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Objective: The aim of this study was to compare the efficacy and safety of minimally invasive percutaneous nephrolithotomy (MIP) and conventional percutaneous nephrolithotomy (PCNL) in the treatment of patients with large renal stone burden. MIP has proven its efficacy and safety in the management of small renal calculi. However, conventional PCNL is still considered the standard method for treatment of large renal stones in the upper urinary tract., Materials and Methods: A search of two longitudinal databases in two tertiary referral centres for complex stone disease identified 133 consecutive patients who were treated by either MIP or PCNL for renal stones 20 mm or larger between January 2009 and August 2012. Clinical data and outcome measures of the two methods were compared by Student's t test, chi-squared test or Fisher's exact test. A p value less than 0.05 was considered statistically significant., Results: Operative time was significantly shorter and hospital stay was significantly longer in conventional PCNL compared to MIP (p = 0.002 and < 0.001, respectively). There were no significant differences in primary stone-free rate or complication rate between the two methods. Only higher graded complications (above Clavien grade II) were significantly more common in conventional PCNL (p = 0.02)., Conclusion: MIP is equally effective as conventional PCNL in the treatment of large renal calculi. Both methods have a similar complication rate. The shorter operative time in PCNL may be based on the larger diameter and quicker retrieval of large fragments; the longer mean hospital stay may be caused by the handling of the nephrostomy tube. The current data suggest that the choice of the method mainly depends on the surgeon's preference.

Purpose: Passive removal of stone fragments in the irrigation stream is one of the characteristics in continuous-flow PCNL instruments. So far the physical principle of this so-called vacuum cleaner effect has not been fully understood yet. The aim of the study was to empirically prove the existence of the vacuum cleaner effect and to develop a physical hypothesis and generate a mathematical model for this phenomenon., Methods: In an empiric approach, common low-pressure PCNL instruments and conventional PCNL sheaths were tested using an in vitro model. Flow characteristics were visualized by coloring of irrigation fluid. Influence of irrigation pressure, sheath diameter, sheath design, nephroscope design and position of the nephroscope was assessed. Experiments were digitally recorded for further slow-motion analysis to deduce a physical model., Results: In each tested nephroscope design, we could observe the vacuum cleaner effect. Increase in irrigation pressure and reduction in cross section of sheath sustained the effect. Slow-motion analysis of colored flow revealed a synergism of two effects causing suction and transportation of the stone. For the first time, our model showed a flow reversal in the sheath as an integral part of the origin of the stone transportation during vacuum cleaner effect. The application of Bernoulli's equation provided the explanation of these effects and confirmed our experimental results., Conclusions: We widen the understanding of PCNL with a conclusive physical model, which explains fluid mechanics of the vacuum cleaner effect.

Purpose: To describe the evolution of the current technique in percutaneous nephrolithotomy (PCNL) with a special focus on access tract closure techniques., Methods: A systematic review of outcomes and complications of tubeless PCNL was conducted using the MEDLINE and Pubmed databases between 1976 and 2014., Results: During the past decade, PCNL underwent fundamental modifications due to miniaturization of the instruments and advancements in technique. The routine use of the nephrostomy tube after PCNL has been subsequently questioned. Currently, the nephrostomy tube is increasingly omitted, and the access tract is usually sealed by haemostatic agents. An additionally ureteric stent is commonly inserted at the end of the procedure. However, the application of haemostatic sealants increases the immediate costs significantly. Still there are inconsistent data because of small study populations, lack of randomization, retrospective character and further more heterogeneous surgical techniques., Conclusion: The current body of literature does not provide high-level evidence for the preferred treatment of the access tract in PCNL. However, most authors agree that a tract sealing can be omitted without increasing the risk of complication in uncomplicated procedures.

