Videolaryngoscopy versus direct laryngoscopy for adults undergoing tracheal intubation

Jan Hansel; Andrew M Rogers; Sharon R Lewis; Tim M Cook; Andrew F Smith

doi:10.1002/14651858.CD011136.pub3

Cochrane Database of Systematic Reviews

Videolaryngoscopy versus direct laryngoscopy for adults undergoing tracheal intubation

Information

DOI:

https://doi.org/10.1002/14651858.CD011136.pub3 Copy DOI

Database:

Cochrane Database of Systematic Reviews

Version published:

04 April 2022see what's new

Type:

Intervention

Stage:

Review

Cochrane Editorial Group:

Cochrane Anaesthesia Group

Copyright:

Copyright © 2016 The Cochrane Collaboration. Published by John Wiley & Sons, Ltd.

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Authors

Jan Hansel

Correspondence to: Royal Oldham Hospital, Manchester, UK

[email protected]
Andrew M Rogers

Department of Anaesthesia, Royal United Hospitals Bath NHS Trust, Bath, UK
Sharon R Lewis

Bone and Joint Health, Blizard Institute, Queen Mary University of London, London, UK
Tim M Cook

Department of Anaesthesia, Royal United Hospitals Bath NHS Trust, Bath, UK

University of Bristol, Bristol, UK
Andrew F Smith

Department of Anaesthesia, Royal Lancaster Infirmary, Lancaster, UK

Lancaster University, Lancaster, UK

Contributions of authors

Jan Hansel (JH), Andrew Rogers (AR), Sharon R Lewis (SL), Andrew R Butler (AB), Joshua Parker (JP), Tim M Cook (TC), Andrew F Smith (AS)

Conceiving the review: AS

Co‐ordinating the review update: JH

Undertaking manual searches: JH

Screening search results: JH, AR

Organizing retrieval of papers: JH

Screening retrieved papers against inclusion criteria: JH, AR, SL

Appraising quality of papers: JH, AR, SL

Abstracting data from papers: JH, AR, SL

Writing to authors of papers for additional information: JH

Managing data for the review: JH

Entering data into Review Manager (RevMan Web 2021): JH, AR

Analysing Review Manager statistical data: JH

Interpreting data: JH, AR, SL, AS, TC

Making statistical inferences: JH, AR, SL, TC, AS

Writing the review: JH, AR, SL, AS, TC

Securing funding for the review: AS

Performing previous work that was the foundation of the present review: SL, AB, TC, AS

Serving as guarantor for the review (one review author): AS

Taking responsibility for reading and checking the review before submission: JH

Sources of support

Internal sources

North West School of Anaesthesia Health Education England, UK

Provided protected non‐clinical time for undertaking the review to JH.

External sources

None, Other

None

Declarations of interest

Sharon R Lewis, systematic reviewer: none known

Jan Hansel: none known

Andrew Rogers: none known

Tim M Cook was paid for lecturing, several years ago (> 36 months), by Intavent Orthofix and the LMA Company. This company manufactures and distributes several supraglottic airway devices and one videolaryngoscope: AP Venner. Dr Cook's department has received free or at‐cost airway equipment from numerous 'airway' companies for evaluation or research. He and his family have no financial investments and no ownership of any such company of which he is aware. Dr Cook has reported no other conflicts of interest. He spoke at a Storz educational meeting in 2015, and the company paid the costs of travel to this meeting and accommodations. He received no financial benefit from the meeting and was not paid to speak.

Andrew F Smith has received funding for market research relating to airway devices, but not for videolaryngoscopes, nor for any company that produces them.

Acknowledgements

We would like to thank Vassilis Athanassoglou (Content Editor, Cochrane Anaesthesia), Philippe Tadger (Statistical Editor, Cochrane Anaesthesia), Janne Vendt (Information Specialist, Cochrane Anaesthesia), Brett Doleman, Kim Widlgaard, Juan Victor Lorente Olazábal (external Peer Reviewers), Janney Wale (Consumer Reviewer, Cochrane Anaesthesia), Denise Mitchell (Senior Copy Editor, Cochrane Central Executive), Vernon Hedge (Managing Editor, Cochrane Anaesthesia) and Harald Herkner (Sign Off Editor, Cochrane Emergency and Critical Care) for their help and editorial advice during the preparation of this systematic review.

We would also like to thank Andrew R Butler and Joshua Parker, who were co‐authors of the original version of this review (Lewis 2016).

