Abstract
OBJECTIVE To determine the most effective hemostatic knot configuration performed by veterinary students following a brief training session with an experienced surgeon and a subsequent deliberate self-training period.
DESIGN Experiment.
SAMPLE 24 fourth-year veterinary students with no previous surgical knot–tying experience.
PROCEDURES In a 1-hour training session, an experienced surgeon showed veterinary students how to perform 5 hemostatic knot configurations (giant, slip, strangle, surgeon's, and transfixing), which they then practiced at home on a hemostasis simulator for 2 weeks. Thereafter, students performed each knot 4 times (twice each with monofilament and multifilament suture) on a hemostasis simulator. An experienced surgeon evaluated the correct execution of knots and measured their effectiveness by use of a manometer to measure vessel pressure distal to the ligature. Each student completed a questionnaire regarding their perceived learning and execution difficulty and sealing security for each knot. Responses were compared among knots and suture materials.
RESULTS Overall, students considered the surgeon's knot the easiest to learn and the strangle knot the most difficult. The slipknot was also considered the easiest knot to perform, and the giant knot was considered the most difficult. The strangle knot was deemed the most effective in reducing vessel pressure distal to the ligature.
CONCLUSIONS AND CLINICAL RELEVANCE The strangle knot was the most effective hemostatic knot in inexperienced hands, although veterinary students considered it more difficult to learn than other, perhaps more commonly taught, knots. Therefore, teaching of the strangle knot should be encouraged in veterinary schools.
Many veterinary educators have moved away from the use of procedures-based methods toward the use of skills-based approaches to teaching surgical techniques to their students.1,2 Because of animal welfare concerns and financial constraints, laboratory-based training programs involving bench models and simulators have been increasingly used for this purpose.1,3 Such programs are designed to equip students with the skills necessary to perform the most common surgical procedures encountered in veterinary practice.4 One of the most important skills is the competent ligation of blood vessels, and performance of efficient and reliable hemostatic knots is important to avoid the potentially fatal sequelae of knot failure or slippage.
Various knot-tying techniques are described in the literature, and surgeons often have their preferences.5–7 Although basic surgical techniques such as knot tying have been traditionally taught in the operating room, according to the traditional model “See one, do one, teach one,”8,9 simulation has become increasingly recognized as a viable method for teaching such techniques in a nonclinical setting.8–10 One study11 showed equivalent long-term retention of basic surgical skills through computer-based video instruction versus summative feedback from experts. Another study12 showed that self-directed video-based learning of knot-tying technique can be improved with a video demonstration of correct techniques and common errors.
To the authors' knowledge, no study has been reported regarding the combined use of expert supervision and self-training for teaching veterinary students hemostatic knot-tying techniques. The purpose of the study reported here was to determine which hemostatic knot-tying technique would be most effective when performed by veterinary students following a short training session with an experienced surgeon and a subsequent deliberate self-training period.
Materials and Methods
Subjects
Fourth-year veterinary students at the University of Turin, Italy were recruited for voluntary enrollment in the study following a general announcement. To be included in the study students were required to have no previous surgical knot–tying experience. Because we believed that the study did not involve manipulations that could adversely affect the participants, no preapproval was sought by an ethics oversight entity.
Knots
Five configurations of hemostatic knots from 3 categories (sliding, friction, and flat) were evaluated in the study: giant knot13 and slipknot14 (sliding), strangle knot (friction), and surgeon's and transfixing15 knots (flat; Figure 1). Each of these knot configurations was evaluated by having students use both monofilament suture (glycomer 631a) and multifilament suture (polyglactin 910b). Size-0 suture material was chosen because it is the most common size used for dog spay procedures16 and horse castration procedures.13 To complete the strangle, surgeon's, and transfixing knots, 5 throws were required with multifilament suture and 7 throws were required with monofilament suture.17 To complete the slipknot and giant knot with either suture material, 2 throws were required.18
Photographs of examples of hemostatic knot configurations: giant knot (A), slipknot (B), strangle knot (C), surgeon's knot (D), and transfixing knot (E).
Citation: Journal of the American Veterinary Medical Association 253, 2; 10.2460/javma.253.2.219
Training program
The training program consisted of a live, 1-hour demonstration of the correct knot-tying technique by an experienced veterinary surgeon and subsequent self-training for a 2-week period. During the live demonstration, technique and force needed to correctly achieve hemostasis were emphasized and students were able to practice, with supervision, all 5 knots on their own hemostasis simulator.3 During the subsequent 2-week period, students were requested to self-train on the same hemostasis simulator at home using video tutorials as an aid to develop the correct technique. The amount of time spent practicing was at the student's discretion.