Introduction: Percutaneous stone removal increasingly plays an important role among the different approaches of interventional stone therapy, particularly since the development of miniaturized instruments is resulting in lower morbidity for the patients. One major drawback of smaller instruments is the increased difficulty of stone retrieval after disintegration due to the reduced tract diameter. This results in longer operation time and the need of additional tools such as disposable retrieval baskets. One of the key factors in the development of minimally invasive percutaneous nephrolitholapaxy (MIP) was the design of an Amplatz sheath which provides a built-in vacuum cleaner effect for stone retrieval., Methods: A series of flow analyses with the gauges and shapes of the most commonly used nephroscopes and sheaths in percutaneous nephrolitholapaxy was performed by computational fluid dynamics. Flow velocity and direction in front of the nephroscope were computed and visualized by the software., Results: In our study, the vacuum cleaner effect developed exclusively when a round-shaped nephroscope was used (Nagele Miniature Nephroscope System, Karl Storz GmbH & Co. KG) and depended on the relation between nephroscope diameter and inner sheath diameter. The strongest effect was observed with a 12 F nephroscope and an inner sheath diameter of 15 F. It did not develop when an oval- or crescent-shaped nephroscope was used. In front of the distal end of the round-shaped nephroscope, a slipstream develops, induced by the excursive change of width of the fluid flow on the outlet of the flushing canal. This allows the adhesion of a stone fragment in the eddy while the fluid flow is circulating around the stone., Conclusion: This study illustrates and explains the vacuum cleaner effect which has been detected in the development of the Nagele Miniature Nephroscope System used in MIP. It combines the reduced morbidity of smaller kidney puncture diameters with the benefit of quick and complete stone removal.

Introduction: Aim of this study was to investigate whether the combination of high-pressure irrigation inflow combined with simultaneous sensor-controlled suction could improve irrigation turnover without leading to high peak intrarenal pressure in small-calibre percutaneous instruments (SCPI). M + M: A MIP XS sheath (9.5 Fr. outer diameter and 8.5 Fr. inner diameter) and a 7.5-Fr. nephroscope (3-Fr. irrigation channel; MIP XS by Nagele, Karl Storz, Tuttlingen, Germany) was inserted into the collecting system of a non-perfused cadaveric porcine kidney, an 8-Fr. mono-J catheter was introduced through the ureter. Irrigation was performed using a pressure-controlled, combined irrigation/suction pump (Uromat E.A.S.I., Karl Storz, Tuttlingen, Germany) in either single-flow or continuous-flow (=combination of irrigation and suction) mode. Intrarenal pressure was measured and irrigation fluid turnover was measured by a cystometry catheter inserted trans-parenchymally into the renal pelvis. Pressure changes were recorded by a urodynamic workstation., Results: Applying pressure-controlled suction, irrigation fluid turnover could be increased by 5 % at an inflow pressure of 75 mmHg (80-84 ml/min) and 15 % at an inflow pressure of 110 mmHg (196-110 ml/min). Suction decreased the intrarenal pressure by 14 % at 75 mmHg (19-14.5 cm H2O) and 28 % at 110 mmHg inflow pressure (37-26.5 cm H2O)., Conclusion: Although combination of pressure irrigation with sensor-controlled suction increases irrigation flow in SCPI, the intrarenal pressure could be reduced with combined suction via a transurethral mono-J catheter. This irrigation method in percutaneous surgery is called purging effect.

Purpose: To widen the understanding of the fluid mechanics during percutaneous nephrolithotomy (PCNL), a new in vitro model for empiric studies was developed. Our first aim was to characterize common PCNL systems with regard to their intrapyelocaliceal pressure and their irrigation flow volume as possible parameters of hydrodynamic invasiveness., Materials and Methods: The model is based on a watertight cylindrical cast. Low pressure miniaturized PCNL (miniPCNL) systems and conventional PCNL systems were tested. Intrapelvic pressure and the total of irrigation flow volume per minute were measured for each PCNL system at 10 predefined levels of irrigation pressure between 40 and 130 cm H2O., Results: Linear regression showed a linear relation between irrigation pressure and intrapelvic pressure. Compared with miniPCNL systems, conventional PCNL sheaths with closed Rutner sidearm generate significantly higher intrapelvic pressures. Opening the Rutner sidearm leads to a decrease in intrapelvic pressure to the level of the open mini PCNL systems. Polynomal regression revealed a square root relation between irrigation pressure and irrigation flow volume., Conclusions: Our in vitro model is suitable for obtaining reliable and valid data of intrapelvic pressure and irrigation flow volume of commonly used PCNL systems. Conventional PCNL sheaths with opened Rutner sidearm provide intrapelvic pressure and irrigation volume similar to miniPCNL. Consequently, a relevant difference of the hydrodynamic impact between conventional and miniPCNL systems are not necessarily to be assumed. Regression analysis revealed a new starting point for further empiric research of fluid mechanics during PCNL.

