A Comparison of Metal Telescopic Dilators and Amplatz Dilators for Nephrostomy Tract Dilation in Percutaneous Nephrolithotomy

Abstract

Background and Purpose:

Nephrostomy tract dilation is one of the important steps in percutaneous renal surgery. We present our experiences with using Amplatz and metal telescopic dilators (Alken) to create a percutaneous tract and compare the advantages and risk factors of both procedures.

Patients and Methods:

We retrospectively reviewed the medical records of 173 patients who had undergone 188 percutaneous nephrolithotomy procedures between April 2007 and December 2010. The nephrostomy tracts had been created by using Amplatz (67 cases) or Alken dilators (121 cases). Total operative time, scope time, tract formation time, decrease in hemoglobin concentrations, blood transfusion rates, tract dilation failures, and the cost of both systems were compared between the groups.

Results:

There were no statistically significant differences in total operative time (103.3±46.5 vs 99.1±44.4 min, P=0.583), scope time (5.23±3.06 vs 5.28±2.52 min, P=0.732), decrease in hemoglobin concentration (−1.5±1.2 vs−1.3±1.1 mg/dL, P=0.230), blood transfusion rates (13.4% vs 11.6%, P=0.709), and tract dilation failure rates (6.0% vs 1.7%, P=0.107) for Amplatz and Alken dilation groups, respectively. A shorter tract formation time (6.56±3.04 vs 5.42±3.07 min, P<0.001) was observed in the Alken dilation group. The approximate costs per each case were $220 and $7.25 for Amplatz and Alken dilation groups, respectively.

Conclusions:

The Alken dilation technique produces similar results to the Amplatz dilators in terms of efficiency, safety, and total operative time. Notwithstanding, it is more cost-effective in comparison.

Introduction

N ephrostomy tract dilation is one of the important steps in percutaneous nephrolithotomy (PCNL). Currently, the instruments most preferred in this procedure are balloon dilators, semirigid polyurethane fascial dilators (Amplatz dilators), and telescopic metal coaxial dilators (Alken dilators).^1
–3 The advantages of using balloon dilators include short dilation and scope time and no risk of forward perforation compared with using Amplatz and Alken dilators. They are expensive, however, can cause disruption of dilated structures, and their effect on blood loss is in controversy.^4,5 In numerous studies, balloon dilators or new one-step methods have mostly been compared with the Amplatz dilators, and Alken dilators, too, which are sequential dilation systems.^5

–9 Although Amplatz and Alken dilators represent sequential dilation techniques, we believe that they have different efficiencies, side effects, and indications. There is no study in the literature, however, that compares these methods directly.

In this retrospective study, we aimed to evaluate efficiency, safety, and cost-effectiveness of Amplatz and Alken dilators. In addition, we present our experiences with using Amplatz and Alken dilators to create a percutaneous tract and compare complications such as blood loss, tract dilation failures, collecting system perforation, procedural times. and the difficulties of both procedures.

Patients and Methods

Retrospective medical records of 180 patients who had undergone PCNL procedures between April 2007 and December 2010 in our clinic were reviewed, and 188 PCNL procedures of 173 patients who matched the inclusion criteria were enrolled in the study and divided into Amplatz (67 cases) and Alken (121 cases) groups.

Preoperative patient evaluation included patient history, clinical examination, serum creatinine levels, complete blood cell count, coagulation profile, and liver function tests. Anteroposterior chest radiography, intravenous urography, and noncontrast CT for patients who had congenital kidney anomaly, nonopaque calculi, previous open renal surgery, or high serum creatinine levels were conducted as radiologic imaging.

