Open Journal of Urology, 2013, 3, 248-252 Published Online October 2013 (
Clinical Analysis of a Coaxial Dilator Set Attached to
Needle Puncture for Percutaneous Nephrolithotomy*
Evandilson Guenes Campos de Barros1#, Salvador Vilar Correia Lima2, Fabio de Oliveira Vilar3,
Eugenio Soares Lustosa4, Roberto Santos Lima4
1Master’s Program of Post Graduation in Surgery, Center of Health Sciences, Federal University of Pernambuco, Pernambuco, Brazil
2Department of Surgery, Federal University of Pernambuco, Pernambuco, Brazil
3Urology Service of the Hospital das Clinicas, Federal University of Pernambuco, Pernambuco, Brazil
4Member of the Brazilian Society of Urology, Recife, Brazil
Received August 19, 2013; revised September 17, 2013; accepted September 25, 2013
Copyright © 2013 Evandilson Guenes Campos de Barros et al. This is an open access article distributed under the Creative Com-
mons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work
is properly cited.
Introduction: Percutaneous approach to the kidney is a very useful alternative in renal surgery which minimizes the
morbidity of a variety of procedures. Objectives: To evaluate the efficacy, practicity of a reusable system of metallic
coaxial dilator coupled to a special puncture needle to perform lumbar puncture and dilation of the percutaneous tract.
Methods: A randomized experimental study was carried out involving 50 individuals. These patients were randomized
as follows: Group 1 had the procedure performed with the conventional disposable Amplatz set traditionally used for
this procedure. Patients in Group 2 were operated utilizing the new reusab le coaxial set specially designed for th is pur-
pose. The following parameters were measured to compare the 2 groups: sex Corporeal Mass Index (CMI), Pre and
postoperative hematocrit and hemoglobin. Time interval between the puncture, dilation and access to the renal pelvis
and insertion of the nephroscope were also analyzed. Results: There was no statistical difference between the 2 groups
concerning hematocrit and hemoglobin changes when comparing pre- with postoperative period. Patients in Group 2
required a significant lower time between puncture and final access to the upper collecting system. Conclusion: The
new coaxial dilator set showed to be as safe as the conv entional Amplatz set with the advan tage of reusability and de-
crease of tract dilation time.
Keywords: Percutaneous Nephrolitho tomy; Metallic Coaxial Dilator; Kidney Stone
1. Introduction
Urinary lithiasis is one of the most common diseases af-
fecting the urinary tract with an incidence rate ranging
from 5% to 15% according to world literature [1]. Offi-
cial data from Brazilian health system indicate that over
300.000 hospital admissions occurred between January
and May 2012. From this group, 8.79% were related to
urinary stone disease [2].
The removal of urinary stones has evolved signifi-
cantly in the last 25 years since the introduction of per-
cutaneous nephrolithotomy (PNL) ureterorenoscopy (URS )
and extracorporeal shockwave lithotripsy (ESWL). The
sophistications introduced to these equipments and dif-
ferent sources of energy to destroy stones gave a new
insight to the adequate definition of the type of treatment
to be applied according to stone size and location and as
such represents a significant advance in the treatment of
this disease [3,4]. In an attempt to reduce costs and time
to perform percutaneous approach to the kidney without
increasing morbidity to th e procedure, we propose a new
reusable dilating system, which significantly decreases
these items and offers new possibilities in performing
percutaneous renal surgery. In this procedure, a path is
created for percutaneous removal of stones by using an
association of principles already used for this purpose.
On the other hand, serial or telescopic, pneumatic dila-
tors have shown to require greater surgical time and in-
creased incidence of bleeding [5]. Most surgeons prefer
to use sequential dilators to create access to the kidney.
*I declare that all information shown in this study are results of ou
work and there is no plagiarism.
#Corresponding author.
With the development of more sophisticated devices, it
is possible to promote a gateway to the kidney with
opyright © 2013 SciRes. OJU
lower diameter (11 - 18 French) and consequently less
morbidity to the patient [6].
The aim of the present study is to test the efficacy and
practicability of this new reusable set of metallic coaxial
dilating system in comparison with the disposable system
normally used in clinical practice (Figures 1 and 2). As
the basic principles of the surgical technique have not
been modified, an experimental trial of the procedure
was not performed in animals.
