World J Urol DOI 10.1007/s00345-015-1486-7
ORIGINAL ARTICLE
Flow matters 2: How to improve irrigation flow in small‑calibre percutaneous procedures—the purging effect Udo Nagele · Ute Walcher · Markus Bader · Thomas Herrmann · Stephan Kruck · David Schilling
Received: 9 November 2014 / Accepted: 6 January 2015 © Springer-Verlag Berlin Heidelberg 2015
Abstract 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.
This is a paper from the Training and Research in Urological Surgical Therapy (T.R.U.S.T.) group.
Keywords Minimally invasive percutaneous stone treatment (MIP) · Microperc · Irrigation flow · Intrarenal pressure · Purging effect
U. Nagele (*) · U. Walcher Department of Urology and Andrology, General Hospital Hall in Tirol, Milser Str. 10, Hall i.T. 6060, Austria e-mail: [email protected] M. Bader Community Hospital Ebersberg, Ebersberg, Germany T. Herrmann Hannover Medical School, Hannover, Germany S. Kruck University Hospital Tübingen, Tübingen, Germany D. Schilling University Hospital Frankfurt am Main, Frankfurt am Main, Germany
Introduction Percutaneous nephrolitholapaxy is a standard procedure for the treatment of renal stone disease. Recently, the use of new-generation small-calibre percutaneous instruments (SCPI) with less than 12 Fr. outer diameter of the sheath has gained popularity due to its reduced invasiveness [2, 3]; especially, the reduced intraoperative blood loss has been pointed out as a major advantage of the miniaturized instruments [9, 16]. However, in our experience, the reduced diameter of the instruments comes to the cost of a reduced irrigation flow due to the small in- and outflow channels,
13
leading to impaired visibility even in case of minor bleeding. Whereas inflow characteristics in small-calibre percutaneous instruments (SCPI) are similar to flexible ureteroscopes and can be improved by the use of high-pressure irrigation systems [8], the outflow in new-generation openbore systems is the limiting factor for high irrigation fluid turnover due to the small calibre of the sheaths. The mismatch between in- and outflow can cause high intrarenal pressure and lead to pyelo-tubular reflux. The open sheath designs of the larger diameter first-generation miniaturized instruments [13] are not sufficient for pressure control in SCPI because of the unfavourable ratio of the small inner diameter of the sheath and relatively larger nephroscope diameter which is necessary for scope stability. To guarantee a high irrigation fluid turnover without risking high intrarenal pressure, the outflow through the ureter can be improved. For this reason, the use of retrogradely placed access sheaths has been proposed in miniaturized percutaneous procedures. However, this has several drawbacks like misplacement or intraprocedural dislocation [6]. These drawbacks can be overcome by the use of a mono-J catheter as it is standard in percutaneous procedures. Aim of this study was to investigate whether the use of a modified 8-Fr. mono-J catheter together with a pressure sensor-controlled pump (Uromat E.A.S.I.) improves irrigation capacity without increasing intrarenal pressure.