All patients with large renal and upper ureteral calculi were included in the study irrespective of the location, side, and number of stones, amount of hydronephrosis, the presence of previous shockwave lithotripsy (SWL) or open renal surgery, and solitary kidney or horseshoe kidneys. Four patients were excluded from the study because of a history of percutaneous nephrostomy tube placement by a radiologist or anticoagulant use. In addition, a patient who had undergone laparoscopy-assisted PCNL on a pelvic ectopic kidney and a child who had undergone open renal stone surgery because of inadequate dilation blocking the access to the collecting system were also excluded. In a case of staghorn calculus, a patient who decided to have “second-look nephroscopy” because of excessive bleeding that occurred later on during the lithotripsy procedure, which began without any initial problems, was not included in the study because the dilation technique was not thought to be the cause of the bleeding. If one procedure failed, we passed to other tract dilation method. These cases were not excluded from the study but recorded as a failure of the initial method. Simultaneous bilateral and tubeless PCNL was not performed.

Informed written consent was obtained from all patients before considering them for the study. Patients were told that the surgeon may select one of the methods referred to above.

General anesthesia was administered in all patients, and a 6F open-ended ureteral catheter was placed transurethrally. Percutaneous access was created by six experienced urologists (authors) in all cases under fluoroscopic guidance, with the patient in the prone position, using an 18-gauge access needle inserted into the selected calix. A 0.89 mm J-tipped guidewire was placed into the collecting system. Before the access needle was removed, the skin and fascia were incised. The nephrostomy tract was dilated with telescoping Alken metal dilators (Karl Storz, GmbH, Tuttlingen, Germany) or polyurethane serial Amplatz dilators (Microvasive, Natick, MA). The metal telescopic dilation system comprised eight stainless steel tubes that extended up to 30F, overlapping at 3F intervals from 9F to 30F. In the Amplatz dilation system, polyurethane catheters that extend up to 30F overlapping at 2F intervals from 8F upward are used. In both methods, a 30F Amplatz sheath (Microvasive) was positioned in the renal collecting system.

Stones were disintegrated using pneumatic lithotripsy. Additional tracts were made, if necessary, with the aim of achieving stone-free status. After complete clearance was confirmed, fluoroscopically and endoscopically, an 18F reentry pigtail catheter (Microvasive) was placed antegradely. If complete clearance could not be confirmed, a 6F Double-J stent was placed antegradely.

Hemoglobin levels were followed up with a complete blood cell count performed the day before and after the operation. Controls were routinely conducted with radiography of the kidneys, ureters, and bladder in the first 24 hours, renal ultrasonography in patients with nonopaque calculi, and anteroposterior chest radiography in patients who underwent a supracostal access. Within the 12 to 24 hours after the clearance of hematuria, the urethral catheter and nephrostomy tube, respectively, were removed.

Total operative time, scope time, dilation time, preoperative and postoperative hemoglobin concentrations, blood transfusion rates, tract dilation failures, and the cost of both systems were compared between the groups. Total operative time was calculated as the duration from the placement of the open-ended catheter until the placement of urethral drainage. To compare the preoperative and postoperative hemoglobin concentrations, the last preoperative and the lowest postoperative values were taken. Blood transfusion was conducted in the cases in which cardiopulmonary compensation mechanisms were insufficient because of anemia in patients with hemoglobin values dropping to 10 mg/dL and in which patients became symptomatic.

Stone surface areas of opaque calculi were estimated with the help of the radiographic film projection of two-dimensional calculi on graph papers. Dimensions established by CT scans were taken as the basis for nonopaque calculi. The cost of one Amplatz system per case was equal to the cost of one Amplatz set package, and the cost of one Alken system per case was equal to the initial cost divided by the number of cases (121).

Statistical data analysis was performed using SPSS 11.5 for Windows Statistical Software Package. The importance of differences between groups for total operative time, scope time, tract dilation time, and stone surface area was assessed using the Mann Whitney U test. The importance of preoperative and postoperative hemoglobin concentration-related differences between groups was assessed using the Student t test. The presence of statistical differences with respect to blood transfusion rates, stone-free and residual fragments status, tract dilation failure, and collecting system perforation between groups was analyzed using the Pearson chi-square test. The results were considered significant for P<0.05.

