Intubation with channeled versus non-channeled video laryngoscopes in simulated difficult airway by junior doctors in an out-of-hospital setting: A crossover manikin study.

Failure to secure the airway is an important cause of morbidity and mortality during resuscitations. We compared the rate of successful intubation of the King Vision™ aBlade™ channeled and non-channeled video laryngoscopes, and McGRATH™ MAC video laryngoscope when used by junior doctors to intubate a simulated difficult airway in an out-of-hospital setting. 105 junior doctors were recruited in a crossover study to perform tracheal intubation with the three video laryngoscopes on a simulated difficult airway using the SimMan® 3G manikin. Primary outcome was the rate of successful intubations. Secondary outcomes were time-to-visualization, time-to-intubation and ease of use. Rates of successful intubations were higher for King Vision channeled and McGrath compared to the King Vision non-channeled (85.7% and 82.9% respectively versus 24.8%; p<0.001). Amongst the participants who had successful intubations, King Vision channeled and McGrath had shorter mean time-to-intubation compared to the King Vision non-channeled (41.3±20.3s and 38.5±18.7s respectively versus 53.8±23.8s, p<0.004;). There was no significant difference in the rate of successful intubation and mean time-to-intubation between King Vision channeled and McGrath. The King Vision channeled and McGrath video laryngoscopes demonstrated superior intubation success rates compared to King Vision non-channeled laryngoscope when used by junior doctors for intubating simulated difficult airway in an out-of-hospital setting. We postulated that the presence of a guidance channel in the King Vision channeled laryngoscope and the familiarity of the blade curvature and handling of the McGrath could have accounted for their improved intubation success rates.

RCT Entities:   Population Interventions Outcomes

Introduction

Failure to secure the airway is an important cause of morbidity and mortality during resuscitations [1,2]. Video laryngoscopes have been consistently demonstrated to be critical in difficult or failed intubations [3-5] and have been incorporated into many difficult airway algorithms [6-8].

The earlier generation of video laryngoscopes were expensive, bulky, and required familiarization training [9]. This precluded widespread use of video laryngoscopes apart from specialised areas such as operating rooms and intensive care units [10]. Newer video laryngoscopes are now more portable, with some models incorporating additional features such as the channeled blade. The presence of this channel can help to reduce the need for complex manipulation of the tracheal tube during intubation [11-12]. Although there are many studies comparing the intubation efficacy of different video laryngoscopes, few studies have compared the success rate and ease of use of the channeled versus non-channeled video laryngoscopes when used by junior doctors in an out-of-hospital or military setting [12-14].

Our primary aim was to compare the rate of successful intubation of the channeled and non-channeled blade video laryngoscopes when used by junior doctors to intubate a simulated difficult airway. Secondary outcomes assessed included time-to-visualization of glottis, time-to-intubation and ease of use of the video laryngoscopes. We also investigated the impact of blade curvature of the non-channeled video laryngoscope blades on their intubating efficacies.

Materials and methods

A crossover study was conducted from January 2016 to March 2017. Study was approved by local institutional research committee SAF Joint Medical Conference (Research) BB52/12-4 on 2 Aug 2015. Written consent was obtained from participants.

All junior doctors from the Medical Officer Cadet Course of the Singapore Armed Forces were considered for this study. Junior doctors were defined as post graduate year two or three medical officers with 10 or less previous intubation attempts in real-life patients. Exclusion criteria were medical officers with more than 10 previous intubation attempts in real-life patients, refusal to give written informed consent or non-physician medical officers.

In this study, we used the acute angled channeled and non-channeled blades of King Vision™ aBlade™ (King Systems, Noblesville, IN, USA) video laryngoscope, and the Macintosh styled blade of the McGRATH™ MAC (Aircraft Medical, Edinburgh, UK) video laryngoscope. We chose the King Vision video laryngoscope because of its cost, portability and design for use in patients with limited mouth opening (≥18mm and ≥13mm for the size 3 channeled and non-channeled blades respectively [15]) and restricted neck movement. These are important considerations in the management of difficult airway in an out-of-hospital or military setting. We also compared King Vision non-channeled with McGrath video laryngoscopes as McGrath uses a Macintosh blade design with a curvature that is less angled than that of King Vision.

