Impact of the suboptimal communication network environment on telerobotic surgery performance and surgeon fatigue.

BACKGROUND: Remote surgery social implementation necessitates achieving low latency and highly reliable video/operation signal transmission over economical commercial networks. However, with commercial lines, communication bandwidth often fluctuates with network congestion and interference from narrowband lines acting as bottlenecks. Therefore, verifying the effects on surgical performance and surgeon fatigue when communication lines dip below required bandwidths are important.
OBJECTIVES: To clarify the communication bandwidth environment effects on image transmission and operability when bandwidth is lower than surgical robot requirements, and to determine surgeon fatigue levels in suboptimal environments.
METHODS: Employing a newly developed surgical robot, a commercial IP-VPN line connected two hospitals 150 km apart. Thirteen surgical residents remotely performed a defined suturing procedure at 1-Gbps to 3-Mbps bandwidths. Communication delay, packet loss, time-to-task completion, forceps-movement distance, video degradation, and robot operability were evaluated before and after bandwidth changes. The Piper Fatigue Score-12 (PFS-12) was used to measure fatigue associated with surgeon performance.
RESULTS: Roundtrip communication time for both 1-Gbps and 3-Mbps lines averaged 4 ms. Video transmission delay from camera to monitor was comparable, at 92 ms. Surgical robot signal transmission rate averaged 5.2 Mbps, so changing to 1-Gbps-3-Mbps lines resulted in significant packet loss. Surgeons perceived significant roughness, image distortion, diplopia, and degradation of 3D images (p = 0.009), but not changes in delay time or maneuverability. All surgeons could complete tasks, but objective measurement of task-completion time and forceps-travel distance were significantly prolonged (p = 0.013, p = 0,041). Additionally, PFS-12 showed post-procedure fatigue increase at both 1-Gbps and 3-Mbps. Fatigue increase was significant at 3-Mbps (p = 0.041).
CONCLUSIONS: In remote surgery environments with less than the optimal bandwidth, even when delay time and operability are equivalent, reduced surgical performance occurs from video degradation from packet loss. This may cause increased surgeon fatigue.

Introduction

Telesurgery holds great promise as a mean way to improve accessibility to high quality healthcare in areas with limited healthcare resources and as a new method in surgical education [1]. In 2001, the world’s first inter-Atlantic telesurgery was successfully performed [2] and a telesurgery system was established in Canada [3]. However, the social implementation of telesurgery was deferred for a long time due to the following: the communication delay time was too long for clinical application with communication lines at the time [4,5], secure dedicated lines were too expensive for most clinical use [6], communication security could not be ensured over internet lines [7], so for various reasons, there was minimal development of new robots for telesurgery [8].

These days, issues of communication delay and security, which were key barriers to remote surgery, are being resolved by the development of high-speed, large-capacity communication networks and advances in information processing technology. In addition, the patent for the surgical robot system of the preceding generation has expired, which has led to the development of new types of surgical robots and the resumption of social demonstration studies of remote surgery [8-11]. Our group conducted a telesurgery experiment in which two hospitals located 150 km apart were connected by a commercial line. A surgical robot under development was used, and a telesurgical operation was possible without significant delay [1].

Remote surgery is performed by transmitting both video signals and control signals for robot operation. Of these, the number of signals which are required to operate the robot arm and control energy devices is small and all can be transmitted over narrow-band communication lines. Video signals, on the other hand, contain a large amount of information and require a bandwidth of more than 1.5 Gbps for full high vision images and more than 6 Gbps for 4K images. This presents the difficulty of achieving uncompressed transmission with the communication bandwidth of ordinary commercial lines. For this reason, compressed transmission of video signals is essential. However, since the relationship of the compression ratio and the delay time is the trade-off, the degree of compression needs to be limited. Also, excessive compression causes video degradation. Therefore, preparing a line with a sufficient communication bandwidth that can transmit the video signal satisfactorily, after compression, is necessary.

Among the currently available commercial lines, a line that guarantees a wide bandwidth is expensive and is not suitable for general clinical use from the viewpoint of economic efficiency [6]. The best effort type line, however, for which the maximum communication capacity is openly stated, is highly economical. Some unfortunate realities of using the best effort type line, are that bandwidth may temporarily become smaller than the required communication line bandwidth when the line is congested, or that bandwidth narrower than the required bandwidth, may bottleneck when multiple lines are connected. In such network environments, with less-than-optimal communication conditions, packet loss and communication delay of transmission signals can occur. In the case of packet loss, video transmission containing a large amount of communication information is greatly affected. The degree of packet loss varies greatly from the degree at which a surgeon cannot detect any change in the image to the degree that the image is clearly changed [12].

