Impact of Surgical Experience on Stone-Free Rates of Ureteroscopy for Single Urinary Calculi of the Upper Urinary Tract: A Matched-Paired Analysis of 600 Patients

Abstract

Introduction:

To evaluate the impact of surgical experience on ureteroscopic stone-free rates (SFR) and complication rates (CR) for the treatment of urinary calculi of the upper urinary tract.

Methods:

We evaluated retrospectively, patients (n=300) having undergone ureteroscopy (URS) for single urinary calculi treated by residents (n=12) at our department over a 6-year period. These patients were matched according to age, gender, body–mass index, and stone side/size/site with patients (n=300) treated by consultants (n=5) of our department during the same period. Patient data, primary SFR, and CR were compared.

Results:

The mean±standard deviation (range) stone size was 6.39±3.26 (2–20) mm. The primary SFR after one URS procedure was 95.2% and did not differ between residents and consultants (95% vs 95.3%, p=0.489). The SFR were 95.9% and 98.5% for ureteral stones (p=0.125) and 93.2% and 89.3% for kidney stones (p=0.298) in the resident and consultant group, respectively. The SFR differed significantly between ureteral and kidney stones (97.2% vs 91.3%, p≤0.001). Perioperative complications occurred in a total of 63 patients (10.5%): Clavien 1: 3.8%, Clavien 2: 2%, Clavien 3a: 1.8%, and Clavien 3b: 2.8%, respectively. There were no differences in the total CR between residents (12%) and consultants (9%) (p=0.2116). However, the ureteral perforation rate was significantly higher in residents compared with consultants (4.3% vs 1.3%, p≤0.027).

Conclusions:

URS is a safe and efficacious procedure for the treatment of single urinary calculi. Resident status does not compromise the SFR after ureteroscopic treatment of single urinary calculi. However, the incidence of ureteral perforation was associated with surgeon's experience.

Introduction

Technological improvements have evolved ureteroscopy (URS) into a safe and efficacious modality for the extraction of urinary calculi from the upper urinary tract. Depending on the stone size and location, the overall ureteroscopic stone-free rates (SFR) of up to 100% have been demonstrated.^1

–5 Complication rates (CR) of up to 30%, but with significant complications (i.e., ureteral avulsion) under 1%, have been reported.^1

–9 It has been demonstrated that experience might be a predictive factor for negative outcome in URS as well as being strongly correlated with the incidence of adverse events.^6,7,9
–11 However, the actual impact of experience on postoperative SFR and perioperative complications of different severities has not been clearly shown.^7,9
–11 The aim of our study was to evaluate the impact of experience on ureteroscopic SFR and postoperative CR using a matched-paired approach.

Patients and Methods

Two thousand three hundred sixty-three patients with urinary calculi underwent URS between January 2006 and December 2012 at our department. A retrospective database analysis of our prospectively managed database was used to evaluate those patients having undergone URS for single urinary calculi (n=300) treated by residents (n=12). These patients were matched according to age, gender, body–mass index, and stone side/size/site with patients (n=300) who have been treated by consultants (n=5) of the department.

The consultant surgeons were board certified urologists with a minimum of 5-year training and a minimum caseload of 250 URS procedures. All residents had to pass a standardized mentor-based URS training program during the 5-year residency at our institution (Table 1). The mentor-based URS training program was as follows: First, the residents performed intensive studies of URS instruments and tools (hands-on training), watched educational videos, and learned the steps of the URS procedure by watching the consultants during a minimum of 10 URS procedures, respectively. Thereafter, all URS procedures were performed by the residents with the consultant serving as a mentor in the operating room. The consultants monitored the adequate use of URS instruments and tools and gave tips and tricks to proceed in difficult situations during surgery. The consultant took over in cases of ureteral perforation or if bleeding impaired the visibility to proceed with the operation. The URS procedures of the resident group included those that were performed from the first to the last year of the 5-year residency.

Table 1.

Standardized URS Mentor-Based Training Program

Step 1	Learn instruments and tools (hands-on)
	Learn the steps of the procedures (educational videos, watch the expert: minimum 10 URS procedures)
Step 2	Resident performs URS with a consultant as a mentor^a
	Distal, ureteral calculi <5 mm
	Calculi in complete ureter, renal pelvis, including lithotripsy
	URS in complete urinary tract, including flexible URS
Step 3	Board certification (>250 URS procedures)

The consultant took over in cases of ureteral perforation or if bleeding hampered to proceed the operation.

