascular injuries, were seen except in three patients. One patient with multiple medical problems and complete complex calculi presented postoperatively a severe hemor- rhage from a nephrostomy tube and received several blood transfusions before being returned to operatory room for nephrectomy. The patient was admitted in the intensive care unit postoperatively and died due to multi organ failure. An- other patient had nephrectomy for persistent bleeding due to a pseudo aneurysm. The embolization was not accessible in our center. The third elderly patient was with a medical history of diabetes and hypertension. He returned on the 6th postoperative day with severe sepsis and received reanima- Figure 1. One shot dilation set. 1578 | tion. The ultrasonography showed a dilation of renal cavities. A double pigtail stent was placed. The patient died 48 hours later from septic shock. No urinary fistula in both groups (ne- phrostomy tube or tubeless procedure) was recorded. Our perioperative complications are summarized in Table 2 according to the Dindo-modified Clavien system proposed as a grading system for perioperative complications in general surgery.(7) At the time of this writing, the cost of the one shot set (Figure 3) in our country is approximately 50 $US. DISCUSSION The dilation of the nephrostomy track is a central step of PCNL and is usually performed by three dilation methods: semirigid fascial dilators (Amplatz) over an 8F guide cathe- ter, metal telescopic dilators (Alken telescopic dilators: ATD) or nephrostomy balloon dilators (BD). Each dilation method has advantages and disadvantages and there have been many attempts and modifications to obtain the best results with minimal kidney damage.(8-11) Balloon dilatation is regarded as the gold standard.(12,13) Although the balloon dilation system has advantages, such as the short dilatation and fluoroscopy time, tamponing of the tract, application of radial forces only and no risk of for- ward perforation,(14) its routine application has been limited because of its relatively high cost especially in centers with limited resources.(15) The use of multiple dilators was time-consuming and with each pass of the dilator injury to the collecting system can result.(12) Also, there is a risk of significant bleeding when a sequential dilator is removed to allow placement of the larger one, because tract is left open, and there is no sheath in place to tamponed the bleeding. To improve dilation results, some authors.(8,16) proposed single-increment dilation and dem- onstrated its safety and feasibility. Travis and colleagues(16) performed percutaneous nephrostomy in dogs with an open approach using a 6F dilator. A comparison of the degree of damage resulting from multi-increment Amplatz dilation, a single increment 24F dilator, metal dilators, and balloon dila- tors was done. This study proved that single-increment dila- tation was as safe as conventional techniques with minimal hemorrhage or parenchymal damage and healing at 6 weeks by a fine linear scar. Frattini and colleagues.(2) who first described the one shot dilation technique, compared ATD, BD and OSD. They showed that mean (standard deviation [SD]) total radiation exposure with telescopic, balloon, and one-shot dilation was 310 (216), 179 (90) and 262 (173) seconds, respectively and found a reduction in the fluoroscopy time during the dilation procedure from 60 to 35 and 20 seconds in the MTD, the BD, and the OSD group, respectively. In our study we observed that tract dilation fluoroscopy time was 25 ± 17 seconds and that total radiation exposure 142 ± 54 seconds. This is similar to the results of other teams using a similar OSD technique. Amjadi and colleagues(3) could re- duce the tract dilation fluoroscopy time from 81 ± 53 seconds in the MDT group to 27 ± 15 seconds in the OSD group. Ziaee and colleagues(15) found a mean time of radiation ex- Figure 2. The Alken guide (arrow) is placed under fluoroscopic guidance (B). Figure 3. The single 25F Amplatz dilator (dark arrow) is pulled in on the Alken guide (white arrow) (A) under fluoroscopic control (B). Endourology And Stone Disease 1579Vol. 11 | No. 03 | May - June 2014 |U R O LO G Y J O U R N A L posure during the whole access of 0.63 ± 0.71 minutes. In our study, mean access time calculated from getting access by needle to the positioning of the working sheath required 2.1 minutes (range 0.7-6.2). This is about 50% decrease in inser- tion time reported by Amjadi and colleagues(3) (5.72 ± 1.75 min for one-shot dilation vs. 10.47 ± 2.97 min for gradual dilation, P = .00) and by Ziaee and colleagues(15) (6.07 ± 4.37 min with no impact of open previous surgery). This shorter time access is probably due to the long experience acquired in ours departments in PCNL since 1997. A much longer ac- cess time of 11.2 minutes for BD, respectively, was recorded by Safak and colleagues.(13) The mean operative time in the present study was 54.8 minutes (range 25 to 137 min). Al- though balloon dilation is generally thought to be associated with shorter operating times,(12,13,17) in a recent PCNL Global Study including 5537 patients,(18) the median operating time with telescopic/serial dilation was 60 minutes vs. 94 minutes for balloon dilation. Our operative time shorter than this reported in the literature was an expected finding. First, because it has been shown that a dilation technique requiring only limited passages or a single step may be less time consuming.(8,16) Secondly, the modified supine position is less time-consuming than the prone position with no need for a position change from the lithotomy to the prone position during the procedure, know- ing that this repositioning is time consuming, more demand- ing for the surgical team and include occupational risk due to shifting of heavy loads, especially in case of obese patients. (4,6) Another advantage of this position is reducing the x-ray exposure because puncture and dilation of the nephrostomy tract are quite perpendicular to the body and the operator’s hands are outside the fluoroscopic field.(19) We believe that combination of one shot dilation and modified supine posi- tion permit the association of advantages of both of these techniques for the patient and for the urologist. Anesthesio- logical advantages to the modified supine position include absence of cardiovascular, respiratory, neuroendocrine and pharmacokinetic problems typical of the prone position, par- ticularly in obese patients.(20) Urological advantages include easier puncture of the kidney, creation of a 2-tiered field to re- spect aseptic conditions and allowed simultaneous antegrade and retrograde endoscopic approach to urinary tract. One shot dilation in modified supine position permits improving radiation safety for both urologist and patient. Bleeding and blood transfusions are common complications of PCNL. Bal- loon dilation is generally considered to cause significantly less blood than did the other techniques.(12) However, in the PCNL Global Study,(18) bleeding was significantly higher with balloon at 9.4% compared with telescopic/serial dila- tion at 6.7%, and transfusions were significantly more com- mon with balloon than telescopic/serial dilation at 7.0% and 4.9%, respectively. Figure 4. A: Insertion of the 30F Amplatz sheath (dark arrow) over the Amplatz dilator (white arrow). B: Fluoroscopic guid- ance allowing the correct placement of the Amplatz sheath in pelvicaliceal system. One Shot Dilatation in PCNL | Harrech et al Table 1. Preoperative patient and stone characteristics. Number of Patients 291 Mean age (years) (range) 50.4 (11 - 81) Male/female 187/104 Number of procedures 320 Solitary kidney 28 Congenital renal abnormalities Horseshoe kidneys 2 Pelvic kidney 5 Calyceal diverticula 6 Previous open surgery 31 Mean stone size (mm) (range) 38 (16-110) Stone location, no. (%) Renal pelvis 135 (42.1) Middle calix 87 (27.1) Lower calix 83 (25.9) Upper calix 45 (14.0) Diverticular calculi 6 (1.8) Staghorn 57 (17.8) 1580 | Our 1.25% transfusion rate does not differ significantly from studies using OSD. In the clinical study by Frattinni and col- leagues(2) one-shot dilation did not lead to more hemorrhagic complications than multiple incremental technique and was statistically less affected by blood losses than pneumatic dilation. In two others studies, Falahatkar and colleagues(1) and Amjadi and colleagues(3) one-shot and telescopic dila- tion had a similar hematologic safety profiles. The mortal- ity in our series was 0.62%. One patient died from urosep- sis despite adequate antibiotic treatment and urine drainage. Sepsis rates reported in the literature vary from 0.97%(21) to 4.7%.