Abstract BACKGROUND Learning to perform a microvascular anastomosis is one of the most difficult tasks in cerebrovascular surgery. Previous studies offer little regarding the optimal protocols to maximize learning efficiency. This failure stems mainly from lack of knowledge about the learning curve of this task. OBJECTIVE To delineate this learning curve and provide information about its various features including acquisition, improvement, consistency, stability, and recall. METHODS Five neurosurgeons with an average surgical experience history of 5 yr and without any experience in bypass surgery performed microscopic anastomosis on progressively smaller-caliber silastic tubes (Biomet, Palm Beach Gardens, Florida) during 24 consecutive sessions. After a 1-, 2-, and 8-wk retention interval, they performed recall test on 0.7-mm silastic tubes. The anastomoses were rated based on anastomosis patency and presence of any leaks. RESULTS Improvement rate was faster during initial sessions compared to the final practice sessions. Performance decline was observed in the first session of working on a smaller-caliber tube. However, this rapidly improved during the following sessions of practice. Temporary plateaus were seen in certain segments of the curve. The retention interval between the acquisition and recall phase did not cause a regression to the prepractice performance level. CONCLUSION Learning the fine motor task of microvascular anastomosis adapts to the basic rules of learning such as the “power law of practice.” Our results also support the improvement of performance during consecutive sessions of practice. The objective evidence provided may help in developing optimized learning protocols for microvascular anastomosis. Bypass, Acquisition, Learning protocol, Power law of practice, Recall, Performance consistency, Performance stability Despite the compelling necessity and increasing interest to learn and perform cerebrovascular bypass procedures, the lack of a science-based efficient training protocol has caused this black box to remain nondecoded so far. Residents and other trainees interested in learning the bypass techniques do not know how to optimally use the available training equipment to reach maximum efficiency.1 Sometimes, they are not even sure if using such equipment is effective at all.1 Furthermore, when trainees embark on practicing anastomosis, they may not have a clear concept of how much progress is expected following each learning stage. Other questions include but are not limited to: How much practice is needed to reach a stable level of learning? How should the practice protocols be designed and organized? How should the performances be scored? Thus, many individuals practicing bypass techniques in the labs, do so by spending a few hours of disorganized practice, without any practice/progress model and scheduled protocol to follow, and/or without proper assessment and feedback plans. This approach frequently leads to practice abandonment. Defining and using a bypass learning curve can reduce many ambiguities in this regard. Delineating the learning curve of bypass can unveil the nature of this task to some extent, and can clarify the minimum number of practice sessions required to progress, and to reach a consistent performance. There have been few attempts to define the bypass learning curve in participants with different levels of expertise and in different fields.2,3 However, a common feature of all these studies is that they have been performed on live bypass models that entailed high economic, temporal, and ethical costs. Moreover, the level of bypass difficulty was not controlled in these studies.2,3 On the other hand, artificial vessels such as silastic tubes (Biomet, Palm Beach Gardens, Florida) offer a simple reproducible practice model with proven transferability to live models.1,4 Also, using progressively smaller tubes during the training process, the level of bypass difficulty is controllable with silastic tubes. The purpose of the present study was to delineate the learning curve for practicing microanastomosis on silastic tubes. METHODS The study did not require Institutional Review Board approval as it did not involve any patients or animal subjects, and the subjects were performing a relatively routine task for neurosurgeons (microscopic suturing) on nonliving material with no interference from the investigators. Informed consent was taken from all participants before the beginning of the study. Participants Five neurosurgeons with a mean practice period of 5 yr in everyday microsurgical techniques used in neurosurgery participated in this study. The participating subjects were general practicing neurosurgeons (with no history of training in fellowship programs or practicing in subspecialty neurosurgery). The participants had the usual exposure to general neurosurgical cases, the treatment of which requires general microsurgical techniques such as intra- and extra-axial tumor resection, clipping of aneurysms, performing subarachnoid dissection (such as splitting the Sylvian fissure), and peripheral microsurgical nerve anastomoses. None of the participants had any previous exposure to microvascular anastomosis. Practice Protocol The participants were first shown a video footage of the end-to-end anastomosis technique performed on the rat's abdominal aorta using the interrupted suture technique (the video is not included in the submission). Next, the practice protocol