Original Article
Transfer of Learning from Practicing Microvascular Anastomosis on Silastic Tubes to Rat Abdominal Aorta Pooneh Mokhtari1, Ali Tayebi Meybodi2, Michael T. Lawton2, Andre Payman1, Arnau Benet2
OBJECTIVE: Learning to perform microvascular anastomosis is difficult. Laboratory practice models using artificial vessels are frequently used for this purpose. However, the efficacy of such practice models has not been objectively assessed for the performance of microvascular anastomosis during live surgical settings. This study was conducted to assess the transfer of learning from practicing microvascular anastomosis on tubes to anastomosing rat abdominal aorta.
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METHODS: Ten surgeons without any experience in microvascular anastomosis were randomly assigned to an experimental or a control group. Both groups received didactic and visual training on end-to-end microvascular anastomosis. The experimental group received 24 sessions of hands-on training on microanastomosis using Silastic tubes. Next, both groups underwent recall tests on weeks 1, 2, and 8 after training. The recall test consisted of completing an end-to-end anastomosis on the rat’s abdominal aorta. Anastomosis score, the time to complete the anastomosis, and the average time to place 1 stitch on the vessel perimeter were compared between the 2 groups.
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RESULTS: Compared with the control group, the experimental group did significantly better in terms of anastomosis score, total time, and per-stitch time. The measured variables showed stability and did not change significantly between the 3 recall tests.
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CONCLUSION: The skill of microvascular anastomosis is transferred from practicing on Silastic tubes to rat’s abdominal aorta. Considering the relative advantages of Silastic tubes to live rodent surgeries, such as lower cost and absence of ethical issues, our results support the
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Key words Aorta bypass - Artificial vessel - Bypass surgery - Cerebral revascularization - Microanastomosis - Practice model - Rodent surgery -
widespread use of Silastic tubes in training programs for microvascular anastomosis.
INTRODUCTION
T
he treatment strategy for complex cerebrovascular lesions frequently requires a bypass, which is probably the most technically demanding part of the procedure. Nevertheless, such cases are not common, and with the increasing number of lesions treated with endovascular techniques, fewer microsurgical procedures may be needed over time.1-7 However, the demand for training cerebrovascular surgeons cannot be eliminated by endovascular techniques. On the contrary, even more competent open cerebrovascular surgeons armed with bypass skills are needed to tackle the most complex and challenging lesions.8 The decreasing number of patients undergoing bypass procedures may negatively affect the training of residents and fellows, especially regarding bypass-related skills. In addition, the most challenging parts of these procedures are rarely performed by residents or fellows. It has been said that “An unspoken contract exists between neurosurgeons, their patients, and the referring physician, with the goal of achieving the optimal result.residents have no place in this contract, and if anything, threaten it.”1 Even with the availability of a large pool of patients requiring cerebral bypass, it is not ethically acceptable to go through the first stages of learning by performing bypass on patients. This situation leads to a dearth of learning opportunities for aspiring trainees, especially when it comes to cerebral bypass skills. Therefore, training for bypass skills is usually started in laboratory settings. The fundamental skill in a cerebrovascular bypass procedure is performing a microvascular anastomosis, which can be learned through a variety of methods. These methods include
From the 1Skull Base and Cerebrovascular Laboratory, University of California, San Francisco, California; and 2Department of Neurological Surgery, Barrow Neurological Institute, Phoenix, Arizona, USA To whom correspondence should be addressed: Arnau Benet, M.D. [E-mail: [email protected]] Citation: World Neurosurg. (2017) 108:230-235. http://dx.doi.org/10.1016/j.wneu.2017.08.132 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2017 Elsevier Inc. All rights reserved.
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using nonliving (low-fidelity) and living (high-fidelity) models. High-fidelity models include anesthetized animals (commonly rodents). Despite several advantages, animal models are costly and require a relatively complex laboratory setting, which is not universally available. Exposure of the target vessel is not always easy, and inadvertent vascular damage can lead to massive hemorrhage and early animal demise. Ethical issues on the use of animals for practicing purposes are another major limitation of high-fidelity models.9-13 Common low-fidelity models include artificial vessels, simulated animal models, and even noodles or worms.12,14-16 Practicing with artificial vessels, such as Silastic tubes (Biomet Inc., Palm Beach Gardens, Florida, USA), has been traditionally considered an efficient way of learning to perform a microvascular anastomosis in various medical specialties, including gynecologic, plastic, urologic, and neurologic surgery.12,17-19 Silastic tubes (or similar materials) have several advantages. First, their use is less expensive compared with live surgeries performed on animals. Second, they do not require time-consuming preparations (e.g., anesthesia and vessel exposure). Third, their use does not involve ethical dilemmas. Fourth, the evaluation of anastomosis in Silastic tubes is more straightforward and accurate than that in live animal surgeries. However, objective data supporting their efficacy in learning of the microvascular anastomosis skill is scarce, and surgical trainees are sometimes skeptical about their utility.20 In addition, Grober et al. believe that low-fidelity laboratory settings (i.e., settings that do not maximally simulate live surgery) might not be useful adjuncts to training programs.19 They argue that low-fidelity settings do not respect the “realistic” settings of live surgery. In other words, it is not known whether a transfer of learning occurs between the low- and high-fidelity models. The idea of transfer of learning is applied to a wide variety of fields, from management paradigms to the learning of motor and nonmotor skills.21 Transfer of learning is seen when practice on one task or in one setting contributes to performance capability in other tasks, other settings, or both.22 Using a flight simulator system in pilot training is a good example of transfer of learning. However, transfer from lessons learned in training programs to the real-life situations may or may not happen, depending on the subject under training, task characteristics, and environment characteristics.21,23,24 In fact, only a small percentage of transferred learning outcomes have been reported in various training fields.25,26 On the other hand, several authors have questioned the existence of learning transfer,27,28 while others have confirmed its existence.29 Therefore, we attempted to quantify learning transfer for the complex skill of microvascular anastomosis. Given the lack of objective evidence of transfer of learning from practicing on low-fidelity models (e.g., Silastic tubes) to high-fidelity models, we assessed this transfer from practice on Silastic tubes to performing microvascular anastomosis on live rats.