We would like to thank study authors who responded to requests for further study information, in particular, Dr Roopali Gupta, Dr Thomas Hamp, Dr David R Janz, Dr Pierre Kory, Dr Marc Kriege and Dr Alice Loughnan.

Version history

Published

Title

Stage

Authors

Version

2022 Apr 04

Videolaryngoscopy versus direct laryngoscopy for adults undergoing tracheal intubation

Review

Jan Hansel, Andrew M Rogers, Sharon R Lewis, Tim M Cook, Andrew F Smith

https://doi.org/10.1002/14651858.CD011136.pub3

2016 Nov 15

Videolaryngoscopy versus direct laryngoscopy for adult patients requiring tracheal intubation

Review

Sharon R Lewis, Andrew R Butler, Joshua Parker, Tim M Cook, Andrew F Smith

https://doi.org/10.1002/14651858.CD011136.pub2

2014 May 28

Videolaryngoscopy versus direct laryngoscopy for adult surgical patients requiring tracheal intubation for general anaesthesia

Protocol

Sharon R Lewis, Amanda Nicholson, Tim M Cook, Andrew F Smith

https://doi.org/10.1002/14651858.CD011136

Differences between protocol and review

We made the following changes to the previous version of this review (Lewis 2016). Changes made from the protocol to the review are reported in Lewis 2016.

Title

We changed the title from the original review "Videolaryngoscopy versus direct laryngoscopy for adult patients requiring tracheal intubation" to "Videolaryngoscopy versus direct laryngoscopy for adults undergoing tracheal intubation" because this better reflects the scope and focus of the review.

Review authors

Andrew Butler and Joshua Parker contributed to the previous version of the review but not to the update. Jan Hansel and Andrew Rogers contributed to this version of the review.

Types of studies

We included cluster‐randomized controlled trials.

Types of participants

We did not exclude adults in cardiac arrest. The rationale for this was that excluding these studies would have rendered a large number of non‐theatre studies ineligible.

Types of interventions

Unlike in the previous version of the review, we conducted three separate comparisons based on videolaryngoscope design: Macintosh‐style, hyperangulated, channelled. Further to optical stylets, we also excluded flexible fibreoptic intubating devices, tracheal tubes with an integrated camera and McCoy or Miller direct laryngoscopy blades. We took a more inclusive approach and included studies that were previously excluded (including the Airtraq videolaryngoscope). We still excluded the Bullard laryngoscope, which is no longer used in routine clinical practice.

Types of outcome measures

In line with current GRADE recommendations, we re‐classified the outcomes as critical or important. We classified four outcomes as critical (failed intubation, hypoxaemia, successful first attempt at tracheal intubation, oesophageal intubation) and eight outcomes as important (number of attempts, dental trauma, patient‐reported sore throat, Cormack‐Lehane grade, Intubation Difficulty Scale (IDS), percentage of glottic opening (POGO) score, time for tracheal intubation, mortality).

We made the following changes to the outcome measures.

We changed the definition of "Failed intubation" to be more specifically defined as: "more than three attempts or change of device or intubator required".
We changed the definition of "Hypoxaemia" to "oxygen saturation less than 94% between start of induction and recovery from anaesthesia".
We removed the outcome of "Serious respiratory complications" as it is a heterogeneous outcome and difficult to define, and our clinical judgement was that we did not expect laryngoscopy to meaningfully impact it.
We changed "Patient‐reported sore throat and hoarseness" to "Patient‐reported sore throat" to simplify the outcome for data extraction and reporting.
We changed "Laryngeal or airway trauma" to "Dental trauma" only. In order to avoid unit of analysis issues we extracted data only for dental trauma. A number of studies reported both combined separate events where they could have occurred in the same individual, but this was not clear from the manuscript. Furthermore, the review group felt the dental trauma outcome measure was the most patient‐centred, albeit infrequently occurring, of the ones listed.
For the outcome "Improved visualization of the larynx as measured on a validated scale" we reported Cormack‐Lehane grade views and POGO scores as separate outcomes.
We added the outcome of "Oesophageal intubation"; the rationale for this was that oesophageal intubation, when unrecognized, can lead to further complications and mortality, and is an easily assessed outcome at the time of intubation.

Measures of treatment effect

We did not collect time‐to‐event data for mortality. We did not convert continuous outcome data to means with standard deviation where they were reported as median (interquartile range) as we could not assume normal data distribution.