All participants had to watch a standardised training video on the laryngoscopy technique using all three video laryngoscopes. We played the training video for KingVision (02m:05s) first, before the Mcgrath teaching video (00m:25s). The participants then undergo a familiarization session with the SimMan advanced patient simulator manikin prior to the start of the simulation session. To minimize the effects of time and fatigue, all the sessions took place during office hours, and none of the participants were post-call/ sleep-fatigued when participating in the study.

The participants intubated with each of the three devices following a sequence based on a 3-period, 3-treatment crossover design (Table 1) to minimise the learning effect on subsequent intubation attempts [11,14,16]. All participants were allowed up to 90 seconds to achieve tracheal intubation in a standardised simulated difficult airway scenario for each device. In the event of an oesophageal intubation, the timer continued and participants were allowed repeated attempts at intubation, up to a maximum of 90 seconds.

Table 1

Intubation sequence based on a 3-period, 3-treatment crossover design.

Sequence	Period 1	Period 2	Period 3
A	McGrath	King Vision channeled	King Vision non-channeled
B	McGrath	King Vision non-channeled	King Vision channeled
C	King Vision channeled	King Vision non-channeled	McGrath
D	King Vision channeled	McGrath	King Vision non-channeled
E	King Vision non-channeled	King Vision channeled	McGrath
F	King Vision non-channeled	McGrath	King Vision channeled

Successful intubation was defined as the ability to achieve tracheal intubation within 90 seconds and was demonstrated with the inflation of the manikin’s lungs with a manual resuscitator. Time-to-visualization was defined as the time from taking hold of the laryngoscope handle to the visualization of the glottis by the participant. Time-to-intubation was defined as the total time taken from holding the laryngoscope handle to the confirmation of tracheal tube position by inflation of the manikin’s lungs. Upon completion of the simulation session, participants were asked to indicate their preferred device in an outfield setting and to rate the ease of use of the video laryngoscopes using a Likert 5-point scale (1 = very easy, 2 = easy, 3 = moderate, 4 = difficult, 5 = very difficult) in an anonymous survey.

A consistent difficult airway scenario was simulated by activating the tongue-oedema feature in the SimMan manikin and by placing a standard cervical collar for cervical immobilisation (Fig 1). The participants also had to intubate the manikin on the ground, simulating intubation in an out-of-hospital setting. All tracheal intubations were performed using the size 3 blade for each of the three video laryngoscopes and a standard size 7 Portex® tracheal tube in the SimMan® manikin. A pre-formed stylet was inserted into the Portex® tracheal tube for intubation with the King Vision non-channeled and McGrath laryngoscopes, while no stylet was used with King Vision channeled laryngoscopes.

Fig 1

(A) Demonstration on the use of the King Vision™ laryngoscope and (B) visualization of vocal cords in the SimMan® 3G manikin during the difficult airway scenario.

A pilot study conducted earlier with 21 junior doctors showed a rate of successful intubation of 85% when using the McGrath in the SimMan® simulated difficult airway scenario. A power analysis was done to determine sample size based on this pilot study. We hypothesised that the King Vision channeled video laryngoscope will improve rate of successful intubation for junior doctors by 10% in the SimMan® simulated difficult airway scenario. Using a two-sided alpha level of 5% and statistical power of 80%, the required sample size to detect a 10% difference in the rate of successful intubation between the groups was calculated to be 77.

Statistical analysis was performed using SPSS Version 24 (SPSS Inc, Chicago IL, USA). The normal distribution of data was tested using the Shapiro-Wilk test. Comparison of success rates was analysed using Chi-squared tests. Analyses of continuous data were performed using one-way ANOVA (for parametric data) and independent-samples Kruskal-Wallis test (for non-parametric data) with Bonferroni correction. The ease of use of video laryngoscopes was analysed using Kruskal-Wallis test. A p-value of < 0.05 was considered significant.