Since the introduction of the percutanous nephrolitholapaxy (PNL), the instruments as well as the technique have experienced a tremendous modification. The miniaturisation of the instruments has led to a decreased hospital stay, reduced analgetic use as well as an extension of the indication for PNL. A nephrostomy tube was normally inserted to prevent urinoma and to provoke renal haemostasis. In 1997, the necessity for the regular use of a nephrostomy tube was first questioned. In a prospective study, the nephrostomy tube was successfully omitted in 50 selected patients. Since then, increasingly, the nephrostomy tube is omitted. Alternatively, different haemostatic substances are used for renal tract closure. The necessity for the use of these agents is still unclear., (© Georg Thieme Verlag KG Stuttgart · New York.)

Purpose: There is a lack of studies comparing shock wave lithotripsy (SWL), retrograde intrarenal surgery (RIRS) and minimally invasive percutaneous nephrolithotomy (MIP) in renal stone treatment. This study compared treatment outcome, stone-free rate (SFR) and stone-free survival (SFS) with regard to stone size and localization., Methods: This analysis included 482 first-time-treated patients in the period 2001-2007. Detailed clinical information, stone analysis and metabolic evaluation were evaluated retrospectively. Outcome, SFR and SFS were analyzed with regard to size (<1 vs. ≥1 cm) and localization (lower vs. non-lower pole)., Results: Higher SFRs in lower and non-lower pole stones ≥1 cm were confirmed for RIRS and MIP (p < 0.0001). A regression model confirmed a higher risk of non-lower pole stone persistence for SWL versus RIRS (OR: 2.27, p = 0.034, SWL vs., Mip (or: 3.23, p = 0.009) and larger stone burden ≥1 versus <1 cm (OR: 2.43, p = 0.006). In accordance, a higher risk of residual stones was found in the lower pole for SWL versus RIRS (OR: 2.67, p = 0.009), SWL versus, Mip (or: 4.75, p < 0.0001) and stones ≥1 cm versus <1 cm (OR: 3.02, p = 0.0006). In RIRS and MIP patients, more complications, stenting, prolonged disability, need/duration of hospitalization and analgesia were noticed (p < 0.05). Overall SFS increased from SWL, RIRS, to MIP (p < 0.001). SWL showed lower SFS for non-lower pole (p = 0.006) and lower pole stones (p = 0.007)., Conclusions: RIRS and MIP were shown to have higher stone-free rates and SFS compared to SWL. The price for better outcome was higher, considering tolerable complication rates. Despite larger preoperative stone burden, MIP achieved high and long-term treatment success.