(22) Another patient died from multi organ failure due to bleeding despite controlling hemostasis after nephrectomy. Post- operative death has been reported in 0.1-0.7% of pa- tients undergoing PCNL.(23) Our mortality rate, even if considered in the range of those reported in the literature, is probably due to the high propor- tion of difficult cases procedures or ‘‘difficult to treat’’ pa- tients (The American Society of Anesthesiologists score III and IV patients, renal anomalies, solitary kidneys, complex calculi and etc.). The presence of comorbidity, such as re- nal insufficiency, diabetes, morbid obesity, and pulmonary or cardiovascular, has been reported to increase the risk of complications during or after PCNL.(24) The success rate of tract dilation in our study using OSD was 97% at the first procedure. All the attempts during the second procedure and using the same technique were successful witch raises the rate to 100%. In four patients, failure occurred because of kidney hypermobility. In three others patients (two with his- tory of open nephrolithotomy), the failure of dilatation has been attributed to the heavy resistance of the fascial layers that prevented the passage of the Amplatz dilator. In our positioning method, the kidney mobility is similar to what has been reported in the supine position.(25,26) However, we can ask the assistant to perform an extra-abdominal com- pression, during dilation to block the kidney displacement. Besides, we need to make sure we well incise the skin to avoid projection movement during dilation. The dilator con- sistency and the rotational movement of the sheath during gradual advancement decrease the risk of kidney migration. (15) These mechanisms together, might explain the signifi- cantly different failure rates between one-shot dilation (7%) and balloon dilation (17% and would increase to 25% in pa- tients with previous renal surgery).(13,27) In our study, the di- lation failures have been managed by the same OSD in a sec- ond procedure with no need to the MTD. This is different to the choice of Amjadi and colleagues(3) who applied the MDT successfully in 4 cases of failure in 17 OSD cases. Ziaee and Table 2. Intraoperative data, postoperative values and procedural outcomes. Mean operative time (range) 54.8 minutes (25-137) Mean access time (range) 2.1 minutes (0.7-6.2) Tract dilatation fluoroscopy time 25 ± 17 seconds Total X-ray exposure 142 ± 54 seconds Success rate of access, (%) (P > .05) 97.81 Previous open surgery 96.6 No previous open surgery 98.1 Staghorn stones 97.2 No staghorn stones 98.6 Puncture site, no. (%) Lower calyx 166 (51.8) Middle calyx 128 (40) Upper calyx 78 (24.3) Number of tracts, no. (%) 1 276 (86.2) 2 36 (11.2) 3 8 (2.5) Postoperative nephrostomy/tubeless 279/41 Surgery abandoned due to bad visual clarity (%) 9 (2.81%) Mean hemoglobin decrease, g/dL (P = .13) 1.17 ± 0.84 Staghorn stones 1.38 No staghorn stones 1.08 Blood transfusions, no (%) 4 (1.25) Injury of neighboring organs 0 Hydrothorax/ Pneumothorax 0 Collecting system injury necessitating stent 0 Postoperative urinary tract infection, no (%) 10 (3.12) Pseudoaneurysm, no (%) 1 (0.31) Death, no (%) 2 (0.62) Clavien grading, (%) I 12.50 II 10.93 IIIA 3.12 IIIB 0.93 IVA 0.31 IVB 0.00 V 0.62 Endourology And Stone Disease 1581Vol. 11 | No. 03 | May - June 2014 |U R O LO G Y J O U R N A L colleagues(15) also reported seven (7%) failures—three with and four without previous surgery—that were managed by using an MTD. No perforation of the collecting system hap- pened during dilation in our study. Safak and colleagues(13) observed perforations of the collecting system in 11.2% of the cases with BD and 16.6% of those with AD. One-shot dilation also reduces the costs of the PCNL as it is less expensive than BD (the cost of The Nephromax BD system was for about 300 $US) and as the Amplatz dilator can be desterilized, according to our experience. Previous studies also confirm these findings.