Surgical robot systems have a minimum required bandwidth for transmission of video signals and operation signals. However, the actual degree of change to the video is unclear, as is the effect on surgical performance when communication bandwidth dips below the system’s minimum bandwidth. In addition, physiological effects such as surgeon fatigue have not been investigated thus far. In this study, we examined the effects on surgical performance and surgeon fatigue of a communication environment with a bandwidth narrower than the required bandwidth during an actual remote surgery experiment using a commercial line.

Methods

Communication environment

Hirosaki University Hospital and Mutsu General Hospital, located about 150 km apart, were connected through a commercial bandwidth-guaranteed line provided by NTT East (NIPPON TELEGRAPH AND TELEPHONE EAST CORPORATION, TOKYO, JAPAN) (Fig 1). The communication bandwidth was initially set at 1-Gbps, and then changed to 3-Mbps. We evaluated the latency of each communication line, the latency associated with signal compression/decompression processing, and the overall latency of video transmission between the laparoscopic camera and the monitor.

Fig 1

Network system.

Hirosaki University Hospital and Mutsu General Hospital, located about 150 km apart, were connected through a commercial bandwidth-guaranteed line. OUN: Optic network unit, CPE RT: Customer premises equipment remote terminal, I/F: Interface.

For CODEC, we used Encoder Zao-SH and decoder Zao-View of Soliton Systems (Tokyo, Japan). This CODEC has a function that reserve 1Mbps of communication bandwidth for robot operation signals preferentially and allocates the remaining bandwidth to video transmission.

Surgical robots and tasks

Using a surgical robot being developed by RIVERFIELD, Inc. [13], thirteen surgical residents, ranging from 2nd to 4th year, who had no experience in robotic surgery, but had robotic procedure experience in actual robotic surgery as assistants, performed suture ligation of an intestinal model by remotely manipulating robotic arms with a controller while viewing the surgical field image on an open 3D monitor. To avoid the influence of habituation, the subjects were divided into two groups: seven subjects performed the procedure in the sequence of 1-Gbps, then 3-Mbps, and the remaining six subjects performed the procedure in the order of 3-Mbps, then 1-Gbps. For both groups, a 10-minute practice period was provided immediately before task performance measurement (Fig 2).

Fig 2

Flowchart of the order of the line speed and subjective evaluation of the task.

The subjects were divided into two groups: Seven subjects performed the procedure in the sequence of 1-Gbps, then 3-Mbps, and the remaining six subjects performed the procedure in the order of 3-Mbps, then 1-Gbps. They answered questionaries pre- and post-procedure for each bandwidth.

The intestinal model was marked to indicate suture sites at 5 mm intervals, and the operation was performed with five sutures and three ligatures in each suture. Operation performance was evaluated by measuring the task completion time from the start of intestinal anastomosis to the end of three ligatures of the final suture, and the distance traveled by the robotic arm forceps during the operation.

Furthermore, using the Global Evaluative Assessment of Robotic Skills (GEARS) score devised by Goh et al. [14] (S1 Table), two robotic expert surgeons evaluated the subject performance (depth of perception, bimanual dexterity, efficiency, force sensitivity, autonomy, robotic control). The mean values of the two evaluators were compared for each line band.

Subjective evaluation of the examinee

Modified System Usability Scale

The m-SUS was created by modifying the System Usability Scale (SUS) [15], which was developed to subjectively evaluate the usability of newly constructed systems, and the usability of the telesurgery system was evaluated (Fig 3). Nine items were rated on a 5-point scale in descending order of usefulness, and the total score was shown as the score.

Fig 3

Modified System Usability Scale.

Robot Usability Score

In order to evaluate the usability of the operation of the robot system, we created the Robot Usability Score, which evaluates eight items: physical comfort, manual operability, foot pedal operability, stereoscopic performance, forceps operability, smoothness, satisfaction, and effectiveness (Fig 4). The usability was evaluated on a 5-point scale in descending order of usefulness, and the average values for each item were compared by line.

Fig 4

Robot Usability Score.

Image quality evaluation scale

In order to evaluate whether image quality degradation due to changes in line conditions interferes with the performance of the procedure, an image quality evaluation scale was developed (Fig 5). A five-point scale was used, with a high score indicating no deterioration in image quality and no effect on the performance of the procedure. The median score was compared by line type.

Fig 5

Image quality evaluation scale.

Piper Fatigue Scale-12 (PFS-12)

The subjective fatigue of the surgeons was assessed using the Piper Fatigue Scale-12 (PFS-12) survey [16] (S2 Table). the PFS-12 consists of 12 questions on fatigue and is divided into four subscales: behavioral, emotional, sensory, and cognitive. The scores are rated on a 10-point scale in descending order of fatigue, and the method of score calculation is reported by Reeve et al. The questionnaire was filled out immediately before and after the procedure, and the changes before and after the procedure were measured. Pre- and post-procedure changes were measured.