Objective: To compare the safety and efficacy of minimally invasive percutaneous nephrolitholapaxy (MIP) between small (<2 cm) and large (>2 cm) renal calculi, because although MIP has proved its efficacy in small lower caliceal stones, the efficacy in large renal calculi has been questioned., Materials and Methods: The data from 191 consecutive minimally invasive percutaneous nephrolithotomy (MIP) procedures at a single institution from January 2007 to March 2011 were reviewed retrospectively. All stone sizes and complexity were included (98 were <2 cm and 93 were ≥ 2 cm). We performed a comparative analysis of procedures for calculi <2 cm and ≥ 2 cm regarding the stone-free rate, the need for auxiliary procedures, and complications. The Student t test for parametric continuous variables and the chi-square test or Fischer's exact test for nominal variables were applied., Results: The primary stone-free rate was significantly lower for the large than for the small stones (76.3% vs 90.8%, P = .007), and the secondary stone-free rate after one auxiliary procedure (second-look percutaneous nephrolithotomy, ureterorenoscopy, or shock wave lithotripsy) was not significantly different between the 2 groups (94.6% vs 98.9%, P = .1). The total complication rate was not significantly different (26.9% vs 19.4%, P = .2) between the 2 groups either. Grade III complications occurred in 5.2% of all patients, and no grade IV or V complications were observed., Conclusion: Using MIP, the total stone-free rate was greater for the small than for the large calculi; however, most patients could be rendered stone-free with the use of one auxiliary procedure. The high success rate and low rate of higher grade complications justify the application of MIP for large stones., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Unlabelled: Study Type--Therapy (case series) Level of Evidence 4. What's known on the subject? and What does the study add? The minimally invasive percutaneous nephrolitholapaxy (MIP) has shown high efficacy and safety for the management of small renal stones. It was initially developed to overcome a gap between the minimally invasive extracorporeal shockwave lithotripsy and invasive conventional percutaneous nephrolitholapaxy (PCNL) in the management of low stone burden but there is debate as to whether the MIP is also effective for larger stones. The present study shows the high efficacy and safety of MIP, which is comparable to conventional PCNL in the treatment of stones of >20 mm, including complex staghorn stones., Objective: • To evaluate the safety and efficacy of minimally invasive percutaneous nephrolitholapaxy (MIP) in the management of large and complex renal calculi., Patients and Methods: • From January 2007 to March 2011, 73 patients with 83 renal units with large renal stones (>20 mm in diameter) were retrospectively evaluated. • Stones were classified into simple (isolated renal pelvis or isolated calyceal stones) or complex (partial or complete staghorn stones, renal pelvis stones with accompanying calyceal stones). • Stone-free rate, complications according to the modified Clavien system, decrease in haemoglobin, creatinine level, operative duration and hospital stay were compared for simple and complex renal calculi., Results: • The mean (sd) stone size was 36.7 (23.37) mm and mean operative duration was 99.2 (48.3) min. • In all, 65 cases (78.3%) were stone-free after the first procedure and another 14 needed an auxiliary procedure (four second-look percutaneous nephrolitholapaxy, nine ureterorenoscopy, and one extracorporeal shockwave lithotripsy) to become stone-free, resulting in a 95.2% stone-free rate. • Complications occurred in 22 procedures (26.5%), 17 of them were Clavien Grade 1 or 2 (20.5%), five were Grade 3 (6%). There were no Grade 4 or 5 complications. • The only significant difference between complex and simple stones was the stone-free rate (96.9% vs 66.7%, P = 0.001)., Conclusion: • The MIP technique is effective and safe for larger stones with low morbidity, good success rate and reasonable operative duration., (© 2012 BJU INTERNATIONAL.)

Purpose: The aim of this study was to compare a novice surgeon with an expert surgeon independently performing minimally invasive percutaneous neprolitholapaxy (PCNL) excluding the influence of the expert in the learning curve., Methods: Clinical records of 84 patients (novice: n = 35; expert: n = 49) undergoing minimally invasive PCNL between 04/2007 and 04/2008 were retrospectively reviewed for the following parameters: drop in hemoglobin, operative and fluoroscopy time, length of hospital stay, stone-free rate and complication rate. Complications were graded according to the Clavien classification. Statistical analysis was carried out by student's t test (Chi-square test) with p < 0.05 considered significant., Results: The novice surgeon experienced longer median operative and fluoroscopy time, lower stone-free rate and higher re-treatment rate (all p < 0.005) but no longer length of hospital stay (p = 0.19) compared to the experienced surgeon. The novice showed a notable improvement in operating time (p = 0.0208). Altogether, 16 complications occurred in 84 minimally invasive PCNL (19.1%) with five patients (6.0%) encountering grade III complications. Four patients (8.2%) treated by the expert surgeon developed complications (all grade I/II) compared to 12 of the patients (34.3%) treated by the novice surgeon (p = 0.0265). All grade III complications occurred in the first 20 patients of the novice surgeon group., Conclusions: Despite longer operating time and a lower initial stone-free rate, the novice showed a significant improvement with growing experience and a low rate of higher grade (≥IIIa) complications. This demonstrates that the concept of minimally invasive PCNL can also be learned by urologists who do not have the support of an experienced colleague without endangering patient safety.