TRANSFER OF LEARNING IN MICROVASCULAR ANASTOMOSIS
(without fellowship training or subspecialty practice) with experience in general microsurgical techniques, including subarachnoid dissection, tumor resection, aneurysm clipping, and peripheral nerve surgery (including microsurgical neural grafting). They did not have any previous experience in performing microvascular anastomosis or practicing anastomosis on artificial vessels. Pretest To compare the baseline microsurgical bypass training skills in all subjects, and to minimize selection bias through matching, both groups underwent a pretest. In brief, the pretest consisted of 1 trial of end-to-end microvascular anastomosis on the abdominal aorta of an anesthetized rat. The pretest was designed, and results were analyzed in the same manner as the posttraining test protocol (discussed later). Training Protocol Subjects in both groups received written and visual didactic training. They were provided with an instruction form describing the basic steps of the end-to-end anastomosis technique as described previously.30 The technique is based on placing the first and second sutures at the 2- and 10-o’clock positions, followed by a third suture placed at the 6-o’clock position on the vessel perimeter. Next, sutures would be placed in the spaces between the first 3 sutures. Subjects were also shown a short video depicting the technique of an end-to-end microanastomosis on the rat’s abdominal aorta using interrupted sutures.31 Hands-on training sessions using Silastic tubes were held every other day at 1:00 PM local time for the experimental group. Subjects were provided snacks before each session to eliminate the confounding factors, such as hunger, affecting their performance. A dedicated microanastomosis instrument set was used for all subjects containing a pair of microscissors, a pair of jeweler’s forceps, a pair of microneedle appliers, and a pair of vessel approximators. Subjects were seated on a standard arm chair to perform microanastomosis using a surgical microscope (Leica, Wetzlar, Germany). The training began with a track of 6 consecutive sessions of microanastomosis on 2-mm Silastic tubes, followed by 12 sessions of microanastomosis on 1-mm tubes. Finally, the subjects performed 6 sessions of microanastomosis on 0.7mm Silastic tubes (measurements represent the outer diameter of the tubes). All anastomoses (including pretests, training, and tests on Silastic tubes and rat aorta) were performed using Ethilon 2830G 10-0 nylon sutures (Ethicon, Somerville, New Jersey, USA). The microanastomosis field was set up by the study supervisor (P.M.), and it included a Silastic tube with vessel approximators, mounted on a green 5 5-cm foam base (Figure 1). Next, the participant was asked to place a cross-sectional cut on the Silastic tube and complete the anastomosis as previously instructed. Anastomosis time was recorded from cutting the tube until completion of the last suture.
METHODS Subjects Ten surgeons with experience in microsurgery participated in the study; they were randomly divided into experimental (n ¼ 5) and control (n ¼ 5) groups. Participants were general neurosurgeons
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Posttraining Testing Protocol Following the training, both groups underwent 3 recall tests consisting of performing an end-to-end microvascular anastomosis on the abdominal aorta of an anesthetized rat. The recall tests were given at weeks 1, 2, and 8 following the hands-on training sessions
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Statistical Analysis Student t test for independent samples was used to compare the average period of experience in microsurgery between the 2 groups. Repeated measures analysis of variance was used to perform between-group and within-group comparisons for the following variables in the 3 recall tests: (1) anastomosis score, (2) total time to complete the anastomosis, and (3) average time for placing a single stitch on the vessel perimeter. RESULTS
Figure 1. Practice setup with the Silastic tube mounted on a foam base with the vessel approximators applied to the tube.
for the experimental group, and immediately after the visual and didactic training for the control group (Table 1). Thirty male Sprague-Dawley rats (weighing >500 g) were used for the recall tests. The study protocol for the use of rats was authorized and supervised by the Institutional Animal Care and Use Committee (#AN157652-01). After induction of inhalant anesthesia, 2 of the authors (A.T.M. and A.B.) performed the surgical exposure of the animals’ abdominal aorta. Following the isolation of a 15-mm segment of the abdominal aorta, below the level of the renal arteries, a background material was placed under the vessel. Next, the exposed aorta was trapped between temporary aneurysm clips, and a pair of vessel approximators were applied (Figure 2). At this point, the participant took over the microscope and started by cutting the vessel and irrigating the lumen with heparinized saline. The anastomosis was completed using the interrupted suture technique as instructed. The total time of performing anastomosis (recorded from the time of cutting the vessel) and the number of sutures placed were recorded. The quality of the anastomosis (anastomosis score) was rated by 2 independent observers blinded to the test group (A.B. and A.T.M), regarding patency and the presence of any stenosis or leak (Table 2). For each anastomosis, the average of the 2 assigned scores was recorded. Patency was confirmed using the “milking” and “lift” tests.30,32 After completion of the test, the animal was euthanized according to the study protocol.