Materials and methods A fresh cadaveric porcine kidney was placed in a tray. The kidney was punctured through the upper calyx in a retrograde fashion (inside out through the ureter) and access was established with a single-step dilatation with an angiographic introducer set 6 Fr. (Cordis Corporation, Miami Lakes, FL, USA). A second puncture was made in the lower calyceal system and a single-step dilatation was performed with an 8.5-Fr. dilatator and a 9.5-Fr.-outerand 8.5-Fr.-inner-diameter nephroscope sheath (both Karl Storz, Tuttlingen, Germany) was placed inside the pyelon. The ureter was stented with a modified 8-Fr. mono-J catheter with multiple large bore holes at the tip of the catheter to avoid occlusion by aspiration of mucosa during suction (Optimed, Karlsruhe, Germany). The ureter was tied around the mono-J catheter for secure fixation. After verification of the correct position of the angiographic introducer in the collecting system using a 7.5-Fr. nephroscope (MIP XS by Nagele, Karl Storz, Germany), a 5-Fr. cystometry catheter (Andromeda, Taufkirchen, Germany) was placed inside the pyelon under nephroscopic guidance. The mono-J catheter, the cystometry catheter and the Amplatz sheath as well as the nephroscope were fixed on the working table to avoid pressure peak artefacts by
13
World J Urol
Fig. 1 Experimental setup—a 9.5-Fr. Amplatz sheath was introduced through the lower calyx and an 8-Fr. ureteric catheter was inserted through the ureter of the collecting system of a non-perfused porcine kidney. An 8-Fr. ureteric catheter was inserted through the upper calyx, and intrapelvic pressure was analysed applying different irrigation pressures with and without sensor-controlled suction via the ureteric catheter
manipulation during the experiment. Intrarenal pressure was measured with a urodynamic workstation (Andromeda, Taufkirchen, Germany) in cm H2O. Irrigation was performed with a Uromat E.A.S.I pump system. This roller pump system can be used either in a single-flow mode (irrigation inflow via nephroscope, passive outflow through mono-J) or continuous-flow mode (irrigation inflow via nephroscope, suction-controlled outflow via mono-J catheter). In continuous-flow mode, the outflow was adjusted by a pressure sensor measuring the inflow pressure, guaranteeing a steady state inside the renal pyelon. The nephroscope was a minimally invasive percutaneous nephroscope system (MIP) by Nagele with a 7.5-Fr. tip and a 3-Fr. irrigation channel and a 2-Fr. working channel. Two 2-min trials were recorded for each setting, measuring with single and continuous flow using 75 mmHg inflow pump pressure and in continuous flow presetting of 60 ml/ min and 110 mmHg pump pressure and presetting of 70 ml/ min in continuous flow. Intrarenal pressure and total irrigation volume per time interval were measured during each trial. The experimental set up is shown in Fig. 1.
Results The intrarenal pressure reached a plateau within seconds after initiating irrigation flow and no pressure peaks
World J Urol
Fig. 2 Intrapelvic pressure and irrigation flow at different inflow pressures with and without sensor-controlled suction: intrarenal pressure at 75 (a) and 110 mmHG (b) inflow. Irrigation flow turnover at
75 (c) and 110 mmHg (d). Each experiment was performed either with continuous-flow (sensor-controlled suction) or single-flow mode
were observed during the whole measurement interval, indicating homogeneous flow conditions throughout the experiment. Independently from the inflow irrigation pressure, single-flow irrigation showed higher intrarenal pressure and a lower irrigation flow than continuous-flow irrigation: at 75 and 110 mmHg, inflow pressure mean irrigation flow turnover was increased by 5 % (80–84 ml/min) and 15 % (96–110 ml/min), respectively, while intrarenal pressure was decreased by 14 % (19–14.5 cm H2O) and 28 % (37– 26.5 cm H2O), respectively when combining high-pressurecontrolled inflow with suction (Fig. 2).
small = S (≤15 Fr.), medium = M (≤20 Fr.), large = L (≤25 Fr.), extra large = XL (≤30 Fr.) and extra extra large = XXL (all bigger sizes). In XS instruments, due to stability reasons, a combination between high inflow for better vision and sufficient outflow is hardly achievable [1]. The irrigation channels are usually small, e.g. 3 Fr. in MIP XS systems, and similar to retrograde intrarenal surgery [8], irrigation capacity is limited and therefore pressure irrigation is helpful to create adequate fluid turnover. If there is no sufficient backflow through the nephroscopy sheath, high intrarenal pressure can cause paravasation, calyceal rupture or pyelo-tubular reflux with potential harm for the renal parenchyma and the risk of sepsis [5, 10, 11]. Whereas pressure alone seems not to be enough for post-operative fever [15], the combination between high intrarenal pressure and operative time could be an important factor for post-operative fever and sepsis [4, 17]. Placing an access sheath through the ureter could be difficult without prior stenting [6], which means an additional procedure for the patient and could be associated with ureteral lesions in up to 46.5 % and lesions beyond the mucosa in 13.4 % [14]. An access sheath maintains low pressure in retrograde intrarenal surgery [7], but currently, there is no scientific evidence about the use of an access sheath in percutaneous surgery with SCPI. High-pressure
