Learning Curve Analysis for Laparoendoscopic Single-Site Radical Nephrectomy

Abstract

Background and Purpose:

Little data are available on the learning curve for laparoendoscopic single-site (LESS) surgery. We aimed to evaluate the learning curve for LESS radical nephrectomy for localized renal-cell carcinoma (RCC).

Patients and Methods:

Data from the first 50 consecutive patients who underwent LESS radical nephrectomy were reviewed for evaluation of the learning curve. The surgical procedure was broken down into its three essential components (medial retraction of colon, hilar dissection, and kidney mobilization) through a video review, and each operative time was separately recorded for learning curve analysis. Patient demographic data, variable surgical outcomes, and pathologic outcomes were analyzed. Overall learning curve for LESS radical nephrectomy was evaluated, as well as individual learning curves for three essential steps of LESS radical nephrectomy.

Results:

Operative time gradually decreased in about the first 15 cases and remained stable in the next 35 cases. The rate of perioperative complications did not differ significantly between groups, although it was higher in cases 1 to 15 and 16 to 30 than in cases 30 to 50 (20% vs 20% vs 0%). Surgeon experience regarding LESS was significantly correlated with time for medial retraction of colon (r=−0.502, P<0.001) and time for kidney mobilization (r=−0.457, P=0.001), but not with time for hilar dissection (r=−0.351, P=0.097).

Conclusions:

LESS radical nephrectomy for localized RCC is a safe and effective procedure needing a short learning curve for achievement of satisfying surgical outcomes in the hands of an experienced laparoscopic surgeon. Kidney mobilization appeared to be the step most affected by the learning curve in the early stage of LESS radical nephrectomy.

Introduction

S ince the first laparoscopic radical nephrectomy by Clayman and colleagues¹ in 1991, laparoscopic radical nephrectomy for management of localized renal-cell carcinoma (RCC) has been performed using multiple trocars around the abdomen. Attempts to minimize invasiveness have been a driving force in the evolution of laparoscopic surgery.

The most recent developments in the field of minimally invasive surgery have been the combined advances in natural orifice translumenal endoscopic surgery (NOTES) and laparoendoscopic single-site (LESS) surgery. Although NOTES offers scarless surgery, it is associated with technical challenges and increased risk for major complications, including bowel perforation and peritonitis. Recently, the development of the multichannel port has allowed laparoscopic surgery to be performed using a single incision, ushering in LESS.^2

–5

Success or failure of laparoscopic surgery is critically dependent on the surgeon's experience, and, thus, the learning period necessary for achievement of surgical competence has been widely investigated. It is currently unknown, however, regarding the learning curve for LESS. This study aimed to evaluate the learning curve for LESS radical nephrectomy for treatment of patients with localized RCC.

Patients and Methods

From January 2009 to February 2010, 50 LESS radical nephrectomies for treatment of patients with localized RCC were performed using the umbilicus as the portal of entry. None of these patients was considered suitable for partial nephrectomy for the following reasons: Tumors larger than 4 cm (n=31), hilar tumors (n=17), multiple tumors (n=1), and tumors developed in nonfunctioning kidney (n=1). After approval by the Institutional Review Board at Seoul National University Hospital, data from the first 50 consecutive patients who underwent LESS radical nephrectomy were retrieved from the medical records and reviewed for evaluation of the learning curve.

Surgical technique

With the patient placed in the flank position with the affected side elevated to 70 degrees, the abdomen was accessed through a vertical incision of 4 ∼ 4.5-cm long around the umbilicus, and the homemade single-port device, or Octo™ Port (DalimSurgnet, Seoul, Korea) was inserted.^6,7 A 5-mm flexible laparoscope with an incorporated light source within the camera head (EndoEye, Olympus, Seoul, Korea) was used for visualization. Using roticulating (Covidien, Norwalk, CT) and standard rigid laparoscopic instruments, steps of LESS radical nephrectomy generally remain the same as the conventional laparoscopic approach. After medial retraction of the colon, dissection then proceeded medially until the hilum was exposed. The renal artery was first ligated with titanium clips, and, finally, the renal vein was transected using Hem-o-lok clips or staplers. The specimen was placed inside the impermeable laparoscopic bag and removed intact through the incision.

Outcome analysis

Patient demographic data, variable surgical outcomes, and pathologic outcomes were reviewed. Operative time was calculated from the time of the first incision to the time of completion of skin closure. The surgical procedure was broken down into its three essential components (medial retraction of the colon, hilar dissection, and kidney mobilization) through a video review by an experienced urologist, and each operative time was analyzed separately. Complications were classified according to the Clavien-Dindo classification of surgical complications.⁸

Comparison of surgical and pathologic outcomes was performed by Mann–Whitney U test for continuous variables and the chi-square test for categorical variables. The moving average method was used to analyze the operative time and construct a learning curve. Averaging of previous values smoothes out individual variations and accentuates any trends in the collected data. A moving average order of 5 was used. The Spearman rho correlation coefficients (r) were calculated for identification of potential correlations between the number of cases and the operative time according to the operative steps. All P values were two-sided, and data were considered statistically significant at P<0.05.