Given a large number of studies with zero events in both arms for three of the four critical outcomes, we conducted a sensitivity analysis of these outcomes in all three comparisons, including zero‐event studies.

Risk of bias

On peer‐review advice, we performed an additional analysis of quantitative statistical testing of funnel plot asymmetry for the Macintosh‐style videolaryngoscope versus direct laryngoscope comparison for the outcome of failed intubation, where there was discrepancy between the funnel plot suggesting visual asymmetry and Harbord's test not confirming this.

Unit of analysis issues

By separately extracting data for different device types into discrete comparisons we avoided the unit of analysis issues encountered in the previous version of this review. However, where studies reported data for multiple devices of the same type, we did combine those data.

For cross‐over studies reporting more than one set of observations for the same participant (such as Cormack‐Lehane grade views), we extracted data from the first attempt, where this was reported clearly.

Effects of interventions

We altered time points for the sore throat outcome to reflect the time points commonly reported in the included studies. When reported, we included data closest to six hours postoperatively.

Subgroup analysis and investigation of heterogeneity

We carried out subgroup analyses for the critical outcome of failed intubation across the three device types for setting, obesity, features of airway difficulty, and intubator experience. These analyses were prespecified. We performed a prespecified sensitivity analysis, where we combined all device designs and looked at the four critical outcomes of failed intubation, hypoxaemia, successful first attempt and oesophageal intubation.

We also performed four post hoc sensitivity analyses, combining all videolaryngoscope designs and comparing subgroups for setting, obesity, features of airway difficulty, and intubator experience.

We added a sentence to the review to explain how we had defined intubator experience by number of uses.

Summary of findings tables

We created three separate summary of findings tables, one for each comparison. We re‐arranged the outcomes of interest reported in the summary of findings tables in the following order. Critical outcomes: failed intubation, hypoxaemia, successful first attempt, oesophageal intubation. Important outcomes: dental trauma, Cormack‐Lehane grade, time for tracheal intubation.

Keywords

MeSH

Medical Subject Headings (MeSH) Keywords

Medical Subject Headings Check Words

Adult; Humans;

PICOs

Population

Intervention

Comparison

Outcome

The PICO model is widely used and taught in evidence-based health care as a strategy for formulating questions and search strategies and for characterizing clinical studies or meta-analyses. PICO stands for four different potential components of a clinical question: Patient, Population or Problem; Intervention; Comparison; Outcome.

See more on using PICO in the Cochrane Handbook.

Figure 1

Flow diagram

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Figure 2

Risk of bias graph: review authors' judgements about each risk of bias item presented as percentages across all included studies

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Figure 3

Risk of bias summary: review authors' judgements about each risk of bias item for each included study. Blank spaces indicate we did not complete a risk of bias assessment because we were not able to extract any relevant data for our chosen outcomes.

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Figure 4

Funnel plot of comparison: Macintosh‐style videolaryngoscopy versus direct laryngoscopy, outcome 1.1, failed intubation

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Figure 5

Forest plot of comparison: hyperangulated videolaryngoscopy, subgroup analysis of failed intubation in participants with predicted, known or simulated features of airway difficulty

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Figure 6

Funnel plot of comparison: channelled videolaryngoscopy versus direct laryngoscopy, outcome 3.3, successful first attempt

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Analysis 1.1

Comparison 1: Macintosh‐style VL versus DL, Outcome 1: Failed intubation

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Analysis 1.2

Comparison 1: Macintosh‐style VL versus DL, Outcome 2: Hypoxaemia

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Analysis 1.3

Comparison 1: Macintosh‐style VL versus DL, Outcome 3: Successful first attempt

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Analysis 1.4

Comparison 1: Macintosh‐style VL versus DL, Outcome 4: Oesophageal intubation

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Analysis 1.5

Comparison 1: Macintosh‐style VL versus DL, Outcome 5: Dental trauma

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Analysis 1.6

Comparison 1: Macintosh‐style VL versus DL, Outcome 6: Cormack‐Lehane (CL) grade

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Analysis 1.7

Comparison 1: Macintosh‐style VL versus DL, Outcome 7: Time for tracheal intubation

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Analysis 1.8

Comparison 1: Macintosh‐style VL versus DL, Outcome 8: Patient‐reported sore throat

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Analysis 1.9

Comparison 1: Macintosh‐style VL versus DL, Outcome 9: Number of attempts

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Analysis 1.10

Comparison 1: Macintosh‐style VL versus DL, Outcome 10: Intubation Difficulty Scale (IDS)