Statistical analysis

Data are presented as frequency for categorical data and as mean ± standard deviation or median (range) for continuous data. EZR software was used for analysis [17]. Normality was tested with the Shapiro-Wilk test, and if normality was not rejected, the paired Student’s t-test was used. When normality was rejected, the Wilcoxon test was used. Statistical significance was determined at p < 0.05.

Ethics statements

There is no need to address this or provide an ethics application as this research does not fall under the category of "life science/medical research on human subjects." The surgeons were using robotic technology to suture inanimate objects in a simulated telesurgery situation. With regard to the above, we obtained a formal waiver from Hirosaki University Ethics Committee for this study. All subjects (participating surgeons) were informed about the study in writing, and we obtained their written consent.

Results

Transmission delay time

Communication delay was comparable with a median of 4 ms (range 3–7) for the 1-Gbps line and 4 ms (3–8) for the 3-Mbps line. Adding 61 ms (48–74) for encoder and decoder delay to the communication delay, the delay caused by the remote surgical operation was 65 ms (51–81) for the 1-Gbps line and 65 ms (51–88) for the 3-Mbps line. The glass-to-glass time, which also includes the time required for the laparoscopic camera to process images of the surgical field and the reaction time of the surgical monitor, was 92 ms (73–117) for the 1-Gbps line and 92 ms (73–118) for the 3-Mbps line.

Video signal packet loss and changes in surgical field images

We simultaneously and continuously measured the communication bandwidth of the transmission signal, frame rate of the video, packet loss, and communication delay time during the surgical task. A typical measurement example is shown in Fig 6. When a line with a communication bandwidth of 1-Gbps was used, the video signal transmission rate was stable at 5.2 Mbps (range 4.8–5.3), and the average packet loss rate was as low as 0.042%. However, when the communication bandwidth was changed to 3-Mbps, the average packet loss rate increased to 4.82%. When a subject started a robotic operation, the video communication bandwidth decreased to 2 Mbps because CODEC allocated 1 Mbps bandwidth to the robot operation signal on a priority basis (arrowhead in the Fig 6). On the contrary, when the surgical operation ended, the degree of packet loss was reduced (arrow in the Fig 6). The communication delay (round-trip transmission time: RTT) was stable at less than 3 ms regardless of the bandwidth. The same results were obtained in all 13 subjects.

Fig 6

An example of the bandwidth, frame rate of the video, packet lost, and delay time.

The video signal transmission rate was steady at 5.2 Mbps, and the average packet lost rate was as low as 0.042% with 1 Gbps. The average packet loss rate increased to 4.82% with 3 Mbps. When a subject began a robotic operation, the visual communication bandwidth was reduced to 2 Mbps because CODEC assigned a priority of 1 Mbps to the robot operation signal (arrowhead). The surgical procedure was completed, the amount of packet loss decreased (arrow). Regardless of bandwidth, the communication delay was less than 3 ms, Framerate (fps): Framerates per second, Video (kbps): Video transmission value loss (kilobits per second), Pkt lost rate: Packet lost rate.

Evaluation of surgical performance

Task completion time was significantly prolonged with the slower 3-Mbps line (350.2 ± 91.7s vs. 386.2 ± 92.6s, p = 0.013). Forceps travel distance was significantly longer for right-handed forceps manipulation (3,786.7 ± 750.8 mm vs. 4,064.2 ± 952.2, p = 0.041), but left-handed forceps manipulation also showed a trend toward longer distance (3,743.0 mm ± 480.6 vs. 4,028.2 ± 742.8, p = 0.10). Evaluation of surgical performance by GEARS score, however, showed no significant difference between the bands (25.4 ± 3.4 vs. 23.6 ± 2.6, p = 0.12). Among the evaluation items, the accuracy of forceps movements and sutures were evaluated under the category of "Depth perception," and it was shown as being equal by bandwidth (3.7 vs. 3.5, p = 0.35).

Usability of the surgical robot

The evaluation of the usefulness of the tele-robotic surgery system by m-SUS showed a lower trend at 3-Mbps than at 1-Gbps (21.31 ± 4.50 vs. 19.08 ± 4.55, p = 0.062).

In the Robot Usability Score, the evaluation of the stereoscopic view was significantly lower for the 3-Mbps line than in the 1-Gbps line (p = 0.009), and hand control operation tended to be lower (p = 0.06). There was no difference by line bandwidth in overall comfort of the surgical robot, smoothness of robot operation, follow-up, effectiveness (Table 1).