2. Patients and Methods
A randomized clinical study, involving 50 patients from
our outpatient clinic suffering from nephrolithiasis with
surgical indication for percutaneous nephrolithotomy was
carried out to prove the feasibility of this method. Pa-
tients were informed about the objectives of the study
and invited to participate.
Patients age ranged between 20 and 60 years and were
Figure 1. Special extra lenght puncturing ne e dle and coupled dilating set.
Figure 2. Schematic drawing of the dilating set and its coupling and operating way.
Copyright © 2013 SciRes. OJU
randomized into two groups: Group 1: patients with medi-
cal records ending in ev en numbers who underwent PN L
technique using conventional disposable sequential Am-
platz dilators. Group 2: patients in the records ending in
odd numbers who underwent the procedure use the new
coupled coaxial d ilators.
Two main parameters were analyzed: time spent be-
tween puncturing and dilating the tract and insertion of
the nephroscope confirming access to the renal collecting
system; blood loss was evaluated by checking HT and
HB in the pre-operative period, 24 hours after the proce-
dure and at discharge. Possible complications of dilation
process—like renal pelvis and renal pedicle vessels injury,
puncture of solid organ or bowel were also analyzed.
Statistical analysis was divided into three steps accord-
ing to the objectives previously established: Comparison
of the groups according to sex, age, BMI, Hb and Ht;
comparison of groups of time dilation; intragroup com-
parison (pre X post) and between groups as related to Hb
and Ht.
To compare the distributions by gender we used the
chi-square test, and the Student t test was applied to com-
pare quantitative variables (age, BMI, Hb and Ht) be-
tween groups.
The nonparametric Mann-Whitney test was used to
compare the groups related to time spent to dilation due
to lack of normality of this variable.
To evaluate the differences between both groups (ex-
perimental standard X) and between times (pre X post)
regarding the variables Ht and Hb, we used a model of
analysis of variance (ANOVA) with repeated measure-
The study was approved by the Ethics Committee for
Clinical Research of the Institution.
3. Results
The results are illustrated in the Tables 1 and 2, which
shows that there was no statistically significant differ-
ence between the groups as related to variables, i.e., the
groups can be cons i dere d h o mogeneous for this pu rp ose.
There is a statistically significant difference between
groups (p < 0.05). The time dilation of the experimental
group was lower than the standard group.
This analysis evaluated the effects of group, time ef-
fects and the interaction effects between groups and time.
Because the interaction was not considered statistically
significant (p > 0.05) for both the Hb and to the Ht, we
evaluated the effect of group (collectively for all times)
and end time (jointly for both groups).
Analyzing the results of ANOVA, it can be stated that:
Hb: no significant difference between groups (p = 0. 4 0 3 )
in the two periods. When analyzing intra-group compari-
son (pre X post) it wa s found that there was a significant
reduction in pre and post results in both groups (p =
Ht: no significant difference between groups (p = 0.204)
in the two periods. When analyzing intragroup compari-
son (pre X post), it w as found that there was a significant
reduction from pre to postop results in both groups (p =
There was only one complication in one patient in
Group 1 (Amplatz dilators). An inadvertent perforation
of the renal pelvis, leading to the development of ascites
urinosa was found. There were no complications in the
group using the new coaxial dilato r. The presence of this
unique complication was not statistically significant in
the study.
4. Discussion
There are various techniques described to perform access
directly to the collecting system, the most frequent being
Amplatz dilators, coaxial Alken dilators and balloon di-
lators. Such techniques have similar complication rates [7].
The ideal technique for percutaneous access must have
acceptable complication rates, promote easy access to the
renal collecting system and at the same time provide low
economic impact. The number of kidney punctures re-
quired to perform an adequate nephrostomy tract is di-
rectly related to bleeding in percutaneous nephrolith-
otripsy [8] .
