Our research was reviewed and granted approval by the institutional research committee of the Singapore Armed Forces. For the purpose of this study, the VLs selected had to be portable, battery-operated with an attached screen, relatively inexpensive, and come with disposable blades for single use appropriate for the trauma victim in an austere environment. Based on the above parameters, the research team selected the King Vision Laryngoscope and the McGrath Video Laryngoscope (MG), to be compared against the DL using a Macintosh size 3 blade in the management of simulated difficult airways (See Fig. 1). The King Vision Channeled Blade Laryngoscope (KVC) and the King Vision Non-Channeled Blade Laryngoscope (KVNC) were evaluated to investigate if channeled blade resulted in any differences in intubation success rates when used by junior medical officers with limited intubation experience.
For this study, we recruited 133 medical officer cadets of the Singapore Armed Forces (SAF) from 2016 to 2017. These doctors were 2 to 3 years post-graduate and would have undergone at least 3 months of anesthesia or emergency medicine department rotations. Written informed consent forms were obtained from all study participants prior to participation in the study.
A standardized simulated difficult airway scenario was created for the participants by activating the tongue-swelling feature in the SimMan® 3G manikins with a standard cervical collar applied for cervical immobilization (See Figs. 2 and 3). To simulate trauma conditions, participants had to intubate the manikins placed on a stretcher lying on flat ground with a standard size #7 ETT.
All participants were shown a training video on the use of KVC, KVNC, and MG. They also had to undergo a familiarization session with the SimMan® 3G manikins where the authors demonstrated intubations on the manikins.
Each participant was given 1 attempt for direct laryngoscopy of the SimMan® 3G manikin placed on a stretcher on the ground for which the time to intubation (TTI) was recorded. TTI was defined as time from when the participant picks up the laryngoscope to when successful tracheal intubation was confirmed by chest rise with manual ventilation via the ETT. Each participant then progressed to use the KVC, KVNC and MG following a sequence based on a 3-period, 3-treatment crossover design (see Table I) to minimize the learning effect of successive intubations on a similar manikin. This meant that Participant #1 was given sequence A, Participant #2 was given sequence B… and Participant #6 was given Sequence F. This cycle would restart again when we reached Participant #7, would be given Sequence A.
Table I. 3-period, 3-treatment crossover design
Sequence | Period 1 | Period 2 | Period 3 |
A | MG | KVC | KVNC |
B | MG | KVNC | KVC |
C | KVC | KVNC | MG |
D | KVC | MG | KVNC |
E | KVNC | KVC | MG |
F | KVNC | MG | KVC |
In the event of oesophageal intubation, the participant was allowed to remove the ETT and re-attempt with no pause in the elapsed time, until either successful intubation was achieved or if 90 seconds had elapsed. A failed intubation was defined as failure to secure the ETT in the trachea within 90 seconds.
Data was collected and analyzed using Statistical Package for the Social Sciences (SPSS). Comparison of success rates was analyzed using Chi-squared tests. Analyses of continuous data (time to visualization and time to intubation) were done using paired t-test. A p-value of < 0.05 was considered significant.