Surgical outcomes and learning curve of complex versus simple segmentectomy for uniportal video-assisted thoracoscopic surgery: an initial experience of 100 cases of a single experienced surgeon

Introduction

Previous research has shown that segmentectomy is effective for early-stage lung cancer (1,2), and it has grown in popularity in recent years (3). However, there are still several controversies surrounding segmentectomy, including defining segmentectomy, prerequisite preoperative planning procedures, procedural steps, appropriate intraoperative lymph node management, intraoperative management of intersegmental planes, management of positive resection margins, and management of unsuspected positive lymph nodes and spread through the air space (4,5). Segmentectomy is categorized as simple or complex based on the ease of intersegmental plane division (6). Simple segmentectomy is performed on a single linear intersegmental plane. In contrast, complex segmentectomy involves multiple segmental divisions of several segments. Regarding to surgical approach of segmentectomy, there have been reports and learning curves that compare simple segmentectomy using multiportal video-assisted thoracoscopic surgery (M-VATS) to complex segmentectomy using M-VATS (6), with a focus on complex segment resection using uniportal VATS (U-VATS) (7-11). U-VATS is less invasive compared to M-VATS (12-14), however, U-VATS, a unidirectional procedure, is more difficult (15,16) than M-VATS, a multidirectional approach. Thus, using U-VATS for complex segmentectomy, which necessitates multidirectional intersegmental preparation, would be difficult and time-consuming. Fewer studies have compared simple and complex segmentectomy using U-VATS (4,5). The combination of U-VATS and complex segmentectomy may create the perception of difficulty, and U-VATS complex segmentectomy is not commonly performed. Demonstrating the perioperative results and proficiency of individual surgeon is believed to influence future dissemination for U-VATS.

Here, we aimed to compare perioperative data and learning curves between simple and complex segmentectomy using U-VATS and the cumulative sum (CUSUM) technique. We present this article in accordance with the STROBE reporting checklist (available at https://jtd.amegroups.com/article/view/10.21037/jtd-24-1028/rc).

Methods

Study design, setting, duration, and participants

This retrospective study followed the Declaration of Helsinki (revised in 2013). The study was approved by the Ethics Committee of Kurobe City Hospital (No. 237) with a waiver of informed consent due to its retrospective design. All participating hospitals were informed and agreed with the study. This study included all segmentectomy patients who were admitted to Kurobe City Hospital (Toyama, Japan), Toyama University Hospital (Toyama, Japan), or St. Marianna University Hospital (Kanagawa, Japan) for elective U-VATS segmentectomy between July 2018 and June 2023. U-VATS in this study was defined as VATS through a single incision ≤4 cm (17). In this study, all segmentectomy patients met the following criteria: (I) have been diagnosed with lung cancer, metastatic lung tumor, or suspected malignant tumor; (II) computed tomography (CT) reconstruction lung window imaging revealed a pulmonary nodule with a diameter of ≤2 cm; (III) a ≥50% ground glass opacity appearance on CT in the cancerous tissue; (IV) the lesion was located far away >2 cm from the visceral pleura, ensuring a safe margin with wedge resection. Preoperative clinical lymph nodes and surgical margins were assumed to be negative. Intraoperative frozen pathological examinations were performed when the surgeon suspected that the intraoperative lymph nodes or surgical margins were positive. If intraoperative frozen pathology was positive, the segmentectomy was converted to a lobectomy. If there were suitable segmentectomy cases, the procedure was performed without regard to the introduction time of simple and complex cases.

The exclusion criteria included the following: age ≤19 years, planned thoracotomy, median sternotomy, robot-assisted thoracic surgery, conversion to another surgical approach, locally invasive lung tumor with bronchoplasty or angioplasty, lobectomy, lung partial resection, and a large tumor with a maximum diameter ≥5 cm based on our previous study (13).

Definition of segmentectomy

In this study, a segmentectomy was defined as a smaller anatomic lung resection than a lobectomy, which included the dissection and division of the corresponding segmental artery/arteries, bronchi, and veins. Segments did not always need to be divided individually because venous tributaries are divided along the intersegmental plane (4).