was presented to the participants both orally and in written form (Appendix, Supplemental Digital Content). The participants were asked not to communicate with others about their experiences throughout the study. They were also asked not to refer to didactic sources about microvascular anastomosis throughout the study. According to the protocol, the participants practiced the technique of end-to-end anastomosis on silastic tubes (Biomet) for 24 consecutive sessions held at 1:00 pm every other day. All anastomoses were performed under magnification using a surgical microscope (Leica, Wetzlar, Germany). Before the start, the participants were provided a snack to control the confounding factor of hypoglycemia, and its interference with performance. A dedicated microanastomosis set was used in all practice sessions to control the instrument effect. The microanastomosis set contained a pair of microscissors, a pair of jeweler's forceps, a pair of microneedle appliers, and a pair of vessel approximators. Before beginning, the participants were asked to adjust the stool, microscope, and the anastomosis field so as to maximize comfort while their elbows rested on the chair's arm, and the silastic tube was at the center of the field. The microanastomosis field was set up by the study supervisor (P.M.). The silastic tube was affixed to a green square-shaped foam, and a vessel approximator was applied to the silastic tube at the point of planned anastomosis (Figure 1A). After being seated, the participant was instructed to place a cross-sectional cut at the approximate mid-point of the segment between the approximator tongs, and begin an end-to-end anastomosis between the 2 ends of the divided tube (Figures 1B and 1C). Anastomoses were performed using a single type of microsuture: Ethilon 2830G 10-0 nylon suture (Ethicon, Somerville, New Jersey). The participants were asked to place the first stitch at 2 o’clock position on the vessel perimeter. The second stitch was placed at 10 o’clock position, and the third was asked to be placed at 6 o’clock position as described elsewhere.5 The rest of the stitches were accordingly placed between the 3 initially placed sutures. This pattern of placing sutures was enforced during the practice period by the study supervisor. The first 6 trials were performed on a 2-mm silastic tube (Biomet). The quality of the anastomosis (anastomosis score) was rated by an independent observer (A.T.M.), regarding patency, and presence of any stenosis or leak by injecting artificial blood to the anastomosed silastic tube (Table, Figure 1D). After each of the first 6 trials, the participant received feedback about the quality of their performance. The next 12 trials were performed on 1-mm silastic tubes, and feedback was given following every other trial. The last 6 trials were performed using 0.7-mm tubes and feedback was given after the first and fourth trials of this row. Faded feedback method was used to promote performance while preventing feedback dependency.6-8 FIGURE 1. View largeDownload slide A, Practice and test setup with the silastic tube mounted on a foam base with the vessel approximators applied to the tube. B, The participant was asked to cut the tube and, C, perform an end-to-end anastomosis. D, The patency and leakage of the anastomosis was checked using a colored fluid infused into the tube. FIGURE 1. View largeDownload slide A, Practice and test setup with the silastic tube mounted on a foam base with the vessel approximators applied to the tube. B, The participant was asked to cut the tube and, C, perform an end-to-end anastomosis. D, The patency and leakage of the anastomosis was checked using a colored fluid infused into the tube. TABLE. Utilized Scale to Assess the Patency and Leakage of the Anastomosis Score Descriptiona 1 Completely occluded 2 High degree of leak 3 Low degree of leak + Significantly stenoticb 4 No leak + Significantly stenotic 5 Medium degree of leak + Nonsignificantly stenotic 6 Low degree of leakage + Nonsignificantly stenotic 7 No leak + Nonsignificantly stenotic Score Descriptiona 1 Completely occluded 2 High degree of leak 3 Low degree of leak + Significantly stenoticb 4 No leak + Significantly stenotic 5 Medium degree of leak + Nonsignificantly stenotic 6 Low degree of leakage + Nonsignificantly stenotic 7 No leak + Nonsignificantly stenotic aWhile assessing anastomoses, patency was assumed to have more importance than the amount of leakage. bSignificant stenosis was defined as stenosis of >50% of the original caliber of the Silastic tube. View Large TABLE. Utilized Scale to Assess the Patency and Leakage of the Anastomosis Score Descriptiona 1 Completely occluded 2 High degree of leak 3 Low degree of leak + Significantly stenoticb 4 No leak + Significantly stenotic 5 Medium degree of leak + Nonsignificantly stenotic 6 Low degree of leakage + Nonsignificantly stenotic 7 No leak + Nonsignificantly stenotic Score Descriptiona 1 Completely occluded 2 High degree of leak 3 Low degree of leak + Significantly stenoticb 4 No leak + Significantly stenotic 5 Medium degree of leak + Nonsignificantly stenotic 6 Low degree of leakage + Nonsignificantly stenotic 7 No leak + Nonsignificantly stenotic aWhile assessing anastomoses, patency was assumed to have more importance than the amount of leakage. bSignificant stenosis was defined as stenosis of >50% of the original caliber of the Silastic tube. View Large Testing Protocol After the practice sessions, 3 