Airway management is one of the pillars of the anesthesiologists’ training. Orotracheal intubation (OTI) is the “criterion standard.” The prevalence of difficult intubations is from 1.8% to 1.9%.1 Difficulty in airway management can have serious consequences, such as serious trauma to the airway, myocardial ischemia, cerebral anoxia, and death.
The low incidence of airway management difficulty and the potential for ethical conflicts in learning airway management necessitate the use of other resources such as airway training heads and simulators that allow for practice under different difficult situations. The use of some techniques of difficult airway management in patients, when not necessary, would produce some complications, and this situation could go against the ethical principles of beneficence and nonmaleficence. One of the most widely used airway training heads in our country for the learning of normal airway management is the Airway Management Trainer intubation head (Ambu, Denmark). It is an older device with limited performance features. The Airsim (Trucorp, Northern Ireland) intubation head is a newer device with more features that is more expensive and less widely available in our location.
We have developed some modifications to the Airway Management Trainer intubation head that are easy to perform and facilitate the simulation of difficult intubation situations. The aim of this report was to explain some modifications to the Airway Management Trainer intubation head that transform it into a difficult airway intubation head and to compare it with the Airsim intubation head.
MATERIALS AND METHODS
Eight volunteer anesthesiologists (5 experienced anesthesiologists and 3 anesthesia residents of third year) participated in the study, performing 80 endotracheal intubations each. Each participant performed 10 consecutive intubations under 4 different situations with both intubation heads.
The airway training used in the study were as follows:
- a. Case intubation head: Airway Management Trainer, designed for training in the management of a normal airway.
- b. Control intubation head: Airsim,2 designed for training in the management of both normal and difficult airways.
The scenarios evaluated on both airway training heads included normal airway, macroglossia, cervical spine rigidity, and a combination of both macroglossia and cervical immobility.
The control intubation head has a valve system that permits the inflation of the tongue with air to simulate macroglossia and a screw that immobilizes the cervical spine.
The modifications to the case intubation head that we propose are to place a squash ball under the tongue, which produces macroglossia, and we obtain cervical immobility with tape placed on the cervical spine to inhibit its extension (Fig. 1 & Fig. 2). Before using a squash ball, we tried to use a small balloon first empty of air and then filled with water, but in both situations, the balloon became herniated for both sides of the tongue without doing any resistance. Then, we tried a ping-pong ball, but it was so hard and not very malleable. Finally, we tried a squash ball, which was hard enough and malleable (Fig. 2). For the cervical immobility, we tried some other devices, such as rope, cellotape, or wire, but they were not as useful as the tape we used. This system allows different degrees of cervical rigidity, depending on the tension we provide to the tape (Table 1).
The cost of Airsim intubation head is €1436.00 (US $1875.85), and the cost of Airway Management Trainer is €1130.00 (US $1475.12). The price of both tapes is €6.30 (US $8.23), and the price of the squash ball is only €0.50 (US $0.65).
Four randomly chosen anesthesiologists began the series of intubations with the case intubation head and four with the control intubation head to prevent learning from interfering with the times and ease of intubation.
In this study, we used a Welch Allyn laryngoscope with a #3 Macintosh blade and an endotracheal tube with an internal diameter of 7 mm. We lubricated the entire airway of both airway training heads with a water-soluble lubricant to facilitate endotracheal tube passage.
The outcome variables included intubation time and intubation degree of difficulty assessed by the same anesthesiologist who performed the intubation.
Intubation time was the time from the introduction of the laryngoscope into the mouth until verification of the correct position of the endotracheal tube via inflation of the mannequin’s lung.
The difficult degree was measured on a 5-point Likert scale (very easy intubation, 1; easy intubation, 2; normal intubation, 3; difficult intubation, 4; and very difficult or impossible intubation, 5).
We also recorded the grade of laryngoscopic view on the Cormack-Lehane scale. According to the original definition by Cormack-Lehane, most of the glottic opening can be seen with grade 1. In grade 2, only the posterior portion of the glottis or only arytenoids cartilages are visible. In grade 3, only the epiglottis but no portion of the glottis is visible, whereas in grade 4, neither the glottis nor the epiglottis can be seen. The airway management becomes more difficult as the quality of the glottic view deteriorates.3
We also indicated needed of maneuvers such as neck extension, laryngeal mobilization or pressure, and observations.
