CLINICIAN'S CAPSULE
What is known about the topic?
Physicians demonstrate lower rates of success when attempting to landmark cricothyroid membranes in female patients.
What did this study ask?
Can emergency physicians predict their likelihood of successfully landmarking the cricothyroid membrane of healthy volunteers?
What did this study find?
This study found no correlation between confidence, perceived likelihood of success, and actual success of cricothyroid landmarking attempts.
Why does this study matter to clinicians?
A physician's inability to predict cricothyroid membrane landmarking accuracy may increase cricothyrotomy complications and necessitates further research into improving training techniques.
INTRODUCTION
Cricothyrotomy is an intervention performed to salvage “can't intubate, can't ventilate” situations. Access to the airway is gained through the cricothyroid membrane to insert a tracheal tube. It is vital for physicians to be able to quickly and accurately landmark the cricothyroid membrane.
Studies have shown poor accuracy when landmarking the cricothyroid membrane, particularly in females.Reference Campbell, Shanahan and Ash1,Reference Hiller, Karni, Cai, Holcomb and Hagberg2,Reference Lamb, Zhang and Hung3,Reference Yıldız, Göksu, Şenfer and Kaplan4,Reference You-Ten, Desai, Postonogova and Siddiqui5 While landmarking accuracy has been well studied in the anesthesia literature, data on emergency physician (EP) success rates are sparce.Reference Alshareef, Al Saawi and Almazroua6 EPs and anesthesiologists have different skillsets and therefore may have different landmarking success. Ultrasonography is an accepted modality for identification of the cricothyroid membrane in controlled and research settings,Reference Siddiqui, Yu and Boulis7 though studies have not shown ultrasonography to be superior in clinical settings.Reference Yıldız, Göksu, Şenfer and Kaplan4,Reference You-Ten, Desai, Postonogova and Siddiqui5 There have been no studies examining perceived EP cricothyroid membrane landmarking accuracy or the correlation of their landmarking confidence with their actual attempt accuracy.
Our objective was to compare the perceived and actual success rate of landmarking the cricothyroid membrane by resident and staff EPs using obese (body mass index [BMI] > 30)8 and non-obese (BMI < 30) males and females.
METHODS
We performed a prospective study using five non-obese and five obese volunteers, determined by self-reported height and weight, and five volunteer assessors (trained laypeople and physicians). We recruited a convenience sample of resident and staff EPs to participate in the study.
Each model was positioned supine with their necks in a neutral alignment. An experienced EP and point-of-care ultrasound expert landmarked the superior and inferior borders of each model's cricothyroid membrane with an invisible marker that becomes visible under black light (Supplemental Appendix 1). A 6-cm × 7-cm clear plastic dressing was placed over the site to protect the invisible markings. All assessors were provided training to standardize their assessments.
Participants were grouped into cohorts of up to 10. Each participant was assigned an anonymous identifier and completed a pre-test survey (Supplemental Appendix 2). Data were collected on each participant's level of training and perceived clinical ability for first pass success for performing a cricothyrotomy on an average male, average female, and obese person.
Each participant was subsequently assigned to five models (combination of obese, non-obese, male, and female). Participants were instructed to landmark each model's cricothyroid membrane as quickly and accurately as possible. They were given one attempt per model to landmark and place a single invisible pen mark at the site of the perceived cricothyroid membrane. Assessors recorded each participant's result using black lights and measuring tapes. Any distance greater than 5 mm from the outer borders of the cricothyroid membrane was considered a missed landmarking.Reference Lamb, Zhang and Hung3 The clear plastic dressing was wiped clean after each attempt for the next participant. Following each attempt, participants completed an in-test survey (Supplemental Appendix 3) to assess their perceived attempt difficulty and confidence in their accuracy. Landmarking confidence was measured on a 10-cm visual analogy scale from “likely unsuccessful” to “successful.” Participants repeated the procedure until they had performed an attempt on five different models.
Data analysis
Data were analysed to determine landmarking accuracy, correlation between actual and perceived accuracy, types of prior training received, perceptions of that training, and comfort with performing the procedure. We performed a subgroup analysis to compare resident and staff EP perceptions versus performance with obese, non-obese, male, and female models. Correlations were calculated as Pearson's correlation coefficient, except between confidence and actual success, which used Fisher's exact test.