Results

A total of 105 junior doctors were recruited in this study. The median number of successful real-life intubations performed based on recall amongst participants was three. None of the participants had used the King Vision and McGrath laryngoscopes for real-life intubations prior to this study.

Rates of successful intubations were higher for the King Vision channeled and McGrath compared to the King Vision non-channeled video laryngoscopes (85.7% and 82.9% respectively versus 24.8%; p<0.001, Table 2). However, there was no significant difference in the rates of successful intubations between the King Vision channeled and McGrath. All participants managed to achieve visualization of the glottis, with a mean time-to-visualization of less than 15 seconds for all three devices.

Table 2

Comparison of successful intubation and time-to-visualization between the King Vision channeled and non-channeled groups, and McGrath.

Values are number (proportion) or mean (standard deviation).

	King Vision channeled (n = 105)	King Vision non-channeled (n = 105)	McGrath (n = 105)	p-value
Successful intubation	90 (85.7%)	26 (24.8%)	87 (82.9%)	<0.001i
Time to visualization (seconds)	12.1 (±7.3)	10.3 (±12.9)	13.9 (±11.7)	0.054ii

i p <0.001 for King Vision channeled versus non-channeled, and McGrath versus King Vision non-channeled; p = 0.569 for King Vision channeled versus McGrath

ii p = 0.651 for King Vision channeled versus non-channeled, p = 0.047 McGrath versus King Vision non-channeled; p = 0.704 for King Vision channeled versus McGrath

Amongst participants who had successful intubations, King Vision channeled and McGrath had shorter mean time-to-intubation compared to the King Vision non-channeled (41.3±20.3s and 38.5±18.7s respectively versus 53.8±23.8s, p<0.004; Table 3). There was no significant difference in mean time-to-intubation between King Vision channeled and McGrath.

Table 3

Comparison of time-to-intubation for King Vision channeled and non-channeled groups, and McGrath.

Results are expressed as mean (standard deviation).

	King Vision channeled (n = 90)	King Vision non-channeled (n = 26)	McGrath (n = 87)	p-value
Time to intubation (seconds)	41.3 (±20.2)	53.8 (±23.8)	38.5 (±18.7)	0.004i

i p = 0.017 for King Vision channeled versus King Vision non-channeled; p = 0.002 for McGrath versus King Vision non-channeled; p = 1.000 for King Vision channeled versus McGrath

On a Likert 5-point scale for ease of use of video laryngoscopes, the median score for King Vision channeled and McGrath groups were 2 [interquartile range of 1–3], while the median score for King Vision non-channeled group was 4 [interquartile range of 3–5]. When asked to recommend a video laryngoscope amongst the three, 45.2% of participants recommended King Vision channeled, 1.5% recommended King Vision non-channeled, and 53.3% recommended McGrath.

Discussion

Video laryngoscopes are designed to provide indirect visualization of the glottis. Acute angled blades, such as the ones in King Vision video laryngoscopes, enable the user to achieve better laryngeal view with less neck and laryngeal manipulation [8,17]. However, without a direct line of vision to the glottis, the passage of tracheal tube into the glottis require deft hand-eye coordination [9,17], which may pose a problem for junior doctors with limited experience in intubation [17-19]. The presence of a tracheal tube guidance channel can help to overcome the need for complex manipulation during intubation [11-12]. Our study showed that the King Vision channeled laryngoscopes had better success rates compared to the King Vision non-channeled laryngoscopes, despite having the same blade angulation and curvature. This is consistent with the study by Akihisa et al that having a guided channel for tracheal tube improved intubation performance compared to a non-channeled blade for novice operators [14].

