Discussion
In this meta-analysis, different aspects of the two different minimally invasive approaches to distal pancreatectomy were compared. The results showed that RDP is associated with a higher spleen preservation rate and Kimura method rate in benign and low-grade malignant tumours than LDP. More importantly, RDP is associated with a lower conversion rate to laparotomy, less intraoperative blood loss, shorter postoperative hospital stay and 30-day mortality, although its cost is higher. Overall, RDP is a safe and feasible approach to distal pancreatectomy.
There are no guidelines regarding whether the spleen should be resected in patients with a benign or low-grade malignant pancreatic tumour. Several studies have reported benefits of spleen preservation, such as prevention of overwhelming postsplenectomy infection (OPSI) [
47] and cardiovascular complications [
48], reduction of intra-abdominal abscess [
49] and clinically relevant pancreatic fistula [
50]. Different from several previous meta-analyses [
13,
51,
52], the spleen preservation rate in our study was the ratio of successful spleen preservation to the planned spleen preservation before surgery, rather than the ratio of successful spleen preservation to the total operations, which can objectively reflect the spleen preservation caused by technical factors. Compared with the meta-analysis by Rompianesi et al. in 2021 [
53], the number of studies included in our study was increased and the heterogeneity was low (
I2 = 20%). Our meta-analysis revealed that the rate of RDP in spleen preservation could be 2.52 times higher than that of LDP, showing the advantages of RDP in spleen preservation due to its superior ability to control bleeding from splenic vessels. Although it is worth noting that publication bias existed in our analysis, after using the trim and fill analysis, the result remained significant, indicating the stability of the high spleen preservation of RDP. Nonetheless, the results should be interpreted cautiously. In clinical practice, the Kimura approach is considered the first option to preserve the spleen, with less risk of spleen infarction and left-sided portal hypertension than that with the Warshaw procedure [
54,
55]. This meta-analysis revealed a considerable increase in the Kimura procedures performed in RDP. Considering this finding, a robotic approach is indicated for benign and low-grade malignant tumours, where the spleen is to be preserved using the Kimura procedure. However, there was a non-negligible publication bias with respect to the Kimura procedure rate of RDP versus LDP. Therefore, a prospective randomized trial is urgently needed to verify the results.
Conversion to laparotomy, estimated intraoperative blood loss and operation time are important indicators for evaluating minimally invasive surgery. Our results are consistent with previous studies, which revealed that RDP can decrease the conversion rate to laparotomy and estimated intraoperative blood loss. This can be explained by improved instrument dexterity and 3D visualization of the operative field to facilitate the performance of procedures in a narrow operation space and convenience in achieving haemostasis under endoscopy. In addition, another intrinsic benefit of the robot’s two lenses may play an important role. When bleeding contaminates one lens, surgeons can switch to a second ‘eye’ to quickly stop the bleeding, and thereby to avoid laparotomy due to excessive bleeding. There was no significant difference in operation time between RDP and LDP with high heterogeneity in the studies included. There was no mention of whether the operation time included the docking time, whether surgeons performing RDP and LDP were experienced and how difficult the surgery was in both groups in several studies, which gave rise to the unreliable result. A previous systematic review reported that the numbers required to surmount the learning curve are 25.3 (95% CI 22.5–28.3) and 20.7 (95% CI 15.8–26.5) for LDP and RDP, respectively [
56]. The number of cases in the RDP group included in this meta-analysis ranged from 8 to 402, and that in the LDP group ranged from 18 to 694. This inevitably incorporates the cases that were in the first phase of the learning curve. More importantly, several studies have reported predictive factors for surgical difficulty in MIDP, including resection line, proximity of the tumour to the major vessel, tumour extension to the peripancreatic tissue, left-sided portal hypertension/splenomegaly and parenchymal thickness at the resection line [
57‐
59], which are likely to increase the operation time and intraoperative blood loss. However, the abovementioned factors in the two groups are not reported in most studies, in which selection bias may exist. Nevertheless, the study by Megga et al. [
36] including 196 patients in RDP and 93 patients in LDP showed that the operation time of RDP was statistically lower than that of LDP. Consequently, it can be anticipated that with the proficiency of robotic techniques, the operation time of RDP will be shorter than that of LDP.