Results

There were no significant differences in demographic data such as age or sex, or in clinical data that can affect the results of PCNL, such as stone side and surface area, number of tracts, position of punctured calix, and the history of open renal surgery between two groups (Table 1).

Table 1.

Comparison of Two Groups: The Demographic and Clinical Data, and the Outcomes During and After Surgery of 188 Cases

	Group 1 (Amplatz) n: 67	Group 2 (Alken) n: 121	P
Median age, y (range)	47 (3–76)	49 (4–79)	0.258
Female/male, n (%)	24 (35.8)/43 (64.2)	57 (47.1)/64 (52.9)	0.134
Stone side right/left, n (%)	24 (35.8)/43 (64.2)	60 (49.6)/61 (50.4)	0.069
Stone surface area, mm² (mean±SD)	673.4±466.9	648.4±553.3	0.486
Number of tracts Single/double (%)	62 (92.5)/5 (7.5)	107 (88.4)/14 (11.6)	0.455
Calix of puncture, n (%)
Lower	50 (74.6)	96 (79.3)	0.231
Middle	10 (14.9)	7 (5.8)
Upper	2 (3.0)	4 (3.3)
Double	5 (7.5)	14 (11.6)
Previous open renal surgery n (%)	5 (7.5)	10 (8.3)	0.846
Preoperative hemoglobin concentrations, g/dL (mean±SD)	13.85±1.68	13.87±1.74	0.945
Decrease in hemoglobin, g/dL (mean±SD)	−1.5±1.2	−1.3±1.1	0.230
Blood transfusion requirement n (%)	9 (13.4)	14 (11.6)	0.709
Tract dilation failure n (%)	4 (6.0)	2 (1.7)	0.107
Collecting system perforation n (%)	2 (3.0)	3 (2.5)	0.836
Operative time, min (mean±SD)	103.3±46.5	99.1±44.4	0.583
Scope time, min (mean±SD)	5.23±3.06	5.28±2.52	0.732
Tract formation time, min (mean±SD)	6.56±3.04	5.42±3.07	0.001
Stone-free status n (%)	57 (85.1)	109 (90.1)	0.306
Residual fragments <5 mm n (%)	6 (9.0)	10 (8.3)	0.871

SD=standard deviation.

There were no significant differences in data, such as bleeding, tract dilation failure, and collecting system perforations, that were observed related to the tract formation procedure directly. Tract dilation failure was observed as 6% in the Amplatz group and 1.7% in the Alken group, and percutaneous access was successfully conducted by switching to the other method in all cases. Fibrotic scar tissue from a previous open calculi operation was present in one of four patients operated on by using the Alken dilation system, because the procedure could not be continued in the Amplatz group. The other two patients had mobile kidney, and the necessary access could not be provided because polyurethane dilators bent round when the kidney moved away from the access area during the procedure. Loss of access occurred in the last patient because the guidewire could not be inserted through the collecting system from the infundibulum of the calix in sufficient length, and the procedure was finalized by using a metal telescopic dilation set.

Issues occurred in two children from the metal telescopic dilation group for which a dilation of up to 20F was planned. Because metal dilators extend at intervals of 3F, they jump from 18F to 21F. This length was not compatible with the 20F tube, and metal dilators had to be pulled back after 18F of tubing was extended and replaced with 18F and 20F Amplatz dilators. A kinking of the guidewire that would normally necessitate switching to the other method was not observed in the groups.

The stone-free and residual fragments (<5mm) rates were also similar. A statistically significant difference was only observed in tract formation time. The Alken group had a shorter tract formation time than the Amplatz group (6.56±3.04 and 5.42±3.07 min, P<0.001). Nevertheless, statistically significant differences in operative time and scope time did not occur (Table 1).

In terms of the evaluation for cost-effectiveness, the Alken group was observed to be dramatically more cost-effective. The approximate cost per case for the Amplatz and Alken dilation groups was $220 and $7.25, respectively.