Simple and complex segmentectomy were defined as follows according to a previous report; simple segmentectomy included resection of the bilateral 6th segment, bilateral basal segment, left upper division segment, or lingula segment, whereas complex segmentectomy included segmentectomy other than simple segmentectomy (6).

Preoperative tests

In all cases, simple chest radiography, contrast-enhanced CT with three-dimensional (3D) reconstruction images, blood tests, urine tests, electrocardiograms, and pulmonary function tests were used. Patients with lung cancer underwent cerebral magnetic resonance imaging and positron emission tomography as well. Patients over the age of 80 years with one or more risk factors for coronary artery disease underwent preoperative cardiac echography and/or a cardiac stress test.

Surgical procedures

All procedures were performed by the single thoracic surgeon who has been accredited by the Japanese Board of General Thoracic Surgery and qualified by the endoscopic surgical skill qualification system by the Japan Society for Endoscopic Surgery and the Japanese Board of General Thoracic Surgery. General anesthesia was induced using a single-lung ventilation technique through a double-lumen endotracheal tube. All the patients were positioned in the lateral decubitus position. The same surgeon carried out all U-VATS procedures (14). The position of the U-VATS port varied according to the segment affected (Table 1). Regardless of the diseased side, the surgeon stood on the patient’s right side, while the assistant surgeon stood on the patient’s left. The assistant handled the scope, allowing for an unobstructed surgical view. U-VATS procedures used the following equipment: a thoracoscope with a 30-degree, 5 mm camera (Endoeye, Olympus, Japan), a curved lung grasping clamp (Foerster lung grasping clamp, Scanlan, USA), a curved suction instrument (Curved blunt tip, Wolf suction instruments, Scanlan, USA), a forceps (Pro DeBakey Grasper, Geister, Germany, and Aesculap uniport XS, B-Braun, Germany), cotton rods (CS two-way handle, Unimedic, Japan) (18), and advanced bipolar devices (LigaSure, Covidien, USA and EnSeal, Ethicon, USA). Lung parenchyma, bronchi, and pulmonary vessels ≥5 mm were divided with surgical staplers. Smaller vessels were sealed using an advanced bipolar device (19). Intersegment planes were identified using anatomic landmarks, inflation-deflation processes, selective segmental inflation, and systemic indocyanine green injection (20). The intersegment division was performed by all staplers with black cartridges for the intersegment line. A 20-Fr chest tube was inserted through the incision and into the same intercostal space. U-VATS would be converted to M-VATS if there was uncontrollable hemorrhage and severe adhesions.

Variables and assessments

In this study, we documented our initial experience with 100 consecutive segmentectomy cases. The following patient characteristics, surgical characteristics, and follow-up parameters were recorded: age, gender, past medical history, comorbidity, smoking history, body mass index, estimated glomerular filtration rate, respiratory function as measured by spirometry, preoperative medication, clinical diagnosis, diseased side, tumor size, procedure type (simple or complex), intraoperative bleeding volume, operative time, number of staples used for the lung, results from intraoperative frozen sections, severe adhesion (which is the need for adhesiolysis requiring more than 30 minutes) (21), chest tube drainage duration, complications (prolonged air leak defined as an air leak lasting >5 days), and postoperative hospitalization. A complication was defined as any deviation from the expected postoperative course, including Clavien-Dindo classification Grade I or higher. After discharge, patients were evaluated as outpatients at 2 weeks, 1 month, 2 months, and 3 months after surgery.

Data management and statistical analyses

Categorical variables were presented as numbers (proportions), with the χ² or Fisher’s exact test used to compare them. The non-parametric Wilcoxon tests were used to evaluate the data distribution. Continuous variables were summarized using mean ± standard deviation (SD) for normally distributed data and median with interquartile range for non-normally distributed data.

Logistic regression analysis was used to determine the propensity score for selecting patients for the matched cohort from both the simple and complex segmentectomy groups. The allowable calipers for matching included 0.2 SD of the logit-transformed propensity score. A matched balance between the groups was determined using standardized mean differences in the variables included in the propensity score estimation. Within the unmatched and matched pairs, the differences between the preoperative values in each group were compared using a paired Student’s t-test or Wilcoxon test. Statistical significance was defined as P<0.05. Every reported P value was two-sided. All statistical analyses were done using JMP Pro version 16.2.0 (SAS Institute, Inc., Cary, NC, USA).