Mean experience period for microsurgery was 5 years for the experimental group. The control group had an average of 5.2 years of experience in microsurgery. The experience period was not statistically different in the 2 groups (P ¼ 0.957). The 2 groups did not perform differently on the pretest in regard to anastomosis score, total anastomosis time, and ‘per-stitch’ times (P > 0.05). In all recall tests, the average anastomosis score in the experimental group (M ¼ 6.1) was significantly higher than in the control group (M ¼ 2.3; P < 0.001; Figure 3). In addition, the within-group anastomosis scores for both groups did not show significant differences among the 3 recall tests (P ¼ 0.46). In other words, the anastomosis scores changed significantly across the 3 recall tests in neither of the groups, and the scores remained stable during the 8-week posttraining period. The experimental group had significantly shorter total (23.7 minutes) and per-stitch times (2.4 minutes) compared with the control group (50.4 and 6.0 minutes, respectively; P < 0.001; Figures 4 and 5). Such a significant difference shows the transfer of learning between practicing on Silastic tubes and live rat surgeries. Within-group analysis showed that total time and perstich time also remained stable (no significant difference) during the 3 recall tests (P > 0.05). DISCUSSION In this study, we have objectively demonstrated that practicing anastomosis on Silastic tubes positively transfers to live surgical settings in rats. To our knowledge, this issue has received little attention in the literature.19,33 In 2004, Grober et al. assessed the transfer of learning to high-fidelity settings after training under low-fidelity settings.19 They evaluated the learning of microanastomosis in 3 groups of junior residents with minimal surgical experience by assigning them to 1 of 3 training modules: didactic, low-fidelity settings (i.e., practicing on Penrose drains), and high-fidelity settings (i.e., practicing on vas deferens of live anesthetized rats). After 2 hours of practice, they
Table 1. Study Design for the Experimental and Control Groups
Pretest*
Visual and Didactic Training
24 Hands-on Training Sessions
1-week Recall Interval
Visual and Didactic Training
First Recall Test (Week 1)
Second Recall Test (Week 2)
Third Recall Test (Week 8)
Experimental
þ
þ
þ
þ
e
þ
þ
þ
Control
þ
e
e
e
þ
þ
þ
þ
Group
*To test the baseline anastomosis skills in subjects and match the experimental and control groups to avoid selection bias.
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Figure 2. Intraoperative image of the rat’s infrarenal abdominal aorta exposed and isolated using vessel approximators. I, inferior; L, left; R, right; S, superior.
performed the anastomosis of vas deferens of live anesthetized rats. The authors found a significant difference between the performance in the 2 groups with hands-on training with that of the group that received only didactic training. However, they did not find any significant difference between the low-fidelity and high-fidelity groups when evaluating the posttraining performance. Although interesting, their methods had several limitations that might render their findings unacceptable as evidence of learning transfer regarding microvascular anastomosis. First, a single 2-hour period of practice for the complex fine-motor skill of microanastomosis cannot lead to “learning,” because learning is defined as a relatively persistent change in behavior through practice and gaining experience.22 Second, the participants in the study by Grober et al.19 were in the initial phase of skill acquisition, which uniformly demonstrates a high slope in
Figure 3. Average anastomosis score for the experimental and control groups in the 3 recall tests. The differences between groups were statistically significant in all 3 tests (P < 0.001). Error bars represent standard deviations.
learning curve. Therefore, the initial acquisition may be remarkable, but its stability and transfer to high-fidelity settings in the long-term is questionable. Therefore, it might not be valid to use the report by Grober et al.19 to conclude that low-fidelity practice transfers effectively to high-fidelity settings. In addition, the average overall performance score reported by Grober et al.19 was 3.5/5, which does not necessarily translate into a patent, flawless anastomosis. Furthermore, Grober et al.19 did not provide any specific detailed training protocol, which undermines the validity and reliability of their results. We used a strict and uniform training protocol, which controlled several confounding factors. The study group
Table 2. Anastomosis Score Scale Used to Rate the Anastomosis of Rat Abdominal Aorta Score
Definition*
1
Total occlusion
2
High leakage
3
Low leakage, significant stenosisy
4
No leakage, significant stenosis
5
Medium leakage, nonsignificant stenosis
6
Low leakage, nonsignificant stenosis
7
No leakage, nonsignificant stenosis
*Patency of anastomosis was considered a more important feature than the amount of leakage. yStenosis greater than 50% of the original diameter was scored as “significant.”
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Figure 4. Average time to complete the anastomosis for the experimental and control groups in the 3 recall tests. The differences between groups were statistically significant in all 3 tests (P < 0.001). Error bars represent standard deviations.
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TRANSFER OF LEARNING IN MICROVASCULAR ANASTOMOSIS
Figure 5. Average time to complete one stitch for the experimental and control groups in the 3 recall tests. The differences between groups were statistically significant in all 3 tests (P < 0.001). Error bars represent standard deviations.