Discussion

PCNL is a reliable and efficient treatment option for large, multiple, and staghorn calculi and replaced open surgery.¹⁰ The percutaneous access procedure is directly or indirectly related to bleeding that occurs during PCNL, operative time, and success. Therefore, a correct access tract through the collecting system and its proper dilation are key procedures in PCNL.

Some of the most common complications of tract formation procedure in percutaneous renal surgery are bleeding, tract dilation failure, and collecting system perforation.^11
–13 A study reports that the nephrostomy tract dilation procedure is related to about half of the total blood loss observed in PCNL.¹² Independently of the type of dilator used during PCNL, the need for blood transfusion was reported to be within the range of 0% and 25% in various series.^{4,13

–21} Studies that compare blood transfusion necessities based on different dilation techniques are summarized in Table 2. According to this, in studies that compare Amplatz and balloon dilators, the need for blood transfusion in the Amplatz dilators was reported as 25%, 16.6%, 21.3%, and 2%, respectively.^4,13,20,21 In a study that compared Alken, one-step, and balloon dilators by Frattini and associates¹⁸ and in another that compared Alken and one-step by Amjadi and colleagues,¹⁶ the need for blood transfusion in the Alken dilators was reported as 1.8% and 5.9%, respectively.

Table 2.

Transfusion Rates

Author	Year	Alken	One step	Amplatz	Balloon
Frattini¹⁸	2001	1.8% (27)	0% (26)		15% (25)
Amjadi¹⁹	2008	5.9% (14)	5.9% (17)
Davidoff¹³	1977			25% (100)	10% (50)
Şafak²⁰	2003			16.6% (30)	13.7 (95)
Gönen²¹	2008			21.3% (192)	18.6% (43)
Wezel⁴	2009	2% (100)			8% (100)

In our study, blood transfusion need was 11.6% in the Alken dilator group and 13.4% in the Amplatz dilator group, which was statistically significant. In a recently published multicenter study by the PCNL study group of the Clinical Research Office of the Endourological Society (CROES), this rate was reported as 5.7% and is significantly lower compared with our results.²² In a study that investigated preoperative and postoperative characteristics regarding bleeding during PCNL, statistically significant variables were reported as stone type, tract count, dilation method, presence of diabetes, and stone surface area.²³ Apart from these, numerous factors such as surgical experience, additional imaging methods used during tract formation, the lithotripsy method, rigid or flexible nephroscope, and preexisting anemia could be used to explain blood transfusion needs that demonstrate change from study to study.

In our study, the relatively high blood transfusion needs could be explained by the absence of a flexible nephroscope, excessive aggressive behavior needed to clean the stones as much as possible, and preexisting anemia. In our study, in that the preoperative and postoperative variables relevant to bleeding were similar, it is significant to establish that hemoglobin levels decreased and that the blood transfusion rates of the semirigid polyurethane Amplatz dilator group were similar to that of the metal rigid Alken dilators when in fact lower levels were expected. The reason for this may be that in the Alken group, the metal dilators constantly put pressure on the blood vessels while continuing dilation over each other until the end, while in the Amplatz group, pressure effect disappears on the vessels and damage is done during the removal of a previous dilator in order to place a dilator one size larger every time.

Tract dilation failure could have occurred as a result of the presence of excessive scarring from previous operations, loss of renal access during dilation, or mobile kidney.^20,21,24 Şafak and coworkers²⁰ reported that the balloon dilation method failed to form a tract because of the presence of excessive scarring in two secondary and two tertiary cases, and that the procedure with Amplatz in three cases and Alken in one case was terminated. Davidoff and Bellman¹³ reported that balloon dilators bore less risk of access loss when compared with serial dilators. Gönen and associates²¹ established a failure in Amplatz from hypermobile kidney in two cases and for balloon dilators from excessive scar tissue in one case.

In our study, we switched to the other method because of tract dilation failure in two cases in the Alken group and four cases in the Amplatz group. In addition, we observed an advantage in Alken dilators over Amplatz dilators in cases in which we were not able to direct the guidewire through the collecting system as a result of stones obstructing the infundibulum.

