Comparison of Dilation Methods in Percutaneous Nephrolithotomy: Which One Is More Successful?

Abstract

Objective:

Creation of the access tract is an important step in percutaneous nephrolithotomy (PNL). In this study, we compared the efficiency and safety of Amplatz, Alken, and balloon dilation methods in the creation of the access tract.

Materials and Methods:

Data from 487 PNL patients admitted to 517 renal units in 3 centers were analyzed. The Amplatz (280 patients), Alken (142 patients), and balloon (95 patients) dilation methods were compared for their success, duration of the dilation, injury to the collecting system, durations of fluoroscopy and surgery, stone-free and complication rates, pre- and postoperative hematocrit levels, and need for blood transfusion.

Results:

The dilation methods did not significantly differ with respect to patient demographic data, mean stone area, decrease in hematocrit, need for blood transfusion, unsuccessful tract dilation, injury to the collecting system, stone-free rate, and rate of postoperative complications. The mean fluoroscopy times during Amplatz, Alken, and balloon dilation were 288.52 ± 164.67, 287.34 ± 164.99, and 169.23 ± 21 seconds, respectively. The mean duration of surgery was 96.48 ± 46.07, 94.72 ± 42.25, and 78 ± 25.96 minutes, respectively. The duration of tract creation was 328.67 ± 172.99, 325.14 ± 175.70, and 203.50 ± 32.76 seconds, respectively. The durations of surgery and tract creation were significantly shorter in the balloon dilation group.

Conclusion:

None of the dilation methods was significantly superior in terms of surgical success, efficiency, or safety. Although balloon dilation was advantageous with respect to time parameters, the role of surgical experience should not be ignored.

Introduction

Urinary tract stones pose therapeutic challenges to urologists. Previously, these patients were typically treated with open surgery, requiring long recovery periods. Currently, however, stones at every level of the urinary tract may be treated noninvasively. Percutaneous nephrolithotomy (PNL) has been recommended as the first-line treatment modality in patients with renal stones >2 cm.¹ Creation of the access tract is an important step in PNL and may be accomplished using Amplatz dilators (semirigid polyurethane fascial dilators), Alken dilators (telescopic metal coaxial dilators), balloon dilators, and one-shot dilators.^2–4 However, there is no consensus regarding the optimal dilation method.^5–7 Therefore, in this retrospective study, we compared the efficiency and safety of the Amplatz, Alken, and balloon dilation methods in patients who underwent PNL.

Materials and Methods

Data on patients who underwent PNL in three different centers between January 2008 and January 2015 were analyzed retrospectively using the patients' medical records. The patients were divided into three groups. Group 1 consisted of patients in whom an Amplatz set was used; group 2 patients were treated using an Alken set and group 3 patients using a balloon dilator. Surgeon preference, anatomical and/or clinical factors, stone characteristics, and procedural costs were among the factors that influenced the choice of dilation method.

The success and duration of the dilation, injury to the collecting system, durations of fluoroscopy and surgery, stone-free rate, complication rate, pre- and postoperative hematocrit levels, and need for blood transfusion were determined and compared among the three groups. The total duration of surgery was defined as the time between the placement of the ureteral catheter at the beginning of the procedure and that of the percutaneous nephrostomy catheter at the end of the procedure. An alternative dilation method was used if a sufficient tract could not be obtained using the originally chosen method, in which case the procedure was considered as unsuccessful.

All patients underwent a complete blood count, serum electrolyte level, serum kidney and liver function parameters, bleeding and coagulation parameters, serological (HBV, HCV, and HIV) testing, and a complete urinalysis with urine culture before surgery. Informed consent was obtained from the patients after they were made aware of their disease and the surgical procedure. Patients on anticoagulant medications were referred to the relevant clinics and prepared for surgery. Patients with positive urine cultures were administered the appropriate antibiotics for at least 1 week before surgery, which was performed only after the subsequent urine cultures were sterile. The location and size of the stone, renal anatomy, and renal function were analyzed using noncontrast computed tomography (NCCT), intravenous pyelography, and other imaging modalities as needed.

The exclusion criteria were previous percutaneous nephrostomy performed in a radiology clinic of the renal unit, in which the PNL was planned, congenital kidney abnormalities, and secondary cases.