The CUSUM technique was used to quantitatively evaluate the learning curve. First, all patients were organized in the chronological order in which their surgeries were performed, and the average operative time was calculated. The CUSUM of the first data point was the difference between the first point and average of all points. The CUSUM of the second data point was the difference between the second point and average of all points, and so on. CUSUM was calculated for all data points and the remaining data were added algebraically to the previous total. This study assessed the learning curve in the first 35 cases except those with severe adhesions or intraoperative frozen sections following previous reports (9-11,21). Both factors were chosen as exclusion criteria based on the patient’s prior risk of longer operation times, which was determined using a logistic regression model from a previous study (22). We evaluated the curve of best fit to detect changes in the slope of the CUSUM learning curve. Positive and negative slope indicated above-average and below-average operative times, respectively. Number of cases required (case acquisition rate) was calculated using the inflection point of the curve of the line that best fits the plot. Based on the slope of the best-fit curve, the learning curve could be categorized into initial learning (the ascending slope of the curve), competence accumulation (the plateau of the curve), and acquisition of expertise (the descending slope of the curve). The CUSUM analyses were done using Microsoft Excel for Mac version 16.81 (Microsoft Corp, WA, USA).

Results

A total of 164 patients underwent segmentectomies during the study period, 64 of whom were excluded (Figure 1). A total of 100 sequential patients were enrolled; 55 underwent simple segmentectomy, and the remaining 45 underwent complex segmentectomy (Table 2). The unmatched cohort showed significant differences in gender, smoking history, diseased side, and tumor size (P<0.05) (Table 3).

Figure 1 Patient selection flowchart. VATS, video-assisted thoracoscopic surgery.

Analysis of propensity score matching patients

Using propensity score matching, 29 patients were chosen from each group. There were no differences in baseline, intraoperative, or postoperative characteristics between the matched cohorts (P≥0.05) (Table 4).

Analysis of the learning curve

The CUSUM of the learning curve for simple segmentectomy was reached in the initial learning curve after 20 cases and surgeons gained expertise without the curve plateauing (Figure 2A). The learning curve for complex segmentectomy was completed in the initial learning curve after 11 cases and acquired expertise without the curve plateauing (Figure 2B).

Figure 2 The learning curve for uniportal VATS segmentectomy. (A) CUSUM of the learning curve for uniportal VATS simple segmentectomy; (B) CUSUM of the learning curve for uniportal VATS complex segmentectomy. CUSUM, cumulative sum; VATS, video-assisted thoracoscopic surgery.

Discussion

Complex segmentectomy is more difficult than simple segmentectomy and requires a longer surgical time (5,6). This study found no difference in perioperative outcomes, including operation time, between simple and complex segmentectomy. No differences were observed between the CUSUM learning curves of two groups. While complex segmentectomy is considered technically challenging in terms of intersegmental division, it is believed that using a uniportal approach, it can be safely performed, as with other anatomical lung resection techniques or other surgical approaches (6-8).

The intersegmental division is an important part of the segmentectomy procedure. Intersegmental plane division can be divided into three types: (I) monopolar; (II) mixed; which combines monopolar and stapler; and (III) a stapler-only method (4,22,23). All intersegmental divisions in this study were made with a stapler. Stapling is a quick and easy way to divide the intersegmental planes; it is also better at controlling bleeding and preventing air leaks postoperatively, but it is less effective than electrocautery at preserving lung volume and achieving an adequate tumor margin (22,24,25). Although experimental data show that monopolar is better for maintaining respiratory function (26), clinical data show that respiratory function is unaffected by the method of intersegmental division (25). The stapler method differs significantly from the monopolar and mixed methods. The direction of progress of intersegmental division is a significant difference between these techniques. Using an electric scalpel, the treated blood vessels serve as indicators for peeling from the center to the periphery (22,23). Staplers, conversely, have a limited opening length and angle of the tip, so they are used from the periphery to the center. Another distinction between these techniques is their degree of freedom of operation. An electric scalpel allows for a wide range of processing options, whereas a stapler has fewer. U-VATS operates unidirectionally and unlike M-VATS, cannot be approached from multiple directions. This disadvantage can be overcome by improving pulmonary mobility by first peeling off the pleura of the hilum, which holds the lungs and interlobar divisions together. Unlike simple segmentectomy, mastery of these techniques is essential in complex segmentectomy procedures.

