Research Article

Effect of Different Years of Resident Training on Complications and Stone Free Rate during Percutaneous Nephrolithotomy for Large Renal Stone Greater Than 20 mm: A Prospective Observational Study Using Balloon Dilator

Pao-Hwa Chen1, Meng-Yi Yan1, Heng-Chieh Chiang1*, Bai-Fu Wang1, Jesun Lin1, Chin-Pao Chang1, Sheng-Hsien Huang1, Chun-Chi Chen1, Hung-Jen Shih1,3,4, Chien-Hsiang Chang1, Jian-Ting Chen1 and Yao-Li Chen2
1Department of Surgery, Changhua Christian Hospital, Changhua, Taiwan
2Changhua Christian Hospital, Changhua, Taiwan
3School of Medicine, Chung Shan Medical University, Taichung, Taiwan
4School of Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan

*Corresponding author: Heng-Chieh Chiang, Department of Surgery, Division of Urology, Changhua Christian Hospital, 135, Nanxiao St., Changhua City, Changhua County 500, Taiwan

Published: 11 Sep, 2018
Cite this article as: Chen P-H, Yan M-Y, Chiang H-C, Wang B-F, Lin J, Chang C-P, et al. Effect of Different Years of Resident Training on Complications and Stone Free Rate during Percutaneous Nephrolithotomy for Large Renal Stone Greater Than 20 mm: A Prospective Observational Study Using Balloon Dilator. Clin Surg. 2018; 3: 2098.


Objective: The endoscopic management of urolithiasis has been the primary choice of treatment for upper urinary tract urolithiasis. For large symptomatic renal calculi, Percutaneous Nephrolithotomy (PCNL) provides the highest stone clearance rate. In this prospective study, we compared patients undergoing PCNL using balloon dilator with sequential Amplatz dilator.
Methods: We started using balloon dilator for nephrostomy tract for PCNL since August 2014. From August 2014 to July 2015, we performed 154 C-arm guided PCNL procedures with balloon dilator at our hospital. We prospectively followed these patients and recorded peri - and post-operative data and complications. We then compared the same data with 155 patients using Amplatz dilator in the previous year.
Results: A total of 309 patients were included in this study (154 patients in balloon and 155 in the Amplatz dilator). The average stone burden was larger in the Amplatz group (1189 vs. 771 mm2). Balloon dilator group has a slightly better stone free rate (78% vs. 75%). Patients with residual stone are the ones with higher stone burden on KUB (1734 and 1512 mm2). Surgeon's experience is also a factor in stone free rate. Most of the complication is Clavien grade 1-2. There were 3 patients Clavien grade 3 or higher in both group and no mortality.
Conclusion: Balloon dilator is non-inferior to sequential dilator in terms of complications. Surgeon’s experience seems to influence stone-free rate and blood loss. Future randomized trials are needed to establish the benefit of balloon dilator.
Keywords: Nephrolithotomy; PCNL; Percutaneous; Stone; Urolithiasis


Due to improvements in technologies and equipment, the treatments for upper urinary tract have shifted from the open and laparoscopic procedures to a more endourological approach. The reported rate of open procedures for upper urinary tract urolithiasis has decreased from 5% to 6% in the late 20th century to less than 1% in the beginning of the 21st century [1]. After Thomas Hillier performed the first therapeutic percutaneous nephrostomy in 1865, Fernstrom and Johannson was the first to report the use of percutaneous tract for stone removal in 1976 [2]. With the advancement in technologies, the first decade of 21st century has seen a shift to miniature instrumentation (smaller than 20 Fr.) in order to minimize wound to decrease complications and morbidities associated with larger instruments [3]. Due to poor stone clearance in larger calculi, the miniature system (mini, nano-perc) has stone size limitation [4]. With advancement in flexible ureterorenoscope (FURS), FURS offers comparable stone clearance to small renal stones without the visible wound of miniature PCNL. In current guidelines on urolithiasis, FURS is recommended in complicated patient such as during pregnancy, patients with urinary diversion, transplanted kidney, calculi in abnormal anatomy, patients whom cannot discontinue anticoagulants, obese patients, and renal diverticulum stone. In cases of large renal stone (>2 cm) or staghorn stones, standard size (24 Fr. to 30 Fr.) PCNL is still the preferred method of treatment. Therefore, the choice of treatment modalities in patients with renal stones need to individualized and a careful balance between stone free rate and minimal complications need to be addressed. In this study, we prospectively observe patients undergoing PCNL using balloon dilator and comparing to sequential Amplatz dilator set. We wanted to identify risk factors for postoperative complications and factors influencing stone free rate.
Statistical analysis
Patient demographics were expressed in mean values with standard deviation and range for each variable. Fisher’s exact tests were used to compare the complication between the 2 data set. Variables with P<0.05 were considered significant.

