numerous procedures are now available for the management of urinary stones . for the management of upper urinary calculi , the method of dilating the tract after percutaneous renal puncture to specifically remove urinary calculi advances in surgical technique and equipment have further contributed to percutaneous nephrolithotomy ( pcnl ) becoming the recommended primary treatment option for most patients with large - volume renal and staghorn calculi . " success " is often defined as the absence of residual stone fragments under conventional x - ray or computed tomography ( ct ) or when clinically insignificant residual fragments ( cirf ) are observed . although large - series pcnl results have been reported in the literature , standardized evaluation of " complications " is lacking . recent attempts to report complication rates of pcnl have focused on stratifying them by severity by use of the clavien grading system . first proposed in 1992 and modified in 2004 , the modified clavien grading system has been validated in a cohort of 6,336 patients . in this article , we retrospectively reviewed our experience with pcnl to grade perioperative complications according to the modified clavien classification . from may 1987 to december 2010 , 1,236 cases of pcnl from 1,066 patients were performed in our center . among these patients , , we retrospectively reviewed and analyzed 826 cases of pcnl from 698 patients , after the first 410 cases of pcnls had already been performed . the stone was classified as a staghorn stone if a renal pelvic stone had calyceal branching into the major calyx . owing to the tertiary hospital setting of our center , numerous patients were referred from other hospitals , and 35% of patients had undergone prior extracorporeal shock wave lithotripsy therapy and 34% of patients were diagnosed as having staghorn stones . all patients also underwent simple x - ray of the kidney - ureter - bladder , along with ct or intravenous urography . once the operation day was chosen , third - generation oral cephalosporin or quinolone was administered for more than 5 days to prevent postoperative sepsis , if pyuria was present in the urinalysis . with the patient under general endotracheal anesthesia , a 5 to 6 fr occlusion balloon catheter was inserted in the ipsilateral ureter , which later allowed for injection of contrast material for opacification and distension of the collecting system to aid in making an appropriate puncture . after ureteral catheterization , the patient 's position was changed to the prone position on a c - arm compatible table . once access was gained with a sheathed needle , the stylet was removed and a guidewire was inserted , through which tract dilatation was performed with either an amplatz dilator or a dilating balloon catheter ( cook urological inc . , indianapolis , in , usa ) . using a rigid nephroscope , stone fragmentation using ballistic or ultrasonic devices was done and the stone was evacuated by using forceps . although some question the need for a nephrostomy catheter , it was routinely inserted for tamponade of bleeding and urine drainage in our center . the success rate was defined as the absence of residual stone fragments under conventional x - ray or ct or when cirf was observed . cirf was defined as residual fragments that were smaller than 4 mm , asymptomatic , nonobstructive , and noninfectious . success was further classified as the initial stone - free rate , which was evaluated immediately after a single pcnl procedure , and the overall stone - free rate , which was evaluated 3 months after the initial pcnl and further ancillary procedure had been performed . perioperative complications were classified by using the modified clavien system , which was stratified into five grades ( table 2 ) . past medical history such as hypertension ( n=221 ) , diabetes ( n=105 ) , pulmonary tuberculosis ( n=30 ) , cerebrovascular accident ( n=21 ) , and skeletal abnormalities ( n=12 ) were included as variables . urologic anatomical factors such as diverticular stone ( n=42 ) , ureteropelvic junction obstruction ( n=25 ) , single kidney ( n=13 ) , megaureter ( n=9 ) , duplicated ureter ( n=5 ) , horseshoe kidney ( n=4 ) , and infundibular stricture ( n=3 ) were also entered as variables . a p - value < 0.05 in the multivariate logistic regression analysis was considered significant . the initial stone - free rate was 69.9% ( 488 patients ) , and the overall stone - free rate was 88.8% ( 620 patients ) . the lowest initial success rate was observed in the staghorn stone group ( 46% , p<0.0089 ) . furthermore , mean operation time ( 157.9176.85 days , p<0.0037 ) and hospital stay ( 5.183.12 days , p<0.0095 ) were significantly longer in the staghorn stone group . grade i complications were recorded in 88 ( 12.6% ) , grade ii in 145 ( 20.8% ) , grade iiia in 31 ( 4.4% ) , grade iiib in 5 ( 0.7% ) , grade iva in 6 ( 0.9% ) , grade ivb in 4 ( 0.6% ) , and grade v in 3 ( 0.4% ) patients . transient peri - nephrostomy catheter urine leakage for less than 24 hours , requiring only simple dressing , was observed in 106 ( 15.2% ) patients . fever , defined as at least a single episode spiking more than 38 , was the next common complication ( 77 patients , 11.0% ) . grade i , ii , iiib , and iva complications were significantly more common in the staghorn stone group . all four patients had both pyuria and hematuria in preoperative urinalysis , and thus preoperative oral antibiotics were given for more than 5 days . of the two patients who died of septic shock , one eventually developed brain edema after continuous renal replacement therapy . the other patient who died of septic shock had a history of parkinson 's disease and