A written informed consent will be obtained from all study participants. Only qualified paramedics will participate in the study. Their experience varies between four and eight years of practice after completion of paramedic training. All study participants had never used the flexible-tip bougie but had a routine intubation experience with the standard gum elastic bougie (more than 40 intubations previously performed).

A 10-minute lecture will be delivered before the start of the study. It will explain how to use the STIG. Following the lecture all participants will be able to familiarise themselves with the equipment and practice for 30 minutes. A skill station will be set up containing an intubation manikin AT Kelly Torso (Laerdal Medical AS, Stavanger, Norway). A reduced movement of the cervical spine will be achieved by application of a Patriot® cervical collar (Össur hf., Reykjavik, Iceland). After completion of the initial practice the intubation manikin with the cervical collar on wall be placed on and secured to the driver's seat of a FIAT Bravo car (FIAT S.p.A., Turin, Italy). The car will then be positioned on its left side and secured in place by firemen from a local fire brigade. The access to the manikin will only allowed from the front i.e. through the opening created after removal of the windscreen. A single digit number will be allocated to each of the two studied devices i.e. 1 for the flexible-tip bougie and 2 for the standard gum elastic bougie (SUMI Sp. z o.o., Sp. K., Sulejówek, Poland). Each study participant will be asked to randomly give a number (either 1 or 2) and will then be given the corresponding tracheal tube introducer to use. The maximum number of intubation attempts is limited to three per device. The time required to intubate and successfully ventilate (Ti) the manikin will be recorded. It will be measured using a stopwatch of a mobile phone (Apple Inc., Cupertino, California, USA). Efficacy of intubation and the ease of use by the operator will also be assessed. The latter will be measured using an 11-point numerical rating scale (NRS) where 0 corresponds to a very difficult to use device and 10 indicates an easy to use and user-friendly introducer. Size 7.5 tracheal tube (SUMI Sp. z o.o., Sp. K., Sulejówek, Poland) will be utilised in the study. A manual resuscitator (Ambu A/S, Ballerup, Denmark) will be used for ventilation and will be readily available to the paramedics. The standard Macintosh-blade laryngoscope (New Waseem Trading Co., Sialkot, Pakistan) will be utilised for direct laryngoscopy. Size three blade will be used. The study participants will perform all intubations with each of the two tracheal tube introducers. A failed intubation will be defined as an attempt during which the trachea cannot be intubated or an attempt that lasts longer than 120 seconds. Only those who failed to intubate will be allowed another attempt. All the obtained data will be analysed using Microsoft Office Excel 2021 spreadsheet (Microsoft Corporation, Redmond, WA, USA) and GraphPad Prism (GraphPad Software, Boston, MA, USA). The Kolmogorov-Smirnov test will be utilised to determine whether the analysed variables matches the characteristics of a normal distribution. A paired Student t-test and the Wilcoxon signed-rank test will be used for data analysis. Based on our previous unpublished pilot study and assuming that the overall success rate of intubation in patients with a difficult airway will be 90% (α =0.05, 2-sided, β =0.1), 46 participants are required. The final adjusted sample size, allowing a drop-out rate of about 10%, will be 50 and this is the final number of participants enrolled into the study. A p value of less than 0.05 (p\<0.05) is considered statistically significant.