Comparison between intra- and postoperative outcomes of the da Vinci SP and da Vinci Xi robotic platforms in patients undergoing radical prostatectomy

The new SP robot incorporates a single trocar that houses a flexible camera and three bi-articulated arms, which minimize the number of incisions needed to assess the surgical site, allowing for a less invasive procedure. To compare the postoperative pain scale and outcomes in patients with similar demographic characteristics undergoing robotic-assisted radical prostatectomy (RARP) with SP and Xi robots, One-hundred consecutive patients undergoing RARP with the SP robot were matched, using a propensity score (PS), with 100 patients from a cohort of 1757 who were operated on with the da Vinci Xi from June 2019 to January 2021. We described and compared the perioperative pain scores and outcomes of both groups. The SP group had less blood loss (50 cc vs. 62.5 cc, P < 0.001) and longer operative time (114 min. vs. 94 min, P < 0.001). The only period we could show a difference in postoperative pain scores was 6 h after surgery, with a small advantage for the SP (2 vs. 2.5, P < 0.001). Both groups had satisfactory postoperative continence recovery, 91% vs. 90% for the SP and Xi, respectively. The groups had a mean follow-up of 24.5 and 22 months for SP and Xi, respectively. The tumor stage and percentage of positive surgical margins were similar between groups (15% vs. 15%, P = 1). Patients undergoing RARP with the SP had longer operative times with less blood loss than the Xi. However, despite the lower number of abdominal incisions on the SP, the groups had similar intraoperative performance, and we were unable to demonstrate clinically significant differences in postoperative pain scores between the groups 6, 12, and 18 h after surgery.


Introduction
After the production of several generations of multiport robotic consoles in the 2000s, the first single-port clinical investigation system, the da Vinci (SP), was described in 2014 by Kaouk et al. [1] in urological procedures, although the Food and Drug Administration (FDA) approved the sale of the SP system just a few years later in November 2018 [2,3]. The new SP robot incorporates a single trocar that houses a flexible camera andthree bi-articulated arms, which minimizes the number of incisions needed to assess the surgical site, allowing for a less invasive procedure. However, due to its recent market launch, the current literature describing radical prostatectomies with the SP is still restricted to some centers, and the perioperative results are still the subject of studies.
Due to the fewer number of trocars and abdominal accesses (1 vs. 4), some authors reported advantages of the SP platform compared to the da Vinci Xi (Xi) regarding postoperative pain improvement and earlier surgical recovery. However, current studies are based on retrospective data analysis, with inherent biases, reduced number of patients, and methodologies that do not compare groups with similar preoperative characteristics. In this scenario, our study aims to compare the postoperative pain scale in patients with similar demographic characteristics undergoing robotic-assisted radical prostatectomy (RARP) with SP and Xi (Fig. 1).

Materials and methods
One-hundred consecutive patients that were operated on with the Da Vinci SP robot from June 2019 to January 2021 were selected and compared with the results of 100 patients operated on the Da Vinci Xi robot in the same period. All procedures were performed by the same surgical team and the retrospective study was approved by the Hospital's Institutional Review Board (IRB) under the number 237998. All patients signed an informed consent form regarding the type of robot used and the use of the operative data in scientific articles and studies, prevailing confidentiality.

Propensity score (PS) matching and statistical analysis
To reduce the effects of bias and potential confounding factors in our data, 100 patients undergoing RARP with the SP robot were matched, using a propensity score (PS), with 100 patients (1:1 ratio), from a cohort of 1757, who were operated on with the da Vinci Xi in the same period. PS was constructed with a multivariable logistic regression model considering the following variables: age, BMI (body mass index), Sexual Health Inventory for Men (SHIM) score, Charlson comorbidity index, American Urological Association symptom score (AUASS), PSA levels, and Gleason score [4]. We performed the matching using the nearest neighbor matching algorithm (0.25 width of logit score standard deviation) with a ratio of 1:1 without replacement [5]. Standardized mean differences were used to assess the balance of covariates and were compared before and after PS to assess how wellbalanced potential confounders were between groups. We considered well-balanced covariates with standardized difference < 0.15 in absolute value [6]. Table 1 illustrates the preoperative characteristics of both groups after 1:1 pairing.
The chi-square association test was used to compare the groups regarding nominal variables, and the t-test to compare the means of continuous variables. For all statistical analyses, p < 0.05 was considered statistically significant.

Objectives
The primary objective of the study is to evaluate and compare differences in postoperative pain scores 6, 12, and 18 h after the procedure. The study hypothesis (H0) is that patients operated with the SP robot have less postoperative pain due to the smaller number of abdominal incisions for placement of the trocars when compared to the Xi. Secondary outcomes are the comparison of perioperative results, such as operative time, blood loss, complications, and pathological analysis of the surgical specimen.

Da Vinci SP Surgical technique
We used the SP + one technique (1 SP switch + 1 assistant switch) in all patients, as illustrated in Fig. 2. We also used trans-peritoneal access with an anterior approach, as described by previous studies performed at our institution [3,[15][16][17][18][19][20][21]. None of the groups had abdominal drains placed after the procedure.

