21 Peter Alken Department of Urology, University Clinic Mannheim, Mannheim, Germany In the past, dilation of the percutaneous nephrolithotomy (PCNL) tract was thought to be essential to extract stones under radiological control [1] or to disintegrate and extract them endoscopically [2]. Today, however, the uses of PCNL tract dilation is decreasing and the options vary between no dilation and one‐shot dilation, which is a kind of penetration. No dilation is needed with the microperc PCNL technique performed through a 16 gauge needle sheath [3]. Even a large tract access can be established by “one‐shot” without any dilation [4]. All dilation or penetration techniques can be applied safely and with comparable good success and low complication rates when the conditions are ideal and when the surgeon is familiar with the technique and experienced. The classical dilation techniques using serial dilators or balloons [5–7] may continue to exist for a certain time and certain indications parallel to the increasingly popular miniaturized and one‐shot PCNL techniques. The essential difference between balloon dilators and fascial, Amplatz, or Alken dilators and one‐shot instruments used in a serial fashion or for one‐shot dilation is that the latter all apply forward forces during their advancement while balloon dilation does not. Fascial dilators made of plastic have a cone‐shaped tip and come in different lengths and sizes. Primarily designed for vascular procedures as catheter introducer sets they are available with thin‐walled simple sheaths or peel‐away sheaths. They are disposable. A reusable metallic 9 Fr dilator and 11 Fr sheath are part of the Alken dilators [8]. For PCNL, fascial dilators are used for preliminary dilation steps before application of the larger dilator systems or together with simple sheaths or peel‐away sheaths in a one‐shot dilation technique for miniaturized PCNL [9, 10]. The Amplatz system [6] consists of 12 plastic dilators with conical tips and sheaths of different length and sizes up to 36 Fr. A long 8 Fr dilator fits over a guidewire for a preliminary dilation and to stabilize the guidewire to prevent kinking. The Amplatz system requires repetitive in‐and‐out movements of the increasing size dilators. As a disposable system it is designed for one‐time use only. The Alken dilators [11, 12] were the first purpose‐built PCNL instruments and were designed for one‐session (pincture–dilation–nephroscopy–stone removal–nephrostomy) PCNL. The system consists of a conical metallic 9 Fr dilator and an 11 Fr metallic sheath which are used for preliminary dilation, introduction of a safety guidewire and atraumatic placement of the 8 Fr hollow guide rod [8]. The eight successive metal dilators up to 30 Fr are advanced over the guide rod, one over the other, up to the required size. The dilators are flat at the dilation end point. Finally a 24 or 26 Fr continuous‐flow nephroscope sheath or any Amplatz sheath is advanced over the dilators. In difficult situations with no passage of the guidewire or the guide rod into the renal pelvis, an 18 Fr nephroscope could be introduced after the third dilation step to inspect the calyx for a safe dilation route into the renal pelvis. The rigid metallic guide rod (Alken guide) is currently frequently used for one‐shot dilations [4, 13–21]. Balloon dilators [7] come with pressure devices to inflate the balloon up to the required diameter of 20 to 30 Fr and sheaths up to 36 Fr and of different length. Preliminary tract dilation with fascial dilators is frequently done. The advantages of balloon dilation are that it is a one‐step process, speed (with consequently reduced fluoroscopy time), and the exclusively radial forces during dilation. Balloon dilation is the most expensive technique available. The miniaturized PCNL technique was first used in 1997 for the treatment of a child [9]. The tract was dilated to 16 Fr, established with a 15 Fr angiocatheter introducer set with a peel‐away sheath, and stones were extracted with a pediatric cystoscope. Jackman et al. were the first to apply the technique in a series of children and adults [10]; they called it “mini‐perc” [22]. They used an 8/10 Fr guidewire introducer set and an 11/13 Fr ureteroscopy sheath set which was cut to the desired working length to introduce ureteroscopes or pediatric cystoscopes. Stones were disintegrated with laser or ultrasonic probes. Lahme et al. [23] developed the first purposely designed instrument for miniaturized PCNL, called the mini PCNL (MPCNL). They used a single‐step dilation with a 14 Fr plastic dilator, 15 Fr and 18 Fr metal sheaths and a 12 Fr nephroscope; the set was designed as a continuous‐flow system with outflow via the sheath. The microperc technique has been designed to allow one‐step instrumental access without the need for dilation by puncture only using a 4.85 Fr needle to puncture the collecting system and a 16 gauge needle sheath with an attached three‐way connector for irrigation, passage of a telescope, and a laser fiber [3]. Other miniaturized techniques frequently initially use fascial dilators. A recent