Table 1

Comparison of Robot Usability Score across line bandwidths.

Speed of the line	1-Gbps	3-Mbps	P-valuea
Physical Comfort	3.07 ± 0.95	2.77 ± 1.01	0.28
Hand Control	3.15±0.90	2.46 ± 0.97	0.06
Foot Control	4.08 ± 0.64	4.07 ± 0.75	1.00
3D Vision	3.31 ± 0.85	2.38 ± 1.04	0.009b
Annoyed or stressed	2.76 ± 0.83	2.62 ± 0.87	0.62
Smoothness	2.85 ± 0.90	2.85 ± 0.90	0.93
Satisfaction	2.84 ± 0.99	2.69 ± 0.85	0.88
Reality	3.00 ± 1.00	2.61 ± 1.04	0.28

The evaluation of the stereoscopic view was significantly lower for the 3-Mbps line than in the 1-Gbps line. There was no statistical difference of the score in the other parameters.

a p values were calculated using the paired t-test.

b p < 0.05.

Subjective image quality evaluation

Video abnormalities such as screen coarseness (4/13), diplopia (3/13), horizontal line delineation (1/13), and stereoscopic difficulty (2/13) were observed on the 3-Mbps line. In terms of the effect of image quality degradation on the performance of the procedure, evaluation by the image quality rating scale showed that the 3-Mbps line was significantly lower than the 1-Gbps line (4 (4–5) vs. 3 (2–4), p = 0.034).

Self-reported fatigue score

On the PFS-12 score, the overall score increased significantly after the procedure for both 1-Gbps and 3-Mbps lines (Table 2A). The 3-Mbps line, in particular, showed an increase on all four subscales. On the contrary, the difference in the overall score of fatigue before and after the procedure on the 3-Mbps line (Δ3 Mbps) was significantly larger than that of the 1-Gbps line (Δ1 Gbps) (Table 2B).

Table 2

Comparison of the Piper Fatigue Scale-12 (PFS-12) between line bandwidths.

(a) PFS-12 score values before and after the task for each line.
Speed of the line	1 Gbps			3 Mbps
	before	after	P-value a	before	after	P-value a
All scores	2.93	3.60	0.049 b	2.16	3.54	0.002 b
Behavioral	2.51	3.53	0.024 b	1.17	3.3	0.004 b
Affective	3.23	3.87	0.070	2.66	4.12	0.016 b
Sensorial	3.26	3.92	0.180	2.79	3.72	0.015 b
Cognitive	2.69	3.10	0.388	1.46	2.99	0.016 b
(b) Comparison of the change in PFS-12 values before and after the procedure for each line.
Speed of the line	⊿1 Gbps	⊿3 Mbps	P-value a
All scores	0.68 ± 1.12	1.37 ± 1.23	0.041 b
Behavioral	1.03 ± 1.43	1.59 ± 1.64	0.062
Affective	0.64 ± 1.17	1.46 ± 1.89	0.126
Sensorial	0.64 ± 1.64	0.92 ± 1.18	0.471
Cognitive	0.41 ± 1.65	1.53 ± 1.37	0.084

The all score increased significantly after the procedure for both 1-Gbps and 3-Mbps lines. The 3-Mbps line, in particular, showed an increase on all four subscales.

The difference in the all score of fatigue pre- and post-procedure on the 3-Mbps line (Δ3 Mbps) was significantly larger than that of the 1-Gbps line (Δ1 Gbps).

a p values were calculated using the paired t-test.

b p < 0.05.

Discussion

In this study, slight disturbances to the video image degraded the surgical performance and increased surgeon fatigue, even though the transmission delay was minor and operability did not change in a communication environment with a bandwidth lower than that required for video transmission from a surgical robot. Since the required bandwidth of surgical robots varies from model to model depending on the number of video pixels and data compression ratio, the results of this study indicate the necessity of measuring the required bandwidth of the surgical robot to be used in advance and preparing a communication line with at least the minimum communication bandwidth.

In general, a dedicated line that guarantees the use of a wide bandwidth maintains the maximum communication bandwidth and has excellent stability and speed for high-capacity communication. However, the cost is remarkably high, making unsuitable for the widespread social implementation of remote surgery [6]. Conversely, the best effort type line, which advertises the maximum communication bandwidth among closed circuits with guaranteed security, is inexpensive and widely used, but has the risk of falling below the minimum bandwidth because the available bandwidth is affected by communication congestion. For this reason, new, more economical line services have been launched, such as lines with secured minimum bandwidth (burst lines) and best effort lines with bandwidth so wide that it surpasses instability.