The statistical analysis was conducted through a univariate analysis. The mean and SD were used as descriptors for the continuous numeric variables. To compare the groups, Student t test was applied. We considered a P < 0.05 to be statistically significant. The absolute frequencies were used as descriptors for the categorical variables. To determine whether 2 categorical variables were independent, the χ2 test was applied. We considered a P < 0.05 to be statistically significant.
For all of the 640 OTI attempts, the intubation time was longer with the case intubation head than with the control intubation head, with a P < 0.05 (Table 2).
With respect to the ease of intubation in the normal airway scenario, intubation with the case intubation head was more difficult than with the control intubation head (P < 0.05). When simulating macroglossia or spinal rigidity, the case intubation head was also more difficult to intubate, but the difference was not statistically significant (P = 0.125 for macroglossia and P = 0.104 for spinal rigidity). Finally, when combining both macroglossia and spinal rigidity, the case intubation head was more difficult to intubate than the control (P < 0.05). In no clinical scenarios did the case or control intubation heads present the maximal degrees of intubation difficulty of 4 or 5 (Table 3).
When we evaluated the glottic view grade according to the Cormack-Lehane scale, there were no differences between the case and control intubation heads in the normal airway scenario (P = 1.000). With macroglossia, the control intubation head had a significantly higher frequency of grade 2 than did the case intubation head (P = 0.011). We did not find differences for cervical rigidity (P = 0.493). When we combined macroglossia and cervical rigidity, the case intubation head presented significantly more cases of Cormack-Lehane grade 3 (P < 0.05). No grade 4 intubation was observed in any of the cases (Table 4).
After the third intubation attempt by an individual anesthesiologist, there were no differences between the case and control airway training heads with respect to the time required for intubation, which leads us to infer that learning altered the results after the third intubation attempt (Fig. 3).
The most frequent observation in the use of the control intubation head was the need to apply greater-than-usual force (71.6%), whereas with the case intubation head, the need to rotate the endotracheal tube to facilitate its passage toward the trachea was the most common (48.9%). To a lesser extent, forces requiring 2 hands, pressure on the teeth, or both were used.
Airway management is a fundamental competency of the anesthesiologist. The low incidence of difficult airways does not exempt the anesthesiologist from being adequately prepared for their management. For practical and ethical reasons, the use of airway training heads and simulators should form part of the training program in acquiring skills in this area.4–6 With these tools, anesthesiologists can learn and practice the different techniques involved in the airway management algorithms of different scientific societies.7,8
The management of difficult airways requires continuous practice.9,10 It is recommended that airway training be repeated approximately every 6 months, especially for skills that are used with low frequency,11 although there is no scientific evidence for this recommended time interval.12
Simulating difficult airways involves placing the learner in contexts that mimic certain aspects of actual clinical practice and establishing scenarios similar to those that will be faced during his or her professional practice. The use of simulation in airway management training is an effective method for the development of the set of skills required under challenging conditions.13
The use of the simulation accelerates and improves the quality of the learning process. Simulations should not constitute an isolated element of the learning process; rather, they are one among a set of integrated factors. However, no studies have scientifically demonstrated a clear transference of performance ability in clinical practice as a direct result of simulator training.14
Actual-scale simulators represent the most realistic model of the environment and work places where anesthesia is practiced. Simulators can be successfully used for training in uncommon techniques and critical situations. These techniques are rarely used, but when they are required, they require the ability and skill of prepared specialists.15–17 The high cost of these simulators limits their access; thus, airway training heads and more economical systems, including the one used in our study, are frequently used. We choose Airsim intubation head for comparing with modified Airway Management Trainer because it allows similar benefits that we could obtain with our proposals.
In all of the situations studied, the time required for OTI in the case intubation head was significantly longer than in the control intubation head, which leads us to conclude that the modified case intubation head may be an effective tool for the practice of difficult intubations.
After analyzing the data on the grades of the glottic views, we can conclude that the case intubation head exhibited a higher overall glottic view grade and, therefore, presented greater difficulty for OTI, when macroglossia and cervical rigidity were combined.
The difference with respect to the ease of intubation shows that the modifications to the case intubation head make it significantly more difficult to intubate than the control intubation head. However, this evaluation is subjective.
The proposed modifications are very easy to conduct and are accessible to anyone who has the Airway Management Trainer intubation head.
In the case intubation head, we observed that the rotation of the endotracheal tube facilitated intubation and that more force was required for the intubation of the control intubation head; this observation leads us to conclude that each airway training head requires a distinct technique to facilitate intubation.