performed 24 consecutive sessions of practice based on a specific protocol. Previous studies have suggested that a learning plateau occurs at around 25 training sessions.34 We chose to select a similar number of practice sessions. Our protocol proved effective in skill acquisition and transfer to live surgical settings. The protocol was designed to increase task difficulty gradually (transition from 2-mm tubes to 1- and 0.7-mm tubes). Such a design would facilitate the process of learning.22 Moreover,
REFERENCES 1. Lawton MT. Basilar apex aneurysms: surgical results and perspectives from an initial experience. Neurosurgery. 2002;50:1-8 [discussion: 8-10]. 2. Aboud E, Al-Mefty O, Yas¸argil MG. New laboratory model for neurosurgical training that simulates live surgery. J Neurosurg. 2002;97:1367-1372. 3. Colpan ME, Slavin KV, Amin-Hanjani S, CalderonArnuphi M, Charbel FT. Microvascular anastomosis training model based on a Turkey neck with perfused arteries. Neurosurgery. 2008;62(5 suppl 2): ONS407-410 [discussion: ONS410-401]. 4. Gruber A, Bavinszki G, Killer M, al Shameri A, Richling B. In vitro training model for endovascular embolization of cerebral aneurysms. Minim Invasive Neurosurg. 1997;40:121-123. 5. Kimura T, Morita A, Nishimura K, Aiyama H, Itoh H, Fukaya S, et al. Simulation of and training for cerebral aneurysm clipping with 3-dimensional models. Neurosurgery. 2009;65:719-725 [discussion: 725-726]. 6. Scholz M, Mücke T, Düring M, Pechlivanis I, Schmieder K, Harders AG. Microsurgically induced aneurysm models in rats, part I: techniques and
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practicing on tubes with different diameters provides the subject with a more flexible learning schema in mind that becomes useful when rat vessels of different diameters are encountered. Our results show that the use of Silastic tubes for practicing microvascular anastomosis leads to improved anastomosis scores and speed on rat abdominal aorta. The absence of significant change in the measured variables during the 3 recall tests in the experimental group implies stability of the learning. These results demonstrate the effective transfer of learning from practicing on Silastic tubes to live rat surgery; however, it is important to note a few limitations of the current study. First, the presence of some previous experience with microsurgery (though not in microsurgical bypass) in the tested subjects may limit the generalizability of our results. Second, because of restrictions in performing nonterminal surgeries in our laboratory, we did not evaluate the anastomosis patency in a delayed fashion in rats. Studies that are more focused on subjects with different levels of pretest experience are warranted. Nevertheless, considering our preliminary results, we conclude that Silastic tubes (and probably other artificial vessels) can be used effectively for training microvascular anastomosis, and their use should be encouraged in the development of microsurgical dexterity. CONCLUSION To our knowledge, this study is the first to provide objective data on the efficacy of transfer of learning from practicing microvascular anastomosis on Silastic tubes to live rat surgeries. These results could have important implications in decreasing training costs while overcoming the ethical concerns (i.e., fewer live animal surgeries required) in cerebrovascular training programs.
histological examination. Minim Invasive Neurosurg. 2008;51:76-82. 7. Sugiu K, Martin JB, Jean B, Gailloud P, Mandai S, Rufenacht DA. Artificial cerebral aneurysm model for medical testing, training, and research. Neurol Med Chir (Tokyo). 2003;43:69-72 [discussion: 73]. 8. Streefkerk HJ, Bremmer JP, van Weelden M, van Dijk RR, de Winter E, Beck RJ, et al. The excimer laser-assisted nonocclusive anastomosis practice model: development and application of a tool for practicing microvascular anastomosis techniques. Neurosurgery. 2006;58(suppl 1):ONS148-156 [discussion: ONS148-ONS156]. 9. Smith R. All changed, changed utterly. British medicine will be transformed by the Bristol case. BMJ. 1998;316:1917-1918. 10. Cuschieri. Medical errors, incidents, accidents and violations. Minim Invasive Ther Allied Technol. 2003;12:111-120. 11. Gates EA. New surgical procedures: can our patients benefit while we learn? Am J Obstet Gynecol. 1997;176:1293-1298 [discussion: 1298-1299]. 12. Higurashi M, Qian Y, Zecca M, Park YK, Umezu M, Morgan MK. Surgical training technology for cerebrovascular anastomosis. J Clin Neurosci. 2014;21: 554-558.
13. Mücke T, Hölzle F, Wolff K, Kesting M, Scholz M. Sealing maneuver for microvascular anastomoses in rats. J Reconstr Microsurg. 2008;24:33-37. 14. Chen WF, Eid A, Yamamoto T, Keith J, Nimmons GL, Lawrence WT. A novel supermicrosurgery training model: the chicken thigh. J Plast Reconstr Aesthet Surg. 2014;67:973-978. 15. Leclère FM, Trelles M, Lewbart GA, Vögelin E. Is there good simulation basic training for end-toside vascular microanastomoses? Aesthet Plast Surg. 2013;37:454-458. 16. Prunières GJ, Taleb C, Hendriks S, Miyamoto H, Kuroshima N, Liverneaux PA, et al. Use of the Konnyaku Shirataki noodle as a low fidelity simulation training model for microvascular surgery in the operating theatre. Chir Main. 2014;33: 106-111. 17. Naik VN, Matsumoto ED, Houston PL, Hamstra SJ, Yeung RY, Mallon JS, et al. Fiberoptic orotracheal intubation on anesthetized patients: do manipulation skills learned on a simple model transfer into the operating room? Anesthesiology. 2001;95:343-348. 18. Scott DJ, Bergen PC, Rege RV, Laycock R, Tesfay ST, Valentine RJ, et al. Laparoscopic training on bench models: better and more cost
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effective than operating room experience? J Am Coll Surg. 2000;191:272-283. 19. Grober ED, Hamstra SJ, Wanzel KR, Reznick RK, Matsumoto ED, Sidhu RS, 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;240:374-381. 20. Anastakis DJ, Wanzel KR, Brown MH, McIlroy JH, Hamstra SJ, Ali J, et al. Evaluating the effectiveness of a 2-year curriculum in a surgical skills center. Am J Surg. 2003;185:378-385. 21. Magill RA. Motor Learning and Control: Concepts and Applications. 8th ed. Boston: McGraw-Hill; 2007. 22. Schmidt RA, Lee TD. Motor Learning and Performance: From Principles to Application. 5th ed. Champaign, IL: Human Kinetics; 2014. 23. Velada R, Caetano A, Michel J, Lyons B, Kavanagh M. The effects of training design, individual characteristics and work environment on transfer of training. Int J Train Dev. 2007;11: 282-294.