Postoperative routine
After surgery, all patients received questionnaires to assess the abdominal pain scale (score from 0 to 10, with 0 being no pain and 10 being the worst pain ever felt). The questionnaires were answered 6, 12, and 18 h after the surgical procedure and the results were recorded in the chart by the nursing team. Postoperative analgesia was performed only with Tylenol every 6 h, if necessary, and Tramadol in cases of refractory pain.
Patients were discharged the next morning and returned five days after surgery to remove the urinary catheter and receive the results of the pathological anatomy. After Foley catheter removal, patients have quarterly appointments to access oncological (PSA) and functional (potency Table 1 Comparison of preoperative demography and nerve-sparing degree in the study groups before and after the 1:1 propensity score (PS) matching reporting the median value with the interquartile range (IQR) and the number of patients with the percentage; standardized differences evaluate the degree of covariate unbalance PSA prostate-specific antigen, BMI body mass index, SHIM sexual health inventory for men, AUA American urological association, ISUP international society of urological pathology and continence) results. Continence was considered in patients with full control of urination and no use of pads. Table 1 illustrates the preoperative variables used to perform the PS matching and the demographics of the groups after selecting and pairing 100 patients operated with the Xi. Table 2 illustrates the intraoperative variables and the pain scores reported 6, 12, and 18 h after surgery. The group operated on with the SP had less blood loss and longer operative time. Regarding the pain scales, the only period we could show a difference between the groups was 6 h after surgery. During this period, the SP group had a 20% reduction in the pain scale. Both groups had satisfactory postoperative continence recovery in the period of the study, 91% vs. 90% for the SP and Xi, respectively (Graph 1).  24.5 (19.3-28) 22 (19)(20)(21)(22)(23)(24)(25)(26) 0.06

Pathology report
The groups had a mean follow-up of 24.5 and 22 months for SP and Xi, respectively. The tumor stage and percentage of positive surgical margins are similar between groups. Table 3 illustrates the details of the pathological anatomy of the groups. Only one patient in the SP group was readmitted after 50 days for infected lymphocele (drained with Intervention Radiology). Overall, only 3 patients had biochemical recurrence (PSA elevation after surgery), 1 in the SP group and 2 in the Xi group.

Discussion
Since the acquisition of the da Vinci SP by our center, we have described in previous studies our experience and results with this platform in patients undergoing robotic radical prostatectomy [17,19,21]. Although minimally invasive techniques such as robotic surgery decrease perioperative impacts, surgical outcomes depend on several different factors, such as preoperative patient characteristics, age, SHIM score, cancer stage, and comorbidities [10,13,22,23]. In addition, surgical technique and nerve-sparing degree also play an important role along with postoperative management and patient follow-up protocols [8,24]. Due to the multifactorial influence on surgical outcomes, to assess the differences and possible benefits of the da Vinci SP and Xi robotic platforms, our study compared two groups with similar preoperative demographics (selected with a Propensity Score matching) undergoing robotic radical prostatectomy. Regarding intraoperative performance, the Xi robot provided faster operative and console time than the SP, mainly due to the greater traction and dissection capacity provided by the arms and instruments. As previously described, the SP has bi-articulated and flexible arms of 6 mm, while the Xi has an independent rigid arm of 8 mm with articulation like the human wrist. Therefore, SP presents greater limitations when used in obese patients, and in those with previous abdominal surgeries or enlarged prostates. When designing our selection criteria, based on our experience in robotic prostatectomy, we selected factors that typically increase surgical challenges or potentially risk surgical outcomes [15][16][17]. Patients with previous abdominal surgeries are more likely to have adhesions, and the SP trocar is a limitation for performing adhesion lysis unless you add extra trocars for a laparoscopic approach, which may contradict the SP concept of performing surgery with only one or two incisions.
In a retrospective study, Vigneswaran et al. compared 50 consecutive patients undergoing prostatectomy with the SP to 113 operated on with the Xi [25]. The authors reported a shorter hospital stay and less postoperative pain in favor of the SP, although both groups were similar regarding the use of morphine. On the other hand, despite the larger cohort, comparing patients with similar preoperative characteristics, our study failed to demonstrate clinically significant differences regarding postoperative pain reported by patients 6, 12, and 18 h after surgery. As we use a TAP (Transversus Abdominis Plane) [26] block in all patients, the pain scores of our study tend to be close to zero in both robots. Our results showed a difference of a half point in the pain scale 6 h after surgery favoring the SP, whereas there was no statistical difference in the other evaluated periods (12 and 18 h). Therefore, we consider that there is no clinically significant difference in postoperative pain between the groups.
With the current technological expansion of robotic surgery and new consoles being launched on the market, it is natural to compare surgical performances and results between different platforms. However, we believe that the current generation SP is not a robot to replace the multiport Xi but to complement its use in patients who are not candidates for the multiport approach, such as patients with ileostomy, colostomy, penile prosthesis with reservoir, kidney transplants, and other intra-abdominal obstacles [27]. Recently, some authors have described the transvesical access that can further expand the use of SP in these patients with a hostile abdomen. [20,21,28]. However, the functional and oncological results of this technique are still under discussion.
Our study is not devoid of limitations, mainly due to the retrospective design and all inherent risks of bias. Furthermore, as described in several studies, the experience of a high-volume center is generally not reproducible in smaller centers with less experienced surgeons [29,30]. However, we believe that with adequate selection criteria, the surgical results of patients operated with the SP tend to be constant even during the learning curve [19]. Finally, to date, this is the largest series comparing perioperative outcomes in patients with similar preoperative characteristics undergoing radical prostatectomy with the SP and Xi robots. However, prospective and randomized studies are still needed to compare the real differences and advantages between both consoles.

Conclusion
Our study demonstrated that patients undergoing robotic radical prostatectomy with the da Vinci SP have longer operative times with less blood loss compared to those with the da Vinci Xi. However, despite the differences in the number of trocars used, and the lower number of abdominal incisions performed in patients operated with the SP, the groups had similar intraoperative performance (without complications) and we were unable to demonstrate clinically significant