In our study, we made the intubation process more realistic by simulating a difficult airway with tongue oedema, cervical immobilisation with standard cervical collar, and requiring participants to intubate the manikin on the ground, similar to an out-of-hospital or military setting. The importance of a guided channel for an acute angled blade is accentuated when intubation becomes more challenging. This was demonstrated in our study where the success rate for King Vision non-channeled was 24.8%, compared to 47.3% for King Vision non-channeled in the study by Akihisa et al, where a standard manikin airway was used. This observation was also echoed in a study by Okada et al, which yielded no significant difference in intubation success rates between the King Vision channeled and non-channeled groups when used by novice operators in standard manikin airways, but demonstrated higher intubation success rates with the King Vision channeled laryngoscopes when compared to the non-channeled ones (25/25 versus 18/25, p = 0.004) when intubation was performed on a manikin with ongoing chest-compressions [12].

McGrath also performed better than the King Vision non-channeled laryngoscopes in terms of intubation success rates. While the McGrath did not have a channeled blade, it had the advantage of a blade curvature similar to the standard Macintosh blade, which the junior doctors were more familiar with. Other studies had also observed that junior doctors were able to translate their intubating skills if the curvature of the video laryngoscope blade was similar to the standard Macintosh blade [20-21]. We postulated that it was possible that our participants found it easier to acquaint themselves with the McGrath and achieved better success rates than with the King Vision non-channeled laryngoscope because of their familiarity with the McGrath blade curvature and handling.

When designing our study, we believe that it was important to break down the intubation process into two components: (1) achieving glottis visualization followed by (2) manipulation of tracheal tube past the glottis. Many studies agreed that the improved laryngeal view associated with video laryngoscope use did not necessarily lead to intubation success [3,13,21-22]. In our study, all 3 video laryngoscopes achieved a mean time-to-visualization of less than 15s. However, the King Vision non-channeled laryngoscope had the longest time-to-intubation. To improve intubation success rates with the King Vision non-channeled laryngoscope, we postulated that operators should be well-trained in the use of stylets, which some considered to be mandatory for intubation with angulated blades without a guiding channel [17,23]. They should be adept at shaping the stylets optimally for intubation, and possess good hand-eye coordination for manipulation of the tracheal tube when the oro-pharyngeal axis and the pharyngo-glotto-tracheal axis are not aligned to provide direct glottic view [9,13,17]. It will be interesting to determine whether the time to intubation using video laryngoscopes with acute angulated blades without a guided channel, such as the King Vision non-channeled video laryngoscope, differs between expert video laryngoscopists and less experienced medical personnel when intubating difficult airways.

There was no significant difference in terms of intubation success rates between the King Vision channeled and McGrath laryngoscopes. There were also no significant differences between King Vision channeled and McGrath in terms of time-to-visualization and time-to-intubation. Participants also rated both King Vision channeled and McGrath to be “easy to use”.

Other studies comparing various video laryngoscopes have also found that a variety of video laryngoscope are potentially appropriate for novice operators [4,11,13,24]. McGrath, with its standard Macintosh blade, offered the advantage of improved laryngeal view for operators who are familiar with its use. In a randomised controlled trial done by B. Alvis et al, experienced laryngoscopists with limited experience in video laryngoscopes were more successful and intubated faster with McGrath compared to King Vision channeled laryngoscopes [20]. On the other hand, novice operators, who might not be as adept with the technique of direct laryngoscopy, might prefer the King Vision channeled laryngoscopes because of its easy manipulation past the tongue for glottis visualization and a channel for tracheal guidance into the glottis [25-28]. King Vision channeled and non-channeled laryngoscopes have also been described for use as an alternative to awake fibreoptic intubation in patients with limited mouth opening and/or neck movement [15,29].

There were several limitations to our study. Firstly, while the SimMan® manikins used in this study are high fidelity advanced patient simulators, intubating a manikin is different from intubating a real patient. Hence the results might not be directly applicable to real-life patients. Secondly, while the SimMan® allowed for standardisation of the difficult airway scenario for our participants, this was limited to cervical immobilisation and tongue oedema. We recognised that difficult airways scenarios in actual trauma or collapsed patients may include other variables such as blood and secretions in the oral cavity, anatomic variations and/or facial injuries, which are beyond the scope of this study. Demographic differences, which were not measured, could have made a difference to the ease of intubation. Taller, heavier participants might find it difficult to kneel down on the ground to intubate compared to smaller participants.