(17) In ‘‘developing coun- tries,’’ there may less access to BD and with budget restric- tions, the treating urologist might move directly to OSD. We believe that there are potential advantages of OSD compared to standard techniques for percutaneous access. Our findings clearly show that the one-shot procedure is fea- sible and effective in modified supine position. It is applicable for almost all patients with minimal potential complications. The advantages of this dilation technique combined to those of modified supine position include reduced radiation expo- sure time and access time, a shorter operative time, lesser risk for injury to the collecting system and neighboring organs. A limitation of the present study was its observational nature and the absence of control group. This is because this tech- nique is now the first choice for tract dilation for PCNL in adult patients in our department. Indeed, in 2002, McCulloch and colleagues(28) proposed that ‘‘detailed prospective audit data collection is essential for surgical research’’ as there are many obstacles to performing randomized controlled trials (RCTs) of surgical techniques, meaning that the quantity and quality of clinical research in surgery is limited, and general surgical practice is less likely to be based on RCT evidence than general medical practice.(28-31) CONCLUSION Percutaneous access can be safely and successfully obtained by one shot dilation even in modified supine position. The use of this dilation technique in modified supine position combines their both advantages including less radiation ex- posure and shorter access and operative time. It is applicable in almost every adult patient regardless of kidney anomalies, previous open renal surgery or staghorn calculi. The one shot dilation is also cost effective, easy to learn and offers a poten- tial alternative to the standard devices particularly in devel- oping countries. Further analysis and comparative studies are necessary to confirm these results. CONFLICT OF INTEREST None declared. REFERENCES 1. Falahatkar S, Neiroomand H, Akbarpour M, Emadi SA, Khaki N. One- shot versus metal telescopic dilation technique for tract creation in percutaneous nephrolithotomy: Comparison of safety and efficacy. J Endourol. 2009;23:615-8. 2. Frattini A, Barbieri A, Salsi P, et al. One shot: A novel method to dilate the nephrostomy access for percutaneous lithotripsy. J Endourol. 2001;15:919-23. 3. Amjadi M, Zolfaghari A, Elahian A, Tavoosi A. Percutaneous neph- rolithotomy in patients with previous open nephrolithotomy: One- shot versus telescopic technique for tract dilatation. J Endourol. 2008;22:423-5. 4. El Harrech Y, Ghoundale O, Zaini R, Moufid K, Touiti D. La NLPC en décubitus dorsal modifié : notre expérience. Can Urol Assoc J. 2011;5:261-5. 5. Saussine C, Lechevallier E, Traxer O. PCNL: technical variations. Prog Urol. 2008;18:897-900. 6. Lezrek M, Ammani A, Bazine K, et al. The split-leg modified lateral position for percutaneous renal surgery and optimal retrograde ac- cess to the upper urinary tract. Urology. 2011;78:217-20. 7. Dindo D, Demartines N, Clavien PA. Classification of surgical compli- cations: a new proposal with evaluation in a cohort of 6336 patients and results of a survey. Ann Surg. 2004;240:205-13. 8. Rusnak B, Castañeda-Zuñiga W, Kotula F, Herrera M, Amplatz K. An improved dilator system for percutaneous nephrostomies. Radiol- ogy. 1982;144:174. 9. Patil AV. A Novel 5-Part Percutaneous Access Needle With Guide- wire Technique (5-PANG) for Percutaneous Nephrolithotomy: Our Initial Experience. Urology. 