Hemostasis simulator
The hemostasis simulator was constructed as reported elsewhere.3 Briefly, a saline solution bag was connected to an IV fluid line. A 5-mm Penrose drain was then attached along the fluid line and wrapped with 2-mm-thick cotton batting. At the opposite end, a 3-way stopcock was connected. On the remaining 2 ports of the stopcock, a manometer and IV fluid line extension were attached. The saline solution bag was then pressurized via air inflation by use of a 50-mm syringe until a manometer pressure of 120 mm Hg was achieved.3 Each simulator, prior to use by the students in both training and evaluation sessions, was tested by an experienced surgeon to confirm that a value of 0 mm Hg could be achieved distal to the attempted ligature with appropriate knot technique.
Performance evaluation
Knot-tying performance was evaluated the day after students completed the 2-week self-training period. For this evaluation, students were asked to first declare the knot configuration they were attempting to perform, and the experienced surgeon supervised the process and evaluated whether the knot was performed correctly. Thus, the order of knot performance remained in the student's control. Each student was required to attempt each of the 5 knot configurations with each type of suture material twice.
The experienced surgeon scored the effectiveness of each knot by reading the pressure value on the manometer; students were blinded to this reading. A knot was considered effective and scored as 1 if the pressure reading on the manometer 20 seconds after knot completion was 0 mm Hg and the knot had been correctly executed. The measurement point of 20 seconds was chosen to avoid the bias of an eventual loosening of the knot itself. If the pressure reading at this point was > 0 mm Hg or the knot was considered incorrectly executed, the knot was scored as 0. Total number of effective knots was recorded for each knot configuration and suture material.
Student self-assessment
At the end of the performance evaluation, each student completed a questionnaire (Supplementary Appendix SI, available at avmajournals.avma.org/doi/suppl/10.2460/javma.253.2.219) that was based on one used in a previous study.1 A visual assessment scale (0 = very low; 10 = very high) was used to allow students to rate their perceptions of how difficult it was to learn and execute each knot configuration and how secure the created seal appeared to them.
Statistical analysis
Data were analyzed by use of statistical software.c Questionnaire scores were first evaluated for normality of distribution with the Shapiro-Wilk normality test. Because the distribution was nonnormal, data are reported as median (range). The Friedman test was used to compare scores for learning difficulty, execution difficulty, and perceived sealing security among knot configurations and between suture materials. Percentages of attempted knots deemed effective by the experienced surgeon were compared among these groupings by use of the Fisher exact test. Values of P < 0.05 were considered significant.
Results
Students
Twenty-four fourth-year veterinary students (18 females and 6 males) with no prior surgical knot-tying experience volunteered for and completed the study, representing 29% of all fourth-year students (n = 82; 31% [18/59] of all females and 26% [6/23] of all males) in the 2014–2015 academic year at the veterinary school.
Student self-assessment
Students' scores indicated that they perceived the surgeon's knot as the easiest to learn among all 5 knot configurations, whereas scores for the strangle knot indicated that they perceived it as the most difficult to learn (P < 0.001; Table 1). Scores for strangle and giant knots performed with monofilament suture indicated that students perceived these knots as the most difficult to execute, although median scores did not differ significantly among the 5 configurations. Scores for the slipknot and transfixing knot performed with monofilament suture indicated that students perceived these configurations as the least secure, although median scores did not differ significantly among configurations.
Median (range) scores* assigned by 24 fourth-year veterinary students regarding their experiences with 5 hemostatic knot configurations and 2 types of suture material following a 1-hour training session by an experienced surgeon and 2-week self-training period, both involving a hemostasis simulator.
| Variable | Surgeon's knot | Strangle knot | Transfixing knot | Giant knot | Slipknot |
|---|---|---|---|---|---|
| Overall difficulty of learning | 0 (0–3)a,b | 5.5 (0–10)a,c,d | 2 (1–7)c | 3.5 (2–7)b | 2 (0–9)d |
| Monofilament suture | |||||
| Difficulty of execution | 3.5 (0–6) | 5 (1–9) | 3 (1–7) | 6 (3–8) | 2.5 (0–9) |
| Security of sealing | 4.5 (1–8) | 7.5 (2–9) | 3.5 (2–7) | 5 (0–7) | 3.5 (1–9) |
| Multifilament suture | |||||
| Difficulty of execution | 1.5 (0–4)b | 3.5 (0–8) | 2 (1–6) | 4 (2–8)b | 1 (0–8) |
| Security of sealing | 6.5 (1–10) | 8 (1–10) | 7 (2–9) | 6 (0–9) | 4 (1–8) |
A visual analog scale was used, with 0 indicating very low and 10 indicating very high.