Nevertheless, the available communication infrastructure varies from country to country and region to region. When promoting the social implementation of telesurgery, several different lines may be connected, and the possibility cannot be excluded that the amount of communication bandwidth may change due to the existence of bottlenecking, which creates narrow bandwidth in some parts of the network, and that the bandwidth may fall below the required level. Therefore, it is necessary to consider in advance the impact on surgical performance that changes in the communication environment will have when conditions fall below the required bandwidth. In addition, since surgeons adapt under stress even when they encounter a less than optimal environment [18,19], including the degree of fatigue surgeons face is a necessary part of constructing an evaluation.

In this study, the surgical robot required a video communication bandwidth of 5.2 Mbps, with a 1-Gbps bandwidth-guaranteed line, the communication delay was 4 ms and the video transmission delay from the endoscope camera to the monitor projection was 92 ms, with no problems in 3D video transmission and good operability. On the other hand, with the 3-Mbps line, the communication delay and video transmission delay were the same without extension, but the average packet loss was 4.82%. As a result, the video was degraded and the Robot Usability Score evaluated the 3D image quality as significantly low. Although they were able to complete all surgeries, the surgeon had to perform accurate suture ligation maneuvers in a suboptimal video environment, resulting in longer forceps travel distances and longer task completion times. The significantly longer forceps travel distance in the right hand than in the left hand was presumably due to the fact that the needle driver was attached to the robotic arm of the right hand when performing the suturing task.

In remote surgery, it is known that delays occur in each step of communication network transmission, information compression and decompression processing, video signal conversion at the camera, and monitor projection, resulting in prolonged task completion time and increased task error rate [19,20]. Furthermore, communication fluctuations (jitter) and packet loss are known to cause video degradation [12] and make equipment operation difficult [21]. The CODEC used in this study has a mechanism that preferentially allocates 1 Mbps for operation signal transmission, yet no obstacle to the operability of the robot on either the m-SUS or Robot Usability Score evaluations. In addition, the video transmission delay is extremely short, 92 ms, which is less than 200 ms, which is considered to be an acceptable delay time for teleoperations [18,22]. In addition, since the delay was less than 100 ms, which is considered to be an acceptable delay time for telesurgery [22,23], the main cause of the prolongation of the task completion time in this study was assumed to be caused by the packet loss of the video transmission, not the delay. In a previous study, a telesurgery experiment was conducted using a 5 Mbps line with the same robot and the same facility conditions, and packet loss of less than 1% with no video degradation was observed [24]. Based on this information, we chose to conduct this experiment using a 3-Mbps line. Video degradation, which can be caused by packet loss, varies, so there is a need to verify the acceptable level of packet loss for each surgical robot.

The Peak signal-to-noise ratio (Peak) method [25,26] and the structural similarity index measure (SSIM) [27] are known as objective evaluation methods for video degradation. However, it is also pointed out that they do not necessarily reflect subjective evaluation [28]. Moreover, the most important aspect of the video quality required for remote surgical images is whether it is good enough for the surgeon to be able to perform the operation. Therefore, we evaluated the image quality in terms of the outcome as to whether it interfered with the procedure or not. As a result, the 3-Mbps line was evaluated as not interfering with the procedure, although video degradation was perceived in comparison with the 1-Gbps line, yet the video degradation was within the range to which the surgeon could adapt. In an objective assessment, completion time was prolonged, which indicated that video degradation certainly had an impact on surgical performance, but it was not recognized to be a serious obstacle to the tasks. In other words, the surgeon adapts to the degradation of the image and subconsciously operates at a slightly slower pace to maintain accuracy and complete the task, so when asked, in the surgeon’s conscious personal experience, the operation is unaffected. Objectively, however, the task completion time is longer. These facts also suggest that there could be a discrepancy between objective and subjective assessments.

On the other hand, it stands to reason that a certain level of burden might be imposed upon the surgeon when performing operations in such a suboptimal environment. Therefore, we also evaluated the degree of surgeon fatigue due to changes in the communication environment. In the past, it was reported that surgeons were able to adapt to an extended transmission delay by training for this sort of delay time [18]. In other words, surgeons were able to adapt to less-than-optimal conditions by expending a certain amount of energy. It is noteworthy that surgeon fatigue would increase in the early stages of such changing conditions. According to the PFS-12 survey, surgeon’ fatigue increased before and after the operation on both lines, but the increase was particularly significant with the 3-Mbps line. This was thought to be a result of the energy spent dealing with the video degradation caused by the change of bandwidth.

