Robotic surgery was first introduced in the field of cardiac surgery1 and has rapidly expanded to other fields because it allows for high surgical precision with minimal invasiveness. In the field of urology, it was mainly applied for total prostatectomy and is now covered by health insurance programs in Japan because it has become a standard procedure.2
In the field of vascular surgery, laparoscope-assisted aortobifemoral bypass was first reported for aortoiliac occlusive disease by Dion et al3 in 1993. Since then, other research groups have reported the use of robot-assisted aortobifemoral bypass for aortoiliac occlusive diseases and vascular prosthesis implantation for abdominal aortic aneurysms.4–6 Clinical reports have also described robot-assisted removal of renal artery aneurysms and surgical reconstruction of renal arteries.7 Robot-assisted surgery has also been used for anastomosis in reconstruction of renal arteries in animal models.8,9 Currently, however, robot-assisted surgery is still underused in the field of vascular surgery when compared with other fields, and the case reports published to date are limited to specific facilities. One possible reason for this is the demand for accurate anastomosis techniques for large arteries while using laparoscopes, which is particularly important when considering the limited time available because of aortic cross-clamping.
In terms of implementing robot-assisted surgery in the field of vascular surgery, an important question is whether the technique provides satisfactory learning curves, even for skilled surgeons with limited experience of performing standard abdominal operations. Here, we defined abdominal operations as vascular surgical procedures that involved laparotomy, including abdominal aortic aneurysm repair or aortobifemoral bypass for aortoiliac occlusive diseases. Therefore, in this study, we examined the impact of the surgeon’s experience of performing abdominal operations on the learning curve of robot-assisted vascular anastomosis.
Six vascular surgeons from the Department of General and Cardiothoracic Surgery, Kanazawa University, and three medical students at Kanazawa University participated in this study. None of the participants had any experience of robot-assisted surgery before this study. The vascular surgeons were divided into two groups according to their experience of performing abdominal surgery, where group A consisted of three surgeons with more than 10 years’ experience (19, 12, and 12 years) and group B consisted of three surgeons with less than 10 years’ experience (7, 5, and 5 years). Although all of the surgeons had experience of digestive system surgery, only their level of experience of performing vascular surgery was considered important. Group C consisted of the three medical students.
The da Vinci standard surgical system (Intuitive Surgical Inc, Sunnyvale, CA USA) was used in this study. Microforceps were installed on the two surgical arms of the system.
In this study, the participants performed end-to-end anastomosis with a continuous suture by placing one stay suture on the posterior wall using a 5-0 Prolene/c-1 needle (Ethicon, Norderstedt, Germany) and Dacron vascular prostheses (Vascutek Ltd, Inchinnan, Scotland) with a diameter of 8 mm. Both prostheses were fixed at both ends, although the region to be anastomosed had some freedom. Using 10-cm arms, the participant created a knot to place the one stay suture on the posterior wall with a double-armed suture. To allow us to count the number of stitches required for the anastomosis, alternate red and black marks at 2-mm intervals were placed on both the exterior and interior walls of the vascular prosthesis to guide the entry point of the needle. The participants used the marks as a guide and inserted approximately 12 stitches. Then, they tied the knot at least six times using a needle holder after dropping both ends of the needle. Fibrin glue was applied to the anastomoses site. All anastomosis procedures were standardized and performed by each participant alone, without assistance from another person.
The participants in groups A and B practiced simple maneuvers, such as grabbing the needle, using the da Vinci system before the experiment. The medical students in group C received a 1-hour lecture describing common methods of anastomosis and were allowed to practice using the system before the experiment.
Each participant performed the anastomosis procedure five times. If the prolene thread snapped during the procedure, it was recorded as a failure. The entire procedure was recorded on video from the start to completion of anastomosis. The following outcomes were assessed: time to perform each anastomosis, number of actions, visual score, and pressure test.
The anastomoses time was recorded as the sum of the suture time and knot tying time. The suture time was defined as the time from first grasping the needle until placing the final suture. The knot tying time was defined as the time from tying the first knot to the time of completing the sixth knot. For failed procedures, the time elapsed at the point of failure was recorded.