Table 1

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Table 1
Patient general data.


After obtaining CCH IRB approval (IRB number: 140315), we prospectively observed patients whom underwent PCNL using balloon dilator at our department from August 2014 to July 2015. Due to the balloon dilator’s ease of use and surgeon preference, balloon dilators were the main method of percutaneous access in all PCNL after August 2014. Prior to the introduction of balloon dilator at our hospital, sequential Amplatz dilator set have been used to establish PCNL tract. Therefore, we retrospectively identify patients prior to introduction of balloon dilator (from July 2013 to July 2014). To match up the patient numbers in both groups, an extra month was added resulting in a total of 309 patients (155 patients in Amplatz dilator group and 154 patients in balloon dilator group). After reviewing the medical records, all post-operative complications, lab data and culture results were recorded and analyzed.
Peri-operative preparation, operative method and postoperative care
The patient preparation and stone extraction method was identical in both group with the only difference being the dilatation of nephrostomy tract (sequential Amplatz dilator set and BARD X-Force® balloon dilator). In our urological training program, residents start performing PCNL in the 4th year of training as the main operator with a supervising senior staff looking over their work. Therefore, most of PCNL (close to 90%) at our hospital is performed by senior resident (4th year resident to fellow). All patients received intravenous pre-operative prophylactic antibiotics with 1 gram of cephalosporin. If the patient is more susceptible to infection (i.e. poor nutrition, immune compromised, DM) or pre-operative urine showed pyuria/bacteriuria then a 3rd generation cephalosporin will then be used. After induction of anesthesia, the patient is placed on lithotomy position for cystoscopy examination and insertion of 5 Fr. retrograde ureteral catheter into the renal pelvis. Prone position is used for the establishment of nephrostomy tract and proper care was taken to protect the pressure points. With more than 90% of PCNL cases using fluoroscopy in our department, adequate surgeon and staff protections are mandatory during the operation (lead aprons, neck shields, lead –containing gloves and lead goggles). The “eye-ofthe- needle” technique used in establishing percutaneous access are the same as described by Dr. Arthur Smith in the 2005 supplement of BJU international [2,5]. Nephrostomy tract dilatations are performed using either the sequential Amplatz dilator set or the BARD X-Force® balloon dilator (BARD-Davol Inc., Cranston, RI USA). After dilating the tract with the balloon dilator using 300 psi (20-22 ATM/bar) of pressure, the balloon was left inflated for 1 to 3 minutes as a tamponade effect in an attempt to minimize bleeding. A 24 Fr. Nephrostomy sheath is routinely used after the establishment of the nephrostomy tract, if the pre-operative image showed small collecting system then a smaller size sheath (18 Fr or 20 Fr.) would be considered at the discretion of the attending. A rigid 24 Fr. Nephroscope and ultrasonic lithotripter with continuous suction was used to break up the stone and a 2 or 3 prong grasper was used for extraction. A 6 Fr. Diameter double-J ureteral stent is routinely used and nephrostomy tube (20- 22 Fr.) is placed at surgeon’s discretion. The external nephrostomy tube (“tubeless” PCNL) is only omitted when the is no extensive bleeding at the end of the stone extraction and the decision is left to the primary surgeon’s discretion. After the placement of the double-J stent and residual stone is checked with fluoroscopy, the patient is turned back to supine position to wait for extubation. Post-operative care includes adequate fluid hydration, use of tranexamic acid and antibiotics for 1 to 3 days depending on the peri-operative finding. Intensive care was mandated if the patient experience severe sepsis with organ dysfunction.
Patient evaluation
A single fellow (P.H.C.) followed the patient after the operation and evaluate medical records for any post-operative complications (Clavien-Dindo classification used to grade severity). Amplatz dilator group was reviewed and recorded in the same fashion.

Table 2

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Table 2
Post-operative outcomes.

Table 3

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Table 3
Categorization of post-operative complication into Clavien-Dindo.

Table 4

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Table 4
Analysis of patients with post-operative infectious complications.


