Effects of the learning curve on operative time and lymph node harvesting during robotic gastrectomy

Gastric cancer is the fifth most frequent cancer globally. The introduction of minimally invasive surgery for gastric cancer aimed at reducing post‐operative morbidity and hospital length of stay. Although the role of laparoscopic gastrectomy has been established, robotic gastric surgery has only recently gained popularity. The purpose of this study was to evaluate, with a multidimensional analysis, the learning curve of a single surgeon with extensive experience in laparoscopic gastrectomy.

more procedures within the same surgery were excluded for the infeasibility of distinguishing surgical times for each specific procedure. The D2 lymph node dissection was performed in accordance with the Japanese Gastric Cancer Association's lymph node classification. 12 Tumours were staged according to the eighth edition of the American Joint Committee on Cancer (AJCC) tumour staging. 13 All the robotic gastrectomies were performed by a single surgeon already proficient in laparoscopic gastrectomy before initiating robotic surgery. All the procedures were performed with Xi or Si daVinci surgical system (Intuitive Surgical Inc., Sunnyvale, CA, USA).
Patient demographic characteristics are summarised in Table 1 (Figure 1). The first robotic arm, located on the patient's left side, was holding either a hook or a monopolar shear. An advanced bipolar energy device (i.e. Vessel sealer) was used for sealing and cutting short gastric vessels. A Maryland bipolar forceps and a Cadiere forceps were held in the second and third arms, respectively, on the patient's right side. Motion scaling was set at 3:1 in all patients. We used a laparoscopic linear stapler in all operations.

| Subtotal gastrectomy
The operative strategy involved 11 steps: (1) partial dissection of the left greater omentum (until the gastric short vessels) and the lymph nodes along the left gastroepiploic vessels (station n. 4sb); (2) dissection of the right omentum and the lymph nodes along the right gastroepiploic vessels (station n. 4d); (3) exposure of Henle's trunk and division of the right gastroepiploic vein and artery for dissection of infrapyloric nodes (station n. 6) ( intracorporeally. The enterotomy after these two anastomoses was closed with a barbed suture. One drain was placed close to the resected duodenum and another close to the esophagojejunal anastomosis. A jejunostomy was placed in those patients with severe malnutrition. In this study, we tried to apply as many items as possible of the Enhanced Recovery After Surgery (ERAS) programme established for gastric surgery. Patients with major comorbidities were monitored in the Intensive Care Unit after surgery. In the first postoperative day, a liquid diet was started in STGs, while enteral nutrition via jejunostomy was adopted in malnourished patients. On post operative day T A B L E 1 Clinicopathological characteristics and operative outcomes of the total and subtotal gastrectomy groups.

| Data collection
Data on preoperative patients' characteristics, intraoperative details, early clinical outcomes, pathological findings, and follow-up were collected and inserted in a prospectively maintained database. Surgical specimens were evaluated by dedicated pathologists experienced in digestive tract oncology. Our cohort of study includes our first experience with robotic gastrectomies at our Institution.

| Statistical analysis
The statistical analysis was carried out using R 4.     Table 1.
We adopted a CUSUM analysis ( Figure 11) that highlights an initial but constant decline in the operative time (from case 1 to case 16) without reaching a plateau. An increase in the operative time was observed from cases 17 to 21. At the same time, a second degree function described a progressive increase of harvested lymph nodes, corresponding to a linear trend without reaching a plateau ( Figure 12).

F I G U R E 5
Dissection of lymph node station n. 8p.

F I G U R E 6
Dissection of lymph node station n. 11p.

| DISCUSSION
Laparoscopic gastric surgery is still regarded as a technically difficult procedure. Indeed, the technical threshold for performing an adequate D2 lymph node dissection remains high and needs a steep learning curve. 15,16 The robotic platform provides some technical advantages, such as an improved 3D vision, wristed instrument, tremor filtration system, and motion scaling, that can help surgeons easily perform precise lymphadenectomy and thus rapidly overcome the corresponding learning curve. Several studies have compared the learning curves of laparoscopic and robotic gastrectomy based on the operative time. [17][18][19] Huang et al. 20 have shown a significant reduction in the operative time after the initial 25 cases in the robotic group compared to laparoscopic groups, which seems to be in the learning curve period after 64 cases. Park et al. 21 have shown that three surgeons with sufficient experience in laparoscopic gastrectomy can quickly overcome the operative time learning curve for robotic gastrectomy, and high-quality surgery is achievable even after a small number of cases. A stable operation time was reached at 9.6 cases by surgeon A, 18.1 cases by surgeon B, and 6 cases by surgeon C.
Even Song et al. 22 have shown that experienced laparoscopic surgeons could perform robotic gastrectomy with a certain level of skill even after an initial series of only 20 consecutive cases. Kang et al. 23 have reviewed data from 100 consecutive patients who had undergone robotic gastrectomy; they conclude that robotic gastrectomy can be considered a safe and feasible procedure after 20 initial cases. In contrast with the results of the previously mentioned F I G U R E 1 3 Cumulative sum method (CUSUM) analysis for subtotal gastrectomies operative time. Vertical lines located in the turning point of curvature indicate the point at which a surgeon transitions from learning to proficiency and from proficiency to mastery phases. Lymphadenectomy is an important step in gastric cancer surgery because removing an adequate number of lymph nodes has been shown to improve staging accuracy and regional disease control. 26 The 15-year update of a Dutch trial 27 has definitively shown the superiority of D2 when compared to D1 dissection in terms of longterm survival. Evidence-based medicine and practical surgical experience now seem to move towards an international agreement.
Nowadays, D2 procedure is recommended as the standard lymphadenectomy for gastric cancer treatment by the Italian 26