Airway management is one of the major challenges in anesthesia, as reflected by its 34% share of anesthesia-related claims.1 The American Society of Anesthesiology practice guidelines describe invasive and noninvasive techniques to secure a difficult airway.2
Insertion of an airway device via a cricothyrotomy is the final option in all cannot-ventilate cannot-intubate airway-management algorithms.3 Training in its performance is essential for health care workers involved in airway management.
Cricothyrotomy is not a routine or common procedure.4 A decline in the need for emergency surgical airways in recent years, due to improvements in airway management, has resulted in a decreased exposure to this life-saving technique.5,6 Consequently, residents, who are often the first physicians on scene during resuscitations, have very little practical experience or confidence in performing this emergent intervention.4,7
Lack of experience has been shown to be the main source of cricothyrotomy failure,8 but hands-on training is also lacking. A study evaluating difficult airway instruction found that although 80% of American anesthesiology residency training programs taught cricothyrotomy, 60% of these courses consisted of lectures only.9 As a result, many physicians do not possess the necessary skills to perform a cricothyrotomy correctly or expediently and may therefore hesitate when such an intervention is needed.
Since this procedure is performed only in emergency situations, it is crucial to optimize teaching and training methods for this skill outside the operating room and emergency department. Simulation is a teaching modality that has gained a prominent role in training programs in recent years. Various simulators have been developed for medical education and instruction, ranging from simple low fidelity to sophisticated high fidelity models. These lifelike high fidelity devices are, however, very costly and therefore of limited availability. No studies have objectively assessed the impact of model fidelity on the acquisition of surgical airway skills.
The purpose of this study was to compare cricothyrotomy skills acquired on a simple and inexpensive model to those learned on a high fidelity simulator using valid evaluation instruments. We tested the transfer of these skills to human cadavers using global assessment scales and task-specific CLs and procedure time.
The study was approved by the Institutional Research Ethics Board of Mount Sinai Hospital, a University of Toronto teaching hospital, Toronto, Ontario, Canada. First and second year anesthesiology residents were recruited for the study and written informed consent was obtained. Subjects who had previously performed or participated in a cricothyrotomy were excluded.
Each subject performed a pretest cricothyrotomy on embalmed adult human cadavers using an un-cuffed 4 mm I.D Melker set (Cook, Bloomington, IN). Participants had no influence on the choice of cadavers. The cadavers were lying flat on the dissecting table. Cadaver exclusion criteria consisted of previous neck surgery or disease and a Body Mass Index >35.
The pretest sessions were videotaped by two of the authors using a tripod-mounted digital camcorder. Videotaping was performed in a blinded manner to ensure proper masking of the identity and level of training of the resident. This was achieved by videotaping only the residents' hands throughout the procedure and by removing the date tags from the videotapes. After the performance, correct placement of the tube was confirmed by dissection and incorrect placement was noted.
Immediately after the pretest, all subjects watched a 20-min instructional video on the performance of cricothyrotomy (produced by Cook Bloomington, IN for the use of the Melker kit) after didactic instruction. They then familiarized themselves with the cricothyrotomy kits during a 10-min orientation session. The subjects were then randomized into two model fidelity groups according to a computer-generated list. The high fidelity group (n = 11) consisted of subjects performing two cricothyrotomies on a full-scale SimMan (Laerdal, Kent, UK) simulator with an anatomically accurate larynx, for airway management and cricothyrotomy. Skin and cricothyroid membrane were replaced after each insertion. The low fidelity group (n = 11) consisted of subjects performing two cricothyrotomies on a low fidelity model, similar to the one proposed by Varaday et al.10 It was constructed from a 20-cm piece of corrugated anesthesia machine tubing. A fissure was cut into the tube and then taped over to simulate the cricothyroid membrane and a small piece of silicon membrane simulating skin was wrapped around the tube. An experienced staff supervised each group throughout the session.
Within 2 wk of the training session all subjects performed a second cricothyrotomy post-test on a cadaver. The post-test sessions were videotaped in the same, blinded manner.