URS=ureteroscopy.

The indications for ureteral prestenting and ureteral stent placement at the end of the URS procedure have been previously reported in detail.¹² The stone size was assessed on kidneys, ureters, and bladder X-ray (KUB), CT, and/or intravenous urogram (IVU) using the largest stone diameter of the solitary calculus. The URS procedure and the used equipment were previously described.¹² Briefly, URS was performed with a 7.5F semirigid and/or a 6.9F flexible ureteroscope using a safety wire. An attempt to clear all stone fragments with a stone basket was made in all cases. A 2.5F tipped nitinol basket and 1.5F or 2.2F tipless nitinol basket were used for ureteral and kidney stone retrieval, respectively. Holmium:YAG laser lithotripsy was performed in combination with a 273 or a 365 μm laser fiber. The URS procedure was aborted in cases of poor visualization, significant edema, and ureteral perforation or persistent extensive stone burden after extensive lithotripsy and stone extraction. Retrograde pyelography was performed at the end of surgery to identify residual stones and to exclude any lesion of the ureter or renal pelvis, as previously reported.¹² The SFR was determined the day after the URS procedure with renal ultrasound and KUB to ensure the absence of residual stones and/or hydronephrosis. An IVU or CT was performed if there was any concern regarding residual stones. Complications were described according to the modified Clavien classification system (CCS).¹³

Statistical analysis was performed using SPSS. Patient data are expressed as mean±standard deviation (range). Differences in the assessed parameters between each group were calculated using the Mann–Whitney U-test. Categorical variables were compared using the χ ²-test. A p-value<0.05 was considered statistically significant.

Results

Table 2 lists the baseline characteristics and the perioperative data of the patients. In the resident group, the majority of the URS procedures (n=234, 78%) were performed in the last (n=149, 49.6%) and next-to-last year of residency (n=85, 28.3%). Two hundred eighty-four patients (94.7%) in the resident and 261 (87%) in the consultant group had preoperative indwelling ureteral stents (p≤0.0009), respectively. The holmium:YAG laser lithotripsy rate differed significantly between residents (13.3%) and consultants (25.3%) (p≤0.0001). The operative time (OT) tended to be shorter in consultants compared to residents (36.73 vs 38.62 minutes), but passed the level of significance (p=0.059).

Table 2.

Patient and Stone Characteristics

	Total	Resident group	Consultant group	p-Value
No. of patients	600	300	300
Age, years	50.95±15.41 (16–89)	51.24±15.27 (16–89)	50.65±15.03 (20–84)	0.651
BMI, kg/m²	27.73±5.27 (16.2–52.8)	27.22±5.27 (16.2–52.8)	28.15±5.25 (16.65–44.64)	0.146
Stone size, mm	6.39±3.26 (2–20)	6.51±3.79 (2–20)	6.31±2.91 (2–20)	0.821
No. of stones/patient	1	1	1	1
No. gender (%)
M	426 (71)	205 (68.3)	221 (73.7)	0.144
F	174 (29)	95 (31.7)	79 (26.3)	0.144
No. side (%)
Right	277 (46.2)	136 (45.3)	141 (47)	0.45
Left	323 (53.9)	164 (54.7)	159 (53)	0.45
Stone location
Lower ureter	152 (25.3)	76 (25.3)	76 (25.3)
Interpolar ureter	132 (22)	66 (22)	66 (22)
Upper ureter	110 (18.3)	55 (18.3)	55 (18.3)
Upper pole	18 (3)	9 (3)	9 (3)
Interpolar	14 (2.3)	7 (2.3)	7 (2.3)
Lower pole	116 (19.3)	58 (19.3)	58 (19.3)
Renal pelvis	58 (9.7)	29 (9.7)	29 (9.7)
No. preoperative stent (%)	545 (90.8)	284 (94.7)	261 (87)	≤0.0009
No. postoperative stent (%)	325 (54.2)	159 (53)	166 (55.3)	0.41
No. Ho:YAG laser lithotripsy (%)	116 (19.3)	40 (13.3)	76 (25.3)	≤0.0001
No. scope type (%)
Flexible	54 (9)	19 (6.3)	35 (11.7)	≤0.0211
Semirigid	418 (69.6)	216 (72)	202 (67.3)	0.198
Flexible+semirigid	128 (21.3)	65 (21.7)	63 (21)	0.488
Operative time (minutes)	37.66±27.45 (4–195)	38.62±26.57 (7–195)	36.73±28.3 (4–170)	0.059

Data indicated as mean±SD (range).