In terms of oncologic outcomes, we included studies on malignant tumours, and our results showed that compared with LDP, RDP increased the number of lymph nodes dissected. A previous meta-analysis conducted by Feng et al. [
60] concluded that RDP appeared to be associated with a higher R0 resection rate (
p < 0.0001). However, we considered extracting the data after propensity score matching (PSM) to be more accurate, and the number of relevant studies increased with the year. In our analysis, more studies were included to comprehensively evaluate the impact of RDP on the R0 resection rate. The current meta-analysis revealed that there was no significant difference between the two procedures. Concerning overall survival, we retrieved six studies [
18,
23,
32,
34,
40,
42], with a total of 1067 patients with a pathological diagnosis of adenocarcinoma. All studies showed no significant difference in survival between RDP and LDP, indicating the comparability of RDP to LDP. However, margin status is strongly affected by the pathologic evaluation and the definition, and is thus potentially biased by the protocols adopted. In terms of R0 resection rate and prognosis, five studies [
23,
26,
33‐
35] and five studies [
18,
23,
32,
34,
42], respectively, showed the definition of R0 (resection margin > 1 mm), while the remaining studies did not show the definition. Therefore, potential bias should also not be neglected and the results should be interpreted cautiously.
Postoperative complications and length of postoperative hospital stay are postoperative indicators reflecting the safety of surgery. Clinical pancreatic fistula, the most common and potentially dangerous complication of DP, may cause lethal haemorrhage and intraperitoneal abscesses [
61]. Our meta-analysis showed no significant difference between RDP and LDP with respect to clinical pancreatic fistula (grade B/C). However, a few studies have reported drain management and the pancreas transection plan. As reported in previous studies, early drain removal can reduce clinical pancreatic fistula [
62], and a transection plan involving the tail of the pancreas and a use of ultrasonic dissector are risk factors for clinical pancreatic fistula [
62‐
64]. Therefore, comprehensive data are required when comparing the impact of the two approaches on clinical pancreatic fistula. With regard to other postoperative complications, the pooled data showed that the 30-day mortality rate was 0.1% in the RDP group and 1.0% in the LDP group (
p = 0.03). It should be pointed out that currently the surgical technique is mature and the 30-day mortality is relatively low, hence, several studies claimed no 30-day mortality. Nonetheless, the unique advantages of the robotic approach mentioned above, which allowed for precise intraoperative manipulation and adequate haemostasis, may account for the lower 30-day mortality. In terms of the postoperative hospital stay, RDP reduced the LOS by approximately 0.57 days compared to that after LDP. This may be related to the low conversion rate to laparotomy and reduced trauma in the RDP group. Based on the aforementioned data, RDP appeared more consistent with ERAS (enhanced recovery accelerated surgery).
Hospitalization cost is one of the factors surgeons and patients consider when choosing surgical methods. Our analysis showed that RDP was more costly in terms of hospitalization and operation costs. However, the heterogeneities are too high. Different charging standards could be one cause of the heterogeneity. Although RDP can shorten the length of hospital stay and thus reduce part of the cost, due to the high cost of robots, the total cost and surgical cost are still higher than those of LDP [
27,
39]. It is believed that with the continuous development of robotic techniques, costs will decrease, allowing more patients to access superior surgical methods.
Recently, several studies based on the data analysis of multicentre and large-scale studies reported the benchmark values of MIDP to identify the best achievable results and define optimal perioperative outcomes, with the intention of assessing and enhancing the surgery quality [
65,
66]. Muller et al. [
66] reported that benchmark values of RDP included: operation time ≤ 300 min, estimated blood loss ≤ 150 ml, conversion rate ≤ 3%, major complication rate ≤ 26.7%, clinical pancreatic fistula rate ≤ 32%, lymph node retrieval for PADC ≥ 9, and R0 resection rate for PDAC ≥ 83%. In the majority of the included studies, there was a disparity between the outcomes and the benchmark values. Although RDP has demonstrated its superiority, surgeons must work towards benchmark levels to maximize its benefits.
This meta-analysis summarizes the relevant data of high-quality literature that could be retrieved thus far and reveals the benefits of RDP over LDP. However, the results should be interpreted with caution due to the following limitations. First the included studies were restricted to retrospective or prospective non-randomized controlled studies published in English, which may affect the accuracy of the results. Second, some of the included literature did not provide complete data. A few articles use an algorithm to estimate the mean and standard deviation (SD) of continuous variables [
67,
68]. We thought that this method had certain flaws, and therefore, in our analysis incomplete data were excluded, which may affect the final results. Third, publication bias existed in several outcomes, which impacted the stability of the results. Meanwhile, some studies reported on data obtained during the learning curve stage, which resulted in marked heterogeneity. Ultimately, we look forward to randomized controlled studies to further demonstrate the difference between the robotic and laparoscopic systems in the short and long-term outcomes of distal pancreatectomy.
Publisher's Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.