Discussion SCPI are a new expansion of tools for kidney stone treatment. An abundance of new names explaining nephroscope and nephroscope sheath sizes are more confusing rather than helpful. There seems to be a race towards even more superlatives to describe SCPIs such as ultramini or microperc [3]. To simplify the terminology, the Training and Research in Urological Surgical Therapy (T.R.U.S.T.) group has defined a new standard, which allows to categorize instrument sizes in extra small = XS (≤10 Fr.),
13
inflow with the use of an access sheath might provoke an ileal valve-like effect as observed in orthotopic urinary diversions: the outflow through the access sheath might be obstructed by prolapsing mucosa [12]. Inserting a transurethral mono-J catheter to drain the collecting systems seems more feasible if a low-pressure situation cannot be achieved by the nephroscopy sheath. The insertion of ureteric catheter (with or without a balloon) is routine in percutaneous procedures, and the J-shaped tip keeps the catheter securely positioned in the renal pelvis. Additionally, the multiple holes prevent obstruction by the mucosa. However, outflow through a mono-J catheter is limited by its small inner diameter and total length (Bernoulli’s law). Therefore, outflow can only be optimized by additional suction if intrapelvic pressure should be maintained at an equal level. Suction on the mono-J might provoke the mucosa of the collecting system to occlude the draining holes of the catheter. For this reason, we use a modified 8-Fr. mono-J catheter with enlarged draining holes ranging from the tip of the catheter in the renal pelvis to the proximal part of the catheter situated in the ureter. Both trials with 75 and 110 mmHg could demonstrate that the intrarenal pressure could be decreased by the use of the continuous-flow mode with sensor-controlled suction. The steady state pressure which can be achieved by continuous flow guarantees a constant intrarenal volume, which can be confirmed by nephroscopic control. This constant filling of the collecting system despite a high fluid turnover facilitates intrarenal surgery and vision, since neither a collapse of the renal pelvis nor distension occurs. An advantage in fluid turnover and therefore faster exchange of intrarenal volume with its benefits for endoscopic vision was present in both 75 and 110 mmHg inflow pressure in continuousflow mode and should proof beneficial in case of bleeding. Supported by the fact that the intrarenal pressure does not exceed 27 cm H2O in continuous-flow mode at inflow pressures of 110 mmHg, a further increase in irrigation pressure could be tested in future, bearing in mind that Bernoulli’s law limits the inflow as well as the outflow capacity in rigid tubes at a pressure levels, not reached in this trials. However, constant high-pressure situation as mentioned above should and could be avoided using this new irrigation principle which is called purging effect while creating increased flow rates resulting in better vision. If the benefit of increased flow time volume will translate into clinical benefits has proved in the clinical setting. In this study, for the first time, we present irrigation flow experiments using a non-perfused organ model. Limitations of our study design represent the in vitro setting with an extracorporal porcine kidney, the non-perfused state of the organ and potential artefacts caused by the indwelling cystometry catheter. However, using an in vivo model will likely show artefacts caused by pressure changes-based
13
World J Urol
intracorporal movement of the organ and/or fluid loss into the retroperitoneal space.
Conclusion This study demonstrates, that sensor-controlled suction in addition to pressure irrigation increases fluid turnover and decreases intrarenal pressure in small-calibre percutaneous surgery. This purging effect prevents hyperdistension or collapse of the collecting system and might improve endoscopic vision, especially in small-calibre instruments. Conflict of interest None of the authors have conflict of interest concerning the data published in this article. Ethical standard The authors declare that the present study has been performed in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki and its later amendments.