Values with the same superscript letter differ significantly (a, P < 0.001; b, P = 0.01; c, P = 0.03; and d, P = 0.03).
For all knot configurations, scores for multifilament suture regarding execution difficulty and perceived sealing security were generally lower than those for monofilament suture, suggesting that students considered multifilament suture easier to handle (Table 1). A significant (P = 0.01) difference was identified in median scores for execution difficulty between the surgeon's knot with multifilament suture (1.5) and the giant knot with multifilament suture (4). Scores for perceived sealing security were greatest (albeit not significantly) for the strangle knot performed with multifilament suture.
Performance evaluation
Evaluation of student performance by the experienced surgeon revealed that the percentage of attempted knots deemed effective was greatest for the strangle knot and least for the slipknot, regardless of the type of suture material used (Table 2). In the comparisons of knot effectiveness with monofilament suture, significant differences were identified between the slipknot and strangle knot (P < 0.001), slipknot and surgeon's knot (P = 0.003), and surgeon's and transfixing knots (P = 0.002). In comparisons of knot effectiveness with multifilament suture, significant (P < 0.001) differences were identified between the strangle knot and all other knot configurations.
Number (%) of knots performed by the students in Table 1 that were judged by the experienced surgeon as effective* during a post-training performance evaluation (2 attempts/student/configuration; n = 48 attempts).
| Configuration | Monofilament suture | Multifilament suture |
|---|---|---|
| Giant knot | 31 (65) | 16 (33) |
| Strangle knot | 39 (81) | 36 (75) |
| Slipknot | 21 (44) | 12 (25) |
| Surgeon's knot | 36 (75) | 12 (25) |
| Transfixing knot | 37 (77) | 16 (33) |
Effective was defined as a manometer reading of 0 mm Hg 20 seconds after the knot was completed and correct knot execution. Students were blinded to the manometer readings.
Comparisons between monofilament and multifilament suture for performing the same knot configuration revealed significant differences for the giant (P = 0.004), surgeon's (P < 0.001), and transfixing (P < 0.001) knots, with a greater percentage of knots attempted with monofilament suture deemed effective in all situations. No such differences between suture materials were identified for the strangle knot and slipknot.
Discussion
The purpose of the present study was to determine which hemostatic knot configuration would be effective in the hands of veterinary students after a brief instruction session with an experienced surgeon and 2 weeks of deliberate practice on a hemostasis simulator. Results of subsequent evaluation by the students themselves and the experienced surgeon suggested that the strangle knot was the most effective and the slipknot the least effective, regardless of the type of suture material used.
Students considered the surgeon's knot the easiest to learn and the strangle knot the most difficult, which was somewhat surprising given that the strangle knot is a relatively simple knot based on a double loop and is considered one of the simplest configurations of friction knots.19 This finding might have been attributable to the students lacking confidence with friction knots altogether or the fact that the strangle knot was the only friction knot configuration evaluated in the study.
Results regarding the effectiveness of the various knot-tying techniques as judged by the experienced surgeon during the post-training performance evaluation not only agreed with the students' perceptions concerning the most secure knot configurations (strangle and giant), but also highlighted that the knot configuration considered relatively difficult to learn or execute (strangle knot) by students was actually performed effectively in a high percentage of attempts. By contrast, few attempts were deemed effective when students attempted the surgeon's and transfixing knots with the multifilament suture material, despite high ratings by the students for perceived sealing security.
The lowest percentage of effectively placed knots was achieved with the slipknot configuration, regardless of suture material used. Although the slipknot is reportedly an effective hemostatic knot,14 these findings suggested it was not effective in the hands of veterinary students. However, we observed an encouraging pattern, in that the fourth slipknots performed by the students during the performance evaluation were judged to be effective by the experienced surgeon. Consequently, we recommend that veterinary students practice this knot configuration before they use it in a clinical setting.
If a novice surgeon needs to perform a sliding knot, we recommend the giant knot configuration among those evaluated. The giant knot was considered relatively difficult to learn and execute by students but was effective in 65% of attempts when performed with monofilament suture. This knot configuration had a poor success rate when performed with multifilament suture. The giant knot is reportedly an effective sliding knot13 and likely, as for the slipknot, requires experience to be performed correctly. Additional research into sliding knots placed by inexperienced people should be conducted with other configurations, such as the Roeder knot configuration, to determine whether results would be different in those circumstances. The giant knot was chosen for the present study because we considered it easier to perform than the Roeder knot.