eventually developed stress - induced cardiomyopathy . one patient died from hypoxemia and respiratory acidosis caused by pulmonary embolism despite mechanical ventilation . to identify determinants of each complication prior stone - related fever and staghorn stones were found to be significant contributing factors for postoperative fever > 38. mean operation time was found to be significant for bleeding requiring transfusion ( table 6 ) . for other objective complications ( embolization , chest tube insertion , collecting system perforation , bowel injury , nephrectomy , sepsis , death ) , determinants could not be identified because of the small number of cases . to identify risk factors for developing complications classified as grade iiia or greater according to the clavien system only operation time was considered a significant contributing factor in the univariate analysis ( or , 0.994 ; 95% ci , 0.989 - 0.999 ; p=0.0255 ) , but it failed to remain a significant factor in the multivariate analysis ( or , 0.993 ; 95% ci , 0.984 - 1.000 ; p=0.1071 ) . the 2005 american urological association ( aua ) and 2008 european association of urology ( eau ) guidelines on the management of staghorn calculi recommend pcnl as the first - line treatment for staghorn calculi , any renal stone that exceeds 20 mm in diameter , and lower calyceal stones . in korea , the first pcnl was performed in july 1984 by koh et al . since may 1987 , our center has begun to treat calculi of the upper urinary tract by use of the pcnl technique . in the first 50 cases , the complication rate reached 53.1% , compared with 20% after the initial 50 patients . at that time , we attributed the complication rates mainly to inexperience and improper technique . the most recent korean report of pcnl performed in single large center was published in 2009 by kwon et al . in their retrospective report comprising 610 patients , the initial stone - free rate was 57.6% and the overall stone - free rate was 84.9% . transfusion was required in 8.7% of patients , similar to the 6.9% in our study . chest tube insertion for thoracic complications was necessary in 1.1% of cases , which was the same as in our study . bleeding requiring embolization occurred in 0.8% and sepsis occurred in 1.0% ( vs. 1.4% and 0.6% in our study ) . reporting a surgical outcome requires not only success rates , but also complication rates . success rates in pcnl are easily defined and most articles use the concept of cirf to define success . however , defining complications is difficult , and without a standardized method of classifying them , comparing complication rates in one study with those in another may be problematic , especially when certain factors are not classified as complications , such as fever or urine leakage . to compare overall complication rates and the severity of complications , the clavien system has been applied to radical prostatectomy [ 14 - 16 ] and radical cystectomy . tefekli et al first adopted the modified clavien classification system to stratify complications of pcnl in 2007 . in their series of 811 pcnls , tefekli et al reported overall complications in 29.2% ( vs. 33.4% in our study ) . grade i , ii , iiia , iiib , iva , ivb , and v complications occurred in 4% , 16.3% , 6.6% , 2.8% , 1.1% , 0.3% , and 0.1% , respectively . recently , de la rosette et al collected prospective data from the clinical research office of the endourological society ( croes ) for 5,803 consecutive patients who were treated with pcnl at centers around the world during november 2007 through december 2009 . in their report , the distribution of scores in the modified clavien grade was i ( 11.1% ) , ii ( 5.3% ) , iiia ( 2.3% ) , iiib ( 1.3% ) , iva ( 0.3% ) , ivb ( 0.2% ) , and v ( 0.03% ) . staghorn stones were present in 27.5% of patients , compared with 33.8% in our study . in their report , however , the number of specific complications in each grade was not provided . tefekli et al accounted for the lower incidence of grade i complications in their study as being biased by the retrospective nature of their study and the omission of certain minor complications . in our study , the most common grade i complication in our study was fever , occurring in up to 11% of cases . in a study by tefekli they attributed such a low incidence of fever to the use of prophylactic antibiotics and the separate classification of other complications that may cause fever ( i.e. , blood transfusion , sepsis , etc ) . we also used prophylactic antibiotics in patients with pyuria , but did not distinguish transient fever that may have been caused by events such as blood transfusion , because that may further contribute to selection bias in a retrospective study such as ours . in the croes study , fever of more than 38.5 degrees occurred in 10.5% of cases , similar to our study . in the literature , both the aua and eau guidelines recommend antibiotic prophylaxis for all patients who are undergoing pcnl . the aua guidelines report the benefits of a single dose of antibiotics . because we have observed death from septic shock grade ii complications occurred in 22.3% of our patients , and most were transient peri - nephrostomy catheter urine leakage ( 15.2% ) . this complication was managed by simple dressing only , but prolonged the hospitalization period ( 5.483.31 days vs 4.352.38 days , p<0.05 ) and therefore was classified as a grade ii complication , as in the study by tefekli et al . however , transient urine leakage occurred in only 4% of cases in a report by tefekli . again , the retrospective design of both studies may contribute to such differences because such minor complications may have been omitted during data collection . blood