Study design and time period
After ethical board approval (State Physicans’ Chamber of Rhineland-Palatinate, Registration Number: 2018–133,000-E., 18. May 2018), we conducted a randomised two-armed simulation research study with medical students as unbound samples. One group applied the FT-LM, and the other group applied the ILTS-D2 at a 1:1 ratio regarding the number of participants in both study groups. The study was conducted in our departmental simulation centre in June 2018.
Participants
Medical students in their final year of medical school represent a sample with good theoretical knowledge but a lack of clinical experience and are therefore recommended for using extraglottic devices in emergency situations. A total of 126 medical students were recruited during their mandatory practical training periods.
ILTS-D2
The revised ILTS-D2 differs from its predecessor in a number of regards [4, 5]; for the sake of clarity and conciseness, all cited lengths are measured from the tip (placed in the oesophagus entrance) along the convex frame of the device. The ILTS-D2 is 27 cm, thus 1 cm shorter than its predecessor. In both devices, the oesophageal cuff is similar, and the laryngeal orifice for ventilation and tube guidance is positioned from 6.5 cm to 9.5 cm from the distal margin. In comparison to the iLTS-D, the pharyngeal cuff of the ILTS-D2 is 2.5 cm more proximal and shorter in its longitudinal dimension (iLTS-D: 7.5–14.5 cm, ILTS-D2: 9.5–16 cm). Thus, the distance between the proximal and the distal cuff is longer in the ILTS-D2 than in its predecessor (iLTS-D: 6 cm, ILTS-D2: 7.5 cm). The ILTS-D2 is slightly wider between the cuffs than the iLTS-D (Fig. 1). Both devices fit sizes 4 and 5 of a classical laryngeal tube and indicate that the maximum size of tracheal tube that can be applied though the device is 8.0. A separately delivered 100 ml syringe for inflating the cuffs is colour coded according to the different sizes. A separately delivered tube can be inserted into the trachea through the laryngeal orifice that is shaped as a ramp. The angle of the tube guidance is approximately 35 to 40 degrees. The ILTS-D2 covers conventional laryngeal tube sizes 2 to 5 [7].
The ILTS-D2 is introduced along the hard palatinate until an elastic resistance indicates a proper fit in the oesophageal entrance. After inflation of the cuffs by the colour-coded syringe, extraglottic ventilation can be established. Then, the tube can be inserted through the device into the trachea.
Fastrach™
The FT-LM is an established device evaluated for extraglottic and tracheal airway management [8]. We used the size 4 FT-LM with the provided tracheal tube.
Manikin
We used the Laerdal Kelly™ ALS (Laerdal® Medical AS, Stavanger, Norway) manikin for this study. Manikins cannot completely replicate human anatomy. However, we have chosen this manikin because its airway offers one of the closest replications of the human anatomy for airway management simulation [9]. The manikin was placed on an emergency room stretcher, and the thorax was exposed.
Data collection
After written informed consent was signed, the following demographic data were recorded: gender, age, and previous experience in airway management in patients: number of applications of 1) tracheal intubations, 2) laryngeal masks and 3) laryngeal tubes. Furthermore, professional qualifications such as paramedic, specialised nurses in anaesthesiology, medical clerkships and electives in anaesthesiology were protocolled. The participants were then randomised by flipping a coin to represent either the ILTS-D2 or the FT-LM. Each participant was familiarised with the particular device by a standardised introduction.
Only the allocated device was shown to the participant. The lubricated device with deflated cuffs, the appropriate tracheal tube, the syringe and the ventilation bag were placed on a table directly beside the manikin. First the extraglottic application then the tracheal intubation were explained by Peyton’s four-step approach: 1) demonstration in real time, 2) deconstruction (explanation and clarifying questions), 3) comprehension (explanation from participant to instructor), 4) execution by the participant [10]. The last step (execution) constituted the first of five attempts to place the device.
A total of five consecutive attempts were performed by each participant with one device. A stopwatch was started as soon as the participant touched the device and was stopped when the first chest rise was detectable [11]. After that, the stopwatch was started again as soon as the participant touched the tracheal tube and was stopped when the first chest rise was detectable. For both extraglottic ventilation and tracheal intubation, the time was not censored. However, censoring would occur due to the participants’ discontinuation. The instructors were not allowed to help during the attempts. If there was a chest rise, the attempt was counted as successful. If there was no chest rise or if the participant himself or herself discontinued the attempt, the attempt was counted as unsuccessful.
Outcome measures
The primary endpoint was the time to ventilation in seconds (s) of extraglottic attempt five. Secondary endpoints were time to ventilation and intubation of all other attempts and success rates.
Sample size
In March 2018, our sample size was determined by the actual number of students beginning the semester, 134, out of which 126 were recruited. The median time to ventilation using the Fastrach in our previous study (used as pilot data) for extraglottic ventilation was 20 s with a standard deviation of 5 s [4]. A reduction of 3 s was considered a clinically relevant difference in time for application of an airway instrument in the fifth attempt. With 63 participants per group, a difference in the medians of 3 s would have been detected with a power of 90.39% using a two-sided, level α = 0.05 Wilcoxon rank-sum test.
Randomisation and blinding
Randomisation was performed by a coin flip (heads or tails) by two of the authors (TO and KT) before data collection. Heads was allocated to FT-LM and tails to ILTS-D2; this allocation was alternated every 20 participants. To gain an equal distribution of the level of previous experience, randomisation was stratified by professional qualification, clerkships and electives at a 1:1 ratio with regard to the devices. The participants could not be blinded to the devices for airway management because they had to apply the device.
Statistical analysis
We used Microsoft Excel 2010 (Microsoft® Corporate Headquarters, Redmond, USA) and IBM SPSS Statistics Version 23 (IBM®, Ehningen, Germany). Considering that the data are non-normally distributed, data are shown as medians, interquartile ranges (IQRs), minima and maxima.
As no censored observations were present for the data of the primary endpoint (time to ventilation in attempt five of extraglottic application), the two groups were compared by a two-sided Wilcoxon rank-sum test. A p-value < 0.05 was considered statistically significant.
Regarding the secondary endpoints, censored observations were present for a few participants. Hence, group comparisons for the secondary endpoints were conducted either with a two-sided Wilcoxon rank-sum test if no attempts were discontinued by participants or with the log-rank test if attempts were discontinued by participants. P-values for secondary endpoints are given for exploratory reasons only.