(PNG)

Click here for additional data file.

Data Set.

(SAV)

Click here for additional data file.

(DOCX)

Click here for additional data file.

(DOCX)

Click here for additional data file.

(DOCX)

Click here for additional data file.

13 Aug 2019

PONE-D-19-18575

Intubation with channelled versus non-channelled video laryngoscopes in simulated difficult airway by junior doctors in an out-of-hospital setting: A crossover manikin study.

PLOS ONE

Dear Dr. Chew

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

==============================

I would appreciate to clarify the clinical importance of your study and in to response to the reviewers queries specially those of the second reviewer.

==============================

We would appreciate receiving your revised manuscript by Sep 20 2019 11:59PM. When you are ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter.

To enhance the reproducibility of your results, we recommend that if applicable you deposit your laboratory protocols in protocols.io, where a protocol can be assigned its own identifier (DOI) such that it can be cited independently in the future. For instructions see: http://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols

Please include the following items when submitting your revised manuscript:

A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). This letter should be uploaded as separate file and labeled 'Response to Reviewers'.

A marked-up copy of your manuscript that highlights changes made to the original version. This file should be uploaded as separate file and labeled 'Revised Manuscript with Track Changes'.

An unmarked version of your revised paper without tracked changes. This file should be uploaded as separate file and labeled 'Manuscript'.

Please note while forming your response, if your article is accepted, you may have the opportunity to make the peer review history publicly available. The record will include editor decision letters (with reviews) and your responses to reviewer comments. If eligible, we will contact you to opt in or out.

We look forward to receiving your revised manuscript.

Kind regards,

Ehab Farag, MD FRCA FASA

Academic Editor

PLOS ONE

Journal Requirements:

1.  When submitting your revision, we need you to address these additional requirements.

Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming. The PLOS ONE style templates can be found at

http://www.journals.plos.org/plosone/s/file?id=wjVg/PLOSOne_formatting_sample_main_body.pdf and http://www.journals.plos.org/plosone/s/file?id=ba62/PLOSOne_formatting_sample_title_authors_affiliations.pdf

2.  Thank you for stating the following in the Financial Disclosure section:

[The author(s) received no specific funding for this work.].

We note that one or more of the authors are employed by a commercial company: 'RS Anaesthesia & Intensive Care,'.

Please provide an amended Funding Statement declaring this commercial affiliation, as well as a statement regarding the Role of Funders in your study. If the funding organization did not play a role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript and only provided financial support in the form of authors' salaries and/or research materials, please review your statements relating to the author contributions, and ensure you have specifically and accurately indicated the role(s) that these authors had in your study. You can update author roles in the Author Contributions section of the online submission form.

Please also include the following statement within your amended Funding Statement.

“The funder provided support in the form of salaries for authors [insert relevant initials], but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of these authors are articulated in the ‘author contributions’ section.”

If your commercial affiliation did play a role in your study, please state and explain this role within your updated Funding Statement.

2. Please also provide an updated Competing Interests Statement declaring this commercial affiliation along with any other relevant declarations relating to employment, consultancy, patents, products in development, or marketed products, etc.

Within your Competing Interests Statement, please confirm that this commercial affiliation does not alter your adherence to all PLOS ONE policies on sharing data and materials by including the following statement: "This does not alter our adherence to  PLOS ONE policies on sharing data and materials.” (as detailed online in our guide for authors http://journals.plos.org/plosone/s/competing-interests) . If this adherence statement is not accurate and  there are restrictions on sharing of data and/or materials, please state these. Please note that we cannot proceed with consideration of your article until this information has been declared.

* Please include both an updated Funding Statement and Competing Interests Statement in your cover letter. We will change the online submission form on your behalf.

