A comparison of Macintosh and video laryngoscopy performed with a prototype rigid anterior 1 commissure laryngoscope by experienced and novice users in a manikin model 2

Background. Intubation is a life-saving skill that can be difficult to learn and perform. Objective. The intubation time and user preference of four intubation techniques, performed by novices or 28 experienced individuals, were compared. 29 Methods. Enrolled participants were randomly assigned to one of four simulated intubation groups. Each 30 groupfirstperformed intubation on the manikin airway without modifications (‘easy’ airway), followed by the 31 same technique on a manikin with modifications to mimic a ‘difficult’ airway. The primary outcome measure 32 was the time taken to inflate the manikin’s lungs with the bag ventilator, with successful intubation. 33 Results. Ninety-eight participants were recruited and grouped according to experience: 59 novices (10 or fewer 34 live intubations) and 39 experts (more than 10 live intubations). The total time to intubation increased 35 significantly from the easy airway to the difficult airway for both expertise levels, and for all intubation 36 techniques except the novel laryngoscope. 37 Conclusion. Repeated exposure to multiple intubation devices can result in an adequate learning curve for the 38 novice participant. The novel laryngoscope is an uncomplicated intubation tool; in this study, itprovided novice 39 users who intubate infrequently with a better chance of successful intubation in manikins. 40 41 42


Introduction 96
Intubation is a life-saving skill that can be difficult to learn 1,2 and retain. 3,4 Intubation protects the airway, 97 prevents hypoxia and death, and is a vital procedure in the operating theatre, as well as in emergencies where a 98 patient's airway may be compromised. Conventionalmethods of intubation include using Macintosh, Miller or 99 video-assisted laryngoscopes, which can all be used with or without the assistance of a bougie. These tools have 100 This study utilised atechnological enhancement of the rigid anterior commissure laryngoscope.Thisnovel 114 laryngoscope wasdevelopedto be a more favourable alternative for the 'non-ideal setting',where fibre-optic or 115 video laryngoscopes are not available, and for patients witha difficult or traumatic airway. The standard metal 116 anterior commissure laryngoscope used in the operating theatre requires a light box, a fibre-optic cable and a 117 Hopkins light carrier that attaches to the laryngoscope. The novel laryngoscope design is based on the metal 118 anterior commissure laryngoscope commonly used by ENT surgeons, but also has a translucent tube and unique 119 light delivery system that radiates light within, through and out of the distal end of the tube, making it more 120 resistant to visual obstruction from airway secretions and blood. The novel laryngoscope is a battery powered, 121 self-contained, lightweight laryngoscope, with a built-inlight-emitting diode light source arranged in a ring at the 7 proximal end of an enclosed clear circular tube (Figure 1). The barrel is a clear enclosed tube measuring 14cm in 123 length from the front of the handle to the tip of the tube. The barrel was made using rapid prototyping with 124 polycarbonate plastic. The handle, which contains the light-emitting diodes and battery, was developed with 125 three-dimensional printing technology. An on-off switch was placed within the handle. 126

127
The novel laryngoscope method utilises a Seldinger technique,which requires the use of a bougie. The bougie is 128 passed through the lumen of the scope past the vocalfolds, the scope is removed with the bougie in place, and 129 then a endotracheal tube is passed over the bougie into the trachea before the bougie is removed. 14 The unique 130 anterior commissure design,with its angled flared open end,gives the user a view of the vocal folds with a direct 131 9 straightline of sight,which allows guidance of the bougie past the glottis and into the tracheaunder direct 133 visualisation ( Figure 1). The design and technique may decrease instances of accidental intubation of the 134 oesophagus, failure to visualise the glottis, and loss of adequate lighting because of secretions and blood. 135 136 ENT surgeons have practised this method of rescue intubation for decades, but because of the capital equipment 137 required, it has not been used by other specialistsor outside of the hospital setting. This process has been 138 advocated in ENT and anaesthesia literature as a rescue technique when patients are unable to be intubated using 139 routine methods. [15][16][17] We hypothesised that the novel laryngoscope intubation technique would 140 bestraightforwardto learn, and would involvea more natural transitioning processwhen a clinical situation 141 changes from an easy to a difficult airwaywith no change in technique or equipment. 142 143