Patient characteristics and peri-operative data
The patient characteristics from both groups are shown on Table 1. One hundred and fifty-four patients underwent PCNL using balloon dilator from August 2014 to July 2015, while PCNL using sequential Amplatz dilator was performed on one hundred fifty-five patients from July 2013 to July 2014. The patient characteristics from both groups are very similar with Amplatz dilator group exhibiting larger stone burden on average. The post-operative data (Table 2) from both groups were similar (change in hematocrit and creatinine, stone-free rate and Clavien-Dindo grades. Most of the complications are self-resolving Clavien-Dindo grade 1 and 2 (Table 3) with three patients requiring further intervention. The sub-analysis of patients with infectious complications and stone free rate are listed on table 4 and 5. A positive pre-operative urine routine does not correlate with post-operative infectious complication (P=0.53), but a “dirty” urine on first puncture is related to infectious complications (P<0.05). The year of training does not correlate with post-operative infectious complications. Previous hospital admission due to urinary tract infection complications prior to PCNL does not seem to correlate with post-operative infectious complications. Balloon dilator showed slightly better stone free rate at 78% (compared to 75% in Amplatz dilator group). Analysis of the patients with residual stones, we noticed that the stone burden is almost twice the average. When comparing between the form of dilatation, the stone free rate is similar in both group (p= 0.59). But when breaking down to surgeon’s experience, we found that Fellow surgeons had better stone free rate using the balloon dilator. Fortunately, all of complications in these two eras are manageable and there were no Clavien-Dindo grade 5 complications (death of patient). No patients require post-operative blood transfusion.

Table 5

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Table 5
Analysis of patients with residual stones.

Figure 1

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Figure 1
Reduction of Hct % among residents of different training period.