Results

Baseline characteristics, overall surgical outcomes, and pathologic outcomes

Fifty patients underwent LESS radical nephrectomy at our institution during a 14-month period: 30 were men and 20 were women. The baseline characteristics of the 50 evaluated patients are summarized in Table 1. The mean age was 52.6 (21–80) years, and mean body mass index was 25.1 (19.0–34.7) kg/m². Thirteen (26.0%) patients had a history of previous abdominal surgeries: Total abdominal hysterectomy (n=7), appendectomy (n=6), cesarean section (n=5), and laparoscopic tubal ligation (n=2).

Table 1.

Preoperative Characteristics of Patients Undergoing Laparoendoscopic Single–Site Radical Nephrectomy

Variables
No. of patients	50
Sex (%)
Male	30 (60.0)
Female	20 (40.0)
Age (y)	52.6 (21–80)
BMI (kg/m²)	25.1 (19.0–34.7)
Previous abdominal surgery (%)	13 (26.0)
ASA score (%)
1	26 (52.0)
2	23 (46.0)
3	1 (2.0)
Operative side (%)
Right	24 (48.0)
Left	26 (52.0)

BMI=body mass index; ASA=American Society of Anesthesiologists.

Operative details for 50 patients undergoing LESS radical nephrectomy are depicted in Table 2. One patient needed placement of an additional 5-mm port along the anterior axillary line at the subcostal level because of difficulty with elevation of the liver. The mean operative time for all patients undergoing LESS radical nephrectomy was 150.9 (120–225) minutes, and mean estimated blood loss was 150.3 (10–610) mL. Two patients with estimated blood loss >500 ml received transfusion of red blood cells. No patient experienced a complication more severe than grade II according to the Clavien-Dindo classification (Table 3).

Table 2.

Various Operative Parameters of Patients Undergoing Laparoendoscopic Single–Site Radical Nephrectomy

Variables
Additional port insertion (%)	1 (2.0)
Conversion (%)	0 (0)
Operative time (min)	150.9 (120–225)
Estimated blood loss (mL)	150.3 (10–610)
Transfusion (%)	2 (4.0)
Complications (%)	6 (12.0)

Table 3.

Complications and Management of Patients Undergoing Laparoendoscopic Single–Site Radical Nephrectomy

Complications	Grade	No. of patients (%)	Management
Wound problem	I	2 (4.0)	Daily dressing, resuture
Postoperative fever	I	2 (4.0)	Intravenous hydration
Postoperative bleeding	II	1 (2.0)	Transfusion
Postoperative urinary retention	I	1 (2.0)	Intermittent catheterization

Final pathology results showed RCC in 45 cases (90.0%), and mean tumor size was 4.5 (1.2–8.0) cm (Table 4). Although the majority of patients had localized RCC, 6% of patients had T₃ disease.

Table 4.

Pathologic Outcomes of Patients Undergoing Laparoendoscopic Single–Site Radical Nephrectomy

Variables
Tumor size (cm)	4.5 (1.2–8.0)
T stage (%)
T₁	40 (80.0)
T₂	2 (4.0)
T₃	3 (6.0)
Histologic subtype (%)
Clear–cell type	33 (66.0)
Chromophobe type	6 (12.0)
Papillary type	3 (6.0)
Unclassified type	3 (6.0)
Fuhrman nuclear grade (%)
2	21 (42.0)
3	23 (46.0)
4	1 (2.0)

Learning curve analysis

Total operative times for the 50 LESS radical nephrectomies are demonstrated in Figure 1A. The Spearman rho correlation coefficients between surgeon experience and operative time were −0.350 (P=0.013). The result of moving average learning curve is shown in Figure 1B. Operative time gradually decreased in about the first 15 cases and remained stable in the next 35 cases.

FIG. 1.

Operative time to perform laparoendoscopic single-site (LESS) radical nephrectomy as a function of the number of cases. (A) Operative time needed to perform a LESS radical nephrectomy; (B) Operative time analyzed by the moving average method.

Surgeon experience with regard to LESS was significantly correlated with time for medial retraction of the colon (Spearman rho correlation coefficient=−0.502, P<0.001) and time for kidney mobilization (Spearman rho correlation coefficient=−0.457, P=0.001), but not with time for hilar dissection (Spearman’ rho correlation coefficient=−0.351, P=0.097) (Fig. 2).

FIG. 2.

