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Keywords:

  • endoscopes;
  • percutaneous lithotripsy;
  • kidney calculi;
  • kidney;
  • percutaneous nephrostomy;
  • miniaturization

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Armamentarium
  5. Technique
  6. Discussion
  7. Conclusions
  8. Acknowledgements
  9. Conflict of Interest
  10. References
  11. Supporting Information

Objective

  • To describe our newly developed technique for the removal of renal stones, which we have called ultra-mini percutaneous nephrolithotomy (UMP).

Methods

  • UMP was performed in 62 patients using a 3.5-F ultra-thin telescope and specially designed inner and outer sheaths. A standard puncture was made and the tract was dilated up to 13 F.
  • The outer sheath was introduced into the pelvicalyceal system and the stone was disintegrated with a 365-μ holmium laser fibre, introduced through the inner sheath.
  • Stone fragments were evacuated using the specially designed sheath by creating an eddy current of saline; the fragments then came out automatically.

Results

  • The mean calculus size was 16.8 mm. Four of the 62 patients were children, three had a solitary kidney and two were obese.
  • UMP was feasible in all cases with a mean (sd) 1.4 (1.0) gm/dL haemoglobin decrease and a mean hospital stay of 1.2 (0.8) days. The stone-free rate at 1 month was 86.66%.
  • In two patients intraoperative bleeding obscured vision, requiring conversion to mini-percutaneous nephrolithotomy. There was one postoperative complication of hydrothorax, but there were no other postoperative complications and no auxiliary procedures were required.

Conclusions

  • UMP is a very safe and effective method of removing renal calculi up to 20 mm. The use of consumables and disposables is minimal and the patient recovery was fast.
  • Further clinical studies and direct comparison with other available techniques are required to define the place of UMP in the treatment of low-bulk and medium-bulk renal urolithiasis. It may be particularly useful for lower calyx calculi and paediatric cases.

Abbreviations
PCNL

percutaneous nephrolithotomy

UMP

ultra-mini PCNL

Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Armamentarium
  5. Technique
  6. Discussion
  7. Conclusions
  8. Acknowledgements
  9. Conflict of Interest
  10. References
  11. Supporting Information

Percutaneous nephrolithotomy (PCNL) is used worldwide for the removal of all sizes of renal calculi; however, even in expert hands, there is sometimes bleeding which leads to blood transfusions and complications. Kukreja et al. [1] conclusively proved that the larger the tract size the more parenchymal damage and bleeding occurs [2]. We have therefore devised a new technique, ultra-mini PCNL (UMP), where the tract dilation is 13 F and stone retrieval does not involve expensive disposables such as baskets and graspers.

The UMP method is particularly useful for lower calyx stones. For lower calyx stones the ESWL stone-free rate is compromised [3] and low stone-free rates with retrograde intrarenal surgery have also been reported for the lower calyx. Moreover, the breakdown rate of flexible ureteroscopes is higher for lower calyx stones [4, 5].

The main difference between UMP and standard PCNL or mini-PCNL lies in the small size of the access sheath and in its design, which allows extraction of fragments without the use of baskets or forceps. We use a 20-gauge thin needle and puncture the desired calyx under fluoroscopy or sonography guidance and restrict the dilation to 13 F and this limits the damage to the renal parenchyma. Even if the infundibulum is narrow, the small-sized UMP sheath can easily be advanced further without damage to the infundibulum. The stone is disintegrated into a fragment size of 1.5–2.5 mm and these fragments are evacuated by creating turbulence with a saline jet injected through a side port which is connected to a very small tubing inside the access sheath (Fig. 1). The fragments come out automatically because they move from a high pressure zone to a low pressure zone and we do not have to use forceps or baskets to remove the fragments [6]. At the end of the procedure, the 13-F sheath can be pulled out and there is no need to place a nephrostomy tube or a JJ stent.

figure

Figure 1. (A) Side port connecting to a small tube. (B) small tube within outer sheath for saline jet. (C) grooved obturator sliding over guidewire. (D) Saline jet.

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This technique should be used only for stones <20 mm in size. In the present paper, we present an initial technical feasibility and safety report for this new technique.

Armamentarium

  1. Top of page
  2. Abstract
  3. Introduction
  4. Armamentarium
  5. Technique
  6. Discussion
  7. Conclusions
  8. Acknowledgements
  9. Conflict of Interest
  10. References
  11. Supporting Information

The procedure was performed with a set of specially designed instruments which we have called the UMP set (Fig. 2). The instruments are manufactured by Schoelly Fiberoptics GmbH (Denzlingen, Germany). The set consists of: (i) an ultra-thin telescope, 1 mm in diameter with a 0° view; the telescope resolution is 17 000 pixels; (ii) an outer 13-F sheath; and (iii) a 6-F inner sheath. The outer sheath has a very small tube of 3 F welded to the inner wall and finally connected to a port outside (Fig. 1). This port is used to inject saline through a 20 mL syringe. The telescope fits into the inner sheath and a 365-μ laser fibre can be inserted through this sheath. The inner sheath also has a connector for irrigation (Fig. 3). Saline escapes through the space between the inner sheath and the outer sheath. The ease with which saline flows out helps us maintain low pressure in the pelvicalyceal system. We documented the pressure in the kidney by taking pressure measurements in the kidney and the bladder at the same time (Fig. 4).

figure

Figure 2. The basic UMP set: telescope, inner sheath, outer sheath and obturator.

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figure

Figure 3. The 3.5-F telescope inserted in the inner sheath.

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figure

Figure 4. (A) 6-F tube measuring intrarenal pressure during UMP. (B) Blue line: intrarenal pressure; red line: bladder pressure.