The size of the stone (in mm²) was determined by multiplying its largest diameter by the diameter perpendicular to it. Both diameters were measured in millimeters using a ruler. In case of multiple stones, all stones were measured independently, and their total size was determined.

Technique

Anesthesia was induced with the patient in the supine position, after which he or she was placed in the lithotomy position. A 6F open-end ureteral catheter was then inserted with the aid of a 20F cystoscope. The locations of the stone and the calyx targeted for entry were marked with a clamp using a C-arm fluoroscopy device. The targeted calyx was reached using an 18-gauge diamond-tipped needle under fluoroscopic guidance. After the collecting system had been entered, the Amplatz (using an 8F catheter, skipping the 4F catheter), Alken (using a 6F catheter, skipping the 3F catheter), or balloon (6F and 8F Amplatz dilation, followed by insertion of the balloon sheath at a pressure of 8–10 cmH₂O) dilator was placed over the guide wire. The renal parenchyma was then dilated until 30F, and the working sheath was then inserted into the collecting system. The stones were shattered using pneumatic lithotripters and removed using forceps after introduction of the nephroscope. When the ureteral catheter had been visually confirmed in the collecting system, a guide wire was inserted into the catheter and then withdrawn from the working sheath, thus providing a through-through access. The anesthesia team induced exhalation in the patient to provide safe access when an intercostal access was used. A reentry catheter was then inserted. However, the procedure was terminated after insertion of a Foley catheter if insertion of the reentry catheter was not possible. The hematocrit was measured intraoperatively in patients who had bleeding during surgery. Blood transfusions were performed in accordance with the hemodynamic evaluation of the patient by the anesthesia team. Postoperatively, a complete blood count was performed, and blood was transfused when needed. The nephrostomy catheter was removed 1–2 days after surgery. A double-J catheter was inserted if urine leakage from the PNL access tract did not stop within 24 hours. Antibiotic prophylaxis was obtained with cephalosporins. A body temperature >38°C was considered as fever. Urine and blood cultures were obtained from patients with fever, who were then treated in accordance with the causative pathogenic agent.

The patients had direct kidney–ureter–bladder X-rays on postoperative day 1. Urinary ultrasonography was carried out when needed. Complete stone-free status was determined on NCCT performed 4–6 weeks later. The results of surgery were classified as stone free (SF), clinically insignificant residual fragments (CIRFs), or failure (presence of residual stones). Asymptomatic noninfectious stones <5 mm and not causing obstruction were considered as CIRFs. The procedure was regarded as successful in patients with a CIRF or SF state.

Statistical analysis

The data were analyzed using the IBM SPSS Statistics 15.0 (SPSS, Inc., Chicago, IL) package. Continuous data were assessed using the Kolmogorov–Smirnov test. Normally distributed data were evaluated using an analysis of variance test and nonnormally distributed data using the Kruskal–Wallis test. Parameters with significant differences were paired and then analyzed using a t-test if their distribution was normal or with a Mann–Whitney U-test if it was not. A χ² test was performed for discontinuous (internal variable) values. A P-value <.05 indicated statistical significance.

Results

We analyzed the data of 487 patients who underwent a PNL procedure in a total of 517 renal units. The number of PNL procedures in groups 1, 2, and 3 was 280, 142, and 95, respectively. There were no statistically significant differences between the groups in terms of patient demographic data, mean stone area, decrease in hematocrit, need for blood transfusion, unsuccessful tract dilation, injury to the collecting system, stone-free rate, and rate of postoperative complications (Table 1). The mean fluoroscopy time, mean duration of surgery, and the duration of tract creation were significantly shorter in group 3 than in groups 1 and 2 (Table 1). The shorter tract creation and surgery times can be explained by the shorter dilation times of the balloon versus Amplatz and Alken dilators.

Table 1.