BMI=body–mass index; Ho:YAG=holmium:YAG; SD=standard deviation.

Table 3 summarizes the primary SFR after one URS procedure. The primary SFR was 95.2% and differed not significantly between residents and consultants (95% vs 95.3%, p=0.489). The SFR were 95.9% and 98.5% for ureteral stones (p=0.125) and 93.2% and 89.3% for kidney stones (p=0.298) in the resident and consultant group, respectively. The SFR differed significantly between ureteral and kidney stones (97.2% vs 91.3%, p≤0.001).

Table 3.

Clinical Characteristics and Surgery Outcome After One URS Procedure

	Total	Resident group	Consultant group	p-Value
No. of patients	600	300	300
No. patients stone free (%)
Overall	571 (95.2)	285 (95)	286 (95.3)	0.489
Ureteral stones	383 (97.2)	189 (95.9)	194 (98.5)	0.125
Stone size	6.11±3 (2–20)	6.11±3.26 (2–20)	6.12±2.86 (2–20)	0.684
Lower ureter	148 (97.4)	74 (97.4)	74 (97.4)	0.5
Stone size	6.01±2.96 (2–20)	5.98±3.37 (2–20)	6.03±2.74 (2–20)	0.617
Interpolar ureter	127 (96.2)	62 (93.9)	65 (98.5)	0.164
Stone size	6.06±3.07 (2–15)	6.07±3.24 (2–15)	6.05±3.01 (2–15)	0.867
Upper ureter	108 (98.2)	53 (96.4)	55 (100)	0.149
Stone size	6.31±2.99 (2–20)	6.29±3.22 (2–20)	6.32±2.86 (2–20)	0.779
Kidney stones	188 (91.3)	96 (93.2)	92 (89.3)	0.298
Stone size	6.86±3.64 (1–27)	7.10±4.4 (1–27)	6.69±2.99 (2–16)	0.821
Upper pole	14 (77.8)	8 (88.8)	6 (66.7)	0.241
Stone size	12.32±6.31 (5–20)	13.19±8.69 (5–20)	11.56±3.47 (5–20)	0.963
Interpolar	13 (92.9)	7 (100)	6 (85.7)	0.274
Stone size	3.9±0.74 (3–5)	4±1 (3–5)	3.86±0.69 (3–5)	0.833
Lower pole	105 (90.5)	53 (91.4)	52 (89.6)	0.471
Stone size	5.39±1.97 (3–12)	5.34±2.07 (3–12)	5.43±1.91 (3–12)	0.638
Renal pelvis	56 (96.5)	28 (96.5)	28 (96.5)	0.5
Stone size	8.66±2.63 (1–13)	9.11±2.97 (1–13)	8.37±2.38 (2–13)	0.171
p-Value^a	≤0.001	0.265	≤0.0002

Data indicated as mean value±SD (range).

Stone-free rate ureteral versus kidney stones.

Table 4 lists detailed information on all complications. Perioperative complications occurred in 63 patients (10.5%). There were no differences in the CR between residents (12%) and consultants (9%) (p=0.2116). Minor complications occurred in 5.8% (Clavien 1: 3.8%; Clavien 2: 2%) and major complications in 4.6% of the patients, respectively (Clavien 3a: 1.8%; Clavien 3b: 2.8%). There were no differences in the occurrence of Clavien 1 (3.3% vs 3.7%, p=0.49), Clavien 2 (2.3% vs 1.7%, p=0.41), and Clavien 3a (1.8% vs 2%, p=0.47) complications between residents and consultants. However, the incidence of Clavien 3b (4.3% vs 1.3%, p≤0.027) complications (ureteral perforation) was significantly higher in residents compared with the consultant group.