Methods 144
The University of Oklahoma Institutional Review Board approved this study with the requirement of written 145 consent for participants in the trial. Participants were recruited using flyers posted within the hospital and 146 medical school. This project included individualswith varying experience at performed intubations, ranging from 147 no experience atintubating to performing intubationsdaily. The study data were stratifiedaccording to 148 participants'expertise:those who had performed more than 10 intubations were classed as experienced, and those 149 who had performed 10 or fewer intubations were considered to have little or no experience.This prospective 150 study was conducted between August 2015 and May 2017. The study used a balanced crossover design wherein data were stratified according to participant expertise 160 (expert and novice), and was designed to ensure a balance of participants assigned to each intubation sequence. 161 Study participantswere allowed three attempts with each of the four intubation techniques, beginning with the 162 manikin with a normal (easy) airway and then moving on to the difficult airway. Every participant had a total of 163 24 intubation scenarios. The trial was randomised by giving each participant a random number that correlated 164 with a unique order in which each technique would be tested on the studymanikins. 165

166
The trial involved the use of: a conventional laryngoscope with a Macintosh 3 blade, with or without a bougie; a 167 GlideScope Advanced Video Laryngoscope (Verathon, Bothell, Washington, USA); and the novel laryngoscope. The ease of which a glottic view could be obtained was measured by recording the time participants required to 186 declare they had a 'good view' of the vocal folds and were ready to place the endotracheal tube or bougie. This 187 meant the participants could see the glottic opening; however, no assessment was made regarding the degree of 188 glottic opening such as by using the Cormack-Lehane classification. 189

190
Participants were asked to rank each intubation method (1 to 4 for all techniques,with 1 reflecting the most 191 preferred method)in terms of the quality of the light source, view of the glottis, perceived intubation difficulty 192 and overall preferred method of intubation, for both the easy and difficult airway scenarios. 193 194

Statistical analysis 195
A randomised, balanced, crossover design was used. In order to reduce learning curve bias, participants were 196 randomised to one of the 24 possible tool sequences. Linear mixed regression models for repeated measures 197 were used to estimate the laryngoscope's effect on timing outcomes, while controlling for other covariates. Mean 198 rankings of the users' preferences were computed and compared via chi-square tests for each intubation tool 199 overall, and for each tool by gender, handedness and experience level.

Primary hypothesis 206
We evaluated the ease of learning the novel laryngoscope technique versus the reference intubation techniques 207 for each airway. The three reference intubation techniques were the Macintosh laryngoscope, with and without a 208 bougie; and the GlideScope Advanced Video Laryngoscope. Each method was evaluated on a manikin ineasy 209 and difficult airwayscenarios. The change in the total time taken to intubate between the attempts for each 210 technique determined the ease of learning for each laryngoscope method. The primary research hypothesis that 211 the novel laryngoscope method is easier to learn was tested by measuring the intubation time between attempts. 212 In orderto support the hypothesis, the duration of each intubation attemptusing the novel laryngoscope needed to 213 decrease at a significantly faster rate than that of the reference intubation techniques. 214 215 Subjective data on each intubation method were also obtained; this information was used to test secondary 216 research hypotheses regarding the preferred technique and the perceived difficulty of each method. 217 218

Results 219
Ninety-eight participants were recruited and grouped according to their intubation experience: 59 (60.2%) were 220 novices(10 or fewer live intubations) and 39 (39.78%) were experienced (more than 10 live intubations). Table 1  221 demonstrates the demographic data of the participants. The vast majority were right-handed (50% medical 222 students and 34.7% residents in training). The 'other' category included a physician assistant and non-medical 223 staff such as administrative personnel. Four participants were excluded, as their data were either not recorded or 224 were recorded incorrectly.   Study participants who accidentallyintubated the oesophagus, aborted attempts or took longer than 90 seconds to 276 intubate were recorded as a 'fail'. Table 3 demonstrates the instances of accidental oesophageal intubations and 277 failed attempts for both the easy and difficult manikin scenarios,according to level of expertise. There were 278 numerous oesophageal intubations when using the novel laryngoscope.Unfortunately, we did not record on 279 which attempt these accidental intubations occurred with any of the laryngoscopes used. We did note that when 280 participants were using the novel laryngoscope,oesophageal intubations mainly occurred on the initial attempt; 281 nevertheless, all failures and oesophageal intubations were recorded together for all attempts,so we are unable to 282 show any improvement with each use.The numbers in the table represent participants who had at least one 283 oesophageal intubation and/or failed attempt for each of the methods used throughout the study, as participants 284 had three opportunities to performeach technique. 285 286