The number of actions was counted using the criteria reported by Nio et al10 and is listed in Table 1. In these criteria, each instance of grabbing the needle or thread, grabbing the vascular prosthesis, piercing the needle into the vascular prosthesis, and forming a loop was defined as one action. Failing to grab the needle or thread and unexpected failures, such as needle snapping, were also recorded as one action. If two different actions were performed simultaneously by both arms, both actions were recorded (Table 1). For failed procedures, the number of actions made until the point of failure was recorded. The total number of actions was compared between the three groups.
In the pressure test, both ends of the anastomosed vascular prostheses were closed, and an albumin solution was injected to increase the internal pressure to 50 to 80 mm Hg for 10 seconds (Fig. 1). Any leakage from the anastomosis was measured. If the anastomosis was unable to cope with the internal pressure, the leakage of more than 10 seconds was calculated as 30 mL.
The completed anastomosis was visually assessed using a demerit scoring system after introducing error points (visual score).10 The maximum score was 10 points, and failed procedures were scored 0 (ie, −10 points). Points were deducted for inconsistent stitch depth, inconsistent anastomosis site, hooking onto the previous stitch, and missing stitches (Fig. 2A–D).
The Statistical Package for the Social Sciences software version 10.1 for Windows (Statistical Package for the Social Sciences Inc, Chicago, IL USA) was used for all statistical analyses. The χ2 test was used to evaluate independency of categorical variables. Continuous variables were compared using the t test for comparisons between two groups or analysis of variance for comparisons among three groups. Continuous variables are presented as mean ± SD. Values of P < 0.05 were considered statistically significant.
Failure of Anastomosis
The procedure failed in 3 (20%) of 15 trials performed in group C (3/15) but not in the procedures performed by groups A or B, which was statistically significant (P < 0.0001). One procedure failed at trial 3 in one medical student in group C, whereas the other two failures occurred in another member at trials 2 and 3.
The mean ± SD anastomosis time for trial 1 was 26.4 ± 1.6 minutes in group A, 26.9 ± 6.4 minutes in group B, and 33.0 ± 4.6 minutes in group C, which was not significantly different between the three groups (P = 0.35). By contrast, the anastomosis time for trial 5 was 14.8 ± 2.8 minutes in group A, 14.2 ± 0.2 minutes in group B, and 20.2 ± 1.9 minutes in group C. Therefore, anastomosis time in group C for trial 5 was significantly longer than that in the other groups (P = 0.04). As shown in Figure 3A, learning curves were apparent in terms of anastomosis time, which decreased significantly in all three groups between trials 1 and 5 (group A, P = 0.007; group B, P = 0.049; group C, P = 0.023).
Number of Actions
The mean ± SD number of actions for trial 1 was 164 ± 16.9, 186 ± 28.9, and 252 ± 23.3 in groups A, B, and C, respectively. The mean number of actions performed by group C for trial 1 was significantly greater than that in the other groups (P = 0.02). The number of actions for trial 5 was 116 ± 11.4, 136 ± 11.1, and 163 ± 12.5 in groups A, B, and C, respectively. Again, group C performed significantly more actions compared with the other groups (P = 0.02). A learning curve was apparent in groups A and C for the number of actions (Fig. 3B), which decreased significantly between trials 1 and 5 in these groups (group A, P = 0.03; group C, P = 0.0088). By contrast, the number of actions was not significantly different between trials 1 and 5 for group B (P = 0.087).
As shown in Figure 4A, the visual scores in each group did not increase between trials 1 and 5, indicating the absence of a learning curve. The mean ± SD visual score for trial 1 was 8.3 ± 0.4, 8.2 ± 0.1, and 6.7 ± 1.8 in groups A, B, and C, respectively. Although the visual score was lower in group C than in groups A and B, this was not statistically significant (P = 0.10).
