Ultrasonography is noninvasive and allows rapid examination without patient relocation. Therefore, the use of point-of-care ultrasound (POCUS), which is performed at the bedside by the clinician to determine treatment goals or assist with procedures, has increased. With increasing importance of ultrasonography, many medical schools have introduced POCUS into the undergraduate medical curriculum [1-3].

POCUS of the airway (POCUS-A) provides a rapid assessment of the airway anatomy and facilitates critical airway management through a highly reliable evaluation of the subglottic airway [4]. POCUS-A enables real-time confirmation of endotracheal tube location and determination of the anatomical position of the cricothyroid membrane (CTM) in cricothyroidotomy. As POCUS-A provides important information quickly and effectively, it is particularly useful in the operating room, intensive care unit, and the emergency department (ED) due to the frequency of airway management requirements [4-6].

In this pilot study, we sought to test our hypothesis that brief POCUS-A education during ED rotation could improve the cognitive and psychomotor skills regarding its use among medical students.

The utility of airway ultrasonography has already been reported several times. Using airway ultrasonography, it is possible to monitor the accurate performance of endotracheal intubation in real time. In addition, in patients for whom the thyroid cartilage cannot be palpated, ultrasound can confirm the position of the CTM to facilitate cricothyroidotomy [9-13]. Chou et al. [7] evaluated the adequacy of endotracheal intubation in 112 patients who underwent tracheal intubation in an ED and confirmed its diagnostic accuracy using quantitative waveform capnography. They reported that the diagnostic accuracy was 98.2%, sensitivity was 98.9%, and specificity was 94.1%. Especially intra-esophageal intubation can be anticipated by the presence of a double tract sign with a false second airway at the esophagus very specifically [14]. Sustic et al. [10] reported a case of tracheostomy using ultrasound in a morbidly obese patient. Siddiqui et al. [15] reported that the use of ultrasound guidance for cricothyroidotomy in cadavers with poorly defined neck anatomy, with impalpable anatomical landmarks, increased the success rate of cricothyroidotomy 5.6-fold and reduced the complications of surgery. Kristensen et al. [16] reported the success rate of locating the CTM in an obese female volunteer with a body mass index of 45 by 35 anesthesiologists with 6 years of experience. The success rate of the conventional method was 37%, and with ultrasound location it was 83%. Thus, POCUS-A is very useful in airway management. However, education on it is not universal, and therefore, it is rarely used clinically.

For developing this educational program and evaluation methods, we assessed content validity by involving six specialists in POCUS-A and determined CVI, face validity, and construct validity with eight EM residents for improving the clarity of the educational items. Our prospective pilot study demonstrates that POCUS-A training for undergraduate students in medical schools facilitated successful ultrasound scanning and adequate interpretation of the test results. The students’ self-assessed technical knowledge and confidence in the use of POCUS-A was enhanced, and their motivation to perform ultrasound was improved by their enjoyment of diagnosis through ultrasound. Although many studies reported successful education of medical students about target ultrasound, this study is the first to report on the effectiveness of teaching airway ultrasound.

Through this curriculum, students were able to improve both cognitive and psychomotor skills. Particularly in terms of knowledge evaluation, all the students answered the six questions by correctly distinguishing tracheal intubation from esophageal intubation. In this study, transverse scanning to detect esophageal intubation was performed in two different probe locations. Students showed a success rate of 92.3% in the location above the sternal notch proposed by Chou et al. [7], but below the cricoid cartilage level, the success rate was higher at 96.2%. Although there was no statistically significant difference, scanning at the lower cricoid cartilage level may help beginners to easily scan the trachea and esophagus simultaneously. Kristensen et al. [9] reported the total success of ultrasonographic identification of the CTM performed by airway experts, but in this study, CTM scanning succeeded only in 92.3% of the students. The difficulty of anchoring the probe in the midline due to the protrusions of the thyroid cartilage might be the cause of failure. Many students complained that the probe was floating and it was difficult to attach it to necks during the scan of thyroid cartilage. Therefore, it is necessary to explain in detail that a vertical scan of the thyroid cartilage should begin at the inferior end of the protrusion in order to keep the probe attached.

Recently, POCUS examinations have become popular, and studies report the need for POCUS education of students [17-22]. However, which type of POCUS programs students should be educated in has not been clarified. We recommend teaching students POCUS-A for the following reasons. First, POCUS-A can be used to instantly determine whether the life-sustaining airway is maintained appropriately, and facilitate identification of the CTM in difficult patients. Second, POCUS-A is associated with a very high success rate because it can be used to examine superficial structures compared to other target ultrasound interventions. Gogalniceanu et al. [17] reported 86.0% success rate with an education involving Focused Assessment for Sonography in Trauma in a group of 25 medical college students. Jeppesen and Bahner [22] trained medical students in the Trinity protocol (hypotensive ultrasound protocol) and reported a 36% success rate. Thus, this study suggests that POCUS-A education can stimulate students’ interest due to the much higher success rate than other target ultrasound education programs suggested above.

There are some limitations to this study. First, it is difficult to generalize the results due to the small sample size of 52 students, from a single medical college. Second, the students did not scan abnormal findings because they conducted ultrasonography on a normal standard patient. However, the purpose of this training was to observe the airway and esophagus simultaneously with ultrasound to confirm accurate intubation, and determine the position and depth of the CTM, which were fully observed in a standard patient. Further, the sonographic findings of esophageal intubation were available as image data for the students to easily distinguish and enhance their cognitive knowledge. Third, because this study was conducted only during their EM rotation, it did not evaluate the degree of knowledge retention in students after a specific period of time. Finally, ultrasonography was performed on healthy standard patients while lying comfortably, which was easier for students to obtain images than in a real-life clinical setting.

In summary, this study shows that a simple airway ultrasound education can improve the knowledge and image acquisition skills and interpretation ability of medical students. We believe that POCUS-A training should be considered when developing undergraduate ultrasonography education. Future studies will need to supplement this evaluation after a certain period of time in order to assess the retention of knowledge.