transfusion , the second most common grade ii complication , was necessary in 6.9% of cases in our study . perhaps the most significant complication of pcnl , bleeding requiring transfusion has been reported to have an incidence as high as 23% . in the croes study , bleeding can occur in every step of pcnl from percutaneous access to tract dilation to stone disintegration . this may be why in our series , only the mean operation time was found to be significant for bleeding requiring transfusion . moreover , 8 patients ( 1.1% ) in our study required selective angioembolization because of uncontrolled bleeding . we could not identify any risk factors in the multivariate analysis because of the relatively small number of patients . however , el - nahas et al , in their retrospective study of 3,878 pcnls to identify risk factors for extensive post - pcnl hemorrhage requiring selective embolization , found that upper calyceal puncture , solitary kidney , staghorn stone , multiple punctures , and inexperienced surgeon were significant risk factors . a similar study by srivastava et al reported that 1.4% of patients required angiography or embolization for bleeding control . they concluded that only stone size was a significant risk factor . in our study , grade iiib , iva , iv , and v complications were extremely rare , each occurring in less than 1% of patients . in fact , the probability of developing a complication of a grade higher than iiib in our center was only 2.6% ( 18/698 ) . two patients had undergone nephrectomy , one because of uncontrolled bleeding and the other because of xanthogranulomatous pyelonephritis . a few variables were missed during data collection , and this may have contributed to selection bias . another flaw of this retrospective study is that very few patients underwent postoperative ct imaging , because of its cost - effective nature in the clinical setting . because our definition of success mainly depended on plain x - ray films and the need for ct imaging was based mainly on the patient 's symptoms and laboratory findings , some unsuccessful pcnls may have been misclassified as successful . in the literature , although the modified clavien classification provides an objective , stratified grading system for complications , there are some drawbacks . for instance , there is a debate over whether to include ancillary treatments as grade iiia / b complication . furthermore , when comparing the complication rate from one center to another , certain minor complications such as atelectasis or urine leakage may not have been recorded . therefore , we believe that a consensus is needed to specify certain complications that should not be omitted . some may assume that certain complications , especially those classified in lower grades , are inherent to general anesthesia or the operation itself . although accurate for obvious complications in higher grades , the disparity in lower - grade complications between centers can be partly explained by this phenomenon . the modified clavien system provides excellent classification of complications of pcnl stratified by their severity . a consensus in describing minor complications and in whether to include ancillary treatment , along with prospective data collection , may facilitate this classification becoming the most objective , unified classification system yet known . the risks of developing clinically significant complications , such as bowel injury , sepsis , and death , remain low . patients with previous stone - related fever and staghorn stone patients are at risk of developing postoperative fever . blood and urine cultures should be obtained in these patients preoperatively to facilitate targeted antibiotic therapy , especially when sepsis develops . a shorter operation time , and thus less manipulation of the pelvocaliceal system , is necessary to achieve less bleeding .
purposeto stratify complications of percutaneous nephrolithotomy ( pcnl ) in a single , tertiary hospital by use of the modified clavien system.materials and methodsfrom may 1987 to december 2010 , 1,236 cases of pcnl were performed at our institute . 
 medical records were available for 826 cases of pcnl from 698 patients , from february 1995 to december 2010 . 
 using multiple factors , we retrospectively reviewed and analyzed 698 patients for complication rates classified by the modified clavien grading system , along with success rates.resultsin 698 patients , staghorn stone patients accounted for 33.8% ( 236 patients ) . 
 initial and overall stone - free rates were 69.9% and 88.8% . 
 a total of 297 complications were documented in 282 patients . according to the modified clavien classification , grade i , ii , 
 iiia , iiib , iva , ivb , and v complications were observed in 88 ( 12.6% ) , 145 ( 20.8% ) , 31 ( 4.4% ) , 5 ( 0.7% ) , 6 ( 0.9% ) , 4 ( 0.6% ) , and 3 ( 0.4% ) patients , respectively . 
 transient peri - nephrostomy catheter urine leakage ( 15.2% ) was the most common complication , followed by transient fever > 38 ( 11% ) and transfusion ( 6.9% ) . 
 other individual complications occurred in less than 1.5% of cases . in patients with staghorn stones , grade i , ii , iiib , and iva complications were significantly more common , and all grade ivb and v complications occurred in patients with staghorn stones.conclusionsthe modified clavien classification provides a standardized grading system for complications of pcnl , although consensus on specific complications would prompt better comparison between centers . 
 a shorter operation time is imperative to achieve less bleeding . 
 previous stone - related fever and staghorn stones are significant contributing factors for developing postoperative fever .