This article illustrates every step of the manufacture of a new multi-purpose low-cost animal bench-model for subglottic airway access management. All the procedures are shown in the video. The model's realism and its suitability for training the given clinical maneuvers were assessed by independent senior otolaryngologists and anesthesiologists.
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Sacco Botto, F., Ingrassia, P. L., Donato, P., Garzaro, M., Aluffi, P., Gentilli, S., Olina, M., Grossini, E. Manufacture of a Multi-Purpose Low-Cost Animal Bench-Model for Teaching Tracheostomy. J. Vis. Exp. (147), e59396, doi:10.3791/59396 (2019).
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Tracheostomy is one of the most frequent procedures, performed through various techniques in the intensive care unit and emergency situations. Despite this, there is a lack of training on this procedure that affects its outcome, which is also dependent on operator's dexterity. Here, we take the specific training and simulation into consideration. This article aims to describe every step of the manufacture of a new multi-purpose low-cost animal bench-model, with the support of video and images, and to obtain an opinion about the quality of this model by administering a questionnaire to professionals with experience in the procedures.
Ten experts in the technique were enrolled. The model scored an average of 3.45/5 for its anatomical realism; 4.75/5 for its usefulness as a training tool for simulation courses and assessments. The time necessary to build the model was 15 minutes, and the cost amounted to 10€. The animal bench-model was considered a very useful simulator for tracheostomy training and assessments. Therefore, it could be used as a tool for medical courses and residencies.
Difficult airway management is a critical skill for every physician dealing with critical, ill, and emergency patients. A review published in 2013 estimates that the incidence numbers of 'cannot ventilate, cannot intubate' situations with the use of surgical airway techniques vary from 0 to 18.5%1.
Tracheostomy is one of the oldest surgical procedures and is extensively used as the method of choice for subglottic airway access for patients requiring prolonged artificial ventilation. Originally performed in the operating theater, it has become a routine practice bedside at many hospitals, especially in the intensive care unit (ICU)2. Several types of techniques have been described, including surgical (ST) and percutaneous tracheostomy (PCT). Tracheostomy has been widely reported to have high complication rates.A national audit reports that 50% of airway-related deaths or brain damage in critical care are caused by tracheostomy complications3. Often, the high complication rates reflect lack of familiarity with the technique and inadequate training.
Another way to subglottically access the airways is to perform a cricothyrotomy (CT), which has been broadly recommended as a strategy to deal with 'cannot ventilate, cannot intubate' situations in both prehospital and intra-hospital care4. Being a fast and potentially lifesaving fallback maneuver in the patients with a failed airway, clinicians responsible for airway management must be familiar with the technique. Practice and training therefore play a pivotal role since its success is dependent on the operator's dexterity5. However, due to improvements in airway management in the past decades, a decline in the need for tracheotomy and emergency surgical airways was observed. This has resulted in a lack of clinical experience and decreased exposure to this life-saving technique, which may negatively affect the quality of procedures and ultimately the safety of patients6,7.
Nowadays, simulation is a common and effective teaching method to train medical and surgical skills, especially for novices who are learning new abilities8,9. Simulation allows to recreate a clinical procedure or situation, providing trainees with first-hand exposure to clinical scenario and complex techniques while eliminating the risk for patients10.
A broad variety of simulators, from virtual reality to animal models, have been used in training surgical airway management11,12,13,14. Practice on models and mannequins is reported to be the most common form of instruction for Anesthesiology and Emergency Medicine residents15,16. Cadavers have also been used to teach neck anatomy and the procedural skills17. However, the cost of all these options are sometimes prohibitive and can pose ethical and moral constrains and challenges. Low cost simulators have also been described and suggested for educational purposes but have not been used to train all the subglottic airway access procedures.
In this manuscript, we describe how to manufacture an easily-made, low-cost and high-fidelity bench-model that simulates the human neck to perform cricothyrotomy, percutaneous and surgical tracheostomy and its evaluation. The main aim was to design an easy-to-make model with readily and regularly available materials so that anyone can simply emulate and reproduce it. The overall time to assemble the model was about 15 minutes and the cost estimate was approximately of 10€ including resources and manufacturing (20€/h).
The animal anatomic segments, normally intended for human consumption, were purchased at a local butcher's shop ( Figure 1). Therefore, they could be easily transported and stored with no specific restrictions or sanitary regulations.
1. Cleaning the swine upper airways
- With the help of a dissecting scalpel, Adson forceps and Metzembaum scissors, clean the trachea and larynx from excess surrounding tissues (lateral muscles, excess of tongue), by cutting and dissecting.
- Remove tissue until the larynx cartilages are almost exposed and the tracheal rings are easy to palpate.