Please know it is PLOS ONE policy for corresponding authors to declare, on behalf of all authors, all potential competing interests for the purposes of transparency. PLOS defines a competing interest as anything that interferes with, or could reasonably be perceived as interfering with, the full and objective presentation, peer review, editorial decision-making, or publication of research or non-research articles submitted to one of the journals. Competing interests can be financial or non-financial, professional, or personal. Competing interests can arise in relationship to an organization or another person. Please follow this link to our website for more details on competing interests: http://journals.plos.org/plosone/s/competing-interests

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Partly

**********

2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: I Don't Know

Reviewer #2: Yes

**********

3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

**********

4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

**********

5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: This is a useful contribution to the airway literature, even though it is a mannequin study with the usual caveats that apply to mannequin airway studies. I could identify no methodological flaws in my reading of the manuscript. While I am not qualified to assess the statistical methodology used in the study, it appears to be sound. My only real concern is that the language used is in some need of polishing. In addition, the manuscript used British rather than American medical spelling.

Reviewer #2: The authors have studied % success rate of intubation of junior doctors with 3 videolaryngoscopic devices (King Vision channeled, King Vision non channeled, McGrath) in a standardized manikin under simulated difficult airway conditions. It is a well conducted study. Certain concerns need to be addressed:

1. Their conclusion is not in line with their results. While the participants recommended KV channeled laryngoscope 45.2% of the times and McGrath 53.3% of the times, the reasons for this were never explored. Instead, the authors assume or hypothesize that presence of the channel for the KV scope and easy handling of McGrath were responsible for these choices. The study does not explore reasons of why did the participants felt that KV channeled and McGrath scopes were preferable. Thus the statement, on page 2, lines 34 -36: "The presence of a guidance

channel in the King Vision channeled laryngoscope and the familiarity of the blade

curvature and handling of the McGrath are important factors, which contributed to the

ease of use for junior doctors." is invalid. This needs to be recognized and changed as this is the authors interpretation and not evidence based.

2. On page 4 lines 89 to 93: "All participants were allowed up to 90 seconds to achieve tracheal intubation in a standardized simulated difficult airway scenario for each device. In the event of an esophageal intubation, the timer will continue and participants were allowed repeated attempts at intubation, up to a maximum of 90seconds." Instead of the timer will continue, it is best reworded as the timer continued. Additionally, I am curious to why the authors did not record intubation attempts over the allowed 90 second period. Intubation attempts often worsen edema in real patients, and this is a meaningful outcome. In addition to success of intubation as defined by the authors, it would be meaningful to know which device was associated with least number of intubation attempts.

3. The Methodology needs more clarification. How many junior doctors were assigned to each sequence? Were effects of time and fatigue taken into account? Did all the doctors participate simultaneously at the same time (For example: 105 doctors intubated between 9 and 11am on 6 standardized manikins) or did they participate in discrete groups at different times (20 doctors at a time on a single manikin at different time periods such as 9 to 11 am , then noon to 2 pm etc)? Were all participants well rested or were some participating after being on call or coming off their regular work shifts? This may affect retention of video content that was played prior to having the participants intubate. Additionally, length of video is important. Retention is best for videos that are under 6 minutes. Reference: Philip J. Guo, Juho Kim, and Rob Rubin. 2014. How video production affects student engagement: an empirical study of MOOC videos. In Proceedings of the first ACM conference on Learning @ scale conference (L@S '14). ACM, New York, NY, USA, 41-50. DOI: https://doi.org/10.1145/2556325.2566239

Thus, if McGrath gets talked about in the early part of the video, participants may remember more about using McGrath than King Vision.

3. Demographic differences are important. Taller participants and heavier participants may find it difficult to kneel on the ground and intubate. If the authors have this information, it may be valuable to see if this affected success of intubation.

4. Time to visualization and Time to intubation make for important statistical outcomes but clinically the difference may not be relevant. For example, time to visualization for KV non channeled scope was 10 seconds vs 12 and 14 s for KV channeled and McGrath scopes. Would a 2 or 4 second difference be important clinically?

5. In Table 2, authors list the number of successful intubations for KV channeled, non channeled and McGrath devices as 90, 26 and 87. This changes to 91, 28 and 88 in Table 3. Could the authors shed more light on this?