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24. Almannie M. Barriers encountered in the transfer of educational training to workplace practice in Saudi Arabia. J Educ Train Stud. 2015;3:10-17. 25. Georgenson DL. The problem of transfer calls for partnership. Train Dev J. 1982;36:75-78. 26. Holton EF, Baldwin TT. Making transfer happen: An action perspective on learning transfer systems. Adv Dev Hum Resour. 2000;8:1-6. 27. Anderson JR, Reder LM, Simon HA. Situated learning and education. Educ Res. 1996;25:5-11. 28. Kozak J, Hancock P, Arthur E, Chrysler S. Transfer of training from virtual reality. Ergonomics. 1993;36: 777-784. 29. Rose DJ, Christina RW. A Multilevel Approach to the Study of Motor Control and Learning. 2nd ed. San Francisco: Pearson/Benjamin Cummings; 2006. 30. MacDonald JD. Learning to perform microvascular anastomosis. Skull Base. 2005;15:229-240. 31. Elghaity A. Microsurgey: Rat End to end Aortic anastomosis (Microvascular anastomosis) 2015, Available at: https://www.youtube.com/watch? v¼3__sZhAwXZs.
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32. Yonekawa Y, Frick R, Roth P, Taub E, Imhof H-G. Laboratory training in microsurgical techniques and microvascular anastomosis. Operat Tech Neurosurg. 1999;2:149-158. 33. Srinivasan J, Ellenbogen RG, Britz GW, Newell DW. Techniques for cerebral bypass: practical laboratory for microvascular anastomosis. Neurosurg Clin N Am. 2001;12, 509-517, viii. 34. Hui KC, Zhang F, Shaw WW, Kryger Z, Piccolo NS, Harper A, et al. Learning curve of microvascular venous anastomosis: A never ending struggle? Microsurgery. 2000;20:22-24. Conflict of interest statement: This study was materially supported through donated Silastic tubes from Biomet, Inc., Palm Beach Gardens, Florida, USA. Received 6 June 2017; accepted 22 August 2017 Citation: World Neurosurg. (2017) 108:230-235. http://dx.doi.org/10.1016/j.wneu.2017.08.132 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2017 Elsevier Inc. All rights reserved.
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235
Transfer of Learning from Practicing Microvascular Anastomosis on Silastic Tubes to Rat Abdominal Aorta Pooneh Mokhtari1, Ali Tayebi Meybodi2, Michael T. Lawton2, Andre Payman1, Arnau Benet2
OBJECTIVE: Learning to perform microvascular anastomosis is difficult. Laboratory practice models using artificial vessels are frequently used for this purpose. However, the efficacy of such practice models has not been objectively assessed for the performance of microvascular anastomosis during live surgical settings. This study was conducted to assess the transfer of learning from practicing microvascular anastomosis on tubes to anastomosing rat abdominal aorta.
-
METHODS: Ten surgeons without any experience in microvascular anastomosis were randomly assigned to an experimental or a control group. Both groups received didactic and visual training on end-to-end microvascular anastomosis. The experimental group received 24 sessions of hands-on training on microanastomosis using Silastic tubes. Next, both groups underwent recall tests on weeks 1, 2, and 8 after training. The recall test consisted of completing an end-to-end anastomosis on the rat’s abdominal aorta. Anastomosis score, the time to complete the anastomosis, and the average time to place 1 stitch on the vessel perimeter were compared between the 2 groups.
-
RESULTS: Compared with the control group, the experimental group did significantly better in terms of anastomosis score, total time, and per-stitch time. The measured variables showed stability and did not change significantly between the 3 recall tests.
-
CONCLUSION: The skill of microvascular anastomosis is transferred from practicing on Silastic tubes to rat’s abdominal aorta. Considering the relative advantages of Silastic tubes to live rodent surgeries, such as lower cost and absence of ethical issues, our results support the
-
Key words Aorta bypass - Artificial vessel - Bypass surgery - Cerebral revascularization - Microanastomosis - Practice model - Rodent surgery -
widespread use of Silastic tubes in training programs for microvascular anastomosis.
INTRODUCTION
T
he treatment strategy for complex cerebrovascular lesions frequently requires a bypass, which is probably the most technically demanding part of the procedure. Nevertheless, such cases are not common, and with the increasing number of lesions treated with endovascular techniques, fewer microsurgical procedures may be needed over time.1-7 However, the demand for training cerebrovascular surgeons cannot be eliminated by endovascular techniques. On the contrary, even more competent open cerebrovascular surgeons armed with bypass skills are needed to tackle the most complex and challenging lesions.8 The decreasing number of patients undergoing bypass procedures may negatively affect the training of residents and fellows, especially regarding bypass-related skills. In addition, the most challenging parts of these procedures are rarely performed by residents or fellows. It has been said that “An unspoken contract exists between neurosurgeons, their patients, and the referring physician, with the goal of achieving the optimal result.residents have no place in this contract, and if anything, threaten it.”1 Even with the availability of a large pool of patients requiring cerebral bypass, it is not ethically acceptable to go through the first stages of learning by performing bypass on patients. This situation leads to a dearth of learning opportunities for aspiring trainees, especially when it comes to cerebral bypass skills. Therefore, training for bypass skills is usually started in laboratory settings. The fundamental skill in a cerebrovascular bypass procedure is performing a microvascular anastomosis, which can be learned through a variety of methods. These methods include
From the 1Skull Base and Cerebrovascular Laboratory, University of California, San Francisco, California; and 2Department of Neurological Surgery, Barrow Neurological Institute, Phoenix, Arizona, USA To whom correspondence should be addressed: Arnau Benet, M.D. [E-mail: [email protected]] Citation: World Neurosurg. (2017) 108:230-235. http://dx.doi.org/10.1016/j.wneu.2017.08.132 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2017 Elsevier Inc. All rights reserved.