References 1. Bach T, Netsch C, TR Herrmann et al (2011) Objective assessment of working tool impact on irrigation flow and visibility in flexible ureterorenoscopes. J Endourol 25:1125–1129 2. Bader MJ, Gratzke C, Seitz M et al (2011) The “all-seeing needle”: initial results of an optical puncture system confirming access in percutaneous nephrolithotomy. Eur Urol 59:1054–1059 3. Ganpule AP, Bhattu AS, Desai M (2014) PCNL in the twentyfirst century: role of Microperc, Miniperc, and Ultraminiperc. World J Urol [Epub ahead of print] 4. Guo HQ, Shi HL, Li XG et al (2008) Relationship between the intrapelvic perfusion pressure in minimally invasive percutaneous nephrolithotomy and postoperative recovery. Zhonghua Wai Ke Za Zhi 46:52–54 5. Gutierrez J, Smith A, Geavlete P, Shah H, Kural AR, de Sio M, Sesmero JHA, Hoznek A, de la Rosette J; CROES PCNL Study Group (2013) Urinary tract infections and post-operative fever in percutaneous nephrolithotomy. World J Urol 31:1135–1140. doi:10.1007/s00345-012-0836-y 6. Kawahara T, Ito H, Terao H et al (2012) Preoperative stenting for ureteroscopic lithotripsy for a large renal stone. Int J Urol 19:881–885 7. Kourambas J, Byrne RR, Preminger GM (2001) Does a ureteral access sheath facilitate ureteroscopy? J Urol 165:789–793 8. Kruck S, Anastasiadis AG, Gakis G et al (2011) Flow matters: irrigation flow differs in flexible ureteroscopes of the newest generation. Urol Res 39:483–486 9. Kukreja R, Desai M, Patel S et al (2004) Factors affecting blood loss during percutaneous nephrolithotomy: prospective study. J Endourol 18:715–722 10. Kyriazis I, Panagopoulos V, Kallidonis P et al (2014) Com plications in percutaneous nephrolithotomy. World J Urol. doi:10.1007/s00345-014-1400-8 11. Liu C, Zhang X, Liu Y, Wang P (2013) Prevention and treatment of septic shock following mini-percutaneous nephrolithotomy: a single-center retrospective study of 834 cases. World J Urol 31(6):1593–1597. doi:10.1007/s00345-012-1002-2 12. Nagele U, Anastasiadis AG, Stenzl A et al (2012) Radical cystectomy with orthotopic neobladder for invasive bladder cancer: a
World J Urol critical analysis of long-term oncological, functional, and quality of life results. World J Urol 30:725–732 13. Nagele U, Horstmann M, Sievert KD et al (2007) A newly designed amplatz sheath decreases intrapelvic irrigation pressure during mini-percutaneous nephrolitholapaxy: an in vitro pressuremeasurement and microscopic study. J Endourol 21:1113–1116 14. Traxer O, Thomas A (2013) Prospective evaluation and classification of ureteral wall injuries resulting from insertion of a ureteral access sheath during retrograde intrarenal surgery. J Urol 189:580–584 15. Sa Troxel, Rk Low (2002) Renal intrapelvic pressure during percutaneous nephrolithotomy and its correlation with the development of postoperative fever. J Urol 168:1348–1351
16. Yamaguchi A, Skolarikos A, Buchholz NPN et al (2011) Operating times and bleeding complications in percutaneous nephrolithotomy: a comparison of tract dilation methods in 5,537 patients in the Clinical Research Office of the Endourological Society Percutaneous Nephrolithotomy Global Study. J Endourol 25:933–939 17. Zhong W, Zeng G, Wu K et al (2008) Does a smaller tract in percutaneous nephrolithotomy contribute to high renal pelvic pressure and postoperative fever? J Endourol 22:2147–2151
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ORIGINAL ARTICLE
Flow matters 2: How to improve irrigation flow in small‑calibre percutaneous procedures—the purging effect Udo Nagele · Ute Walcher · Markus Bader · Thomas Herrmann · Stephan Kruck · David Schilling
Received: 9 November 2014 / Accepted: 6 January 2015 © Springer-Verlag Berlin Heidelberg 2015
Abstract 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.
This is a paper from the Training and Research in Urological Surgical Therapy (T.R.U.S.T.) group.