In our study, greater tissue rigidity and more challenging laryngeal anatomy were observed for the case intubation head when modifications were introduced to convert it to a difficult airway intubation head, requiring an increase in the force required during laryngoscopy and an increase in the pressure applied to the teeth. The control intubation head has good internal anatomy; however, its external appearance was critiqued.
It was also notable that after the third intubation attempt by an individual anesthesiologist, there were no differences between the case and control airway training heads with respect to the time required for intubation, which leads us to infer that learning altered the results after the third intubation attempt.
We can conclude that the price of the case intubation head with both tapes and the squash ball is cheaper than the control intubation head.
A limitation of the study was the lack of previous calculation of the sample size; however, in a post hoc sample size calculation accepting an α risk of 0.05 in a bilateral contrast, with 80 attempts of OTI in the case intubation head and 80 in the control, the power of the hypothesis test was found to be 100% in detecting a statistically significant difference between the means of both groups (Table 5).
We conclude that the modifications we propose to the Airway Management Trainer intubation head lend this airway training head features similar to those provided by the Airsim intubation head for training in difficult airway management in the 4 studied scenarios: normal airway, macroglossia, cervical rigidity, and the combination of both macroglossia and cervical rigidity.
1. Massó E, Borràs R. Evaluación clínica de la vía aérea. In: Rull M, Añez C, eds. Manual de manejo de la vía aérea. Barcelona, Spain: Ergon; 2009: 13–18.
3. Krage R, van Rijn C, van Groening D, Loer SA, Schwarte LA, Schober P. Cormack-Lehane classification revisited. Br J Anaesth 2010; 105 (2): 220–227.
4. Jordan GM, Silsby J, Bayley G, Cook TM. Evaluation of four manikins as simulators for teaching airway management procedures specified in the Difficult Airway Society guidelines and other advanced skills. Anaesthesia 2007; 62 (7): 708–712.
5. Plummer JL, Owen H. Learning endotracheal intubation in a clinical skills learning center: a quantitative study. Anesth Analg 2001; 93: 656–662.
6. Wahlen BM, Roewer N, Lange M, Kranke P. Tracheal intubation and alternative airway management devices used by healthcare professionals with different level of pre-existing skills: a manikin study. Anaesthesia 2009; 64: 549–554.
7. Hendenrson JJ, Popat M-T, Latto IP. Difficult Airway Society guidelines for management of the unanticipated difficult intubation. Anaesthesia 2004; 59: 675–694.
8. American Society of Anesthesiologists Task Force on Management of the Difficult Airway. Practice guidelines for management of the difficult airway: an updated report by the American Society of Anesthesiologists Task Force on Management of the Difficult Airway. Anesthesiology 2003; 98 (5): 1269–1277.
9. Parry K, Owen H. Small simulators for teaching procedural skills in a difficult airway algorithm. Anesth Intensive Care 2004; 32 (3): 401–409.
10. Rosenstock C, Østergaard D, Kristensen MS, Lippert A, Ruhnau B, Rasmussen LS. Residents lack knowledge and practical skills in handling the difficult airway. Acta Anaesthesiol Scand 2004; 48: 1014–1018.
11. Kuduvalli PM, Jervis A, Tighe SQM, Robin NM. Unanticipated difficult airway management
in anaesthetized patients: a prospective study of the effect of mannequin training
on management strategies and skill retention. Anaesthesia 2008; 63: 364–369.
12. Pérez-Calvo C, Villanueva MA, Del Moral I, Alcalá MA, González-Arenas P, Suárez-Sipman F. Capítulo 11. Internet. simuladores. Torres Morera LM, ed. Tratado de anestesia y reanimación. Aran: Tomo 1; 2001: 281–315.
13. Villalonga R. Docencia en el manejo de la vía aérea. In: Rull M, Añez C, eds. Manual de manejo de la vía aérea. Barcelona, Spain: Ergon; 2009: 167–173.
14. Nestel D, Groom J, Eikeland-Husebo S, O’Donell JM. Simulation for learning and teaching procedural skills: the state of the science. Simul Healthc 2011; 6 (Suppl): S10–S13.
15. Cook TM. Still time to organize training
in airway management in the UK. Anaesthesia 2006; 61: 727–730.
16. Baker PA, Weller JM, Greenland KB, Riley RH, Merry AF. Education in airway management. Anaesthesia 2011; 66 (Suppl 2): 101–111.
17. Pratt SD. Simulation in obstetric anesthesia. Anesth Analg 2012; 114: 186–190.