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using nonliving (low-fidelity) and living (high-fidelity) models. High-fidelity models include anesthetized animals (commonly rodents). Despite several advantages, animal models are costly and require a relatively complex laboratory setting, which is not universally available. Exposure of the target vessel is not always easy, and inadvertent vascular damage can lead to massive hemorrhage and early animal demise. Ethical issues on the use of animals for practicing purposes are another major limitation of high-fidelity models.9-13 Common low-fidelity models include artificial vessels, simulated animal models, and even noodles or worms.12,14-16 Practicing with artificial vessels, such as Silastic tubes (Biomet Inc., Palm Beach Gardens, Florida, USA), has been traditionally considered an efficient way of learning to perform a microvascular anastomosis in various medical specialties, including gynecologic, plastic, urologic, and neurologic surgery.12,17-19 Silastic tubes (or similar materials) have several advantages. First, their use is less expensive compared with live surgeries performed on animals. Second, they do not require time-consuming preparations (e.g., anesthesia and vessel exposure). Third, their use does not involve ethical dilemmas. Fourth, the evaluation of anastomosis in Silastic tubes is more straightforward and accurate than that in live animal surgeries. However, objective data supporting their efficacy in learning of the microvascular anastomosis skill is scarce, and surgical trainees are sometimes skeptical about their utility.20 In addition, Grober et al. believe that low-fidelity laboratory settings (i.e., settings that do not maximally simulate live surgery) might not be useful adjuncts to training programs.19 They argue that low-fidelity settings do not respect the “realistic” settings of live surgery. In other words, it is not known whether a transfer of learning occurs between the low- and high-fidelity models. The idea of transfer of learning is applied to a wide variety of fields, from management paradigms to the learning of motor and nonmotor skills.21 Transfer of learning is seen when practice on one task or in one setting contributes to performance capability in other tasks, other settings, or both.22 Using a flight simulator system in pilot training is a good example of transfer of learning. However, transfer from lessons learned in training programs to the real-life situations may or may not happen, depending on the subject under training, task characteristics, and environment characteristics.21,23,24 In fact, only a small percentage of transferred learning outcomes have been reported in various training fields.25,26 On the other hand, several authors have questioned the existence of learning transfer,27,28 while others have confirmed its existence.29 Therefore, we attempted to quantify learning transfer for the complex skill of microvascular anastomosis. Given the lack of objective evidence of transfer of learning from practicing on low-fidelity models (e.g., Silastic tubes) to high-fidelity models, we assessed this transfer from practice on Silastic tubes to performing microvascular anastomosis on live rats.
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(without fellowship training or subspecialty practice) with experience in general microsurgical techniques, including subarachnoid dissection, tumor resection, aneurysm clipping, and peripheral nerve surgery (including microsurgical neural grafting). They did not have any previous experience in performing microvascular anastomosis or practicing anastomosis on artificial vessels. Pretest To compare the baseline microsurgical bypass training skills in all subjects, and to minimize selection bias through matching, both groups underwent a pretest. In brief, the pretest consisted of 1 trial of end-to-end microvascular anastomosis on the abdominal aorta of an anesthetized rat. The pretest was designed, and results were analyzed in the same manner as the posttraining test protocol (discussed later). Training Protocol Subjects in both groups received written and visual didactic training. They were provided with an instruction form describing the basic steps of the end-to-end anastomosis technique as described previously.30 The technique is based on placing the first and second sutures at the 2- and 10-o’clock positions, followed by a third suture placed at the 6-o’clock position on the vessel perimeter. Next, sutures would be placed in the spaces between the first 3 sutures. Subjects were also shown a short video depicting the technique of an end-to-end microanastomosis on the rat’s abdominal aorta using interrupted sutures.31 Hands-on training sessions using Silastic tubes were held every other day at 1:00 PM local time for the experimental group. Subjects were provided snacks before each session to eliminate the confounding factors, such as hunger, affecting their performance. A dedicated microanastomosis instrument set was used for all subjects containing a pair of microscissors, a pair of jeweler’s forceps, a pair of microneedle appliers, and a pair of vessel approximators. Subjects were seated on a standard arm chair to perform microanastomosis using a surgical microscope (Leica, Wetzlar, Germany). The training began with a track of 6 consecutive sessions of microanastomosis on 2-mm Silastic tubes, followed by 12 sessions of microanastomosis on 1-mm tubes. Finally, the subjects performed 6 sessions of microanastomosis on 0.7mm Silastic tubes (measurements represent the outer diameter of the tubes). All anastomoses (including pretests, training, and tests on Silastic tubes and rat aorta) were performed using Ethilon 2830G 10-0 nylon sutures (Ethicon, Somerville, New Jersey, USA). The microanastomosis field was set up by the study supervisor (P.M.), and it included a Silastic tube with vessel approximators, mounted on a green 5 5-cm foam base (Figure 1). Next, the participant was asked to place a cross-sectional cut on the Silastic tube and complete the anastomosis as previously instructed. Anastomosis time was recorded from cutting the tube until completion of the last suture.