meta‐analysis comparing miniaturized PCNL with standard PCNL showed that dilation was best done with fascial dilators of 13–18 Fr [24]. One study [25] used the minimally invasive PCNL one‐shot technique described by Nagele et al. [26] with a metallic one‐shot 16 Fr dilator/18 Fr sheath. Depending on the type of miniaturized instruments, various dilation procedures are used. In a large series on children, serial fascial dilators and 14–16 Fr peel‐away sheaths were used [27]. Zeng et al. reduced the fluoroscopy access time by using scaled fascial dilators and sheaths of 18 Fr [28]. With their >10 000 Chinese minimal invasive percutaneous nephrolithotomies Zeng et al. dilated the main tract to 18– 20 Fr and secondary tracts to 14–18 Fr [29]. Bhattu et al. used miniaturized systems from different instrument makers and dilated in single‐step or sequential fashion to sheath sizes of 18, 19.5, and 20 Fr [30]. In super‐mini percutaneous nephrolithotomy (SMP), tracts are dilated to between 10 and 14 Fr with fascial dilators [31]. Datta et al. dilated with fascial dilators to 7 Fr and 12 Fr and introduced the 13 Fr ultra mini percutaneous nephrolithotomy (UMP) outer sheath [32]. Karakan et al. did a one‐shot dilation to 14 Fr using a modified UMP technique [33]. There are various different competing miniaturized PCNL instruments on the market. With all techniques the dilation is less important than what is offered for instrumentation, irrigation, and/or suction within the sheaths and the nephroscopes used. The small tract of a miniaturized PCNL will forgive a bad puncture much more than a large dilated tract because the trauma is limited size‐wise and so puncture‐driven complications, such as bleeding or extravasation, will be less frequent and less severe. Complications include (i) vascular lesions of intra‐ or extraparenchymal vessels, (ii) collecting system lesions by a nontranspapillary access, (iii) rupture of the collecting system in the case of a mismatch between dilation size and collecting system, and (iv) frontal forward perforations. Establishment of a large tract by “one‐shot” access was first used by Frattini in 1998. After puncture of the collecting system and guidewire placement “a single 25 F or 30 F Amplatz dilator was pulled in on the Alken guide or on the 8 F first polyurethane dilator of the Amplatz set. This single passage allowed the insertion of the 34 F working sheath. … Each procedure was performed by a surgeon with great experience in the field of endourology” [4]. Successfully applied for large tract diameters, the one‐shot technique can of course also be applied independent of size in all miniaturized PCNL procedures. Previous open surgery on the same kidney had no influence on the good success rate of one‐shot dilation [34]. In children, one‐shot dilation compared favorably with the Alken technique [17]. A one‐shot principle for all sizes is made available by the minimally invasive PCNL (MIP) instruments of Karl Storz, which come in seven dilators sizes between 8,5 and 26 Fr with matching operating sheaths between 8.5 and 26 Fr (Figure 21.1) [35, 36]. Figure 21.1 Minimally invasive percutaneous nephrolithotomy dilators, sheaths, and nephroscopes. Source: Karl Storz Endoscopy‐America, Inc., 2017. Reproduced with permission of Karl Storz GmbH. The data in Table 21.1 show that access time and access fluoroscopy time are approximately halved with one‐shot procedures. Table 21.1 Overview of published dilation procedures, tract sizes, transfusion rates, fluoroscopy, and access times.
Dilation of the Nephrostomy Tract
Introduction
Dilators
Fascial dilators
Amplatz dilators
Alken dilators
Balloon dilators
Dilation in miniaturized percutaneous nephrolithotomy
One‐shot dilation
Dilation technique, tract size (Fr)
Dilation technique, transfusion rate (%)
Author, year,
RCT
One‐shot
Alken
Amplatz
Balloon
One‐shot
Alken
Amplatz
Balloon
Fluoroscopy time
Access time
Frattini [4] 2001
34
0
Guidewire to sheath 20 ± 3 s
n.a.
34
4
60 ± 7 s
n.a.
34
12
35 ± 7 s
n.a.
Safak [37] 2003
32
15.6
n.a.
Tract formation time 16.3 ± 2.4 min
32
13.7
n.a.
11.2 ± 3.0 min
Ziaee [21] 2007
Without previous open surgery 30
5.6
Before insertion of access needle to nephroscopy 0.60 ± 0.68 min
Access by needle to nephroscopy 5.93 ± 4.94 min
With previous open surgery 30
10.9
0.65 ± 0.75 min
6.24 ± 3.63 min
Gönen [38] 2008
34
21.3
n.a.
n.a.
34
18.6
n.a.
n.a.
Amjadi [39] 2008
Previous open surgery,
RCT
28
5.9
Guidewire to Amplatz sheath 27 ± 15 s
n.a.
28
5.9
81 ± 53 s
n.a.
Wezel [40]
2009
26
2
n.a.
n.a.
30
8
n.a.
n.a.
Falahatkar [41] 2009
RCT
30
3
Insertion of needle to Amplatz sheath 22 ± 4 s
Puncture by needle to Amplatz sheath 6 ± 2 min
30
4
65 ± 12 s
7 ± 2 min
Aminsharifi [13] 2011
RCT
30
0
Before insertion of access needle to nephroscopy 0.77 ± 0.41 min
From getting access by needle to nephroscopy 5.72 ± 1.75 min
30
0
1.12 ± 0.68 min
10.47 ± 2.97 min
Ozok [42] 2012
30
11.6
n.a.
Tract formation time 5.42 ± 3.07 min
30Fr
13.4
n.a.
6.56 ± 3.04 min
Amirhassani [14] 2014 RCT
28–30
2
“X‐ray exposure time” 41.2 ± 17 s
n.a.
28–30
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