While at the beginning of the study the choice of dilation method to be used depended on the preference of the surgeon, indications for Alken or Amplatz dilators began to become clearer in the course of the study. Anecdotally, we could maintain that Alken dilators should be the first choice in secondary or tertiary cases, in the presence of mobile kidney, and when the guidewire cannot be sufficiently inserted through the kidney; however, Amplatz dilators should be the first choice in children.

Collecting system perforation is another significant complication of percutaneous renal surgery. In the CROES PCNL global study,²² renal pelvic perforation was established as 3.4%; in the study that compared balloon and fascial dilators by Şafak and associates,²⁰ perforation rates of balloon and fascial dilators were reported as 11.6% and 16.6%, respectively. In the same study, such high rates were found to gradually decrease along with the learning curve of surgeons.²⁰ In our study, collecting system perforation for Amplatz and Alken dilator systems is 2% and 2.5%, respectively, and is in parallel with the results of the CROES PCNL global study, a statistically similar and a newer study.²² We believe that the advancing technology in addition to increasing knowledge on PCNL contribute to these rates being relatively lower compared with the results of the older study.

When retrospectively evaluated, we observed that surgeons preferred Amplatz dilators in 67 cases and Alken dilators in 121 cases. We believe that the cost per case plays as much of a significant role in these choices as the experience of the surgeon. Frattini and coworkers¹⁸ reported the price of an Alken dilator set as $500 in 2001. Gönen and colleagues²¹ reported the price of Amplatz and Alken dilator sets as $250 in 2008. Although Falahatkar and associates⁹ did not note the prices of sets individually, they determined that the order from the cheapest to the most expensive was Alken, Amplatz, and balloon dilators. In our study, the approximate cost per case was $7.25 for Alken dilators and $220 for Amplatz dilators; demonstratively, the most significant difference between the two groups in the study was cost. The starting price for Alken dilators is high ($875); however, the cost is reduced as the number of cases increase because these sets are reusable. Although Amplatz dilators are mentioned in the instructions manual by the manufacturing firm as for single use only, dilators can be resterilized in practical applications. Even though previous studies claim otherwise, based on our experience, dilators lose their quality with reuse and patient safety is compromised.²¹

We observed that Alken dilator use shortened the time spent on tract formation. While Alken dilators form the tract by intertwining, time is wasted on the Amplatz dilator system because the previous dilator has to be pulled back every time in order to insert another dilator one size larger. The fact that the nephrostomy tract formation time is shorter in the Alken dilator group, however, does not create a statistical difference in the total operative and scope time between the two groups. Similarly, stone-free rates and the rates of residual fragments smaller than 5 mm demonstrate a resemblance between the two groups and parallelism with the literature.²⁵

In this study, an exact comparison of Alken and Amplatz dilators was conducted for the first time and their efficiency, reliability, and cost efficiency were evaluated. Nevertheless, because this is a retrospective study, some factors that may have an influence specifically on the efficiency, such as body mass index or presence of diabetes, could not have been tested. Further, because the selection of cases was not random but based on the preferences of the surgeon, the surgeon chose in favor of the Alken group, especially in secondary cases. Therefore, there is a need for prospective studies that take preoperative and postoperative risk factors into consideration.

Conclusions

This study demonstrated that the two different dilation techniques used in PCNL cases are not dissimilar in terms of operative and postoperative results, except for tract formation duration. Although, in the Alken group, tract formation duration was shorter compared with the Amplatz group, this did not create a statistical difference in total operative time or scope time, and is clinically insignificant. Even though the indications of each technique were similar, it is possible to say that Alken dilators are more advantageous in the presence of a hypermobile kidney, in cases where the guidewire cannot be directed through the kidneys, and in the presence of excessive scar tissues, and Amplatz dilators are more advantageous in children. Notwithstanding, in comparison, Alken dilators are more cost-effective.

Footnotes

Disclosure Statement

No competing financial interests exist.

Abbreviations Used

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