The pretest and posttest sessions were copied from the camcorder to a DVD in random order before being assessed and graded. The performances were graded by two blinded examiners (staff anesthesiologists) using a three-point task specific checklist (CL) (Appendix 1), and a global rating scale (GRS) (Appendix 2). The sessions were timed from the opening of the set until the tube was inserted into the trachea. The authors who videotaped the sessions were not involved in grading them.
Analysis was performed using SPSS 11.0 software (Chicago, IL). In a previous study, we examined the difference between model training and didactic teaching for acquisition of fiberoptic bronchoscopy skills.11 The effect size between the model and control groups was 1.6 standard deviations. In the field of psychology, an effect size of more than 1.0 standard deviation is considered a large but acceptable difference for assessing teaching intervention.12 With 11 subjects in each group, using a β of 0.20 and a two tailed α of 0.05, we had 80% power to detect 1.3 standard deviations.
To assess our primary outcome, the efficacy of training between low and high fidelity models, the pretest to posttest changes in GRS, CL, and time scores were compared. The mean changes in each score were compared using an independent measures t-test for parametric data, and Mann-Whitney U-test for nonparametric data. A two-tailed P < 0.05 was considered significant.
To assess our secondary outcome and confirm whether both low and high fidelity models are effective teaching tools, we compared pretest and posttest GRS and CL scores for each model using paired t-tests for parametric data, and a signed rank test for nonparametric data. A two-tailed P < 0.05 was considered significant.
Overall posttest success between model training groups was compared using a χ2 test. Inter-rater reliability was assessed using a Pearson's product moment correlation coefficient. A two-tailed P < 0.05 was considered significant.
Twenty-two subjects were recruited over a period of 6 mo. Subjects' characteristics and baseline pretest results were similar between study groups (Table 1).
Inter-rater reliability was strong for both measures (CL: r = 0.90; GRS: r = 0.89) (both P < 0.05).
There was no significant difference in the change from pretest to posttest cricothyrotomy performance (primary outcome) between the low-fidelity and high-fidelity model groups as evaluated by the CL, GRS, and time to completion of procedure (all P = NS)(Fig. 1).
Training on both models significantly improved cricothyrotomy performance (secondary outcome) as evaluated by the CL, GRS, and time (low fidelity group: all P < 0.001; high fidelity group: all P < 0.001)(Figs. 2–4).
Dissection revealed tube malposition outside the trachea in two pretest cricothyrotomies (one in each model training group)(P = NS) and in one posttest session (low fidelity model training group)(P = NS).
The results of our study show that subjects improved significantly between their pretest and posttest; however, there was no difference in cricothyrotomy skills acquired on a low fidelity simple model versus those acquired on a high fidelity model, as reflected by the posttest performance on cadavers.
The usual practice in which trainees observe the senior staff and then perform the procedure under their direct guidance cannot apply to emergency surgical airway procedures. Despite previous didactic teaching of surgical airway performance during their residency, all residents performed poorly in the pretest and would have probably performed just as poorly in a real-life scenario, highlighting the fact that our current teaching of this lifesaving procedure is inadequate. After either low or high fidelity simulation training, their performance in the posttest improved significantly, as reflected in the CL and GRS scores as well as in time-to-completion. These results are similar to other studies showing that hands-on teaching of manual skills is superior to conventional didactic instruction.11,13
We chose to test the residents' cricothyrotomy performance using the Melker set. An airway management review suggested that experience with a specific device might be just as important as the device itself.14 Most anesthesiologists are comfortable with a Seldinger technique and many would prefer it to an open surgical technique.15 A previous comparison between the open and the Seldinger cricothyrotomy techniques showed equally poor performance in both groups.16 The most common and time-consuming mistakes we witnessed were due to the fact that the dilator was not inserted into the tube and both advanced as one unit. This mistake was likely caused by the different technique used for central line insertion, in which the dilator is inserted before and separate from the catheter. When teaching novices cricothyrotomy, this point should be emphasized.