Keywords Minimally invasive percutaneous stone treatment (MIP) · Microperc · Irrigation flow · Intrarenal pressure · Purging effect
U. Nagele (*) · U. Walcher Department of Urology and Andrology, General Hospital Hall in Tirol, Milser Str. 10, Hall i.T. 6060, Austria e-mail: [email protected] M. Bader Community Hospital Ebersberg, Ebersberg, Germany T. Herrmann Hannover Medical School, Hannover, Germany S. Kruck University Hospital Tübingen, Tübingen, Germany D. Schilling University Hospital Frankfurt am Main, Frankfurt am Main, Germany
Introduction Percutaneous nephrolitholapaxy is a standard procedure for the treatment of renal stone disease. Recently, the use of new-generation small-calibre percutaneous instruments (SCPI) with less than 12 Fr. outer diameter of the sheath has gained popularity due to its reduced invasiveness [2, 3]; especially, the reduced intraoperative blood loss has been pointed out as a major advantage of the miniaturized instruments [9, 16]. However, in our experience, the reduced diameter of the instruments comes to the cost of a reduced irrigation flow due to the small in- and outflow channels,
13
leading to impaired visibility even in case of minor bleeding. Whereas inflow characteristics in small-calibre percutaneous instruments (SCPI) are similar to flexible ureteroscopes and can be improved by the use of high-pressure irrigation systems [8], the outflow in new-generation openbore systems is the limiting factor for high irrigation fluid turnover due to the small calibre of the sheaths. The mismatch between in- and outflow can cause high intrarenal pressure and lead to pyelo-tubular reflux. The open sheath designs of the larger diameter first-generation miniaturized instruments [13] are not sufficient for pressure control in SCPI because of the unfavourable ratio of the small inner diameter of the sheath and relatively larger nephroscope diameter which is necessary for scope stability. To guarantee a high irrigation fluid turnover without risking high intrarenal pressure, the outflow through the ureter can be improved. For this reason, the use of retrogradely placed access sheaths has been proposed in miniaturized percutaneous procedures. However, this has several drawbacks like misplacement or intraprocedural dislocation [6]. These drawbacks can be overcome by the use of a mono-J catheter as it is standard in percutaneous procedures. Aim of this study was to investigate whether the use of a modified 8-Fr. mono-J catheter together with a pressure sensor-controlled pump (Uromat E.A.S.I.) improves irrigation capacity without increasing intrarenal pressure.
Materials and methods A fresh cadaveric porcine kidney was placed in a tray. The kidney was punctured through the upper calyx in a retrograde fashion (inside out through the ureter) and access was established with a single-step dilatation with an angiographic introducer set 6 Fr. (Cordis Corporation, Miami Lakes, FL, USA). A second puncture was made in the lower calyceal system and a single-step dilatation was performed with an 8.5-Fr. dilatator and a 9.5-Fr.-outerand 8.5-Fr.-inner-diameter nephroscope sheath (both Karl Storz, Tuttlingen, Germany) was placed inside the pyelon. The ureter was stented with a modified 8-Fr. mono-J catheter with multiple large bore holes at the tip of the catheter to avoid occlusion by aspiration of mucosa during suction (Optimed, Karlsruhe, Germany). The ureter was tied around the mono-J catheter for secure fixation. After verification of the correct position of the angiographic introducer in the collecting system using a 7.5-Fr. nephroscope (MIP XS by Nagele, Karl Storz, Germany), a 5-Fr. cystometry catheter (Andromeda, Taufkirchen, Germany) was placed inside the pyelon under nephroscopic guidance. The mono-J catheter, the cystometry catheter and the Amplatz sheath as well as the nephroscope were fixed on the working table to avoid pressure peak artefacts by
13
World J Urol
Fig. 1 Experimental setup—a 9.5-Fr. Amplatz sheath was introduced through the lower calyx and an 8-Fr. ureteric catheter was inserted through the ureter of the collecting system of a non-perfused porcine kidney. An 8-Fr. ureteric catheter was inserted through the upper calyx, and intrapelvic pressure was analysed applying different irrigation pressures with and without sensor-controlled suction via the ureteric catheter
manipulation during the experiment. Intrarenal pressure was measured with a urodynamic workstation (Andromeda, Taufkirchen, Germany) in cm H2O. Irrigation was performed with a Uromat E.A.S.I pump system. This roller pump system can be used either in a single-flow mode (irrigation inflow via nephroscope, passive outflow through mono-J) or continuous-flow mode (irrigation inflow via nephroscope, suction-controlled outflow via mono-J catheter). In continuous-flow mode, the outflow was adjusted by a pressure sensor measuring the inflow pressure, guaranteeing a steady state inside the renal pyelon. The nephroscope was a minimally invasive percutaneous nephroscope system (MIP) by Nagele with a 7.5-Fr. tip and a 3-Fr. irrigation channel and a 2-Fr. working channel. Two 2-min trials were recorded for each setting, measuring with single and continuous flow using 75 mmHg inflow pump pressure and in continuous flow presetting of 60 ml/ min and 110 mmHg pump pressure and presetting of 70 ml/ min in continuous flow. Intrarenal pressure and total irrigation volume per time interval were measured during each trial. The experimental set up is shown in Fig. 1.
