percutaneous nephrolithotomy ( pnl ) is the gold standard for treating patients with kidney stones over 2 cm in diameter .
it has replaced open surgeries due to equal efficacy , less morbidity , and higher patient acceptance . however , the most common complications are still urine extravasation , infection , and bleeding .
the classic procedure consists of four major steps : insertion of a ureteral catheter , execution of percutaneous access to the kidney with tract dilation , lithotripsy and stone extraction , and finally protection of the tract with a nephrostomy tube .
tract dilation may be conducted with the aid of metallic alken dilators , plastic amplatz dilators , or a pneumatic dilator .
one - stage tract dilation is also a well - known technique ; however , it is not utilized in our department .
it has been previously suggested that blood loss during renal dilation with amplatz instruments is higher .
it has also been suggested that with sequential application of fascial dilators , the hemostatic pressure on the kidney parenchyma is lost , resulting in intermittent bleeding from renal vessels . on the other hand ,
the rate of other complications seems to be comparable . as there are various methods of tract performance ( inter / infracostal approach , various calyx punctures , utilization of access sheath , etc . )
we hypothesized that it may not be the dilator type itself but rather the way they are utilized that may influence the type of complications .
the aim of our study was to compare these two methods of tract dilation in terms of efficacy and safety , and to find out what may be the source of differences in complication rates .
between august 2008 and april 2016 , pnl was performed in 283 patients in our department .
two methods of tract dilation were utilized : group i ( n=123 ) comprised patients where alken dilatator was used ; group ii ( n=99 ) comprised patients where the amplatz dilator was used .
both procedures were conducted by two experienced endourologists ( one used the alken dilator and the other used the amplatz dilator ) .
efficacy was assessed based on ultrasound and x - ray examination one month after the procedures .
the presence of residual stone <3 mm in diameter was considered insignificant and patients were classified as stone free .
urosepsis was diagnosed if there was positive urine and blood cultures and two out of the following four : temperature > 38.5c or < 36c , white blood cells > 12,000 cells / mm or < 4,000 cells / mm , respiratory rate > 20 breaths per minute or paco2 < 32 mm hg , and pulse over 90 beats per minute .
other variables were also analyzed including : operating room time , scope time , and hospitalization time .
this study was performed in accordance with the ethical standards of the 1964 declaration of helsinki . in a supine position ,
the patient was rotated on a table to the prone position . at an angle of 30
a hydrophilic guidewire was inserted into the needle and placed in the ureter . over the wire ,
after the lithotripsy , re - entry malecot catheter was inserted over the amplatz wire within the kidney and the ureteral catheter was withdrawn .
our amplatz dilator technique was a standard technique , well - described in the literature where the final stages may be replaced with a tubeless option .
the procedure used for the alken dilator was similar , up to the point of introduction of the amplatz wire . instead of a straight amplatz wire , a stiff wire with a coiled end was inserted into the pyelocalyceal system .
subsequently , the metallic dilator was introduced over the wire to widen the tract up to 26-fr .
the access sheath and safety wire were not used . at the end of the lithotripsy ,
a drain was left in the pyelocalyceal system and the ureteral catheter was left in place . after the procedure , each patient received 1 g paracetamol intravenously every six hours .
antibiotic prophylaxis consisted of cephalosporin ( second generation ) given during induction of general anesthesia .
student t - test for continuous variables with normal distribution was used . for continuous variables without normal distribution ,
for categorical variables , the chi - square test was used . to show dependence between categorical variables we used correspondence analysis .
power analysis was conducted with the assistance of g*power statistical tool . a p value <
this study was performed in accordance with the ethical standards of the 1964 declaration of helsinki .
in a supine position , a 6-fr ureteral catheter was inserted into the appropriate kidney .
the patient was rotated on a table to the prone position . at an angle of 30
a hydrophilic guidewire was inserted into the needle and placed in the ureter . over the wire ,
after the lithotripsy , re - entry malecot catheter was inserted over the amplatz wire within the kidney and the ureteral catheter was withdrawn .
our amplatz dilator technique was a standard technique , well - described in the literature where the final stages may be replaced with a tubeless option .
the procedure used for the alken dilator was similar , up to the point of introduction of the amplatz wire . instead of a straight amplatz wire , a stiff wire with a coiled end was inserted into the pyelocalyceal system .
subsequently , the metallic dilator was introduced over the wire to widen the tract up to 26-fr .
the access sheath and safety wire were not used . at the end of the lithotripsy ,
a drain was left in the pyelocalyceal system and the ureteral catheter was left in place . after the procedure , each patient received 1 g paracetamol intravenously every six hours .
antibiotic prophylaxis consisted of cephalosporin ( second generation ) given during induction of general anesthesia .
student t - test for continuous variables with normal distribution was used . for continuous variables without normal distribution ,
the chi - square test was used . to show dependence between categorical variables we used correspondence analysis .
power analysis was conducted with the assistance of g*power statistical tool . a p value <
patients in both groups did not differ in terms of age , sex , bmi , or stone size and affected side ( table 1 ) .
we did not find any differences in total operative time , tract formation time , or fluoroscopy time .
tract dilation failures , although more frequent in group i , were not significantly different between the groups . the hemoglobin drop and
most of the procedures in group i were performed with infracostal access while in group ii more procedures were conducted with intercostal access . the number of accesses did not differ between groups . in the amplatz group ( group ii )
most accesses were through middle calyx while in group i ( alken group ) most were through the lower calyx .
we found significant differences in postoperative complications as shown in table 2 and figure 1 .