- Remove the hyoid bone and surrounding soft tissues: find the eminence of the greater horn and follow the horn with the blade, then pass to the contralateral one and repeat the same operation until the whole part is removed.
- Cut the trachea at its distal side approximatively at 15 cm from the larynx using a dissecting knife.
NOTE: The removed part, composed by mediastinal organs, will be used for the next step in the procedure.
2. Preparing the thyroid
- Take the previously discarded mediastinal organs and search for the thymus.
NOTE: The thymus is usually located on the frontal portion of the mediastinum right over the right atrium. Adult pigs may have a very small thymus.
- With dissecting forceps, detach the thymus from the surrounding tissue.
- Carve the just obtained pig thymus into a butterfly shape to recreate a simulated thyroid.
- With a dissecting knife, cut a flat slice of thymus 1.5 cm thick.
- With Metzembaum scissors, cut the slice in a butterfly shape with two 3 cm x 2 cm lobes connected by a hystmus.
NOTE: The overall dimensions of the thyroid should be 3 cm long, 6 cm large and 1.5cm thick.
3. Suturing the thyroid to the tracheal wall.
NOTE: For the next step, use the previously prepared upper airways and the simulated thyroid.
- Place the simulated thyroid between the first and third tracheal ring.
- Take a needle holder and surgical forceps. Grab a 2/0 silk suture.
- Suture the thyroid with two lateral horizontal mattress stitches passing in each lobe and in the lateral portion of the trachea.
NOTE: The horizontal mattress stitch wraps more tissue than the normal stitch. This is important when suturing soft tissues, as pig thymus, that tends to tear up.
- Pass the needle only in the superficial part of the trachea to prevent the possibility of seeing the thread in the tracheal lumen if performing fibroscopy.
NOTE: Identification and preservation of the thyroid gland avoiding postoperative bleeding represent crucial surgical steps during tracheotomy procedure.
4. Preparing the esophagus
- Use the esophagus, which is located on the backside of the trachea, to simulate the neck fascia and muscles.
- Remove the esophagus from its larynx connection by cutting it with a scalpel or with surgical scissors.
- Cut and open the esophagus on its length with surgical scissors.
- Hold the muscle and mucosa with toothed forceps to help the cutting procedure. The result of this operation will be a rectangle of muscle covered by esophagus mucosa.
5. Suturing the esophagus to the trachea
- Place the just obtained layer of muscles on top of the trachea and larynx with the mucous membrane face up. The aim is to cover the larynx: from the thyroid cartilage summit to the last tracheal rings.
- Suture the opened esophagus with at least 6 simple stitches:
One on the proximal side of the model, on the summit of the Thyroid cartilage.
One on the distal side of the preparation, on the frontal portion of the last tracheal ring.
At least one on each side of the trachea.
One on each side of the lower lateral portion of the thyroid cartilage where cricothyroid muscles are.
- Mark a line on the esophagus mucosa with white India ink to simulate the linea alba.
NOTE: Identification and proper dissection through the linea alba is an important step during tracheotomy procedure (Figure 2).
- To do so, use white India ink and an insulin syringe.
- Withdraw some ink and then track a line on the simulated fascia by scratching it with the needle while spilling little drops of ink.
- Remove the excess of ink gently with a small swab.
6. Preparing the foam base for the model
- Cut a square of foam of 3 cm x 10 cm x 15 cm.
- Shape a furrow 2.5 cm large and 10 cm long in the center of the foam.
- To do this, fold half of the square of foam so that it creates a longitudinal hump on one side.
- Cut 1 cm of the hump off all its length with scissors.
- Unfold the foam square and trim the just formed furrow smoothly.
7. Stapling the model to the wooden tablet
- Take a wooden tablet of the same dimensions of the foam.
- Place the foam square on the wooden tablet and insert the model in the foam furrow.
- With a wood stapler, place a clip on the end of the trachea, on the remaining lateral muscles of the thyroid cartilage and on the epiglottis.
8. Preparing the skin
- Take the pig skin collected from the butcher shop and cut it in a square shape big enough to cover the whole model. Usually, a square of 25 cm x 20 cm is sufficient.
- Cut the skin with a dissecting knife and cover the model with it.
9. Stapling the skin to the wooden tablet
- Take the stapler and fix the skin to the tablet with about 10-15 clips. Place them on the vertical sides of the tablet
- Trim the excess skin on each side of the tablet with the help of a knife.
- Use cocker forceps to firmly hold the skin to allow a safer cutting.