METHODS Subjects Ten surgeons with experience in microsurgery participated in the study; they were randomly divided into experimental (n ¼ 5) and control (n ¼ 5) groups. Participants were general neurosurgeons
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Posttraining Testing Protocol Following the training, both groups underwent 3 recall tests consisting of performing an end-to-end microvascular anastomosis on the abdominal aorta of an anesthetized rat. The recall tests were given at weeks 1, 2, and 8 following the hands-on training sessions
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Statistical Analysis Student t test for independent samples was used to compare the average period of experience in microsurgery between the 2 groups. Repeated measures analysis of variance was used to perform between-group and within-group comparisons for the following variables in the 3 recall tests: (1) anastomosis score, (2) total time to complete the anastomosis, and (3) average time for placing a single stitch on the vessel perimeter. RESULTS
Figure 1. Practice setup with the Silastic tube mounted on a foam base with the vessel approximators applied to the tube.
for the experimental group, and immediately after the visual and didactic training for the control group (Table 1). Thirty male Sprague-Dawley rats (weighing >500 g) were used for the recall tests. The study protocol for the use of rats was authorized and supervised by the Institutional Animal Care and Use Committee (#AN157652-01). After induction of inhalant anesthesia, 2 of the authors (A.T.M. and A.B.) performed the surgical exposure of the animals’ abdominal aorta. Following the isolation of a 15-mm segment of the abdominal aorta, below the level of the renal arteries, a background material was placed under the vessel. Next, the exposed aorta was trapped between temporary aneurysm clips, and a pair of vessel approximators were applied (Figure 2). At this point, the participant took over the microscope and started by cutting the vessel and irrigating the lumen with heparinized saline. The anastomosis was completed using the interrupted suture technique as instructed. The total time of performing anastomosis (recorded from the time of cutting the vessel) and the number of sutures placed were recorded. The quality of the anastomosis (anastomosis score) was rated by 2 independent observers blinded to the test group (A.B. and A.T.M), regarding patency and the presence of any stenosis or leak (Table 2). For each anastomosis, the average of the 2 assigned scores was recorded. Patency was confirmed using the “milking” and “lift” tests.30,32 After completion of the test, the animal was euthanized according to the study protocol.
Mean experience period for microsurgery was 5 years for the experimental group. The control group had an average of 5.2 years of experience in microsurgery. The experience period was not statistically different in the 2 groups (P ¼ 0.957). The 2 groups did not perform differently on the pretest in regard to anastomosis score, total anastomosis time, and ‘per-stitch’ times (P > 0.05). In all recall tests, the average anastomosis score in the experimental group (M ¼ 6.1) was significantly higher than in the control group (M ¼ 2.3; P < 0.001; Figure 3). In addition, the within-group anastomosis scores for both groups did not show significant differences among the 3 recall tests (P ¼ 0.46). In other words, the anastomosis scores changed significantly across the 3 recall tests in neither of the groups, and the scores remained stable during the 8-week posttraining period. The experimental group had significantly shorter total (23.7 minutes) and per-stitch times (2.4 minutes) compared with the control group (50.4 and 6.0 minutes, respectively; P < 0.001; Figures 4 and 5). Such a significant difference shows the transfer of learning between practicing on Silastic tubes and live rat surgeries. Within-group analysis showed that total time and perstich time also remained stable (no significant difference) during the 3 recall tests (P > 0.05). DISCUSSION In this study, we have objectively demonstrated that practicing anastomosis on Silastic tubes positively transfers to live surgical settings in rats. To our knowledge, this issue has received little attention in the literature.19,33 In 2004, Grober et al. assessed the transfer of learning to high-fidelity settings after training under low-fidelity settings.19 They evaluated the learning of microanastomosis in 3 groups of junior residents with minimal surgical experience by assigning them to 1 of 3 training modules: didactic, low-fidelity settings (i.e., practicing on Penrose drains), and high-fidelity settings (i.e., practicing on vas deferens of live anesthetized rats). After 2 hours of practice, they
Table 1. Study Design for the Experimental and Control Groups
Pretest*
Visual and Didactic Training
24 Hands-on Training Sessions
1-week Recall Interval
Visual and Didactic Training
First Recall Test (Week 1)
Second Recall Test (Week 2)
Third Recall Test (Week 8)
Experimental
þ
þ
þ
þ
e
þ
þ
þ
Control
þ
e
e
e
þ
þ
þ
þ
Group
*To test the baseline anastomosis skills in subjects and match the experimental and control groups to avoid selection bias.
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Figure 2. Intraoperative image of the rat’s infrarenal abdominal aorta exposed and isolated using vessel approximators. I, inferior; L, left; R, right; S, superior.
performed the anastomosis of vas deferens of live anesthetized rats. The authors found a significant difference between the performance in the 2 groups with hands-on training with that of the group that received only didactic training. However, they did not find any significant difference between the low-fidelity and high-fidelity groups when evaluating the posttraining performance. Although interesting, their methods had several limitations that might render their findings unacceptable as evidence of learning transfer regarding microvascular anastomosis. First, a single 2-hour period of practice for the complex fine-motor skill of microanastomosis cannot lead to “learning,” because learning is defined as a relatively persistent change in behavior through practice and gaining experience.22 Second, the participants in the study by Grober et al.19 were in the initial phase of skill acquisition, which uniformly demonstrates a high slope in
Figure 3. Average anastomosis score for the experimental and control groups in the 3 recall tests. The differences between groups were statistically significant in all 3 tests (P < 0.001). Error bars represent standard deviations.