Participants'preferences 287
Participants were asked to assess their preferences regarding the four different techniques. Each laryngoscope 288 and its features were ranked 1 through 4 in various categories, with '1' being the most preferred and '4'being the 289 least preferred. Preferences were recorded for the entire group for both easy and difficult scenarios, as well as by 290 level of experience in both easy and difficult scenarios. 291 292 Table 4 shows the participants' preferences for the techniques, in both airwayscenarios. For both the easy and 293 difficult scenarios, not all techniques were equally preferred (p<0.0001 and p<0.0001, respectively). 294 Specifically, for the easy scenario, the mean rankings were the lowest (most preferable) for the Macintosh 295 laryngoscope, followed by the GlideScope, novel laryngoscope, and then the Macintosh withbougie (rankings of 296 2.11, 2.31, 2.57 and 3.02, respectively). The novel laryngoscope was favoured by female participants (ranking of 297 2.65 for males and 2.42 for females; p = 0.0386) and by novice participants (ranking of 3.17 for experts and2.18 298 for novices; p = 0.0069). For the difficult scenario, the mean rankings were the lowest (most preferable) for the 299 GlideScope, followed by the novel laryngoscope, Macintosh with bougie, and Macintoshlaryngoscope (rankings 300 of 1.71, 2.14, 2.89 and 3.27, respectively). The novel laryngoscope was the most preferred method for novice 301 users in both the easy and difficult airway scenarios (Tables5and6). Novice users reported a significantly lower 302 mean ranking (most preferable) for the novel laryngoscope (ranking of 1.92) in thedifficult airway scenario than 303 the expert users (ranking of 2.48; p = 0.0165)( Table 6). In the difficult scenario,the novel laryngoscope had a 304 trend towardsa more preferable mean ranking than that of the Macintosh or Macintosh with bougie,across 305 gender, handedness and experience level.The novel laryngoscope was also ranked second out of the four 306 methods for novice users in terms of light source, ease of use andview of the glottis, and was the overall 307 preferred method (Table 6). In the difficult airway scenario, experienced users preferred the GlideScope overall, 308 followed by the novel laryngoscope. For experienced participantsin the easy scenario, the most preferred method 309 was the Macintosh blade (ranking of 1.57); the novel scope was the least preferred (ranking of 3.17) ( Table 5). Intubation is a challenging skill to learn. 1,2 This study suggests that the novel laryngoscope is easier for those 342 individuals with limited intubation experience to use competently and effectively within a manikin simulation, 343 compared with other tools. However, the novel laryngoscope was not the quickest intubating device, in either the 344 easy or difficult airway scenario.This is because the novel laryngoscope technique first requires the insertion of a 345 bougie into the airway,prior to insertion of the endotracheal tube(i.e. Seldinger technique). The use of a bougie 346 adds to the total time required for intubation,and this additional 'bougie use' time was not measured during this 347 study. Previous studies comparing intubation with or without the use of a bougie suggest that its use adds a 348 median time of 10-14 seconds onto the intubation time. 18,19 In bothof those studies, however, the use of a bougie 349 contributed to improved 'first pass success.'In a recent randomised clinical trial, performed on patients with 350 difficult airways in the emergency department, the use of a bougie was associated with a significantly higher 351 'first-attempt' success rate than the use of an endotracheal tube and stylet (96% vs 82%). 20 352 353 Along with having the most significant reduction in time to intubation between the first and secondattempts, the 354 novel laryngoscope users also demonstrated a reduction in the time to intubation between the easy and difficult 355 airway scenarios compared to the other groups( Figure 4). This result reached statistical significance. These 356 findings suggest that with the novel laryngoscope, learners find it is easier to utilise skills acquired on amanikin 357 in an easy scenario andcan perform intubation more easily inchallenging airways when compared to other 358

laryngoscopes. 359 360
This study has shown that in relatively routine cases, the Macintosh blade will suffice. The overall preferred 361 device used on the manikin in the difficult airwayscenario was the GlideScope,followed by the novel 362 laryngoscope. The GlideScope also demonstrated the quickest times for intubation in the difficult airway 363 scenario. Those experienced in intubating patients are familiar with the GlideScope, andthis device has been 364 introduced into the hospital operating theatre setting for cases with difficult airways. 365