Armijo et al. previously reported the difference in fatigue between laparoscopic and robotic surgery by measuring upper body muscle activity and self-reported fatigue using PFS-12. [29] Also, it was reported that more than half of the surgeons performing robotic surgery for a long period of time experienced physical issues [30]. In this study, we showed that not only the robotic surgery itself but also the video degradation that occurs specifically in teleoperations affected surgical performance and surgeon fatigue. In the future, communication environments will rapidly advance; the telesurgery environment will change to be more stabilize with fewer communication interruptions. However, there is no doubt that constructing a minimum environment necessary for safe and economic telesurgery is needed. Furthermore, the telecommunications environment is not always sufficient in some of the very regions of the world where telesurgery is badly needed. In order to succeed in such environments, both objective and subjective evaluations are likely necessary to set appropriate standards for acceptable packet loss and video quality, because there will be some discrepancy between subjective and objective evaluations.

This study is meaningful because it was conducted in an actual telesurgery environment using a real commercial line. On the other hand, it also has the following limitations: (1) Communication bandwidth was tested with only two types, a 1-Gbps line and a 3-Mbps line, and the bandwidth changed discontinuously. Therefore, we were unable to evaluate the effect of the bandwidth on the video degradation continuously and quantitatively. However, in a previous study conducted under similar conditions, in which a 5-Mbps line was used, the video image and the task completion time did not change, despite the packet loss that existed. Hence, the 3-Mbps line is assumed to be the approximate critical bandwidth. (2) Since the required bandwidth varies depending on the types of surgical robots and encoders, the limit of the bandwidth in this study applies only to this environment. (3) The surgical tasks were only basic movements. Since negative effects were observed even for simple procedures in a suboptimal environment, considerable negative effects might be seen in actual surgery. (4) The test subjects were limited to residents who had no experience in robotic surgery. Acceptable limits for video degradation and delay would expand for those with extensive robotic experience. (5) The evaluating methods for surgical performance were subjective. However, using three different metrics: m-SUS, Robot Usability Score, and GEARS, and evaluating the performance quantitatively is surely valuable. In addition, we examined the effects of video degradation on the technique and the fatigue level of the surgeons. They completed the operations despite the energy it consumed, even in a suboptimal operating environment thanks to adaptation. Therefore, evaluating the physiological effects on the surgeon has proven to be important.

Conclusions

In a communication environment with less than the required bandwidth, video image degrades due to packet loss, the task completion time is prolonged, and this can be a cause of increased surgeon fatigue, even when no prolongation of transmission delay or degradation of operability is seen. Establishing an acceptable standard environment is necessary for performing telesurgery when temporary suboptimal communication conditions are encountered. In addition, the selection of an appropriate communication line is essential for the social implementation of this modality.

Global Evaluative Assessment of Robotic Skills (GEARS).

(DOCX)

Click here for additional data file.

Piper Fatigue Scale-12 (PFS-12).

(DOCX)

Click here for additional data file.

1 Mar 2022

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Reviewer #1: This manuscript explores the impact of narrow communication bandwidth on surgical operation and surgeon fatigue during remote surgery. I appreciate the fact that you are simulating a real remote surgery, and the manuscript is generally well-written.

The following are some questions to ask.

1) Is there a clear reason why you chose surgical residents instead of skilled surgeons as subjects?

2) It is stated that there was no difference in communication delay. In this study, did you observe any overshoot of forceps manipulation due to communication delay?

3) Even though the task completion time was extended, the subjects judged that the image degradation by packet loss did not affect the surgery, and this part is very confusing. Isn't the extended task completion time caused by a decrease in image quality, if there is no communication delay? You should be able to describe the issues you have considered more clearly.

4) This study has an important implication on the impact of narrow-banding due to network congestion and interference on tele-surgery. Based on the premise that ultra-high speed, high capacity, low latency, and multiple connections in communications will rapidly advance, could you suggest another implication of this paper for the future of tele-surgery?

Reviewer #2: The authors reports combined communication network environment on telerobotic surgery performance and surgeon fatigue.

I recommend to address following points for the paper more informative.

Overall, it is difficult to evaluate the results obtained by surgical residents without prior robotic surgery experience.

It seems that factors other than the communication environment had a significant impact on the results.

It seems that same results are obtained when the same procedure is performed by a skilled surgeon？

Authors should describe the information whether packet loss is more likely to occur in the case of motion and images (e.g., far field or near field).

There is any difference in the accuracy of sutures performed at 1 Gbps or 3 Mbps?

Please provide a representative image of each of different communication speeds.