In the pressure test, there was no decrease in the volume that leaked from the anastomotic site with repetition of the procedure in any group, indicating the absence of a learning curve for this parameter (Fig. 4B). The mean ± SD leakage volume in trial 1 was 8.3 ± 1.8, 12.2 ± 2.7, and 11.8 ± 5.8 mL per 10 seconds in groups A, B, and C, respectively. Although the leakage volume was higher in groups B and C compared with group A, this was not statistically significant (P = 0.45).
Quality of Anastomosis Based on Visual Score and Leakage
In terms of the visual score and leakage for trial 1, visual score was high and leakage was low in group A. By contrast, leakage was higher in group B. Furthermore, the visual score was low and leakage was high in group C. However, because there were no significant differences in these parameters among the three groups, the quality of anastomosis was considered to be equivalent in all three groups.
Vascular anastomosis is a technically demanding procedure in laparoscopic surgery. Surgeons with some experience of performing abdominal and laparoscopic surgery participated in the earlier experimental studies that examined the speed and the quality of anastomosis. To our knowledge, the medical students did not participate in any of the prior reports describing the learning curves of robot-assisted vascular anastomosis.10–12 In the present study, we examined the impact of the surgeon’s experience of abdominal operations on the learning curve of vascular anastomosis. Our study is also the first to include both vascular surgeons and medical students as participants.
There are numerous reports comparing robot-assisted surgery and laparoscopic surgery. For example, some reports revealed that robot-assisted surgery provides a quicker learning curve for simple tasks, such as continuously threading a needle into a loop that was fixed beforehand and ligation, allowing greater precision.13 Although the precision of ligation at the time of introducing laparoscopic surgery was high, another report revealed that robot-assisted surgery allows higher precision of ligation in the final trial.14 In another report, which did not specifically assess learning curves, the suture time, number of actions, and sutures failures were less with laparoscopic surgery compared with robot-assisted surgery for anastomosis of vascular prostheses within a training box.10 On the other hand, in another study, anastomosis time and the precision of implantation of a blood vessel prosthesis in pigs were better with robot-assisted surgery compared with laparoscopic surgery.11
Many studies focusing on robot-assisted vascular anastomosis have included surgeons skilled in performing laparoscopic surgery.10–12 In studies aimed at determining the learning curve of vascular anastomosis, the surgeon’s experience of performing laparoscopic surgery had a significant impact on the extent of the learning curve.11 However, some reports have suggested that the introduction of robot-assisted surgery is not associated with fluctuations in the learning curve.12 The present study was not designed to compare learning curves or surgical efficiency between robot-assisted surgery and laparoscopic surgery. Instead, we sought to evaluate whether the surgeon’s experience of performing standard abdominal operations affects the learning curve for robot-assisted vascular anastomosis. Therefore, surgeons with extensive experience of laparoscopic surgery were not included in the study.
There are several features of the da Vinci surgical system that facilitate its use for robot-assisted anastomosis by operators with limited experience. These features include a broad three-dimensional visual field; its compatibility with the Endowrist, which has seven degrees of freedom; the ability to scale the reduction ratio of the movement of the robot relative to the surgeon’s movement; and dampening/filtering the physical vibrations of the surgeon in the movement of the robot. In addition, it has been reported that the da Vinci surgical system allows the surgeon to manipulate the needle with forceps in the nondominant hand, which is not possible in standard open procedures under direct vision or in laparoscopic surgery.15,16 Furthermore, techniques that require high precision are often particularly difficult in laparoscopic surgery, unless the surgeon has achieved a high level of experience, because the visual field is two dimensional and movement of the forceps is very restricted.
In the present study, the procedure failed because of snapping of the prolene thread in procedures performed by the medical students. One reason for this could be the absence of tactile feedback in robot-assisted surgery. However, even without tactile feedback, it may be possible to visually assess the tension of the suture, and experience of performing abdominal operations may contribute to the acquisition of this skill.10
To assess the technical ability of the participants, we recorded the anastomosis time and the number of actions for each trial. A learning curve was apparent in all three groups of participants in terms of the anastomosis time and in groups A (surgeons with ≥10 years’ experience) and C (medical students) for the number of actions. Although anastomosis time and number of actions for trial 5 were greater for the medical students than the other groups, the trends in improvements suggest that, with more trials, they might reach a performance level similar to that of both groups of surgeons. In a study that evaluated robot-assisted vascular anastomosis microsurgery, it was shown that anastomosis time was already quite short in the initial trial and reached a plateau immediately.17 Similar results were obtained in the present study. Although the participants in our study performed standard vascular anastomosis, the anastomoses time was short, even for the participants with little experience, and they reached a plateau immediately.