Comparison of Three Groups: Demographic and Clinical Data and the Outcomes During and After Surgery of Renal Units

	Group 1 (Amplatz) n = 280	Group 2 (Alken) n = 142	Group 3 (Balloon) n = 95	P
Median age, years (range)	47 (3–76)	50 (4–79)	44 (13–74)	.645
Female/male, n (%)	92 (32.8)/188 (67.1)	68 (47.9)/74 (52.1)	40 (42.1)/55 (57.9)	.110
Stone side, right/left, n (%)	92 (32.8)/188 (67.1)	72 (50.7)/70 (49.3)	38 (41.5)/57 (58.5)	.040
Stone surface area, mm² (mean ± SD)	678.05 ± 546.10	671.75 ± 548.74	748.96 ± 639.88	.202
Decrease in hematocrit, g/dL (mean ± SD)	4.09 ± 3.10	4.08 ± 3.04	3.51 ± 2.96	.150
Tract dilation failure, n (%)	15 (5.35)	6 (4.2)	7 (7.36)	.342
Collecting system damage, n (%)	7 (2.5)	6 (4.2)	3 (3.1)	.060
Operative time, minutes (mean ± SD)	96.48 ± 46.07	94.72 ± 42.25	78 ± 25.96	<.001
Fluoroscopy time, seconds (mean ± SD)	288.52 ± 164.67	287.34 ± 164.99	169.23 ± 21	<.001
Tract creation duration, seconds (mean ± SD)	328.67 ± 172.99	325.14 ± 175.70	203.50 ± 32.76	<.001
Stone-free status, n (%)	245 (87.5)	128 (90.1)	82 (86.3)	.141

SD, standard deviation.

Tract dilation was unsuccessful in 15 (5.35%) patients in group 1 due to localization of the stone in the inferior calyx, which cannot be dilated, or to insufficient introduction of the guide wire into the collecting system, due to excessive mobility of the kidney; the Alken method was used instead in those patients. In group 2, the method was unsuccessful in 6 (4.2%) patients. In three, a reliable fluoroscopy image could not be obtained due to extravasation of the radiopaque material during dilation; the procedure was therefore terminated, and an elective second PNL procedure was performed. The other three patients were children in whom use of the 20F access sheath was planned; however, the Amplatz rather than the Alken dilator was preferred because the diameters of the latter set increase by 3F increments, such that the first dilator following the 18F dilator is the 21F dilator. The balloon set could not be introduced completely in 7 (7.36%) patients in group 3; thus, one of the other two methods was used instead. The three groups were not significantly different with respect to tract dilation failure rates (Table 1).

Injury to the collecting system during PNL occurred in 7 (2.5%) patients in group 1, 6 (4.2%) patients in group 2, and 3 (3.1%) patients in group 3. The differences between groups were not significant (Table 1). In these 16 patients, antegrade double-J stents were inserted during surgery. No complications were observed during the follow-up period. The complications and the need for a second procedure were analyzed in accordance with the modified Clavien classification, which did not show statistically significant differences between groups 1, 2, and 3 (Table 2).

Table 2.

Comparison of the Rate of Complications Between the Groups According to the Modified Clavien Classification

Clavien grade	Group 1, n = 280	Group 2, n = 142	Group 3, n = 95	P
1. Conservative treatments, n (%)	41 (14.6)	22 (15.4)	13 (13.6)	.442
2. Blood transfusion, n (%)	36 (12.8)	16 (11.2)	7 (7.3)	.326
3a. Retrograde DJ, n (%)	13 (4.64)	9 (6.33)	4 (4.21)	.741
3b. Ureterorenoscopy, n (%)	3 (1.07)	2 (1.40)	0	.544
Total, n (%)	93 (33.2)	49 (34.5)	24 (25.2)	.284

DJ, double-J.

Discussion

PNL is the first-line treatment option for patients with large renal stones.¹ However, access tract creation may affect bleeding risk, duration of surgery, treatment success, and the development of complications. Therefore, both entry of the target calyx and the dilation process itself are important steps in PNL. The choice of instruments to achieve entry and dilation includes the Amplatz, Alken, and high-pressure balloon dilators.

Bleeding may occur at every step of a PNL, from access tract creation until the termination of surgery. Among the factors that influence bleeding are the dilation method, type of stone, number of tracts, stone load, lithotripter type, experience of the surgeon, and patient-related factors.⁸ Several studies have investigated the effect of nephrostomy tract creation on bleeding.^6,9,10 While some claimed that balloon dilation resulted in less bleeding,^6,8,9 others were unable to find a difference when the different methods were performed by experienced surgeons.^10,11 Based on their series of 127 PNL patients, Stoller et al. concluded that total blood loss did not correlate with the dilation method used.¹² They did find, however, that multiple procedures and renal pelvis perforation increased blood loss twofold.¹² In another study, the authors suggested that approximately half of the bleeding incidents during surgery occurred during creation of the nephrostomy tract.¹³ In our study, all PNL procedures were performed by experienced surgeons, and we found no evidence of a relationship between dilation method and either bleeding or the need for blood transfusion.