RESULTS
Residents from PGY1 to PGY4 and staff EPs composed the participant pool. There were 35 total participants, 20 of which were residents (PGY1 = 7, PGY2 = 4, PGY3 = 5, PGY4 = 4) and 15 staff. The average BMI for non-obese female models was 26.5 (range 25–28), obese female models was 34.1 (33–35.1), non-obese male models was 24.7 (23.6–25.8), and obese male models was 36.0 (32.4–39.5).
The overall mean accuracy was 58% (SD = 18%) (Figure 1). A significant difference in accuracy was found for obese males (88%) versus obese females (40%) (difference = 48%, 95% CI = 30–65%, p < 0.0001); and non-obese males (77%) versus non-obese females (46%) (difference = 31%, 95% CI = 12–51%, p = 0.004). No difference between accuracy in obese and non-obese models of the same gender (males: difference = 11%, 95% CI = −7–28%, p = 0.24; females: difference = 6%, 95% CI = −25–13%, p = 0.52) was observed. A subgroup analysis of residents and staff found that they performed similarly.
Figure 1. Participant attempt accuracy stratified by level of training.
The perceived attempt difficulty was not associated with success (correlation = 0.07, 95% CI = −0.081–0.214, p = 0.37). This finding remained consistent in our subgroup analysis of both residents and staff physicians. Confidence levels overall were higher amongst staff physicians (3.0) than residents (2.7) (difference = 0.3, 95% CI = 0.1–0.6, p = 0.02), but, despite this confidence difference, there was no correlation between attempt confidence and success (Fisher's exact test, p = 0.33).
DISCUSSION
Our study demonstrated no correlation between participants’ perceptions of landmarking difficulty or confidence and landmarking success rates. Furthermore, while staff physicians demonstrated more confidence in their landmarking, they did not outperform residents in regard to accuracy. This may be because this is an uncommon procedure. Our results suggest that physicians are not able to discriminate between patients in which it will be difficult to landmark the cricothyroid membrane and those who will not be. The overestimation of success in female patients and the poor correlation between confidence and success suggest that additional steps are needed. One potential solution is to use a larger than traditionally taught vertical incision, regardless of perceived difficulty or physician confidence. This is supported by a recent study that recommended an 8- to 10-cm vertical incision to account for all potential cricothyroid membrane locations.Reference Fennessy, Drew, Husarova, Duggan and McCaul9
Given the lack of ability of EPs in this study to predict their accuracy in landmarking cricothyroid membranes, improved training modalities would be useful for refining this skill. One modality that has shown to improve landmarking accuracy employed instant feedback on cricothyroid landmarking accuracy by ultrasound.Reference You-Ten, Wong and Arzola10 While not definitively studied, it stands to reason that more accurate landmarking would reduce the time to secure the airway and improve chances for success.
Limitations
Each model's neck was kept in a neutral position instead of an extended position, as would be customary for a cricothyrotomy. This was done both for the comfort of the models and to maintain consistency. This neutral positioning could have made landmarking models more difficult, resulting in a higher miss rate, but would be typical of patients in C-spine precautions.
Participants were recruited as a convenience sample of available residents and staff physicians. This may have introduced selection bias. While this could not be controlled for, our results appear to correlate with previous research. The smaller size of the participant group was chosen based on feasibility.
The assessors were not blinded to the attempts. While a lack of blinding can introduce bias, the distance from the invisible marking of the borders of the cricothyroid membrane is objective and less prone to bias than subjective measures.
CONCLUSION
This study supports the finding that physicians demonstrate significantly lower levels of accuracy when landmarking cricothyroid membranes of female models. EPs appear unable to predict their own accuracy while landmarking, which can potentially lead to increased failed attempts and a longer time to secure the airway. Improved training techniques, such as using ultrasound to provide instant landmarking feedback, as well as using larger initial incisions, may reduce the risk of failed attempts and improve the time taken to secure the airway.
Presentations
Department of Emergency Medicine Research Day, University of Ottawa, May 23, 2019, The Ottawa Hospital, Ottawa, Ontario, Canada
Author contributions
NS participated in the study concept and design, acquisition of the data, analysis and interpretation of the data, drafting of the manuscript, critical revision of the manuscript for important intellectual content, and statistical analysis. MYW participated in the acquisition of the data, interpretation of the data, and critical revision of the manuscript for important intellectual content. AP and WJC participated in the study concept and design, acquisition of the data, and critical revision of the manuscript for important intellectual content. JJP participated in the study concept and design, analysis and interpretation of the data, and critical revision of the manuscript for important intellectual content.
Competing interests
None declared.