Interestingly, markers of the quality of anastomosis (ie, visual score and leakage during the pressure test) did not exhibit learning curves with repeated trials in any group. A possible explanation for this is that each participant attempted to achieve a certain level of quality in each trial. Another explanation is that, had we included a larger number of trials, a learning curve may have been apparent in terms of the markers of anastomosis quality.
The mean visual score was lowest for the medical students (ie, group C). This was mainly due to procedural errors, such as skipping of two stitches and failed procedures that occurred only in this group. Although the most experienced surgeons had a high visual score and the anastomoses hardly leaked, there were no significant differences between the three groups. Therefore, the basic quality of anastomosis was considered to be equivalent among the three groups.
Although end-to-end anastomosis of vascular prostheses is the easiest vascular anastomosis technique, it is considered to be more difficult for medical students, who may experience difficulties in performing basic surgical techniques. The 1-hour lecture conducted beforehand described important factors of relevance to anastomosis, including the following: the method of anastomosis was limited to the single-point support method and the exterior and interior walls of the vascular prostheses were alternately marked to help guide the needle entry point. Therefore, although the medical students took a long time to complete trial 1, the time taken to complete the subsequent trials improved, demonstrating a satisfactory learning curve.
One limitation of this study is that the learning curves may be influenced by the characteristics of the individual participants. However, there are currently no objective criteria for the appropriate selection of participants. In addition, because the participants performed the five trials sequentially, they probably started to tire and their concentration declined as the trial progressed, which may have affected the learning curves. It is also notable that, although marking the vascular prosthesis was helpful to the students, this created a very different situation from that in actual surgical conditions, in which the surgeon must appropriately determine and adjust the “bite” and “pitch” of the prostheses. Nevertheless, the inclusion of medical students in this study highlights the impact of experience of vascular surgery on performing robot-assisted vascular anastomosis and allowed more detailed comparisons.
It requires much skill and experience to accurately anastomose the entire circumference of an 8-mm vascular prosthesis with a 2-mm pitch. This present study showed that surgeons with greater experience of performing abdominal operations had greater skill in performing vascular anastomosis skills and achieved better quality of anastomosis. However, even the medical students with almost no experience of abdominal operations quickly acquired proficient vascular anastomosis skills through task repetition.
By using the da Vinci surgical system, it was possible to acquire proficient vascular anastomosis skills of an experienced vascular surgeon with a short period of training, including medical students with little experience of abdominal surgery. Consequently, we think that robot-assisted vascular anastomosis will increasingly be performed in the field of vascular surgery, with the potential of becoming a standardized method.
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This is an interesting experimental study from the group at Kanazawa University Hospital in Japan examining learning curves for robotic-assisted vascular anastomoses. They studied three groups of surgeons. Group A comprised three vascular surgeons with more than 10 years’ experience, group B included vascular surgeons with less than 10 years’ experience, and group C included three medical students with no experience. They were tasked with using the da Vinci Surgical System to anastomose an 8-mm–diameter vascular prosthesis in an end-to-end manner with continuous 5-0 Prolene. The procedure was performed five times by each participant, and outcomes were measured. They found a significant learning curve for each group during this short period of training. Interestingly, the mean visual score and leakage rate were not significantly different among the three groups in each trial.
This study adds to the body of literature that demonstrates the learning curve with the use of robotic assistance. The authors are to be commended for their attempt to quantitate performance. The main weakness of the study was the small number of participants in each group and the fact that they performed only five repetitions of the procedure. The small number of both participants and repetitions does not allow for a full definition of the entire learning curve for this task. Moreover, the clinical utility of this simulation requires further validation.