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Reviewer #1: No

Reviewer #2: No

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8 Apr 2022

Responses to Reviewers

Responses to the Comments by the Associate editor:

1. Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming. The PLOS ONE style templates can be found at https://journals.plos.org/plosone/s/file?id=wjVg/PLOSOne_formatting_sample_main_body.pdf and https://journals.plos.org/plosone/s/file?id=ba62/PLOSOne_formatting_sample_title_authors_affiliations.pdf

Reply:

Thank you for your help. We have consulted the template and we are confident that our revised manuscript meets your style requirements.

2. You indicated that ethical approval was not necessary for your study. We understand that the framework for ethical oversight requirements for studies of this type may differ depending on the setting and we would appreciate some further clarification regarding your research. Could you please provide further details on why your study is exempt from the need for approval and confirmation from your institutional review board or research ethics committee (e.g., in the form of a letter or email correspondence) that ethics review was not necessary for this study? Please include a copy of the correspondence as an ""Other"" file.

Reply:

Thank you very much for this important comment. We have attached a confirmation letter from our ethical committee as an “Other” file.

3. Thank you for stating the following in the Competing Interests section: "I have read the journal's policy and the authors of this manuscript have the following competing interests: Kenji Kawashima is employed by RIVERFIELD and owns stock in the company. Takahiro Kannno is employed by RIVERFIELD and serves as CTO. Harue Akasaka and other co-authors have no conflict of interest."

Please confirm that this does not alter your adherence to all PLOS ONE policies on sharing data and materials, by including the following statement: "This does not alter our adherence to PLOS ONE policies on sharing data and materials.” (as detailed online in our guide for authors http://journals.plos.org/plosone/s/competing-interests ). If there are restrictions on sharing of data and/or materials, please state these. Please note that we cannot proceed with consideration of your article until this information has been declared.

Please include your updated Competing Interests statement in your cover letter; we will change the online submission form on your behalf.

Reply:

Thank you for your help. We have included the following statement: "This does not alter our adherence to PLOS ONE policies on sharing data and materials.” As requested, our Competing Interest statement also appears in our new cover letter. Thank you for changing the online submission form for us.

4. PLOS requires an ORCID iD for the corresponding author in Editorial Manager on papers submitted after December 6th, 2016. Please ensure that you have an ORCID iD and that it is validated in Editorial Manager. To do this, go to ‘Update my Information’ (in the upper left-hand corner of the main menu), and click on the Fetch/Validate link next to the ORCID field. This will take you to the ORCID site and allow you to create a new iD or authenticate a pre-existing iD in Editorial Manager. Please see the following video for instructions on linking an ORCID iD to your Editorial Manager account: https://www.youtube.com/watch?v=_xcclfuvtxQ

Reply:

Thank you for your kind suggestion. The corresponding author has an ORCID iD and configured it to be enabled in Editorial manager.

ORCID iD, https://orcid.org/0000-0001-6513-1202

Responses to the Comments by Reviewer 1:

1) Is there a clear reason why you chose surgical residents instead of skilled surgeons as subjects?

Reply:

Thank you very much for your important question. Telesurgery is destined to be further developed in clinical settings in the near future; many surgeons, including young surgeons, as well as experts, will be involved. We work at a teaching hospital, so we thought that young surgeons, who are the core players in the surgical field of the future, should evaluate this new surgical system and clarify the issues they deem meaningful. This is the reason why we chose residents as subjects for this study.

2) It is stated that there was no difference in communication delay. In this study, did you observe any overshoot of forceps manipulation due to communication delay?

Reply:

Thank you for your question. Overshooting due to communication delay was not observed. We evaluated it using GEARS which has an evaluation item that includes overshoot of forceps called “Depth perception.” There was no significant difference in “Depth perception” by line (3.7 vs. 3.5, p = 0.35). We have added text to the Results section to clarify this. (Page 16-17, Lines 267-269).

3) Even though the task completion time was extended, the subjects judged that the image degradation by packet loss did not affect the surgery, and this part is very confusing. Isn't the extended task completion time caused by a decrease in image quality, if there is no communication delay? You should be able to describe the issues you have considered more clearly.

Reply:

Thank you very much for your invaluable comments. The prolonged task completion time was certainly due to the degraded image quality. However, according to their subjective evaluation, the subjects evaluated it as not affecting the task. This suggests that there is a certain acceptable range of environment in which the surgeons can perform the tasks. In other words, the surgeon adapts to the degradation of the image and unconsciously operates slightly slower to pursue accuracy and complete the task, so the surgeon feels that surgical operation, itself, is unaffected. Objectively speaking, yes, the task completion time is extended. Therefore, a discrepancy between objective and subjective assessments exists. We have added text to the Discussion section (Page 24-25, Lines 389-396) to address this phenomenon.