We assessed the feasibility and acceptability of the easily-made, low-cost and high-fidelity bench-model that simulates the human neck as a tool for cricothyrotomy, percutaneous and surgical tracheostomy training. After a review of current literature about simulation in surgical education, a survey instrument was designed. The questionnaire consisted of the following content sessions:
a. general data and demographics of the participants;
b. fidelity of the bench-model;
c. suitability of cricothyrotomy, percutaneous and surgical tracheostomy for training by the manufactured model.
Participants were asked to rate statements with a five-point Likert scale (1: strongly disagree, 5: strongly agree). All participants were also given the opportunity to add positive and negative aspects of the bench model as well as to recommend improvements. A detailed description of the survey instrument is provided in Table 1. A panel of experts composed of simulation educationalists, Ear, Nose and Throat (ENT) physicians, anesthesiologists and surgical education tutors reviewed the survey instrument content for accuracy and provided appropriate modifications to ensure validity of the study.
Participation to the study was voluntary, anonymous, and independent. Confidentiality of information was ensured and no financial incentive to participate in the study was offered. The study was conducted in accordance with the principles of the Declaration of Helsinki. Data were analyzed using a spreadsheet and are presented as mean and interquartile range (IQR). Qualitative data from the open-ended question were interpreted using content analysis.
Ten independent senior ENT physicians and anesthesiologists with experience in cricothyrotomy, percutaneous and surgical tracheostomy were enrolled. The mean age and the mean seniority were 31 years and 7 years, respectively. The overall mean rating for realism of the model, including anatomy, tactile feedback, reaction of the tissues to palpation, perception of landmarks, was 3.45/5. Suitability of model training for the given subglottic airway access procedures was highly rated with an overall mean of 4.75/5. All responders listed positive and negative aspects in the open-ended part of the survey. A total of 24 suggestions were collected. Three positive and 3 negative aspects were identified (Table 1). Among the positive ones, the most often suggested was the tactile feedback of the model compared to the synthetic alternatives. Whilst the sliding of the layers of the model was the negative aspect most often found. Four participants suggested possible improvements, which are reported in Table 1.
Figure 1: Different animal segments needed to make the model. From the top-left: Swine upper airways, pig thymus cut in a butterfly shape, swine esophagus opened longitudinally, pig skin. Please click here to view a larger version of this figure.
Figure 2: Fascial dissection. In this picture, the finished model during the surgical open tracheostomy procedure is shown. In the center, the blunt dissection of the simulated neck fascia and muscles with Metzembaum scissors are shown. Please click here to view a larger version of this figure.
|Session 1: Demographics||31,3 (6)|
|3||Professional seniority (in years)||6,6 (7)|
|Session 2: Fidelity of the bench-model|
|4||The model represents accurately human neck anatomy (for what concerns the performed procedure)||3,2 (0,25)|
|5||The model tissues reacts to my movements in a realistic way and give me a realistic tactile feedback||3,6 (1)|
|Session 3: Suitability of cricothyrotomy, percutaneous and surgical tracheostomy for training by the manufactured model|
|6||The model is a useful instrument to simulate the procedure||4,8 (0,25)|
|7||The model enables to train on all the essential technical skills needed for the procedure (excluding communication with patient or clinical decision making)||4,6 (1)|
|8||The simulator could be used for training purpose||4,8 (0,25)|
|9||The simulator could be used as a test/assessment in surgery school||4,8 (0,25)|
|Positive aspects of the bench model|
|Better tactile feedback than the synthetic simulator
Possibility to enhance manuality and technical skills of students/residents
Could allow students to better understand the steps of the procedure
|Negative aspects of the bench model|
|Skin is too thick and hard to penetrate
Skin slides over deeper layers
Difficult to find landmark
|Prevent the sliding movements by suturing the layers together
Experiment skin of different animals (turkey, rabbit)
Table 1: Description of the survey instrument and results.
The manufactured low-cost and high-fidelity bench-model simulated the human neck and enabled practice of cricothyrotomy, percutaneous and surgical tracheostomy. The designed survey filled by senior ENT physicians and anesthesiologists evaluated the extent to which the model replicates the physical characteristics of the neck and its suitability for training the given subglottic airway access procedures.
Several home-made models or simulators have been reported and we tried to overcome their limitations. The porcine model presented by Netto et al.18 lacks anatomical structures between the skin and trachea, making it suitable for cricothyrotomy only. Two studies describe synthetic models assembled with candies and anesthesia room materials (tubes, gauzes) compromising the fidelity and excluding the model for ST training19,20. To our knowledge, our bench model is the first multipurpose model suitable for the three main tracheostomy procedures (CT, PDT, ST).