**********

6. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #2: Yes: Sandeep Khanna

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files to be viewed.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email us at figures@plos.org. Please note that Supporting Information files do not need this step.

26 Sep 2019

Dear Ehab Farag (Academic Editor PLOS ONE),

Thank you for the reply. Our responses are as follows:

1. We will adhere to the formatting guidelines, and update the manuscript accordingly

2. Financial Disclosure Statement. The author(s) received no specific funding for this work. The affliated commercial company 'RS Anaesthesia & Intensive Care' was set up by last author R. C. H. Siew RS after completion of study and played no role in the design or conduct of the study. The rest of the authors do not receive salary nor funding from R. C. H. Siew’s private anaesthesia practice. The company did not have any role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.

3. Competing Interests. There are no competing interest. The affliated commercial company 'RS Anaesthesia & Intensive Care' was set up by last author R. C. H. Siew RS after completion of study and played no role in the design or conduct of the study. The rest of the authors do not receive salary nor funding from R. C. H. Siew’s private anaesthesia practice. This does not alter our adherence to PLOS ONE policies on sharing data and materials.

4. Review Comments to the Author

Reviewer #1: This is a useful contribution to the airway literature, even though it is a mannequin study with the usual caveats that apply to mannequin airway studies. I could identify no methodological flaws in my reading of the manuscript. While I am not qualified to assess the statistical methodology used in the study, it appears to be sound. My only real concern is that the language used is in some need of polishing. In addition, the manuscript used British rather than American medical spelling.

We will re-work the language, and align the manuscript to use American medical spelling.

Reviewer #2: The authors have studied % success rate of intubation of junior doctors with 3 videolaryngoscopic devices (King Vision channeled, King Vision non channeled, McGrath) in a standardized manikin under simulated difficult airway conditions. It is a well conducted study. Certain concerns need to be addressed:

1. Their conclusion is not in line with their results. While the participants recommended KV channeled laryngoscope 45.2% of the times and McGrath 53.3% of the times, the reasons for this were never explored. Instead, the authors assume or hypothesize that presence of the channel for the KV scope and easy handling of McGrath were responsible for these choices. The study does not explore reasons of why did the participants felt that KV channeled and McGrath scopes were preferable. Thus the statement, on page 2, lines 34 -36: "The presence of a guidance

channel in the King Vision channeled laryngoscope and the familiarity of the blade

curvature and handling of the McGrath are important factors, which contributed to the

ease of use for junior doctors." is invalid. This needs to be recognized and changed as this is the authors interpretation and not evidence based.

We will adjust our statement to reflect that this is the authors’ interpretation of the results.

2. On page 4 lines 89 to 93: "All participants were allowed up to 90 seconds to achieve tracheal intubation in a standardized simulated difficult airway scenario for each device. In the event of an esophageal intubation, the timer will continue and participants were allowed repeated attempts at intubation, up to a maximum of 90seconds." Instead of the timer will continue, it is best reworded as the timer continued. Additionally, I am curious to why the authors did not record intubation attempts over the allowed 90 second period. Intubation attempts often worsen edema in real patients, and this is a meaningful outcome. In addition to success of intubation as defined by the authors, it would be meaningful to know which device was associated with least number of intubation attempts.

We did not record intubation attempts over the allowed 90 second period, as timing is of essence during emergent airway intubation. This is in line with the ASA Difficult Airway Guidelines, which discourage repeated attempts at intubation for the same reason cited by the reviewer – because repeated intubation attempts often worsen oedema in real patients.

3. The Methodology needs more clarification. How many junior doctors were assigned to each sequence? Were effects of time and fatigue taken into account? Did all the doctors participate simultaneously at the same time (For example: 105 doctors intubated between 9 and 11am on 6 standardized manikins) or did they participate in discrete groups at different times (20 doctors at a time on a single manikin at different time periods such as 9 to 11 am , then noon to 2 pm etc)? Were all participants well rested or were some participating after being on call or coming off their regular work shifts? This may affect retention of video content that was played prior to having the participants intubate. Additionally, length of video is important. Retention is best for videos that are under 6 minutes. Reference: Philip J. Guo, Juho Kim, and Rob Rubin. 2014. How video production affects student engagement: an empirical study of MOOC videos. In Proceedings of the first ACM conference on Learning @ scale conference (L@S '14). ACM, New York, NY, USA, 41-50. DOI: https://doi.org/10.1145/2556325.2566239

Thus, if McGrath gets talked about in the early part of the video, participants may remember more about using McGrath than King Vision.