recall tests were given at weeks 1, 2, and 8 to assess the stability of learning during “no practice” (retention) period. The recall tests were performed on 0.7-mm silastic tubes using the same equipment and settings as practice sessions. The anastomosis was completed using the interrupted suture technique as instructed. Anastomosis score was assigned as described in “Practice Protocol.” Statistical Analysis The 1-way repeated measure analysis of variance test was used to compare the mean anastomosis scores of the first and last practice session, and the 3 recall tests. RESULTS In order to determine the basic anastomosis skill level, average anastomosis scores and performance durations for the first 3 practice sessions were compared between subjects. Analysis of variance did not show any statistically significant difference between the subjects regarding average anastomosis scores (P = .3) and performance durations (P = .93) in the first 3 sessions, hence confirming a comparable basic skill level between the subjects. The mean anastomosis score at the conclusion of the practice period (ie, acquisition phase; 6.6; 95% confidence interval: 6.3-6.9) was significantly higher than the first practice trial (2.2; 95% confidence interval: 1.7-2.7; P < .001). Mean duration of performing the anastomosis was 29΄ 11″ for the first session, and 13΄ 04″ for the last practice session, with a statistically significant difference (P = .002). The recall test scores were not significantly different from each other (average score 6.4), nor from the last acquisition trial (P = .585). Figure 2 shows the average learning curve for end-to-end anastomosis on silastic tubes. FIGURE 2. View largeDownload slide Performance curve of the task of microscopic anastomosis of silastic tubes according to the practice and testing protocol of the current study. Dashed lines show transition to a smaller caliber tube. FIGURE 2. View largeDownload slide Performance curve of the task of microscopic anastomosis of silastic tubes according to the practice and testing protocol of the current study. Dashed lines show transition to a smaller caliber tube. DISCUSSION The results of the present study show that 24 sessions of practice on silastic tubes (Biomet) according to the study protocol leads to the learning of the silastic tube anastomosis task. All participants progressed significantly regarding the anastomosis score and performance duration. The plotted curve of average anastomosis scores during 24 acquisition trials and 3 recall tests shows the features of (1) performance progress, (2) performance consistency, and (3) stability, confirming the “learning” of the practiced task of anastomosis. Performance Progress The slope of the learning curve is greater during the initial trials; a phenomenon concordant with the “power law of practice.”9,10 This means that in the beginning of learning, the participants have a lot of information bits to learn (cognitive stage of learning).9-11 Thus, a high degree of change in performance is seen from one trial to another during the initial phase of learning. More feedback provided during this phase helps the trainees answer their questions, and form a model of how to perform the task in their mind (ie, task schema).9,10,12 The overall direction of the learning curve is ascending, indicating the general progress in performance. However, temporary plateaus are seen in certain segments of the curve, and thereafter progress is seen again. These are performance plateaus.6,7 Although learning is in process, the trainee is passing through a stage in which the results of the learning are not visible in performance. For example, the trainee may only be involved in a specific part of the task (eg, trying not to rip the tube), precluding them from paying attention to the entire task. This causes a temporary pause or deceleration in performance gain. Plateaus may be important sources of discouragement or losing motivation during learning a difficult task such as microvascular anastomosis. Therefore, trainees aware of this feature of the learning curve would pass through it more smoothly. Similarly, instructors aware of such critical points during the learning process can significantly help trainees by providing motivational and instructional feedback.9,13 Such feedback was included in our protocol to address this issue. After each transition to a smaller caliber tube, a small temporary decline occurred in the performance which was due to the increasing difficulty of the task (decreased caliber of the tube). However, this decline quickly resolved during the second practice trial on the silastic tube with new caliber. Resolution of the decline took a shorter duration than the initial learning period for a 2-mm tube. The reason of this phenomenon is that by learning to perform the anastomosis on a 2-mm tube, the task schema has mainly formed in the trainee's mind. Therefore, when a smaller caliber tube is introduced, only one parameter is added to the task that takes less time for the trainee to improve their performance on that single parameter. Performance Consistency After the tenth trial, the performance seems to be more consistent; ie, trials show progressively decreasing difference with their previous and subsequent trials. Consistency is one of the features of learning. During learning, a specific schema of the task forms in the brain that is recruited every time the performance is taking place. As the schema matures