most grade i ( postoperative fever over 38.5c ) complications were more common in group i. similarly grade ivb complications ( urosepsis ) were more frequently observed in group i. pleural injury ( grade iva ) were more common in group ii . other complications ( ii  blood transfusions , iiia 
extravasation , iiib  arterio - venous fistula ) and non - complicated course of the disease were similarly distributed between groups .
pnl is an efficacious procedure with a more than 80% stone - free rate independent of type of access .
it has replaced open surgeries due to the same efficacy , less morbidity , and higher patient acceptance .
still , one of the most common complications after pnl is infection , sepsis , and bleeding resulting in hemoglobin drop and occasionally the need for blood transfusion .
as stated earlier , the alken dilators are allegedly safer than the amplatz dilators due to maintenance of continuous hemostatic pressure on the kidney parenchyma . in our study , both types of tract dilation were comparable in terms of blood loss . similarly , blood transfusions were not different between groups , supporting the previous reports that both types of tract dilation are equally safe .
other parameters such as total operative time , fluoroscopy time , and tract formation time were not different between the two groups . similarly , the tract dilation failure rate was comparable between the two groups , which is consistent with other study outcomes . in our cohort , in the amplatz group there was insignificantly fewer failures . in our experience this may be due to the fact that in the alken group , the puncture was most often through the lower calyx and the wire was positioned in the renal pelvis .
on the other hand , in the amplatz group , the puncture was usually directed at the middle calyx and the wire was positioned within the ureter . positioning the wire in the ureter makes it more stable and less prone to fall out of the kidney during tract dilation .
other factors may influence tract dilation failure ( e.g. , bmi , gender ) due to kidney movement during the procedure , however , we did not observe differences in distribution of the aforementioned characteristics as showed in figure 1 , postoperative fever and sepsis in our cohort were more common in the alken group .
other complications , such as contrast extravasation , arteriovenous fistula or postoperative hematoma , were comparable between groups .
we may only speculate why there were differences in rates of grade i and ivb between the two groups , as there was no simple explanation .
we hypothesized that the cause lies in the fact that in the alken group we did not use an access sheath .
this may cause higher irrigant pressure inside the kidney during lithotripsy as most of the influent water departs through the ureter instead of the access sheath .
a similar situation was described in micro - percutaneous nephrolithotomy , where there was no need for an access sheath and higher irrigant pressures were observed in comparison with classic pnl .
as some of the stones were infected , this , with the combination of high irrigant pressure , may cause more septic complications after pnl .
the clavien - dindo classification is usually used to evaluate major complications ( 3a ) after pnl .
however , we showed that even postoperative fever ( grade i ) may vary between methods .
this suggests the source of this difference may be important , and even minor complications should be reported after pnl . as more procedures in the amplatz group
were conducted through the middle calyx it was not surprising that many of them were intercostal . however
, this fact did not have an influence on blood loss , and supports reported evidence that inter / infracostals access is equally safe in this regard . on the other hand , intercostal access results in more frequent pleural injury ( figure 1 ) .
both procedures were characterized by mild pain the day after the operation ( table 2 ) .
the way in which pnl may be performed with alken and amplatz dilators differs among urological departments .
indeed our study did not compare two different dilators but rather two different methods of tract dilation where both have their pros and cons .
based on our study , we can not determine the superiority of one method of tract dilation over the other as these two approaches were completely different in terms of punctured calyx , inter / infracostal access , and utilization ( or not ) of a sheath .
however , it is clear that irrespective of the dilator type used , the important differences result from other aforementioned factors .
total operative time , tract dilation time , fluoroscopy time , and tract dilation failure were comparable between the two groups .
fever over 38.5c and urosepsis were more common in the alken group . on the other hand , pleural injuries were more common after pnl with amplatz dilators .
it is clear that all differences resulted from the punctured calyx , type of access to the kidney ( inter / infracostal ) , and utilization ( or not ) of an access sheath rather than the type of dilator itself .
 backgroundpercutaneous nephrolithotomy ( pnl ) is the standard procedure for patients with renal stones over 2 cm in diameter . 
 we analyzed complications after this procedure focusing on two different methods of tract dilation.material/methodsbetween august 2008 and april 2016 222 percutaneous nephrolithotomies were performed in a total of 208 patients . 
 the group i ( n=123 ) comprised patients where alken dilatators were used , while group ii ( n=99 ) comprised patients where amplatz dilators were used . 
 efficacy was examined based on ultrasound and x - ray examination one month after the procedure . 
 complications were recorded using clavien dindo classification.resultsefficacy was 85.3% and 86.8% in group i and ii , respectively ( p=0.77 ) . 
 grade i complications were present in 14.6% and 3% , grade ii were present in 9.7% and 8% , grade iiia were present in 2.4% and 2% , grade iiib were present in 1.6% and 2% , grade iva were present in 1.6% and 7% , grade ivb were present in 3.2% and 1% in group i and group ii , respectively . 
 these differences were statistically significant ( p=0.03).conclusionsefficacy was comparable between alken dilator and amplatz dilator groups . in group 
 i , there were more postoperative fevers > 38.5 c and a higher rate of urosepsis . 
 on the other hand , in group ii we observed more pleural injuries . 
 all differences resulted from the type of access to the kidney ( inter / infracostal ) , punctured calyx , and utilization ( or not ) of access sheath rather than type of dilators itself . 
Background
Material and Methods
Compliance with ethical standard
Description of procedure
Statistics
Results
Discussion
Conclusions