Detecting cervical esophagus with ultrasound on healthy voluntaries: learning curve

Study design and setting

Our work was a monocentric descriptive prospective study carried out from March to June 2021 by the French Emergency Medical Service of department 92 [Service d’Aide Médicale Urgente (SAMU) 92] team of Raymond Poincaré University Hospital, composed of 60 doctors and 30 nurses or nurse anesthetists.

The study was approved by a local ethics committee. An IRB-type declaration has been registered under the number 2022-A01184-39. Participation in the study was voluntary. No material or financial compensation was foreseen. The database has been declared to the National Commission for Computing and Liberties under the number 2227441.

Selection of participants

The population studied was that of the SAMU 92 teams, namely medical staff (seniors, residents, medical students) and nurses or nurse anesthetists, regardless of their experience and prior practice of ultrasound.

The criterion for non-inclusion was the regular use, over the past three months, of ultrasound in clinical practice for esophageal visualization.

Protocol

The participants first received theoretical training, then two hands-on workshops on healthy volunteers (models), spaced 1 to 2 months apart.

The theoretical training was provided in e-learning, available on the SAMU 92 website. The didactic presentation, in the form of a commented slide show including iconography and videography, was to be consulted before accessing hands-on workshops. Participants could consult the presentation as many times as necessary. It contained (i) the basics of ultrasonography: basic physics on ultrasound and beam formation, use of the equipment, transverse and longitudinal incidences; (ii) an anatomical reminder of the cervical region as well as its sonographic aspects; (iii) the techniques for tracheal−esophageal ultrasound; and (iv) the ultrasound loops with normal views, swallowing artifacts, tracheal intubation, and esophageal intubation.

A hands-on workshop then brought together one or two study investigators, a group of two to four participants and two models who could be learners in turn. The ultrasound device was composed of an ultraportable high-frequency linear probe (Lumify®, Philipps™) connected to a tablet computer (SAMSUNG™ A5). At the start of each hands-on workshop, one of the investigators recalled the ultrasound technique without demonstrating and then answered all possible questions. The models were placed in the supine position, each on a separate examination table. Each participant was placed between the two models with, at his side, the ultrasound device switched on in soft tissue mode, ready to use. He had to perform 10 tries, changing the model at each attempt.

The ultrasound technique involved several steps: (i) manipulation of the linear probe, (ii) transverse placement of the probe on the anterior cervical midline to visualize the trachea, (iii) sliding down to the jugular notch, and (iv) translating the probe to the left in order to visualize a tracheal−esophageal cross section.

Measurements

The investigator was responsible for collecting information from each participant by completing a specific form (Appendix 1). Participant characteristics included: age, gender, function, level of training in ultrasound, and frequency of usage: none, occasional (more than once a month), frequent (more than once a week). The frequency of usage was then split into regular (occasional or frequent practice) or no usage (none).

For each attempt, the acquisition time and the number of attempts to achieve a tracheal−esophageal cross section were recorded. The timer was started by the investigator as soon as the learner was taking the ultrasound probe (T0). When the learner thought he had obtained the tracheal−esophageal section, the timer was paused by the investigator (intermediate time, Ti). The investigator then controlled the ultrasound image and asked the model to swallow down to provoke an air artifact in his esophagus. In case of non-visualization of the artifact, the timer was restarted from Ti and a new attempt was counted. If the air artefact was visualized the test was terminated and Ti was the final acquisition time (final time, Tf).

If the image was still not obtained within 3 min, the investigator stopped the timer at Tf = 180 s. The try was then considered as completed and counted as a failure. A new explanation of the technique to the participant was carried out in another room, this time with a demonstration. The participant was then resuming his session of tries.

During the second hands-on workshop, 1 to 2 months after the first one, the frequency of use of tracheal−esophageal ultrasound since the first session was added to previous data.

Outcome

The main objective was to define the learning curve of ultrasound identification of a tracheal−esophageal cross section.

The secondary objectives were to assess the risk of unlearning, i.e., the level of knowledge retention, through time and to compare performance according to the level of ultrasound experience.

Analysis

Quantitative variables are expressed as mean and standard deviation or as median and interquartile range depending on the number of data and/or their distribution. They were compared by repeated data tests. Qualitative variables are presented as numbers and percentages. They were compared by chi-square tests, after checking the conditions of use.

The distribution of the image acquisition time not following a Normal law and its comparisons according to the test were carried out by a Friedman test. The effect size of the Friedman test was determined using a Kendall’s W test. Comparisons of image acquisition times as a function of several factors were made using mixed ANOVA type tests. The first kind of risk (alpha) was set at 5%. Analyses were performed using R software (version 3.6.0).

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