as a holistic model, subsequent practice leads to change/improvement in smaller parameters.14,15 For example, during the first trials, general features of the task such as the optimal sequence of movements to pass and tie a suture are learned, whereas during the latter trials, smaller details such as the force needed to tighten the knots or the optimal distance of each bite from the tube edge are focused on. Development of consistency is a sign of passing beyond the cognitive stage of learning, and formation of a motor pattern.7 The timing for such phenomenon is different for various tasks based on the complexity of the task; a more complex task has more cognitive parameters which take longer to process. Our results show that for the task of microvascular anastomosis, a general figure of 10 initial practice trials is required to pass through the cognitive stage and beginning of consistency build-up. Performance Stability Learning is characterized by relatively stable changes, ie, a “no practice” time lapse does not cause significant forgetting of the learned skill.16,17 Indeed, performance declines after a period of “no practice” (Figure 2; compare the first recall performance with the final practice session). However, with established learning, performance is quickly restored to the previous level after a few trials.6 To identify the stability of learning in a learning curve, it is imperative to include recall tests in addition to acquisition trials in the learning protocols. No statistically significant difference was observed between anastomosis scores of the last acquisition trial and the recall tests. In other words, after 1, 2, and 8 wk from the final practice trial, a significant decline did not occur in learning, showing that the changes brought about by learning were stable. Extrapolation to Intraoperative Settings While the proposed learning curve provides insight into some aspects of a viable anastomosis (ie, patency, stenosis, and leakage), it may not be easily extrapolated to intraoperative settings in which several other parameters play major roles to achieve a successful bypass. Factors such as the occlusion time of cerebral vessels, depth of the operative field, and the complexity of the anastomosis (eg, side-to-side vs end-to-end) have significant influence on the learning curve of a particular bypass location/configuration. However, our study lays foundations for future studies implementing the aforementioned variables to enhance our understanding of the learning of a cerebrovascular bypass procedure. All the participants agreed that this study was of benefit to them regarding general microsurgical skills. Although it is difficult to draw conclusions based on subjective comments of the participants, it is plausible that such training protocols enhance the skills shared between microsurgical anastomosis and other microsurgical procedures such as eye-hand coordination, handling the microscope, planning the task before beginning, and problem-solving (such as when the tube is inadvertently torn). Indeed, these issues are subjects of separate controlled studies. Limitations Several limitations of the present study are worth mentioning. First, the number of participants in this study is relatively low. This might affect the external validity of the results. However, the narrow confidence interval of the results of the first and last session scores shows the reliability of the results. Second, we chose the matching “duration on service” of the participants as a measure for matching basic skill levels. This criterion oversimplifies the issue of “experience” and may lead to bias. However, we also compared the basic anastomosis skill levels of the participants through comparing the average duration and score of anastomosis of the first 3 practice sessions. Absence of statistically significant difference between the participants is a further ensuring sign for matched basic anastomosis skill levels. Finally, we chose to provide minimal feedback to our participants during the learning process. This might not be the real case in actual training curricula. Nevertheless, the rationale was to delineate the nature of the learning task with minimal external interference with the task. A one-on-one training protocol including frequent feedbacks to the trainee might be a superior teaching technique. However, the optimized protocol for providing feedbacks to enhance the learning process is subject to further studies. CONCLUSION Microvascular anastomosis is a relatively uncommon, yet challenging procedure for the general neurosurgeon, and this study shows the importance of understanding the nature of this task. The results of the present study may facilitate optimization of microvascular anastomosis training protocols in subspecialized cerebrovascular surgery curricula. Disclosures This study was materially supported through donated Silastic tubes from Biomet, Inc. The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article. REFERENCES 1. Grober ED , Hamstra SJ , Wanzel KR et al. The educational impact of bench model fidelity on the acquisition of technical skill: the use of clinically relevant outcome measures . Ann Surg . 2004 ; 240 ( 2 ): 374 - 381 . Google Scholar CrossRef Search ADS PubMed 2. Lascar I , Totir D , Cinca A et al. Training program and learning curve in experimental microsurgery during the residency in plastic surgery . Microsurgery . 