Table 4.

Detailed Analysis of Complications According to the Clavien Classification System Stratified by Group of Surgeons

Complication	Treatment	Total	Resident group	Consultant group	p-Value
No. of patients		600	300	300
Clavien grade 1 complications
Prolonged pain	Oral analgesics	2 (0.3)	0 (0)	2 (0.7)	0.15
Hematuria	Bedside catheterization and/or bladder irrigation and/or prolonged catheterization	8 (1.3)	5 (1.7)	3 (1)	0.369
Paravasation [mucosal injury without visible mucosal perforation (contrast media outflow)]	Prolonged Double-J stenting without further therapy	13 (2.2)	5 (1.6)	8 (2.7)	0.327
Clavien grade 2 complications
Urinary tract infections with signs of bacteremia (fever>38.5°C)	Parenteral antibiotics	12 (2)	7 (2.3)	5 (1.7)	0.408
Clavien grade 3a complications
Hydronephrosis with flank pain	Ureteral stent (Double-J stent)	11 (1.8)	6 (2)	5 (1.7)	0.473
Clavien grade 3b complications
Ureteral perforation^a	Prolonged Double-J stenting, control URS after stent removal	17 (2.8)	13 (4.3)	4 (1.3)	≤0.0266
Clavien grade 4 complications
Life-threatening complications	ICU management	0 (0)	0 (0)	0 (0)	-
Clavien grade 5 complications
Death	—	0 (0)	0 (0)	0 (0)	-
Total no. of complications		63 (10.5)	36 (12)	27 (9)	0.2116

A follow-up IVU 1 month after ureteral stent removal documented the absence of extravasation and ureteral stricture in these patients in addition to control URS.

IVU=intravenous urogram.

Discussion

The key results of our large-scaled matched-paired analyses were comparable outcomes after ureteroscopic treatment of single urinary calculi of the upper urinary tract by consultant and resident surgeons. Resident status did not compromise the SFR and total CR after ureteroscopic treatment of single urinary calculi, although the ureteral perforation rate differed significantly between residents and consultants.

URS has gained broad acceptance for the treatment of urinary calculi of the upper urinary tract.^5,14 Only few series have analyzed the impact of experience on URS outcome. It has been suggested that a lack of experience impairs URS outcome and the incidence of adverse events.^6,7,9
–11 Due to the multiplicity of potential surrogates defining the learning curve for URS, there has not been any study published on this issue yet.¹⁵ Different training models for improving URS skills have been proposed, but the costs and complexity of these training models restrict the widespread worldwide use.^15

–20 Till date, there have not been any publications assessing URS outcomes of conventional URS training programs. We retrospectively evaluated our mentor-based URS training program by a matched-paired comparison of resident and consultant URS outcomes.

The total primary SFR for the extraction of single upper tract urinary calculi was 95.2% for kidney stones and 97.2% for ureteral stones and did not differ between residents and consultants, respectively. These SFR are in line with the current URS literature,^1,2,5,21 although the SFR for proximal ureteral stones was higher than in previous series, presumably due to the smaller sized stones in this study.^2,5,14 The total SFR (95.2%) in this study was in contrast to the series that analyzed the impact of experience on URS (84.8%–87.5%).^6,7,10 These different SFR are based on the following issues: First, the mean overall stone size was 6.39±3.26 mm in this series and lower than in other studies (mean stone size 8–14 mm).^6,7,9
–11 Second, only patients with single urinary calculi were included, while treatment of multiple urinary calculi might have led to lower SFR and higher CR in residents and consultants.^2,7,11 Third, a substantial number of patients had preoperative indwelling ureteral stents in the resident (94.7%) and the consultant group (87%), which have been shown to facilitate stone extraction resulting in higher SFR.^12,22
–24 The high primary SFR in the resident group might also be a result of our standardized URS training program, which implies an accurate selection of patients according to the resident's skills. To note, consultant surgeons had no supervision during URS. The outcomes of consultant URS procedures are therefore limited by the lack of supervision. Theoretically, experienced surgeons will only allow a result of the supervised resident URS procedure that is in line with their experience, but the SFR in the resident and the consultant group were exceptionally high in this study. Due to the retrospective nature of the study, it is not possible to clarify the impact of the mentoring consultant on the resident's SFR entirely. Finally, patients were not routinely followed with CT in our study, which may have caused an overestimation of the SFR.^2,25 However, the proposed definition of clinically insignificant residual urinary calculi (<3 mm) together with a mean stone size of 6.39 mm, a high rate of in toto stone extraction, and the low holmium:YAG lithotripsy rate (19.3%) in this series minimizes the probability to overestimate the SFR.^2,26
–28