Results The intrarenal pressure reached a plateau within seconds after initiating irrigation flow and no pressure peaks
World J Urol
Fig. 2 Intrapelvic pressure and irrigation flow at different inflow pressures with and without sensor-controlled suction: intrarenal pressure at 75 (a) and 110 mmHG (b) inflow. Irrigation flow turnover at
75 (c) and 110 mmHg (d). Each experiment was performed either with continuous-flow (sensor-controlled suction) or single-flow mode
were observed during the whole measurement interval, indicating homogeneous flow conditions throughout the experiment. Independently from the inflow irrigation pressure, single-flow irrigation showed higher intrarenal pressure and a lower irrigation flow than continuous-flow irrigation: at 75 and 110 mmHg, inflow pressure mean irrigation flow turnover was increased by 5 % (80–84 ml/min) and 15 % (96–110 ml/min), respectively, while intrarenal pressure was decreased by 14 % (19–14.5 cm H2O) and 28 % (37– 26.5 cm H2O), respectively when combining high-pressurecontrolled inflow with suction (Fig. 2).
small = S (≤15 Fr.), medium = M (≤20 Fr.), large = L (≤25 Fr.), extra large = XL (≤30 Fr.) and extra extra large = XXL (all bigger sizes). In XS instruments, due to stability reasons, a combination between high inflow for better vision and sufficient outflow is hardly achievable [1]. The irrigation channels are usually small, e.g. 3 Fr. in MIP XS systems, and similar to retrograde intrarenal surgery [8], irrigation capacity is limited and therefore pressure irrigation is helpful to create adequate fluid turnover. If there is no sufficient backflow through the nephroscopy sheath, high intrarenal pressure can cause paravasation, calyceal rupture or pyelo-tubular reflux with potential harm for the renal parenchyma and the risk of sepsis [5, 10, 11]. Whereas pressure alone seems not to be enough for post-operative fever [15], the combination between high intrarenal pressure and operative time could be an important factor for post-operative fever and sepsis [4, 17]. Placing an access sheath through the ureter could be difficult without prior stenting [6], which means an additional procedure for the patient and could be associated with ureteral lesions in up to 46.5 % and lesions beyond the mucosa in 13.4 % [14]. An access sheath maintains low pressure in retrograde intrarenal surgery [7], but currently, there is no scientific evidence about the use of an access sheath in percutaneous surgery with SCPI. High-pressure
Discussion SCPI are a new expansion of tools for kidney stone treatment. An abundance of new names explaining nephroscope and nephroscope sheath sizes are more confusing rather than helpful. There seems to be a race towards even more superlatives to describe SCPIs such as ultramini or microperc [3]. To simplify the terminology, the Training and Research in Urological Surgical Therapy (T.R.U.S.T.) group has defined a new standard, which allows to categorize instrument sizes in extra small = XS (≤10 Fr.),
13
inflow with the use of an access sheath might provoke an ileal valve-like effect as observed in orthotopic urinary diversions: the outflow through the access sheath might be obstructed by prolapsing mucosa [12]. Inserting a transurethral mono-J catheter to drain the collecting systems seems more feasible if a low-pressure situation cannot be achieved by the nephroscopy sheath. The insertion of ureteric catheter (with or without a balloon) is routine in percutaneous procedures, and the J-shaped tip keeps the catheter securely positioned in the renal pelvis. Additionally, the multiple holes prevent obstruction by the mucosa. However, outflow through a mono-J catheter is limited by its small inner diameter and total length (Bernoulli’s law). Therefore, outflow can only be optimized by additional suction if intrapelvic pressure should be maintained at an equal level. Suction on the mono-J might provoke the mucosa of the collecting system to occlude the draining holes of the catheter. For this reason, we use a modified 8-Fr. mono-J catheter with enlarged draining holes ranging from the tip of the catheter in the renal pelvis to the proximal part of the catheter situated in the ureter. Both trials with 75 and 110 mmHg could demonstrate that the intrarenal pressure could be decreased by the use of the continuous-flow mode with sensor-controlled suction. The steady state pressure which can be achieved by continuous flow guarantees a constant intrarenal