2010;75:1206-8. 10. Baldwin DD, Maynes LJ, Desai PJ, Jellison FC, Tsai CK, Barker GR. A Novel Single Step Percutaneous Access Sheath: The Initial Human Experience. J Urol. 2006;175:156-61. 11. Maynes LJ, Desai PJ, Zuppan CW, Barker BJ, Zimmerman GJ, Baldwin DD. Comparison of a Novel One-Step Percutaneous Nephrolithoto- my Sheath with a Standard Two-Step Device. Urology. 2008;71:223- 7. 12. Davidoff R, Bellman GC. Influence of technique of percutane- ous tract creation on incidence of renal hemorrhage. J Urol. 1997;157:1229-31. 13. Safak M, Gogus C, Soygur T. Nephrostomy tract dilation using a balloon dilator in percutaneous renal surgery: Experience with 95 cases and the comparison with the fascial dilator system. Urol Int. 2003;71:382-4. 14. Wezel F, Mamoulakis C, Rioja J, Michel MS, de la Rosette J, Alken P. Two Contemporary Series of Percutaneous Tract Dilation for Percu- taneous Nephrolithotomy. J Endourol. 2009;23:1655-61. One Shot Dilatation in PCNL | Harrech et al 1582 | Endourology And Stone Disease 15. Ziaee SA, Karami H, Aminsharifi A, Mehrabi S, Zand S, Javaherfo- rooshzadeh A. One-Stage Tract Dilation for Percutaneous Nephroli- thotomy: Is It Justified? J Endourol. 2007;21:1415-20. 16. Travis DG, Tan HL, Webb DR. Single-increment dilatation for percutaneous renal surgery: an experimental study. Br J Urol. 1991;68:144-7. 17. Gönen M, Istanbulluoglu OM, Cicek T, Ozturk B, Ozkardes H. Balloon dilatation versus Amplatz dilatation for nephrostomy tract dilata- tion. J Endourol. 2008;22:901-4. 18. Lopes T, Sangam K, Alken P, Barroilhet BS, Saussine C, Shi L, de la Rosette J. Clinical Research Office of The Endourological Society Percutaneous Nephrolithotomy Study Group. The Clinical Research Office of the Endourological Society Percutaneous Nephrolithoto- my Global Study: tract dilation comparisons in 5537 patients. J En- dourol. 2011;25:755-62. 19. Valdivia Uria JG, Valle Gerhold J, Lopez Lopez JA, et al. Technique and complications of percutaneous nephroscopy: experience with 557 patients in the supine position. J Urol. 1998;160:1975–8. 20. Ibarluzea G, Scoffone CM, Cracco CM, et al. Supine Valdivia and modified lithotomy position for simultaneous anterograde and ret- rograde endourological access. BJU Int. 2007;100:233-6. 21. Aron M, Yadav R, Goel R, et al. Multi-tract percutaneous nephroli- thotomy for large complete staghorn calculi. Urol Int. 2005;75:327- 32. 22. Vorrakitpokatorn P, Permtongchuchai K, Raksamani EO, Phettong- kam A. Perioperative complications and risk factors of percutane- ous nephrolithotomy. J Med Assoc Thai. 2006;89:826-33. 23. Unsal A, Resorlu B, Atmaca AF, et al. Prediction of Morbidity and Mortality After Percutaneous Nephrolithotomy By Using the Charl- son Comorbidity Index. Urology. 2012;79:55-60. 24. Labate G, Modi P, Timoney A, et al, Rosette On Behalf Of The Croes Pcnl Study Group J. The percutaneous nephrolithotomy global study: classification of complications. J Endourol. 2011;25:1275-80. 25. Valdivia-Uria JG, Valle J, Villarroya S. Why is percutaneous nephros- copy still performed with patient prone? J Endourol. 1990;4:269-72. 26. De Sio M, Autorino R, Quarto G, et al. Modified supine versus prone position in percutaneous nephrolithotomy for renal stones treat- able with a single percutaneous access: a prospective randomized trial. Eur Urol. 2008;54:196-202. 27. Joel AB, Rubenstein JN, Hsieh MH, Chi T, Meng MV, Stoller ML. Failed percutaneous balloon dilation for renal access: Incidence and risk factors. Urology. 2005;66:29-32. 28. McCulloch P, Taylor I, Sasako M, Lovett B, Griffin D. Randomised trials in surgery: Problems and possible solutions. BMJ. 2002;324:1448- 51. 29. Farrokhyar F, Karanicolas PJ, Thoma A, et al. Randomized controlled trials of surgical interventions. Ann Surg. 2010;251:409-16. 30. Ellis J, Mulligan I, Rowe J, Sackett DL. Inpatient general medicine is evidence based. A-Team, Nuffield Department of Clinical Medicine. Lancet. 1995;346:407-10. 31. Howes N, Chagla L, Thorpe M, McCulloch P. Surgical practice is evi- dence based. Br J Surg. 1997;84:1220-3.