Several studies have used CUSUM to assess the segmentectomy learning curve. In a previous report, 16 to 57 cases were required to achieve (14-16). In this study, with 20 cases of simple segmentectomy and 11 cases of complex segmentectomy, learning was completed faster than previous reports for most cases. Our initial experience with uniportal anatomic lung resection involved lobectomy. We subsequently performed simple segmentectomy in the 2nd and complex segmentectomy in the 18th case. The order of procedures was not planned but it is rather a reflection of the clinical indications for surgery. The difficulty of dividing intersegmental planes with a stapler in U-VATS is influenced by port placement. Setting the port at the 7th intercostal space for lower lobe segmentectomy may be an important factor to learn early, even in complex segmentectomy (Table 1). Our definition of complex segmentectomy is consistent with that used in previous literature (6). However, the technical difficulty associated with complex segmentectomy can vary substantially based on the procedure. Upper lobe complex segmentectomy is often less challenging and has comparable complexity to simple segmentectomy. Conversely, lower lobe complex segmentectomy tends to be more technically demanding. These variations in technical difficulty along with the somewhat subjective nature of the term “complex” may obscure the interpretation of our findings. Therefore, we plan to further delineate the technical nuances between upper and lower lobe segmentectomies in future studies.

Limitations

This study had some limitations, including the surgeon’s surgical skill level, the exclusion of patients who required a longer operation time, and the intersegmental identification technique. The procedures were performed by an experienced surgeon who is familiar with M-VATS and U-VATS (8). Our findings indicate that surgeons with the requisite experience and endoscopic skills can safely and effectively perform procedures like complex segmentectomy via U-VATS. The endoscopic surgical skill qualification system designed by the Japan Society for Endoscopic Surgery and Japanese Board of General Thoracic Surgery may serve as a cornerstone for ensuring the requisite technical proficiency. However, because the adaptation time of simple segmentectomy was not different from that of complex segmentectomy, it is assumed that the impact of using an individual surgeon was minimal. Furthermore, cases with severe adhesions and intraoperative frozen section factors that would necessitate a longer surgical time were excluded from the CUSUM analysis. Nonetheless, excluding potential risk factors that may affect learning time is a well-known and widely reported approach to CUSUM (27). Several methods were used for intersegmental identification. Indocyanine green was used in limited cases and may have shortened surgical time when the tumor was close to intersegmental boundaries. However, despite variations in identification methods, proficiency was maintained in each technique, so the potential impact on surgical time was minimal.

Conclusions

U-VATS complex segmentectomy is safe and non-inferior to U-VATS simple segmentectomy in terms of perioperative outcomes and the learning curve of an experienced surgeon. Therefore, U-VATS should be considered a viable surgical approach for complex segmentectomy. Longer-term studies for patients undergoing complex segmentectomy using U-VATS are needed.

Acknowledgments

We would like to thank Enago (www.enago.jp) for English language editing.

Funding: None.

Footnote

Reporting Checklist: The authors have completed the STROBE statement checklist. Available at https://jtd.amegroups.com/article/view/10.21037/jtd-24-1028/rc

Data Sharing Statement: Available at https://jtd.amegroups.com/article/view/10.21037/jtd-24-1028/dss

Peer Review File: Available at https://jtd.amegroups.com/article/view/10.21037/jtd-24-1028/prf

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jtd.amegroups.com/article/view/10.21037/jtd-24-1028/coif). H.I. serves as an unpaid editorial board member of Journal of Thoracic Disease from August 2024 to July 2026. Takahiro Homma developed the device, CS two-way Handle^TM, Unimedic, Japan. The other authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. This retrospective study followed the Declaration of Helsinki (revised in 2013). The study was approved by the Ethics Committee of Kurobe City Hospital (No. 237) with a waiver of informed consent due to its retrospective design. All participating hospitals were informed and agreed with the study.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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