volume, which can be confirmed by nephroscopic control. This constant filling of the collecting system despite a high fluid turnover facilitates intrarenal surgery and vision, since neither a collapse of the renal pelvis nor distension occurs. An advantage in fluid turnover and therefore faster exchange of intrarenal volume with its benefits for endoscopic vision was present in both 75 and 110 mmHg inflow pressure in continuousflow mode and should proof beneficial in case of bleeding. Supported by the fact that the intrarenal pressure does not exceed 27 cm H2O in continuous-flow mode at inflow pressures of 110 mmHg, a further increase in irrigation pressure could be tested in future, bearing in mind that Bernoulli’s law limits the inflow as well as the outflow capacity in rigid tubes at a pressure levels, not reached in this trials. However, constant high-pressure situation as mentioned above should and could be avoided using this new irrigation principle which is called purging effect while creating increased flow rates resulting in better vision. If the benefit of increased flow time volume will translate into clinical benefits has proved in the clinical setting. In this study, for the first time, we present irrigation flow experiments using a non-perfused organ model. Limitations of our study design represent the in vitro setting with an extracorporal porcine kidney, the non-perfused state of the organ and potential artefacts caused by the indwelling cystometry catheter. However, using an in vivo model will likely show artefacts caused by pressure changes-based
13
World J Urol
intracorporal movement of the organ and/or fluid loss into the retroperitoneal space.
Conclusion This study demonstrates, that sensor-controlled suction in addition to pressure irrigation increases fluid turnover and decreases intrarenal pressure in small-calibre percutaneous surgery. This purging effect prevents hyperdistension or collapse of the collecting system and might improve endoscopic vision, especially in small-calibre instruments. Conflict of interest None of the authors have conflict of interest concerning the data published in this article. Ethical standard The authors declare that the present study has been performed in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki and its later amendments.
References 1. Bach T, Netsch C, TR Herrmann et al (2011) Objective assessment of working tool impact on irrigation flow and visibility in flexible ureterorenoscopes. J Endourol 25:1125–1129 2. Bader MJ, Gratzke C, Seitz M et al (2011) The “all-seeing needle”: initial results of an optical puncture system confirming access in percutaneous nephrolithotomy. Eur Urol 59:1054–1059 3. Ganpule AP, Bhattu AS, Desai M (2014) PCNL in the twentyfirst century: role of Microperc, Miniperc, and Ultraminiperc. World J Urol [Epub ahead of print] 4. Guo HQ, Shi HL, Li XG et al (2008) Relationship between the intrapelvic perfusion pressure in minimally invasive percutaneous nephrolithotomy and postoperative recovery. Zhonghua Wai Ke Za Zhi 46:52–54 5. Gutierrez J, Smith A, Geavlete P, Shah H, Kural AR, de Sio M, Sesmero JHA, Hoznek A, de la Rosette J; CROES PCNL Study Group (2013) Urinary tract infections and post-operative fever in percutaneous nephrolithotomy. World J Urol 31:1135–1140. doi:10.1007/s00345-012-0836-y 6. Kawahara T, Ito H, Terao H et al (2012) Preoperative stenting for ureteroscopic lithotripsy for a large renal stone. Int J Urol 19:881–885 7. Kourambas J, Byrne RR, Preminger GM (2001) Does a ureteral access sheath facilitate ureteroscopy? J Urol 165:789–793 8. Kruck S, Anastasiadis AG, Gakis G et al (2011) Flow matters: irrigation flow differs in flexible ureteroscopes of the newest generation. Urol Res 39:483–486 9. Kukreja R, Desai M, Patel S et al (2004) Factors affecting blood loss during percutaneous nephrolithotomy: prospective study. J Endourol 18:715–722 10. Kyriazis I, Panagopoulos V, Kallidonis P et al (2014) Com plications in percutaneous nephrolithotomy. World J Urol. doi:10.1007/s00345-014-1400-8 11. Liu C, Zhang X, Liu Y, Wang P (2013) Prevention and treatment of septic shock following mini-percutaneous nephrolithotomy: a single-center retrospective study of 834 cases. World J Urol 31(6):1593–1597. doi:10.1007/s00345-012-1002-2 12. Nagele U, Anastasiadis AG, Stenzl A et al (2012) Radical cystectomy with orthotopic neobladder for invasive bladder cancer: a
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