Although students in the present study considered the surgeon's knot among the easiest to perform, this knot configuration is unreliable and should not be chosen as a hemostatic ligature when multifilament suture is used. This statement reflects the results of a previous study.15 Students' scores for sealing security when multifilament suture was used were slightly higher for the other flat knot configuration (transfixing knot) than for the surgeon's knot, but the former, according to performance evaluation, was also unreliable for hemostasis when multifilament suture was used. When monofilament suture was used, either flat knot configuration was deemed effective by the experienced surgeon in ≥ 75% of attempts. This finding agrees with a previous report14 that monofilament suture has greater knot-holding properties than multifilament suture, owing to the elastic properties of monofilament suture.
Although the students' scores suggested that the strangle knot was the most difficult configuration to learn and perhaps more difficult to execute than some other knot types, this configuration yielded the greatest percentage of effective knots with both types of suture material during the performance evaluation. This finding may have been attributable to the peculiarity of friction knots, which generate more friction in the suture material than do other conformations. In addition, this double loop acts as a pulley when the knot is tied, thereby halving the force needed to achieve effective ligation.
Knot security has been found to be poorly correlated with surgeon experience but strongly influenced by knot-tying technique and knot configuration.6 These results were supported by those of the present study. When a student performed the knot correctly, a pressure reading of 0 mm Hg was obtained with the hemostasis simulator. In another in vitro study15 involving several friction knot configurations, the strangle knot was effective and reliable as the first throw during vascular pedicle ligation and, as supported by our findings, was the best knot in the hands of an inexperienced surgeon. Our results also suggested that the surgeon's knot was not reliable as the first throw for vascular pedicle ligation, which was also in agreement with other similar studies.20,21
The present study revealed differences between monofilament and multifilament suture in hemostatic effectiveness of the evaluated configurations. Previous research has shown that knots performed with multifilament suture have twice the rate of slippage as knots performed with monofilament suture.6,16 In the present study, the percentage of effective attempts was significantly greater for monofilament versus multifilament suture during performance of the giant, surgeon's, and transfixing knots but not the strangle knot and slipknot. It should be noted that the strangle knot was generally well executed with both materials, whereas the slipknot was generally poorly executed with both materials.
Self-training may be a useful approach to encourage students to take responsibility for developing their competence and professional skills. In a previous study1 similar to the present study, residents were evaluated for their knot-tying skills on a simulator following an autonomous knotting-techniques training period. All residents in that study had improved self-confidence, and their acquired skills were maintained after this training period. Although a laboratory setting may poorly mimic an operating room environment, we speculate that any lack in technique and self-confidence observed during performance of hemostatic ligatures would likely be generalizable to a clinical setting with live animals, with catastrophic consequences. Although self-learning is useful, supervision by an experienced surgeon is advisable to assess the acquired skills and correct mistakes at the beginning of the learning curve as well as to preserve proper technique for the future.
The educational approach used in the present study was self-guided, involving training by an experienced surgeon, deliberate practice of the learned techniques at home with the aid of video tutorials and a hemostasis simulator, and a final examination.10 This methodology allowed each student to attain a minimal level of competency in simple but fundamental surgical skills10 and to recognize their errors. During the 2-week deliberate practice period, students had an opportunity to attempt all 5 knot configurations and assess them for proper configuration by viewing the video tutorials. When at home, they could also immediately assess knot effectiveness by checking the pressure distal to the ligature with the manometer. No information was collected regarding the amount of time each student spent practicing during the 2-week period, nor was any time requirement imposed, because we believed that any interstudent variability in this regard would be a natural element of deliberate self-training.
The present study had some limitations. First, appropriate knot configuration was not confirmed with any particular tool such as a microscope22 during the performance evaluation. Nevertheless, each student was visually monitored by the experienced surgeon while completing the ligature to assess proper technique. It is common belief that knot configuration contributes to knot strength; therefore, if the knot was considered incorrectly executed or the manometer reading distal to the ligature was > 0 mm Hg, the knot was scored as ineffective. Second, the force applied to tie the knots was not standardized because such standardization was deemed of limited application in the clinical setting; however, this lack of standardization could have influenced the results. Third, the home practice sessions were not standardized but left to the students' own judgment instead; however, the amount of and approach to practice could also be expected to influence the results. Fourth, a small, single cohort of students was used, and it remains unclear whether the findings could be extrapolated to other veterinary students.
We believe that appropriate choice of knot configuration with monofilament or multifilament suture can compensate for the limited experience of a student surgeon and decrease the risk of knot slippage or failure, which may have fatal consequences for veterinary patients. In the hands of students at our university, the strangle knot was the best hemostatic knot among those tested, and its teaching should be encouraged in veterinary schools.
Footnotes
Biosyn 0, Covidien, Milano, Italy.
Vicryl 0, Ethicon, Somerville, NJ.
GraphPad Prism, version 50, GraphPad Software, La Jolla. Calif.
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