Purpose: The optimal treatment options for lower pole stones with a diameter below 15 mm are controversially discussed. Extracorporeal shock wave lithotripsy (ESWL) is non-invasive but is hampered by low stone-free rates and a significant retreatment rate. Flexible ureterorenoscopy (URS) has been demonstrated to have high stone-free rates but the treatment costs - consisting of OR time, repair costs and expenditure for laser fibers, guide wires and stone baskets - as well as low stone-free rates with increasing stone size render this procedure highly expensive. Minimally invasive percutaneous litholapaxy (MIP) has shown low morbidity and high efficacy in the treatment of nephrolithiasis. The goal of this study was to investigate the efficacy and -safety of MIP for the treatment of small lower pole stones., Patients and Method: The charts of 29 patients who were treated with MIP were reviewed and clinical data like OR time, drop in haemoglobin, complication rate, stone-free rate and duration of hospital stay were collected., Results: 28 of 29 patients were primarily stone-free; one had to undergo additional flexible URS to become stone-free. All procedures were undertaken with only one access, no severe complications occurred; none of the patients had to be transfused., Conclusions: The MIP concept has a low complication rate and has been shown to be safe and effective in previous studies. We demonstrate that the feasibility and efficacy justify the percutaneous approach also for small lower pole stones., (Georg Thieme Verlag Stuttgart * New York.)

Minimally invasive percutaneous nephrolithopaxy (MIP) was developed to combine the excellent stone-free rates of the conventional percutaneous nephrolithopaxy (PCNL) technique with the low morbidity of the miniaturized PCNL (Mini-Perc) and, at the same time, achieve a high level of patient comfort. The procedure is characterized not only by the diameter of the miniaturized 18-Fr Amplatz sheath that was adopted from the Mini-Perc but also by the following features: ultrasound-guided puncture of the kidney; single-step dilatation of the access tract; ballistic lithotripsy; a low-pressure irrigation system together with stone retraction by irrigation with a specially designed nephroscope sheath, for the so-called vacuum cleaner effect; and a sealed and tubeless access tract with primary closure of the channel independent of hemorrhage and without a second-look procedure.The results of the first 57 patients demonstrate primary stone-free rates of 92.9% with operating times averaging 62 (25-123) min. Severe complications, such as sepsis or bleeding requiring blood transfusion, did not occur. The high and predictable stone-free rate and a low morbidity comparable to that of ureteroscopy and extracorporeal shock-wave lithotripsy make MIP an attractive option for patients and urologists. The "vacuum cleaner effect" with quick removal of stone fragments reduces operating time and prevents new stone formation by avoiding residual fragments. The direct and primary closure of the access tract increases patient comfort and is justified by the reintervention rate of less than 8% in the presented cohort.The lack of a need for second-look nephroscopies, the vacuum cleaner effect, improved patient comfort without nephrostomy tubes, as well as surgery times comparable to that of traditional PCNL demonstrate a consequent evolution of the Mini-Perc. MIP therefore represents a promising and future-oriented module in modern stone therapy.

Due to its particular anatomical position below the ureteropelvic junction, the lower pole group of calices plays a special role in the treatment of nephrolithiasis. The extracorporeal shock-wave lithotripsy (ESWL) often attains dissatisfactory stone-free rates, even after optimal disintegration of lower pole stones, and thus necessitates secondary therapeutic procedures. Due to the favorable stone-free rates, retrograde intrarenal surgery with its low complication rate has taken up an important role in the treatment of lower pole stones since the development of modern flexible ureterorenoscopes. The long treatment times in the case of a large stone burden and considerable costs for materials constitute limiting factors. In line with the advancement of percutaneous nephrolitholapaxy (PCNL), a promising method also for the treatment of larger lower pole stones is available today with minimally invasive PCNL (MIP).