4) This study has an important implication on the impact of narrow-banding due to network congestion and interference on tele-surgery. Based on the premise that ultra-high speed, high capacity, low latency, and multiple connections in communications will rapidly advance, could you suggest another implication of this paper for the future of tele-surgery?

Reply:

Thank you very much for your helpful recommendations. We have added the following implication to the Discussion section (Page 26, Lines 414-422).

: “In the near future, the communication environment is likely to advance rapidly, telesurgery situations will evolve and become more stabilized with fewer communication interruptions. However, there is no doubt that determining the minimum environment necessary for safe and economic telesurgery is necessary. Furthermore, the state of telecommunications is not always adequate in the very regions of the world where telesurgery is most needed. In order to achieve both objective and subjective evaluations of telesurgery protocols, it is necessary to set appropriate standards for acceptable packet loss and video quality, because some discrepancy between subjective and objective evaluations is always likely to exist.”

Responses to the Comments by the reviewer 2:

Overall, it is difficult to evaluate the results obtained by surgical residents without prior robotic surgery experience. It seems that factors other than the communication environment had a significant impact on the results. It seems that same results are obtained when the same procedure is performed by a skilled surgeon?

Reply:

Thank you very much for your invaluable comments. In fact, the residents had trained and practiced robotic surgery prior to this study and had experienced actual robotic surgery as assistants. We believe that they were capable of evaluating the telesurgery environment in the study in contrast to actual robotic surgery. However, as Reviewer 2 pointed out, such factor may be viewed as limitations of this study. The acceptable range of image quality degradation and communication delay could be quite different for experts. We have added a description of the subject's experience of robotic surgery to the Methods section (Page 9, 145).

Authors should describe the information whether packet loss is more likely to occur in the case of motion and images (e.g., far field or near field).

Reply:

Thank you very much for your excellent suggestion. In this study, more packet loss occurred when robot operation was performed. This is because the communication environment of this study was set to reserve 1Mbps for robot operations, and the bandwidth was reduced by 1Mbps when robot operation was started. However, we are afraid to say that we cannot comment on exactly where it affects the field of view, the far or near side, because we evaluated image changes in terms of whole images.

There is any difference in the accuracy of sutures performed at 1 Gbps or 3 Mbps?

Reply:

Thank you for your question. The accuracy of sutures was equal at each bandwidth. We evaluated it using GEARS, which has an evaluation item that includes the accuracy of the movement of the instruments called “Depth perception.” There was no significant difference “Depth perception” by line (3.7 vs. 3.5, p = 0.35). We have added text to the Results section. (Page 16-17, Lines 267-269).

Please provide a representative image of each of different communication speeds.

Reply:

Thank you very much for your important comments. We regret to say that we did not record individual images for the various stages of the procedures. Instead, we evaluated image quality using an image quality evaluation system as shown in Figure 5 to indicate how image quality changed and whether or not it affected the procedures.

Submitted filename: Response to Reviewers.docx

Click here for additional data file.

28 Apr 2022

10 May 2022

Responses to the Comments by the Associate Editor:

1. Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice.

Reply:

Thank you very much for your helpful comment. We confirmed that the reference list is complete and correct. Also, there was no retracted reference.

Responses to the Comments by Reviewer 1:

1) Thank you for your response to my comments.

In response to the second comment, "We have added text to the Results section to clarify this.(Page 16-17, Lines 267-269)", but unfortunately I could not find the changed section.

Reply:

Thank you for pointing this out. We are very sorry that there was an incorrect statement in the description of the modification. We revised the description regarding overshooting as follows.

Overshooting due to communication delay was not observed. We evaluated it using GEARS, which has an evaluation item that includes the concept of overshooting of forceps called “Depth perception.” There was no significant difference in “Depth perception” by line (3.7 vs. 3.5, p = 0.35). Furthermore, we have added text to the Results section to clarify this (Page 17, Lines 270-272).

Submitted filename: Response to Reviewers.docx

Click here for additional data file.

3 Jun 2022

Impact of the suboptimal communication network environment on telerobotic surgery performance and surgeon fatigue

PONE-D-22-03175R2

Dear Dr. Kenichi Hakamada,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

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If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they’ll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org.

Kind regards,

Norikatsu Miyoshi, M.D., Ph.D., FACS

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: All comments have been addressed

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

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5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: (No Response)

**********

7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

**********

9 Jun 2022

PONE-D-22-03175R2

Impact of the suboptimal communication network environment on telerobotic surgery performance and surgeon fatigue

Dear Dr. Hakamada:

I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department.

If your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information please contact onepress@plos.org.

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Thank you for submitting your work to PLOS ONE and supporting open access.

Kind regards,

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on behalf of

Dr. Norikatsu Miyoshi

Academic Editor

PLOS ONE