The study was carried out with the prior permission of the Institutional Scientific and Human Research Ethics Committee of the University of Pécs (7176 – PTE 2018). The investigation was performed at the Medical Skills Lab of Medical School, University of Pécs, Hungary. Based on previous studies, we defined both the devices to examine and the required minimum sample size. All participants provided written consent prior to the study. The following laryngoscopes were selected for our study: direct laryngoscopy with a Macintosh blade, size 4, (KaWe®, Asperg, Germany); (b) VividTrac® with an adult channeled blade (Vivid Medical, Palo Alto, USA); and King Vision®(KV) with a size 3 channeled blade (Ambu, Copenhagen, Denmark). For the previously estimated sample size, using α=0.05 and β=0.1, we calculated that the minimum of 44 participants is required for pairwise comparison of our results. For nonprofessionals without broad intubation experience, medical students were invited to participate in our study. Novice users took part in 15-minute trainings supervised by consultant anesthesiologist experienced investigators. During practice, participants acquired manual skills and theoretical knowledge to use each laryngoscope in the normal airway scenario and in the difficult airway scenario. The utilization of optimization maneuvers, the use of bougie, and the estimation of the Percentage of Glottic Opening (POGO) score were also explained and practiced. Their attention was drawn to the mechanism and the relevance of dental injuries. Airway trainings were carried out on the Laerdal® Airway Management Trainer (Laerdal®, Stavanger, Norway). The study was performed using an Advanced Life Support (ALS) simulator (Ambu® Man Advanced) during continuous chest compression by one of the study supervisors. Both the frequency and depth of chest compressions were in accordance with the protocol. This was verified by the provided Ambu ALS monitoring program. Two airway management scenarios were assessed. In the normal airway scenario (Scenario A), during continuous chest compression, head tilt was allowed, and in the difficult airway scenario (Scenario B), the cervical spine was immobilized with manual in-line stabilization (MILS) according to the advanced trauma life support algorithm. Each endotracheal intubation attempt was performed with a standard, 7.0 mm internal diameter, cuffed, plastic, endotracheal tube (Mallinckrodt®, Covidien, Dublin, Ireland). Participants were asked to perform intubation with each device in both scenarios in random order. The primary endpoint was successful endotracheal intubation. Additional endpoints included the number of intubation attempts, laryngoscopy time (LT), tube insertion time (TIT), and intubation time (IT); furthermore, the best achieved POGO was determined. We recorded esophageal intubation, tooth injury, and bougie application. The laryngoscopy time was defined from when the laryngoscope blade passed through the interdental line until the achievement of the best POGO indicated by the beginning of tube manipulation. Intubation time ranged from the passage of the tube through the interdental line to successful intubation. The difference between exploration and intubation time is tube insertion time. An attempt was considered unsuccessful if the attempt took more than 120 seconds or if the tube was removed from the oral cavity. The intubation failed after 3 unsuccessful intubations, if the participant did not recognize esophageal intubation, or if the participant gave up the attempt. After each scenario, we asked the participants to rate the devices on the basis of ease of technical use (1 = easy, and 5 = difficult), ease of physical use (1 = easy, and 5 = difficult) and willingness to reuse (1 = would never use again and 5 = would like to use) to the relevant scenario without ranking.
Statistical analysis
Analyses were conducted by Statistical Package for the Social Sciences (SPSS) Statistics software, version 22.0 (IBM Corporation, Armonk, NY, USA). Continuous and ordinal data are presented as the median and interquartile range(IQR), while categorical data are presented as raw numbers and as frequencies. Nonparametric tests were used since the data were not normally distributed, including the Kolmogorov-Smirnov and Shapiro-Wilk tests. The Kruskal-Wallis test and one-way ANOVA with Dunn’s post hoc test were used to assess pairwise differences between devices regarding the following variables: LT, TIT, IT, POGO score, ease of technical use, ease of physical use and willingness to reuse. Chi-square tests were used to evaluate differences between the categorical data results of devices regarding the rate of successful tracheal intubation, esophageal intubation, dental injury, and bougie usage. Values of P < 0.05 were considered significant.