366
The current study is the first to give users an opportunity to use the novel laryngoscope. We do not find it 367 surprising that inexperienced users preferred the novel laryngoscope, as the method is simple, and the user has a 368 straight line of sight to the glottis to pass the bougie through. Novice users also have no dogma regarding 369 intubation with traditional laryngoscopes with their use in an anterior-superior direction. The novel laryngoscope 370 involves gentle pressure against the upper teeth and gums, which allows the scope to obtain a laryngeal axis 371 more easily. In contrast, other methods utilise anupwards and forwards movement to displace the tongue, in 372 order to obtain a view of the glottis and to avoid damaging teeth. The tongue does not need to be swept aside to 373 intubate a patient when using the novel laryngoscope, and access can be attained on either the left or right side of 374 the mouth.Individuals learning how to intubate patients are currently taught to stay off the teeth, but can easily 375 damage the teeth because of the standard blade's high profile and metal construction. 21 It should be stated that 376 ENT surgeons routinely place rigid metal laryngoscopes against the teeth and gums using a tooth guard,exerting 377 significant pressure against them,and rarely encounter tooth damage. The amount of pressure applied to the teeth 378 and gums with the anterior commissure scope for intubation,by contrast,is minimal. Our study also showed no difference between novice and experienced participantsin terms of vocalfold 391 visualisation ( This lack of experience is often evident in cases where the glottic larynx is visualised but the user cannot pass 395 the endotracheal tube through the vocalfolds. This may account for the novel laryngoscope being the most 396 preferred tool for intubation in the novice group for both the easy and difficult manikin scenarios (Tables 5  397 and6), whereas experienced users preferred the Macintosh blade forthe easy scenario and the GlideScope for the 398 difficult airway. It should be noted that the novel laryngoscope was thesecond preferred choice (after the 399 GlideScope) for experienced users in the difficult airway manikin, which is important if a GlideScope or another 400 video laryngoscope is not available or fails to function. Ultimately, the novel laryngoscope will be at a 401 disadvantage in any study of intubation timing because of the need for a bougie, to gain access through the 402 vocalfolds. Nevertheless, in this study, we have shown that the novel laryngoscope method was the quickest to 403 learn (Figures 3and 4),and that there was no statistical difference in the time taken to intubate the manikin from 404 the easy to difficult scenario (Table 2). 405 406 Table 2also showed that the different techniqueswere associated with variable intubation times in the easy 407 airway scenario, whereas in the difficult airway scenario the Macintosh with bougie and the novel laryngoscope 408 had similar times. This is not surprising,as both of these methods require the use of a bougie, and there is an 409 obvious time increase associated with its use. 410

411
Experienced participants had no significantdifficulties in the easy airway scenario, but we found it interesting 412 that a number of them did have problemsinthe difficult airwayscenario. In addition, some novice participants 413 experiencedissues in the difficult scenario for the process of intubation itself (i.e. passing the endotracheal tube). 414 415 Intubation failures for the GlideScope concerned not being able to pass the endotracheal tube through the 416 vocalfolds even though they were visualised.Regarding the Macintosh with bougie and the novel laryngoscope, 417 whichboth required use of a bougie, investigators noted that when the participant picked up the bougie, they did 418 not keep the scope in position or reposition the scope to view the vocalfolds, even though they had visualised 419 them before obtaining the bougie. In this study, there was no assistant to pass a bougie to the participantand they 420 sometimes had to look away from the scope to obtain it from the table. These participants were then noted to 421 pass the bougie in some cases without looking down the scope again, so the bougie was not seen to pass the 422 vocalfolds initially. This may explain the high total number of accidental oesophageal intubations in this group. 423 Unfortunately, we cannot discern from the data on which attempt these oesophageal intubations occurred. 424 Participants were quick to learn that the use of a bougie requires direct visualisation of the glottic larynx, and, 425 just as importantly, direct visualisation of the passage of the bougie past the vocalfolds, in order for the 426 The need for a reliable, safe, easy to use and transportable laryngoscope is apparent in the medical and 479 emergency medical services community, as there is still a high incidence of failed intubations. 23 Difficult 480 airways are common in the emergency situation,accounting for 20% or more cases. Although studies have 481 assessed the extent of training needed to perform endotracheal intubation, 1,2 there is no clear consensus regarding 482 the amount and type of training required to prepare someone in an emergency. This study has shown that the 483 novel laryngoscope is an easy-to-handle intubation tool, with a simple and easy-to-learn technique.The novel 484 laryngoscope lends itself to novice users who intubate infrequently. Its usemay increase the chance of successful 485 intubation outside of the operating theatre and in difficult airway situations. We believe future study designs 486 should endeavour to assess the novel laryngoscope against other laryngoscopes in an appropriate,institutional 487 review board approved, patient study.  Data represent mean subjective use ratings, with 1 being the highest rated to 4 being the worst rated (numbers in 539 parentheses indicate the rank of the device within the row).  Data represent mean subjective use ratings, with 1 being the highest rated to 4 being the worst rated (numbers in 545 parentheses indicate the rank of the device within the row). 546 28 547 548 Table 6.Participants' ratings of techniqueratings in difficult airway scenario according to intubation experience 549 Data represent mean subjective use ratings, with 1 being the highest rated to 4 being the worst rated (numbers in 550 parentheses indicate the rank of the device within the row). 551