We tested the transfer of cricothyrotomy skills to the cadavers by using a GRS and task-specific CL. These tools have been shown to be highly valid and reliable methods of evaluating proficiency in surgery and anesthesiology.17,18
We conducted the testing on cadavers, which are probably the best available substitute for a live encounter and have been used to train physicians and test new procedures.19,20 Cadavers are not always readily available in the large numbers needed for routine training. Simulation centers where trainees can practice on various models are an alternative that allow for the acquisition of skills in a safe and monitored environment. However, there are still very little data in the literature comparing the efficacy of training methods, and the added value of high fidelity models on manual skills acquisition remains controversial.
A previous study compared the effect of hands-on endoscopy training using two different bench models.13 Similar to our results, subjects in the high fidelity model group did not perform significantly better than those in the low fidelity group. In a study by Wong et al. that evaluated training physicians for cricothyrotomy on manikins, 96% of participants were able to perform the cricothyrotomy successfully on the manikin in 40 s or less by the fifth attempt.21 When divided into age groups, the younger group achieved a significantly higher degree of success during the first and second attempts and plateaued afterwards. Similar to these results, in the current study, two supervised insertions on a simple model were enough to bring skills to adequate levels.
Other studies dealing with motor learning have shown that high fidelity simulation does not necessarily result in better skills acquisition and, in fact, may even impede performance.22,23 Novice operators learn better on simple models until they achieve a level of automation that enables them to divert attentional capacity to other tasks. Since in the current study, a simple manual task was assessed, skill acquisition was comparable between the low and high fidelity model.
The limitations of our study warrant comment. We did not have a control group, since we were obligated to provide the participating residents with instruction. However, most of the problems encountered in the pretest originated from inadequate familiarity with the specifics of the cricothyrotomy kit and procedure. These problems were only solved through the instruction process. The literature shows that hands-on teaching is superior to didactic teaching (which is what residents in a control group would have had as part of their residency) when evaluating transfer of manual skills.11,13 Accordingly, we feel that simply performing the procedure without proper instruction would not have led to improvement, since the mistakes we witnessed could not have been corrected otherwise.
We were unable to perform a follow-up retention test for logistical reasons of cadaver supply. Future studies will test the attrition of these skills to determine optimal training and potentially need for recertification.
Our study shows that a simple model, which can be easily constructed for less than $10 Canadian, achieved the same effect on objectively rated skill acquisition, as did an expensive simulator. The lower cost will enable a wider and repeated exposure to the procedure with results comparable to those achieved on a costly high fidelity simulator. The skills acquired on both models transferred effectively to performance on cadavers. Training for this lifesaving skill does not need to be limited by simulator accessibility or cost.
We thank Professor Michael Wiley, BSc, MSc, PhD, Division Chair, Division of Anatomy, Department of Surgery, University of Toronto, Toronto M5S 1A8, Ontario, Canada.
Examiner's Checklist for Cricothyrotomy Performance Correctly identifies cricothyroid membrane
- Stabilizes the cartilage.
- Makes an incision in the midline using the #15 short handle scalpel blade.
- Advances syringe attached to the introducer needle and catheter through the incision and cricothyroid membrane into the airway at a 45-degree angle.
- Verifies entrance into the airway by aspiration syringe resulting in free air return.
- Removes the needle, leaving the catheter in place.
- Advances the soft, flexible end of the wire guide through the catheter and into the airway several centimeters.
- Removes the catheter, while maintaining control over the wire guide and leaving it in place.
- Advances the handled dilator, tapered end first, into the connector end of the airway catheter until the handle stops against the connector.
- Advances the assembly over the wire guide until the proximal stiff end of the wire guide is completely through and visible at the handle end of the dilator.
- Maintaining wire guide position, advances the assembly over the wire guide with a reciprocating motion, and completely into the trachea.
- Removes the wire guide and dilator.
- 0 = did not perform.
- 1 = inadequately performed.
- 2 = adequately performed.
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