2007 ; 27 ( 4 ): 263 - 267 . Google Scholar CrossRef Search ADS PubMed 3. Hui KC , Zhang F , Shaw WW et al. Learning curve of microvascular venous anastomosis: a never ending struggle? Microsurgery . 2000 ; 20 ( 1 ): 22 - 24 . Google Scholar CrossRef Search ADS PubMed 4. Mokhtari P , Meybodi AT , Lawton MT , Payman A , Benet A . Transfer of learning from practicing microvascular anastomosis on silastic tubes to rat abdominal aorta . World Neurosurg . 2017 ; 108 : 230 - 235 . Google Scholar CrossRef Search ADS PubMed 5. MacDonald JD . Learning to perform microvascular anastomosis . Skull Base . 2005 ; 15 ( 03 ): 229 - 240 . Google Scholar CrossRef Search ADS PubMed 6. Schmidt RA , Lee TD . Motor Learning and Performance: From Principles to Application . 5th ed. Champaign, IL : Human Kinetics ; 2014 . 7. Muratori LM , Lamberg EM , Quinn L , Duff SV . Applying principles of motor learning and control to upper extremity rehabilitation . J Hand Ther . 2013 ; 26 ( 2 ): 94 - 103 . Google Scholar CrossRef Search ADS PubMed 8. Chiviacowsky S , Campos T , Domingues MR . Reduced frequency of knowledge of results enhances learning in persons with Parkinson's disease . Front. Psychol. 2010 ; 1 : 226 . Google Scholar CrossRef Search ADS PubMed 9. Coker CA . Motor Learning & Control for Practitioners . 2nd ed. Scottsdale, AZ. : Holcomb Hathaway ; 2009 . 10. Palmeri T . Theories of automaticity and the power law of practice . J Exp Psychol: Learn, Mem, Cogn . 1999 ; 25 ( 2 ): 543 - 551 . Google Scholar CrossRef Search ADS 11. Tenison C , Anderson JR . Modeling the distinct phases of skill acquisition . J Exp Psychol: Learn, Mem, Cogn . 2016 ; 42 ( 5 ): 749 - 767 . Google Scholar CrossRef Search ADS 12. Meira CJ , Maia J , Tani G . Frequency and precision of feedback and the adaptive process of learning a dual motor task . Rev Bras Educ . 2012 ; 26 ( 3 ): 455 - 462 . 13. Brinko K . The practice of giving feedback to improve teaching: what is effective? J High Educ . 1993 ; 64 ( 5 ): 574 - 593 . 14. Sherwood DE , Lee TD . Schema theory: critical review and implications for the role of cognition in a new theory of motor learning . Res Q Exerc Sport . 2003 ; 74 ( 4 ): 376 - 382 . Google Scholar CrossRef Search ADS PubMed 15. Pacheco MM , Newell KM . Transfer as a function of exploration and stabilization in original practice . Hum Mov Sci . 2015 ; 44 : 258 - 269 . Google Scholar CrossRef Search ADS PubMed 16. Magill RA . Motor Learning and Control: Concepts and Applications . 8th ed . Boston : McGraw-Hill ; 2007 . 17. Frank C , Land WM , Schack T . Perceptual-cognitive changes during motor learning: the influence of mental and physical practice on mental representation, gaze behavior, and performance of a complex action . Front Psychol . 2015 ; 6 : 1981 . Google Scholar PubMed Acknowledgment The authors are thankful to Biomet, Inc for its contribution to this project through the donation of silastic tubes. Supplemental digital content is available for this article at www.operativeneurosurgery-online.com. Supplemental Digital Content. Appendix. Written form of practice protocol. COMMENT Microvascular anastamosis is perhaps the most challenging skill for a neurosurgeon to learn and to master. In this manuscript, the authors have attempted to quantitate the learning curve for this highly technical skill. Their protocol evaluated the progress of 5 “experienced” neurosurgeons that had no prior experience with bypass surgery. Each participant was given an oral and written tutorial and shown a video before then performing a series of 24 end-to-end anastomoses on rubber tubing over several weeks. Each session was timed and each anastamosis was scored for integrity. As expected, each participant showed improvement in both indices with practice. It is difficult to design and implement a study of this nature because it is nearly impossible to establish a baseline of equal skill among participants. Nonetheless, the data shows that in spite of individual differences, there appeared to be no statistical difference among the participants in terms of anastomosis quality or time after 3 wk of practice. This should not be construed to imply that anyone can learn to expertly perform a microvascular anastomosis but rather, that in this small group there seemed to be comparable skill and aptitude. It would be interesting now that a timeline for learning this skill has been established to examine factors that might shorten the learning curve or perhaps optimize performance among those with less inherent aptitude. Many technical tasks benefit from 1-on-1 coaching, demonstration, and close supervision, such as learning to drive or pilot airplane. I have always felt that the skills learned during practice of microvascular anastomosis and the self-analysis of technical obstacles as they are encountered under high power magnification accrue to improved “macro” surgical facility. Trainees often comment that soft tissue management with their naked eye is better after learning the physics of needle and suture manipulation under the microscope. The authors are to be congratulated for attempting to understand this classic neurosurgical teaching task. Sadly, the clinical opportunities to perform this elegant procedure are declining but the underlying techniques should always be preserved. Joel D. MacDonald Salt Lake City, Utah Copyright © 2018 by the Congress of Neurological Surgeons
Operative Neurosurgery – Oxford University Press
Published: Apr 14, 2018
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