Comparison of learning curves for the different steps of laparoendoscopic single-site radical nephrectomy.

Total operative time, time for medial retraction of colon, time for kidney mobilization, and time for hilar dissection significantly reduced with increasing experience (Table 5). The rate of perioperative complications did not differ significantly between groups, although it was higher in cases 1 to 15 and 16 to 30 than in cases 30 to 50 (20% vs 20% vs 0%).

Table 5.

Operative Outcomes According to Surgeon Experience

	Cases
	1–15	15–30	31–50	P value
Conversion (%)	0 (0)	0 (0)	0 (0)	1.000
Operative time (min)
Total	167.0 (130–225)	141.3 (120–160)	146.1 (120–210)	0.004
Medial retraction of colon	51.3 (35–90)	37.3 (25–45)	35.9 (12–55)	0.002
Hilar dissection	35.7 (25–55)	30.0 (20–50)	29.3 (15–40)	0.046
Kidney mobilization	71.0 (35–140)	34.3 (15–40)	38.7 (18–60)	< 0.001
Estimated blood loss (mL)	158.0 (100–300)	123.3 (50–300)	164.8 (10–610)	0.105
Complications (%)	3 (20.0)	3 (20.0)	0 (0)	0.103

Discussion

A universal goal of any innovative surgical technique should be its reproducibility and safety, which will enhance its applicability by large numbers of surgeons and to large numbers of patients. There has been a sudden increase in the scientific literature devoted to the subject of LESS in urology.^2,4,7,9 There are several limitations to its wide-spread use, however; these include the inherent technical difficulties in performance of LESS. Understanding the learning curve of LESS might benefit the individual surgeon in careful preparation for the difficult surgical steps that will ensure that patient welfare is not compromised.

The learning curve of laparoscopic radical nephrectomy has been evaluated in previous studies.^10

–13 The number of patients needed to overcome the learning curve is still controversial, however. Results from these studies have demonstrated that approximately 15 to 50 cases were needed for competent performance of laparoscopic radical nephrectomy. In our study, mean operative time taken to perform LESS radical nephrectomy gradually decreased in about the first 15 cases and remained stable.

The short learning curve for LESS radical nephrectomy can be speculated because it stands on the basis of previous extensive laparoscopic experience. This finding is consistent with that of previous studies. To the best of our knowledge, two reports have evaluated the learning curves of LESS cholecystectomy.^14,15 These studies reported that the learning curve for an experienced laparoscopic surgeon in adoption of LESS cholecystectomy is approximately 5 to 10 cases, with outcomes similar to those of conventional laparoscopic surgery.

Learning an innovative surgical skill is a complex process that involves significant changes in conduct and memory. Studies conducted in the clinical setting with regard to the learning curve of LESS are inherently weak for the purpose of evaluating the learning process.^14,15 In the current study, each step (medial retraction of colon, hilar dissection, and kidney mobilization) was analyzed in an attempt to identify the specific learning curves involved in the performance of each step. As a result, hilar dissection appeared to be the step unaffected by the learning curve and kidney mobilization to be the challenging step in its early stage.

Difficulty during kidney mobilization is probably related to the requirement for an effective retraction and extensive dissection, especially at the upper posterolateral aspect of the kidney. The upper pole of the kidney may be too far from the umbilicus to be reached by conventional laparoscopic instruments. Use of curved laparoscopic instruments may improve accessibility between the umbilicus and the upper posterolateral aspect of the kidney; however, insufficient strength at the tip of curved laparoscopic instruments may cause problems associated with retraction. After many trials and errors, we overcame these problems using a combination of curved and standard rigid laparoscopic instruments.

The potential limitations of this study should be addressed as a means for improvement or for mapping of strategies for further study. The major limitation was the nonrandomized and retrospective nature of the study design, susceptible to all limitations and biases inherent in a retrospective design. Also, the learning curve in this study reflects the experience of a single experienced laparoscopic surgeon. There might be interpersonal variations among learning curves of different surgeons based on their skills and experiences. Few studies, however, have evaluated the learning curves of each step of LESS radical nephrectomy. We believe that a study to assess which steps of LESS radical nephrectomy are most affected by a learning curve would be of particular interest, because no studies have been conducted for analysis of that point of LESS radical nephrectomy.

Conclusions

The present study demonstrated that, in the hands of an experienced laparoscopic surgeon, LESS radical nephrectomy for treatment of patents with localized RCC is a safe and effective procedure needing a short learning curve for achievement of satisfying surgical outcomes. Also, kidney mobilization appeared to be the step most affected by the learning curve in the early stage of LESS radical nephrectomy.

Footnotes

Acknowledgment

This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2010-0008492).

Disclosure Statement

No competing financial interests exist.

Abbreviations Used

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