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Technique

  1. Top of page
  2. Abstract
  3. Introduction
  4. Armamentarium
  5. Technique
  6. Discussion
  7. Conclusions
  8. Acknowledgements
  9. Conflict of Interest
  10. References
  11. Supporting Information

A 6-F ureteric catheter is introduced transurethrally under general anaesthesia. The patient is placed in a prone position and the desired calyx is punctured under fluoroscopy or sonography guidance. Using a guidewire, dilatation is carried out with 8-F and 11-F teflon dilators. Then the UMP outer sheath, with the obturator, is advanced over the guidewire and, with a gentle twisting motion, the sheath is introduced into the pelvicalyceal system. The entire procedure takes place under low pressure (Fig. 4) and the saline can easily be seen flowing out of the outer sheath. The thin 3.5-F nephroscope is placed in the inner sheath which is introduced into the outer sheath (the access sheath). The pelvicalyceal system is visualized and the stone is also visualized. A 365-μ laser fibre (Laserscope; AMS, Minneapolis, MN, USA) is introduced through the inner sheath (Fig. 3). The stone is disintegrated into ∼2.0-mm fragments. Once the stone is disintegrated, the manoeuvre to extract the fragments is carried out. The inner sheath with the telescope is withdrawn. With a 20-mL syringe, the assistant injects saline through the side port; this produces a small jet of fluid in the calyx (Fig. 1). The small stone fragments are agitated and an eddy of water current is produced. A high pressure zone is created in a small area and the fragments will automatically start escaping from the low pressure zone which is just adjacent [6]; the larger bore of the outer sheath is the low pressure area. At the end of the procedure, the UMP outer sheath is removed and firm pressure is applied on the tract for 3–4 min. There is no need to place a nephrostomy tube or a JJ stent.

The ureteric catheter is kept in the ureter for 12–16 h. The patient is monitored for postoperative complications. The Foley catheter and the ureteric catheter are removed after 12–16 h. The patient is sent home after 14–24 h. Sonography is performed to assess the stone-free rate in all patients at day 1. CT is performed after 30 days. Clearance is defined as no residual stones on CT.

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Armamentarium
  5. Technique
  6. Discussion
  7. Conclusions
  8. Acknowledgements
  9. Conflict of Interest
  10. References
  11. Supporting Information

The design of the outer sheath with its small inner tube has the advantage of stone fragment retrieval without the use of baskets or graspers. This inner tube could be used to create turbulence in the pelvicalyceal system and, when an eddy was created, the fragments got sucked into the sheath and were automatically evacuated (see Video S1). In fluid dynamics, an eddy is the swirling of a fluid and the reverse current created when the fluid flows past an obstacle. The moving fluid creates a space devoid of downstream-flowing fluid on the downstream side of the object. Fluid behind the obstacle flows into the void creating a swirl of fluid on each edge of the obstacle, followed by a short reverse flow of fluid behind the obstacle flowing upstream, toward the back of the obstacle [6]. This principle of fluid dynamics is used in UMP surgical technique, albeit in a minute version. The small fragments pose as an obstacle for the saline jet and when an eddy is created they are sucked inside the sheath and come out automatically. A simple suction through a 13-F tube will not be effective because the fragments lying in corners will not be sucked out. These fragments have to be agitated and displaced from a dormant situation before they are expelled by an eddy. This agitation can only be created by a saline jet which hits the fragments and the turbulence draws them into the mini-whirlpool that is created.

The efficacy of any stone removal technique is judged by three criteria: (i) complication rate; (ii) stone-free rate; and (iii) auxilliary procedure rate. UMP has a minimal complication rate, a high stone-free rate and a very low auxiliary procedure rate; however, it is best for treating stones <20 mm in size, lower calyx stones and stones in children.

Conclusions

  1. Top of page
  2. Abstract
  3. Introduction
  4. Armamentarium
  5. Technique
  6. Discussion
  7. Conclusions
  8. Acknowledgements
  9. Conflict of Interest
  10. References
  11. Supporting Information

Our preliminary experience with UMP has demonstrated feasibility and safety in urological surgery. Comparative investigations with traditional ESWL, conventional PCNL and retrograde intrarenal surgery are required. Widespread adoption of this new approach will probably require a multicentre study by institutions routinely involved in performing PCNL. UMP is safe and easy to learn but should be restricted to medium-sized stones (<2.0 cm). It can be particularly helpful for stone removal in children and in adults where the stone is in the lower calyx.

Acknowledgements

  1. Top of page
  2. Abstract
  3. Introduction
  4. Armamentarium
  5. Technique
  6. Discussion
  7. Conclusions
  8. Acknowledgements
  9. Conflict of Interest
  10. References
  11. Supporting Information

The prototype instruments of UMP were made from designs provided by us to Endosys, Mumbai, India and then by Schoelly Fiberoptics GmbH. Mr Devang Mehta of Endosys and Mr Werner Schoelly of Schoelly Fiberoptics GmbH, helped in the various stages of instrument development. Dr Eric Suter and Mr Marco Schlegel of Schoelly Fiberoptics GmbH contributed much valuable input.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Armamentarium
  5. Technique
  6. Discussion
  7. Conclusions
  8. Acknowledgements
  9. Conflict of Interest
  10. References
  11. Supporting Information

Supporting Information

  1. Top of page
  2. Abstract
  3. Introduction
  4. Armamentarium
  5. Technique
  6. Discussion
  7. Conclusions
  8. Acknowledgements
  9. Conflict of Interest
  10. References
  11. Supporting Information
FilenameFormatSizeDescription
bju12193-sup-0001-si.avi38082K

Video S1 Ultra-Mini PCNL (UMP).

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