Tract dilation failure has been examined in several studies. Joel et al. performed balloon dilation to treat primary kidney stones; they reported tract dilation failure in 17% of the cases.¹⁴ Osman et al. reported a dilation failure rate of only 3.5% in patients undergoing Alken dilation.¹⁰ In the study by Ozok et al., the failure rates were 6% in the Amplatz group and 1.7% in the Alken group.¹⁵ PNL failure has been attributed to patient-related factors, characteristics of the study population, experience of the surgeons, previous procedures that resulted in scar tissue in the tract route, a mobile kidney, and an inability to introduce the guide wire to a sufficient depth in the undilated calyx.^14,16–18 Although balloon dilation seems to often fail when used in secondary cases,^15–17,19 the actual reason may be displacement during insertion of the balloon into the collecting system,¹⁹ but this explanation is not universally accepted.⁶ Some authors have reported failure of the Amplatz dilation method in patients with a mobile kidney, in some secondary cases, and when the stone completely fills the undilated target calyx.^15,17 In children, the access sheath should be as small as possible, which essentially rules out the use of the Alken dilator set because it does not enable the creation of a 20F sheath. The Amplatz method may be advantageous in secondary cases, in patients with a mobile kidney, when the guide wire cannot be advanced safely, and in children and adolescents.¹⁵ In our retrospective study, secondary cases were excluded from the analysis, but the other reasons for tract dilation failure and the rates of dilation failure among the three groups were in accordance with those described in the literature.

The balloon dilation method enables one-step creation of a suitable tract, without the need for serial dilations. Accordingly, some authors have reported that the durations of surgery, tract creation, and fluoroscopy were shorter using this method than either the Alken or Amplatz dilation method.²⁰ In other comparisons of Alken versus balloon dilation and Alken versus Amplatz dilation methods, the differences in the durations of surgery and fluoroscopy were not significant.^15,19 A study comparing balloon and Amplatz dilation showed that surgery and tract dilation durations were shorter in the former.¹⁶ In agreement with that result, in our study, the durations of surgery, fluoroscopy, and tract creation were significantly shorter in the balloon dilation group than in the Alken and Amplatz groups.

Injury to the collecting system may occur during tract creation and is an important complication of PNL. The probability of collecting system perforation was suggested to be higher when rigid and semirigid dilation methods are used.²⁰ Safak et al. reported a collecting system injury rate of 11.6% in their balloon group and 16.6% in their Amplatz group but concluded that those rates would decrease as the experience of the surgeon increased.¹⁶ In a study of the Amplatz and Alken dilation methods, the rates of collecting system injury were 2% and 2.5%, respectively.¹⁵ In our study, the rates of collecting system injury were similar among the three groups. Some authors have associated collecting system injury with both greater bleeding and a loss of endoscopic vision.⁷

In accordance with previously reported results,^7,15,19 we did not find any effect of the dilation method on the success of the procedure.

In conclusion, using data obtained from patients at three different centers, this study compared the effectiveness, safety, advantages, and disadvantages of the dilation methods used in PNL. Due to the retrospective nature of the study, the randomization of patients and methods was not possible. In evaluating the role of cost as a factor determining the choice of dilation method, it seems that the less frequent use of balloon dilation, as opposed to the other methods, is related to its higher cost; however, it is expected that with increasing use, balloon dilation will provide better results, thus justifying the greater expense. A limitation of our study was that it did not take into account patient factors (diabetes mellitus, hypertension, body mass index, etc.), such that subgroup analysis was not possible. Nonetheless, ours is the first study to compare all three dilation methods. The results remain to be confirmed in prospective randomized trials.

Conclusion

Tract creation is one of the most important steps determining the success of PNL. In this study, we found no evidence of the superiority of one dilation method over another with respect to surgical success. The durations of surgery, fluoroscopy, and tract creation were shorter with the balloon dilation method than with either the Alken or Amplatz methods; however, in PNL, the experience of the surgeon may be just as important as the choice of instruments.