In the rapid evolving field of endourology, the armamentarium is growing and evolving with each passing year. With improved instrumentation, endourological treatment of upper urinary tract urolithiasis has made open/laparoscopic procedures obsolete (<1%) [1]. Ever since the introduction of Donier HM3 extracorporeal shockwave lithotripter (ESWL) in 1980’s, ESWL has been a valuable tool in the treatment of urolithiasis but patient and stone characteristics limit its use. Since the stone free rate for ESWL decrease if the stone size exceeds 10 mm, guidelines suggest ESWL for stones less than 10 mm and favoring endourological procedures for stones greater than 10 mm. The improvement of FURS gives endourologist another added option in treating renal stones up to 20 mm, but the cost and durability of the scope is a major drawback. Miniature PCNL were used to minimize PCNL complications, but stone burden is still a major deciding factor in using miniature instruments [3,4,6,7]. Therefore, per guidelines, standard size (24 Fr to 30 Fr.) PCNL is the first line of treatment for renal stones larger than 20 mm.
The most common complications associated with PCNL are infection and hemorrhage [8-12]. A major roadblock in comparing post-operative complication in PCNL from different studies and hospital is the classification [13-15]. The use of Clavien-Dindo classification for complication in urological surgeries has been used and validated in several procedures such as prostatectomy (open and laparoscopic), donor nephrectomy and several urological laparoscopic procedures [14]. Numerous articles have investigated the use of Clavien-Dindo post-PCNL complications including two articles by Clinical Research Office of the Endourological Society (CROES) group [13-15]. In the article by Dr. de la Rosette, the agreement between different urologists is highest among higher grade classifications (grade 4 and 5) and the agreement decreases with decrease grades with the lowest among the lower grades (grade 1 and 2). There were high agreements for grade 3 and 4 but the agreement is low among the subgroups (grade 3a, 3b, 4a, 4b), which could be attributed to the use of anesthesia dividing the subgroups. Even our departments depending on attending’s preference, same procedures are performed using different anesthesia methods. Therefore, reporting minor complications in different hospitals with different cultures will vary significantly. In the article, a more specific definition between the classifications is formulated for PCNL based on expert opinions from 74 urologists [13]. Due to the high variable in the reported complication rate, PCNL complications can be as high as 83% [6]. Our complication rate of 50% for Amplatz dilator and 40% for balloon dilator includes transient fever and patients whom experienced extreme pain not controlled with oral medication and required intravenous or intramuscular injection for pain control (Table 3). In our study, we combined the subgroups in grade 3 and 4. If we modify our complication per the article by Dr. de la Rosette, more than 90% of our complications would be classified as grade 1 and only 1.9% (3 patients from each group) of our patients suffered severe life-threatening complications (grade 4) with no grade 5 complications.
Our combined stone free rate for both group of 76% (75% in Amplatz dilator and 78% in balloon dilator) is similar to the results of previous studies [11]. When comparing between the two dilatation methods, the stone free rate is slightly better for the balloon dilator (78% and 75%, p=0.59). An explanation would be the stone burden is much less on average in the balloon dilator group (771 mm2) than the Amplatz dilator group (1189 mm2). Analyzing the data from the residual stone patients (Table 5), we can see that the average stone burden is almost twice than the average (1734 mm2 and 1513 mm2). In theory, increase surgical experience will improve the stone-free rate but surgeon’s experience is hard to quantity. Since most of our PCNL are performed by senior residents, we decided to compare the stone free rate among the different year of resident training. As the year of training increases, the stone free rate increases and complication decreases (Table 5). The improvement of stone-free rate and decrease in complications could all be attributed to improved intra-operative instrument manipulation. Previous studies have demonstrated the importance of instrument manipulation during prone versus supine PCNL [16,17]. Due to the increase range of instrument manipulation, prone position resulted in a better stone free rate. An interesting data in our study showed that surgeons in their Fellowship years had better stone free rate using the balloon dilator compared to Amplatz dilator (p<0.05), while the junior residents and attending had similar stone free rate using either method. This finding seem contradictory to the previous statement of increase experience will result in higher stone free rate. But looking at the data closely, the Amplatz dilator data showed that attending surgeons had the highest stone free rate (86%). Since attending only has sequential dilators during their training, the attending surgeons are more familiar with the sequential Amplatz dilator. On the other hands, balloon dilator is only recently covered by Taiwan’s National Healthcare Insurance (NIH) in 2014. Due to the ease of use, the residents preferred dilatation with balloon dilator which resulted in residents being more familiar with its use than attending surgeons. The data from Table 5 seems to support our explanation. NIH also limits the initial survey and follow-up modality for urolithiasis. Even though guidelines suggest CT scan as the standard initial image modality, the NIH in Taiwan only allow intravenous pyelography and renal ultrasound as the initial image modalities with KUB image as follow-up. All of our patients will have at least 1 KUB image within 1 month after the procedure to check for residual stone.
The reported rate of hemorrhagic complications after PCNL needing blood transfusion ranged from 1% to 17% among different studies, therefore numerous studies have been trying to identify variables that increase the chance of hemorrhage [1,6,8,18-22]. In the CROES global study investigating complications and outcomes of PCNL, hemorrhagic complication requiring blood transfusion was about 5% [10]. Variables that have been identified as risk factors for severe hemorrhage requiring blood transfusion are multiple punctures, stone burden, surgeon inexperience, operative time, [8,19,21]. Studies comparing different dilatation methods have not been able to determine which dilatation method results in higher hemorrhagic complications [20-23]. In our study period, no patients required blood transfusion and the hematocrit percentage in both groups were similar (5.3% vs. 5.13%, P=0.81). We did notice a decrease in hematocrit percentage as the year of training increases (Figure 1). When creating the dilatation tract, the balloon dilator uses a spreading force rather than lacerating or tearing the tissues [20,24]. An advantage of balloon dilator is the fast one step dilatation method, rather than a series of 10-12 dilatations. This advantage is extremely useful in patients with hypermobile kidney during dilatation. With the help of the anesthesiology, hypermobility can be corrected but at the cost of patients experiencing apnea conditions for the duration of the dilatation process. This can be extremely dangerous in severe obese patients whom are already in danger for cardiopulmonary complication during prone position [25]. In our study, we were not able to quantify that balloon dilator decreases time of tract dilatation (the time from insertion of guide wire to insertion of working sheath) but the feedbacks from the residents has been favorable toward balloon dilator. The time difference between the dilator methods could be an interesting data in the future studies. An explanation for longer operative time in the balloon dilator group (95 min vs. 80 min) is surgeon experience. Nearly 50% of primary surgeons in balloon dilator were 4th and 5th year resident, while 70% of primary surgeons in the Amplatz dilator were Fellow or Attending. The value of surgeon experience can be seen in our study by the higher rate of residual stone, higher change of hematocrit percentage and longer operative time in junior residents (4th and 5th year trainee) performing PCNL (Figure 1).
In this prospective study, we demonstrated that balloon dilator is non -inferior to traditional tract dilatation methods with similar complication and stone-free rate. After the introduction of PCNL procedure to our department in the early 2000’s, our case numbers have progressed to average 150 cases per year from 2007 to 2015 (ranging from 120 to 177 cases/year) which coincide with the definition of high volume center described in the CROES study (more than 100 cases/year). Several points would be a good discussion topic in the future large randomized control trial, such as tract dilatation time from puncture to insertion of nephrostomy sheath or surgeon comfort/preference. As endourologist, we need to keep our eyes and mind open to these new technologies and have an unbiased view to evaluate the usefulness of their uses to add them to our growing armamentarium.


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