learning curve. Therefore, the initial acquisition may be remarkable, but its stability and transfer to high-fidelity settings in the long-term is questionable. Therefore, it might not be valid to use the report by Grober et al.19 to conclude that low-fidelity practice transfers effectively to high-fidelity settings. In addition, the average overall performance score reported by Grober et al.19 was 3.5/5, which does not necessarily translate into a patent, flawless anastomosis. Furthermore, Grober et al.19 did not provide any specific detailed training protocol, which undermines the validity and reliability of their results. We used a strict and uniform training protocol, which controlled several confounding factors. The study group
Table 2. Anastomosis Score Scale Used to Rate the Anastomosis of Rat Abdominal Aorta Score
Definition*
1
Total occlusion
2
High leakage
3
Low leakage, significant stenosisy
4
No leakage, significant stenosis
5
Medium leakage, nonsignificant stenosis
6
Low leakage, nonsignificant stenosis
7
No leakage, nonsignificant stenosis
*Patency of anastomosis was considered a more important feature than the amount of leakage. yStenosis greater than 50% of the original diameter was scored as “significant.”
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Figure 4. Average time to complete the anastomosis for the experimental and control groups in the 3 recall tests. The differences between groups were statistically significant in all 3 tests (P < 0.001). Error bars represent standard deviations.
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Figure 5. Average time to complete one stitch for the experimental and control groups in the 3 recall tests. The differences between groups were statistically significant in all 3 tests (P < 0.001). Error bars represent standard deviations.
performed 24 consecutive sessions of practice based on a specific protocol. Previous studies have suggested that a learning plateau occurs at around 25 training sessions.34 We chose to select a similar number of practice sessions. Our protocol proved effective in skill acquisition and transfer to live surgical settings. The protocol was designed to increase task difficulty gradually (transition from 2-mm tubes to 1- and 0.7-mm tubes). Such a design would facilitate the process of learning.22 Moreover,
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practicing on tubes with different diameters provides the subject with a more flexible learning schema in mind that becomes useful when rat vessels of different diameters are encountered. Our results show that the use of Silastic tubes for practicing microvascular anastomosis leads to improved anastomosis scores and speed on rat abdominal aorta. The absence of significant change in the measured variables during the 3 recall tests in the experimental group implies stability of the learning. These results demonstrate the effective transfer of learning from practicing on Silastic tubes to live rat surgery; however, it is important to note a few limitations of the current study. First, the presence of some previous experience with microsurgery (though not in microsurgical bypass) in the tested subjects may limit the generalizability of our results. Second, because of restrictions in performing nonterminal surgeries in our laboratory, we did not evaluate the anastomosis patency in a delayed fashion in rats. Studies that are more focused on subjects with different levels of pretest experience are warranted. Nevertheless, considering our preliminary results, we conclude that Silastic tubes (and probably other artificial vessels) can be used effectively for training microvascular anastomosis, and their use should be encouraged in the development of microsurgical dexterity. CONCLUSION To our knowledge, this study is the first to provide objective data on the efficacy of transfer of learning from practicing microvascular anastomosis on Silastic tubes to live rat surgeries. These results could have important implications in decreasing training costs while overcoming the ethical concerns (i.e., fewer live animal surgeries required) in cerebrovascular training programs.
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24. Almannie M. Barriers encountered in the transfer of educational training to workplace practice in Saudi Arabia. J Educ Train Stud. 2015;3:10-17. 25. Georgenson DL. The problem of transfer calls for partnership. Train Dev J. 1982;36:75-78. 26. Holton EF, Baldwin TT. Making transfer happen: An action perspective on learning transfer systems. Adv Dev Hum Resour. 2000;8:1-6. 27. Anderson JR, Reder LM, Simon HA. Situated learning and education. Educ Res. 1996;25:5-11. 28. Kozak J, Hancock P, Arthur E, Chrysler S. Transfer of training from virtual reality. Ergonomics. 1993;36: 777-784. 29. Rose DJ, Christina RW. A Multilevel Approach to the Study of Motor Control and Learning. 2nd ed. San Francisco: Pearson/Benjamin Cummings; 2006. 30. MacDonald JD. Learning to perform microvascular anastomosis. Skull Base. 2005;15:229-240. 31. Elghaity A. Microsurgey: Rat End to end Aortic anastomosis (Microvascular anastomosis) 2015, Available at: https://www.youtube.com/watch? v¼3__sZhAwXZs.
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32. Yonekawa Y, Frick R, Roth P, Taub E, Imhof H-G. Laboratory training in microsurgical techniques and microvascular anastomosis. Operat Tech Neurosurg. 1999;2:149-158. 33. Srinivasan J, Ellenbogen RG, Britz GW, Newell DW. Techniques for cerebral bypass: practical laboratory for microvascular anastomosis. Neurosurg Clin N Am. 2001;12, 509-517, viii. 34. Hui KC, Zhang F, Shaw WW, Kryger Z, Piccolo NS, Harper A, et al. Learning curve of microvascular venous anastomosis: A never ending struggle? Microsurgery. 2000;20:22-24. Conflict of interest statement: This study was materially supported through donated Silastic tubes from Biomet, Inc., Palm Beach Gardens, Florida, USA. Received 6 June 2017; accepted 22 August 2017 Citation: World Neurosurg. (2017) 108:230-235. http://dx.doi.org/10.1016/j.wneu.2017.08.132 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2017 Elsevier Inc. All rights reserved.
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