Thank you for the input. We will add more clarity in our methodology. About 10-25 subjects were tested in discrete groups at different times over multiple sessions. All of these sessions took place during office hours, and none of the participants were post-call/ or under the effects of sleep fatigue when participating in the study.

3. Demographic differences are important. Taller participants and heavier participants may find it difficult to kneel on the ground and intubate. If the authors have this information, it may be valuable to see if this affected success of intubation.

The reviewer raised a valid point that demographic variations may affect ease of intubation. Our study group did not record the height and weight of participants. While it may be true that taller and heavier participants may find it more difficult to kneel on the ground and intubate, the research was scoped to study how curvature and presence of channelled video laryngoscopy blade. In real life, we do not discriminate doctors based on their height and weight during deployment.

4. Time to visualization and Time to intubation make for important statistical outcomes but clinically the difference may not be relevant. For example, time to visualization for KV non channeled scope was 10 seconds vs 12 and 14 s for KV channeled and McGrath scopes. Would a 2 or 4 second difference be important clinically?

The differences in Time to Visualisation (TTV) are not as clinically important as differences in Time to Intubation, which may have implications such as hypoxic brain injury. In reality, a delay of 2-4s is unlikely to have significant clinical impact.

5. In Table 2, authors list the number of successful intubations for KV channeled, non channeled and McGrath devices as 90, 26 and 87. This changes to 91, 28 and 88 in Table 3. Could the authors shed more light on this?

The correct values should be n= 90, 26, and 87. I ran the statistics again, and realised that this error occurred when we input missing values (failed intubations) as 99.0s. This led to additional n values during analysis of TTI. We have corrected this, and have included the raw analysis from SPSS below.

Submitted filename: Response to Reviewers.docx

Click here for additional data file.

4 Oct 2019

Intubation with channelled versus non-channelled video laryngoscopes in simulated difficult airway by junior doctors in an out-of-hospital setting: A crossover manikin study.

PONE-D-19-18575R1

Dear Dr. Shi Hao Chew

We are pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it complies with all outstanding technical requirements.

Within one week, you will receive an e-mail containing information on the amendments required prior to publication. When all required modifications have been addressed, you will receive a formal acceptance letter and your manuscript will proceed to our production department and be scheduled for publication.

Shortly after the formal acceptance letter is sent, an invoice for payment will follow. To ensure an efficient production and billing process, please log into Editorial Manager at https://www.editorialmanager.com/pone/, click the "Update My Information" link at the top of the page, and update your user information. If you have any billing related questions, please contact our Author Billing department directly at authorbilling@plos.org.

If your institution or institutions have a press office, please notify them about your upcoming paper to enable them to help maximize its impact. If they will be preparing press materials for this manuscript, you must inform our press team as soon as possible and no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org.

With kind regards,

Ehab Farag, MD FRCA FASA

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

15 Oct 2019

PONE-D-19-18575R1

Intubation with channeled versus non-channeled video laryngoscopes in simulated difficult airway by junior doctors in an out-of-hospital setting: A crossover manikin study.

Dear Dr. Chew:

I am pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department.

If your institution or institutions have a press office, please notify them about your upcoming paper at this point, to enable them to help maximize its impact. If they will be preparing press materials for this manuscript, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information please contact onepress@plos.org.

For any other questions or concerns, please email plosone@plos.org.

Thank you for submitting your work to PLOS ONE.

With kind regards,

PLOS ONE Editorial Office Staff

on behalf of

Dr. Ehab Farag

Academic Editor

PLOS ONE