Background: The spectrum of percutaneous stone treatment was significantly widened following the introduction of the miniaturized percutaneous nephrolitholapaxy. At the end of the procedure usually a nephrostomy tube was placed to avoid urine paravasation and prolonged bleeding. In this work the tube-less mini-PCNL with direct closure of the access tract was compared to traditional mini-PCNL with placement of the nephrostomy tube., Patients and Methods: Twenty consecutive patients undergoing mini-PCNL with placement of a nephrostomy tube at the end of the procedure were compared to 20 consecutive patients with direct closure of the access tracts following percutaneous stone removal. Clinical data like decrease in Hb, complications, need for analgesics and duration of hospital stay were compared., Results: Both groups underwent the procedure without complications. There was no need for blood transfusions. The difference in total analgetic dose was not statistically significant; however, patients in the nephrostomy group needed analgetics for a longer period of time. There was no difference in duration of hospital stay (3.2 days in the tube-less group versus 3.4 days in the nephrostomy group). The primary stone-free rate was higher in the group with direct closure of the access tract (95 versus 85%)., Conclusions: Closure of the percutaneous access following mini-PCNL with a gelatine-thrombin-haemostatic sealant is a safe alternative to the commonly used nephrostomy tube and can help to reduce postoperative pain and patient discomfort.

Introduction: Whereas a retrograde attempt to insert an indwelling stent is performed in lithotomy position, usually renal access is gained in a prone position. To overcome the time loss of patient repositioning, a renal puncture can be performed in a modified lithotomy position with torqued truncus and slightly elevated flank. There is a two-fold advantage of this position: transurethral and transrenal access can be obtained using a combined approach. In the present study, this simple technique is used to position a floppy guide wire through a modified needle directly through the renal pelvis into the ureter., Materials and Methods: The kidney is punctured in the modified lithotomy position under sonographic control using an initial three-part puncture needle. A floppy tip guide-wire is inserted into the collecting system via the needle after retrieving the stylet. The retracted needle is bent at the tip while the guide-wire is secured in the needle and the collecting system. The use of the floppy tip guide-wire helps to insert the curved needle back into the kidney pelvis, which becomes the precise guidance for the now steerable wire. The desired steerable stent is positioned under radiographic control in a retrograde fashion over the endoscopically harbored tip of the guide-wire. Two patient cohorts (newly described method and conventional method) were compared., Results: The presented steering procedure saves 16.5 mean minutes compared to the conventional antegrade stenting and 79.5 Euros compared to the control group., Conclusion: The described combined antegrade-retrograde stent placement through a bent three-part puncture needle results in both clinical superiority (OR time, success rate) and financial benefits.

Objectives: To investigate the outcomes using gelatine matrix hemostatic sealant to close the tract after mini-percutaneous nephrolithotomy (mini-PCNL), resulting in a tubeless setting., Methods: After complete stone removal after mini-PCNL, a double-J ureteral stent was placed in an antegrade manner. After withdrawing the 17F Amplatz sheet from the collecting system under direct vision without irrigation, the urothelium collapsed. While retracting the sheet further, the gelatine matrix hemostatic sealant was injected. The skin incision was closed with glue. An ultrasound examination was performed on the first postoperative day to exclude the presence of urine extravasation., Results: Mini-PCNL was performed in 11 patients, either as a primary, small stone, single-access procedure or as a second-look mini-PCNL because of small residual fragments after extracorporeal shock wave lithotripsy. The time to seal the mini-PCNL tract through the kidney parenchyma was 2 to 5 minutes. The mean operative time was 79 minutes. In the first 5 cases, intravenous urography was performed in addition to ultrasonography and demonstrated an intact collecting system. The subsequent procedures demonstrated similar findings, with the exception of 1 case of temporary paravasation. In all other patients, the catheter was removed on the first postoperative day. Ten of 11 patients had an uneventful follow-up until removal of the double-J catheter. No major complications were observed., Conclusions: Closing the tract of the mini-PCNL with gelatine matrix hemostatic sealant is a safe and fast alternative and provides the option of discharging the patient in good condition without the commonly used nephrostomy tube.