The total CR in this series was 10.5% and well comparable with the literature.^{5,6,8,14,21,23} CR of 30% have been reported when the CCS was used to assess perioperative complications.⁶ CR depend on various factors and are supposed to be lower in high-volume centers, which have been demonstrated for percutaneous nephrolithotomy.²⁵ When complications are classified according to the CCS, CR will increase in contrast to the severity of the complications that do not change. The disadvantages of the CCS are well known; complications with different morbidities may be classified similarly and, as a consequence of complications, some operations may be performed under local or general anesthesia. In addition, minor events classified as complications at the end of studies may have been considered normal at the beginning as stated by Gross and coworkers.²⁹ There were no differences in the occurrence of the overall CR between residents and consultants, which is in contrast to the literature where minor experience was strongly related to increased CR.^6,7,9
–11 Complications were not further specified in these series according to their severity. The ureteral perforation rate (2.8%) differed significantly between residents (4.3%) and consultants (1.3%), even though the ureteral perforation rate in both groups was in accordance with the current literature (up to 14.7%).^5,9,30 Different definitions of ureteral perforation might have led to the wide range of perforation rates in the literature: the presence of visible fat and/or contrast extravasation as in our series,^7,11 contrast media extravasation³⁰ or a lack of a clear definition.^9,10 The Postureteroscopic Lesion Scale (PULS) and the ureteral access sheath related ureteral wall injury endoscopic classification have been therefore currently proposed to standardize the classification of ureteral wall injuries.^22,31

The incidence of preoperative ureteral indwelling stents was exceptionally high (90.8%) in this series compared to the current literature.^1,2 The benefit of preoperative ureteral stenting on SFR could be demonstrated in prior URS series.^12,22,24 Traxer and coworkers also found a decrease in the incidence of ureteral injury and Chu and coworkers a decrease in the OT by preoperative ureteral stenting, respectively.^23,24 Due to the lack of a nonstented control group and the inclusion of patients with only single urinary calculi of an average size of 6.39 mm, we were not able to demonstrate these differences in the OT and CR.^23,24 Conversely, the need for postoperative ureteral stenting was found in 54.2% of the patients without differences between residents and consultants (53% vs 55.3%). These rates were lower than in the current multicenter URS series ranging up to 81.4%.^1,2

The limitations of our study lie within the retrospective, nonrandomized matched-controlled study design. Preoperative selection biases between the consultant and resident group cannot be excluded [e.g., preoperative ureteral stenting rate (87% vs 94.7%) and intraoperative lithotripsy rate (25.3% vs 13.3%)], which could explain the comparable results of OT, SFR, and CR. Due to the retrospective approach, we cannot assess the impact of the consultants who served as the mentors for the residents with regard to SFR and CR completely. The URS procedures in this series were performed by a total of 12 residents and 5 consultant surgeons, while most of the URS literature except the current multicentric URS series report a single-surgeon single-institution experience.^1,2 Since all URS procedures have been performed by a total of 12 resident surgeons at different moments of their learning curve, we assume that the URS outcomes regarding SFR and CR are robust. The CR are well comparable with the literature in both groups, although the ureteral perforation rate was significantly elevated in residents. Further studies are necessary to confirm our URS outcomes for single upper urinary tract calculi in patients with multiple calculi.

Conclusions

URS for single urinary calculi of the upper urinary tract provides a high primary SFR with a low total CR in the hands of the consultants and residents. With residents undergoing a standardized training program, the learning curve has no impact on the SFR and total CR in this series, except for the ureteral perforation rate.

Footnotes

Disclosure Statement

No competing financial interests exist.

Abbreviations Used

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