Ethical Standards

This study has been granted local ethical committee approval and carried out in the patients concerned according to the ethical standards of our institution and with the 1964 Declaration of Helsinki and its later amendments or comparable ethical standards.

Footnotes

Disclosure Statement

No competing financial interests exist.

References

Turk

, Knoll

, Petrik

, Sarica

, Skolarikos

, Straub

, Seitz

. The European Association of Urology Guidelines on Urolithiasis. 2015. Available at https://uroweb.org/guideline/urolithiasis

Alken

, Hutschenreiter

, Gunther

, Marberger

. Percutaneous stone manipulation. J Urol, 1981; 125:463–466.

Clayman

, Surya

, Miller

, et al. Percutaneous nephrolithotomy. An approach to branched and staghorn renal calculi. JAMA, 1983; 250:73–75.

Amirhassani

, Mousavi

SHB

, Kashkouli

, Torabian

. Comparison of the safety and efficacy of one-shot and telescopic metal dilatation in percutaneous nephrolithotomy: A randomized controlled trial. Urolithiasis, 2014; 42:269–273.

Lopes

, Sangam

, Alken

, Barroilhet

, Saussine

, Shi

, et al. The Clinical Research Office of the Endourological Society. Percutaneous nephrolithotomy global study: Tract dilation comparisons in 5537 patients. J Endourol, 2011; 25:755–762.

Davidoff

, Bellman

. Influence of technique of percutaneous tract creation on incidence of renal hemorrhage. J Urol, 1997; 157:1229–1231.

Özçift

, Bal

, Dinçel

. A comparison of balloon and Amplatz dilators in percutaneous nephrolithotomy: A retrospective evaluation. Turk J Urol, 2013; 39:226–231.

Turna

, Nazli

, Demiryoguran

, Mammadov

, Cal

. Percutaneous nephrolithotomy: Variables that influence hemorrhage. Urology, 2007; 69:603–607.

Muslumanoğlu

, Tefekli

, Karadağ

, Tok

, Sari

, Berberoğlu

. Impact of percutaneous access point number and location on complication and success rates in percutaneous nephrolithotomy. Urol Int, 2006; 77:340–346.

10.

Osman

, Wenor-Nordabl

, Heger

, Mitchel

, Alken

, Knoll

. Percutaneous nephrolithotomy with ultrasonography-guided renal access: Experience from over 300 cases. BJU Int, 2005; 96:875–878.

11.

Lee

, Stoller

. Minimizing and managing bleeding after percutaneous nephrolithotomy. Curr Opin Urol, 2007; 17:120–124.

12.

Stoller

, Wolf

Jr. , St. Lezin

. Estimated blood loss and transfusion rates associated with percutaneous nephrolithotomy. J Urol, 1994; 152:1977–1981.

13.

Kessaris

, Bellman

, Pardalidis

, Smith

. Management of hemorrhage after percutaneous renal surgery. J Urol, 1995; 153:604–608.

14.

Joel

, Rubenstein

, Hsieh

, Chi

, Meng

, Stoller

. Failed percutaneous balloon dilation for renal access: Incidence and risk factors. Urology, 2005; 66:29–32.

15.

Ozok

, Sagnak

, Senturk

, et al. A comparison of metal telescopic dilators and Amplatz dilators for nephrostomy tract dilation in percutaneous nephrolithotomy. J Endourol, 2012; 26:630–634.

16.

Safak

, Göğüs

, Soygür

. Nephrostomy tract dilatation using a balloon dilatation percutaneous renal surgery. Urol İnt, 2003; 71:382–384.

17.

Gönen

, Istanbulluoglu

, Cicek

, Ozturk

, Ozkardes

. Balloon dilatation versus Amplatz dilatation for nephrostomy tract dilatation. J Endourol, 2008; 22:901–904.

18.

Kumar

, Keely

. Percutaneous nephrolithotomy: Why do we use rigid dilators?. J Endourol, 2008; 22:1877–1879.

19.

El-Shazly

, Salem

, Allam

, Hathout

. Balloon dilator versus telescopic metal dilators for tract dilatation during percutaneous nephrolithotomy for staghorn stones and calyceal stones. Arab J Urol, 2015; 13:80–83.

20.

Nouri

, Tligui

, Flahaut

, et al. Balloon catheter parieto-renal dilatation in percutaneous kidney surgery. Prog Urol, 2000; 10:1131–1134.