Table 1. Results of the analysis of homogeneity between
Standard Experimental
Variable p-valor
Females 13 (52%) 13 (52%) 1.00
Age (years) - Mean (SD)
Min imum - Ma xi mum 42.3 (11.5)
24 - 66 37.6 (10.9)
22 - 58 0.146
BMI - Mean (SD)
Min imum - Ma xi mum 28.3 (4.5)
21.6 - 41.0 29.6 (4.1)
23.1 - 38.20.282
Hb - Mean (SD)
Min imum - Ma xi mum 13.9 (1.4)
11.4 - 17.5 13.76 (1.2)
11.7 - 16.40.387
Ht - Mean (SD)
Min imum - Ma xi mum 42.0 (4.2)
35 - 51 40.4 (3.1)
35.8 - 46.50.134
SD = standard deviation; BMI = body mass index.
Table 2. Results of the comparison between the groups with
respect to tim e dilation.
Standard Experimental
Dilation Time (minut es) p-valor
Median 12 2.2
P25 - P75 8.6 - 12.5 1.5 - 2.4 <0.001
P25: Percentile 25, P75: Percentile 75.
Copyright © 2013 SciRes. OJU
The preference for the comparative study between the
coaxial dilator and coupled sequential dilators refers to
the failure rate of inflatable dilators (17%). This rate rises
to 25% when applied to patients with previous surgery
[9]. Pneumatic dilators have not shown better results than
the Amplatz dilators concerning decreased surgical time
and decreased postoperative complications and a higher
cost [10].
According to data collected, there was homogeneity
between groups A and B, related to gender, age, body
mass index (BMI), and hematological: hemoglobin (Hb)
and hematocrit (Ht).
The concern about having homogeneous groups refers
to the possibility of difficulty in performing the proce-
dure on specific groups, mainly related to BMI. This
confirmation supports the reduction rates of research
biases. Kessaris et al. [11] analyzed 2200 percutaneous
renal procedures and stated that it was not a risk factor
for renal bleeding: age, sex, number of punctures renal
and procedure duration.
The measurement of efficacy in performing the ne-
phrostomy tract was defined as the time required estab-
lishing the path after percutaneous puncture of the col-
lecting system and insertion of the nephroscope. The
time dilation was lower in the group that used the new
coaxial dilator: The mean time spent with the standard
technique 12 was minutes, and 2.2 minutes with the new
set (p < 0.001). This can be explained by the elimination
of some steps in the dilating processs, which leads to
savings in time such as switching stabilizer using a punc-
ture needle as a guide; stabilizer safety valve “stop”,
which prevents the progression of the device in addition
to the limit established by the surgeon, decreasing com-
plication rates; sequential dilators and coupled to the
system in monoblock; stabilizer removed en bloc and
dilator set, maintaining 30 French (F) sheath and guide
The level of bleeding caused by the dilato r was similar
in both groups, as shown by comparing drop in Hb and
Ht between groups and within groups. No patient in both
groups required blood transfusion. These data confirm
reports of the literature [12]. Michel et al. [13] in a series
of 315 cases reported 17.5% of bloo d transfusion.
Bleeding is the most common complication and is as-
sociated with the number of punctures, stone volume and
diameter of the surgical material [8]. All patients under-
went only one puncture per treatment session, the di-
ameter of the material used was 30 F in the two groups.
As described before the bleeding rates are similar to the
reports by others [13].
The overall rate of complications in percutaneous ne-
phrolithotomy can reach up to 83% [14]; however, the
vast majority of these complications are minor, such as
bleeding or fever without further repercussions. Major
complications occur between 0.4% - 4.7% to sepsis and
0.6% - 4% to renal bleeding needing surgical interven-
tion [6]. In the present study, one lesion of the renal pel-
vis was observed in the control group. No complications
were seen in the study group.
When considering costs to perform perctaneous neph-
rolitotripsy, although no specific studies were performed
specifically considering this item the new set of dialato rs
promotes significant savings according to the literature
without increasing the surgical risks to patients and
maintaining similar efficacy [15].
5. Conclusion
Data obtained in the present stu dy support the idea that a
reusable coaxial metallic set may represent a feasible
option in the percutaneous approach to the kidney and
produces significant savings especially for institutional
use without increasing surgical risks.
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List of Abreviations
PNL: Percutaneous nephrolithotomy
URS: Ureterorenoscopy
ESWL: Extracorporeal shockwave lithotripsy
BMI: Body mass index
Hb: Hemogl o bin
Ht: Hematocrit
ANOVA: Analysis of varianc e
F: French