Porcine trachea with all the annexes (muscles, cervical fascia, thyroid gland) and skin are relatively similar to human tissue21. Nevertheless, it is hard to find the whole animal piece since the neck is usually cut through all its length and many structures are lost in the pig slaughter procedures. For this reason, we assembled a simulated thyroid to allow inter-isthmic tracheotomy. The pig thymus was chosen as the most suitable organ for this purpose due to its texture.
The pig skin was sometimes too thick, making the trachea prone to collapse when putting force on the neck to penetrate it with needles and dilators in the percutaneous approach. The anatomical difference among the assembled models due to the variety of animal tissues could pose some challenges in terms of reproducibility and quality of the models. However, this could equate to the anatomic variability of human necks. The lack of bleeding and tissue secretion is another limit of ex vivo models. Simulation of bleeding remains a challenging problem because of the complexities of the circulatory system and the physics of viscous fluid flow. Due to this limitation, the reported model could be considered as a middle-fidelity simulator.
Traditionally, mannequins, live, and anaesthetized animals are used in cricothyrotomy and tracheotomy teaching. Nevertheless, mannequins are not similar enough to the human anatomy and do not provide a realistic model to learn this technique. Animals would be ideal but the cost is prohibitive and only a limited number of residents may have this opportunity22.
The lack of funds is considered a barrier to medical training. The cost of commercial mannequins and synthetic devices ranges from 1000$ to 3000$ and replacement pieces are expensive too. We tried a synthetic simulator23 that can be reused no more than 10 times. In addition, after the first incision, only the dilation and insertion of the tube can be performed several times, making the educational procedure incomplete. On the contrary, a cheap, disposable model such as the one described here can be assembled and used in a few minutes with no expensive components. The model can be reused up to three times, reducing the cost of the model per number of attempts. The 3 different techniques can be performed consequently, since they are executed in different portions of the model: (1) emergency cricothyrotomy, (2) percutaneous dilatational tracheostomy, and (3) surgical open tracheostomy.
Difficult airway management is a critical skill and it is still associated to a high complication rate. Since its success is dependent on operator's experience and dexterity, practice and training play a key role. Generally, the training is still limited to explanation and seeing the technique. Most of the residents have the opportunity to see the procedure only a few times before performing it in a clinical setting. This article presents step-by-step instructions to manufacture an experimental airway bench-model based on low technology and cost for teaching the three main tracheostomy procedures (CT, PDT, ST). However, the evaluation survey showed that the model, although realistic, should be perfectioned.
In the future, we would like to compare skins from different animals (e.g., a calf, a turkey, and a rabbit) to find the best choice and how much this can affect procedure quality and ultimate learning. Finally, we would like to adopt and improve the idea by Fiorellia et al.22 to mix synthetic simulators and animal tissues. We will build a synthetic shell scaffold representing the head, neck and upper thorax, where a pig trachea can be inserted. This might help to tear down the manufacture time and reach higher fidelity, reproducibility and cost efficiency. Further studies should be carried out to compare this model to other animal models and other synthetic task trainers in terms of fidelity and training effectiveness.
The authors have nothing to disclose.
The authors thank the Azienda Ospedaliera Universitaria Maggiore della Carità, Novara, for its help.
|Foam||BRICOSELF ITALIA, vercelli||na||Used to stabilyze the model on the wooden tablet|
|Insuline Syringe||na||na||Used to draw linea alba with india ink|
|Pig Esophagus||Butcher shop (Il mercato carni, di Dutto Srl. - 28100, Novara (Italy)||na||Wet material used to build the simulated muscular layers and fascia|
|Pig skin||Butcher shop (Il mercato carni, di Dutto Srl. - 28100, Novara (Italy)||na||Wet material used to obtain the simulated skin|
|Pig thymus||Butcher shop (Il mercato carni, di Dutto Srl. - 28100, Novara (Italy)||na||Wet material used to build the simulated thyroid|
|SILK suture - Vetsuture SILK 2/0 (Metric 3) Ago 3/8 30mm Reverse Cutting (12 pz)||Sanitalia Care Srl||SILK2CN||Sutures to tight all the parts of the model|
|Surgical instruments scissors, forceps, knife, needle holder||na||na||na|
|Swine upper airways||Butcher shop (Il mercato carni, di Dutto Srl. - 28100, Novara (Italy)||na||Wet material used to build the model|
|white india ink - pelikan 10ml||Cartoleria Manzoni di Lo Monaco Rosaria s.a.s. 97019 Vittoria, Italy||36340||Ink used to mark the linea alba on the esophagus|
|Wood stapler||BRICOSELF ITALIA, vercelli||na||Used to staple on the model|
|Wooden tablet||BRICOSELF ITALIA, vercelli||na||Used to stabilyze the model with the stapler|
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