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Analysis 1.11

Comparison 1: Macintosh‐style VL versus DL, Outcome 11: POGO Score

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Analysis 1.12

Comparison 1: Macintosh‐style VL versus DL, Outcome 12: Mortality

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Analysis 1.13

Comparison 1: Macintosh‐style VL versus DL, Outcome 13: Subgroup analysis of failed intubation: airway difficulty

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Analysis 2.1

Comparison 2: Hyperangulated VL versus DL, Outcome 1: Failed intubation

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Analysis 2.2

Comparison 2: Hyperangulated VL versus DL, Outcome 2: Hypoxaemia

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Analysis 2.3

Comparison 2: Hyperangulated VL versus DL, Outcome 3: Successful first attempt

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Analysis 2.4

Comparison 2: Hyperangulated VL versus DL, Outcome 4: Oesophageal intubation

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Analysis 2.5

Comparison 2: Hyperangulated VL versus DL, Outcome 5: Dental trauma

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Analysis 2.6

Comparison 2: Hyperangulated VL versus DL, Outcome 6: Cormack‐Lehane (CL) grade

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Analysis 2.7

Comparison 2: Hyperangulated VL versus DL, Outcome 7: Time for tracheal intubation

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Analysis 2.8

Comparison 2: Hyperangulated VL versus DL, Outcome 8: Patient‐reported sore throat

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Analysis 2.9

Comparison 2: Hyperangulated VL versus DL, Outcome 9: Number of attempts

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Analysis 2.10

Comparison 2: Hyperangulated VL versus DL, Outcome 10: Intubation Difficulty Scale (IDS)

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Analysis 2.11

Comparison 2: Hyperangulated VL versus DL, Outcome 11: POGO Score

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Analysis 2.12

Comparison 2: Hyperangulated VL versus DL, Outcome 12: Mortality

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Analysis 2.13

Comparison 2: Hyperangulated VL versus DL, Outcome 13: Subgroup analysis of failed intubation: airway difficulty

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Analysis 3.1

Comparison 3: Channelled VL versus DL, Outcome 1: Failed intubation

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Analysis 3.2

Comparison 3: Channelled VL versus DL, Outcome 2: Hypoxaemia

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Analysis 3.3

Comparison 3: Channelled VL versus DL, Outcome 3: Successful first attempt

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Analysis 3.4

Comparison 3: Channelled VL versus DL, Outcome 4: Oesophageal intubation

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Analysis 3.5

Comparison 3: Channelled VL versus DL, Outcome 5: Dental trauma

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Analysis 3.6

Comparison 3: Channelled VL versus DL, Outcome 6: Cormack‐Lehane (CL) grade

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Analysis 3.7

Comparison 3: Channelled VL versus DL, Outcome 7: Time for tracheal intubation

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Analysis 3.8

Comparison 3: Channelled VL versus DL, Outcome 8: Patient‐reported sore throat

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Analysis 3.9

Comparison 3: Channelled VL versus DL, Outcome 9: Number of attempts

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Analysis 3.10

Comparison 3: Channelled VL versus DL, Outcome 10: Intubation Difficulty Scale (IDS)

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Analysis 3.11

Comparison 3: Channelled VL versus DL, Outcome 11: POGO Score

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Analysis 3.12

Comparison 3: Channelled VL versus DL, Outcome 12: Subgroup analysis of failed intubation: airway difficulty

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Analysis 4.1

Comparison 4: VL versus DL (all devices combined), Outcome 1: Failed intubation

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Analysis 4.2

Comparison 4: VL versus DL (all devices combined), Outcome 2: Hypoxia

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Analysis 4.3

Comparison 4: VL versus DL (all devices combined), Outcome 3: Successful first attempt

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Analysis 4.4

Comparison 4: VL versus DL (all devices combined), Outcome 4: Oesophageal intubation

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Analysis 4.5

Comparison 4: VL versus DL (all devices combined), Outcome 5: Subgroup analysis of failed intubation: theatre versus non‐theatre

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Analysis 4.6

Comparison 4: VL versus DL (all devices combined), Outcome 6: Subgroup analysis of failed intubation: obesity

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Analysis 4.7

Comparison 4: VL versus DL (all devices combined), Outcome 7: Subgroup analysis of failed intubation: airway difficulty

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Analysis 4.8

Comparison 4: VL versus DL (all devices combined), Outcome 8: Subgroup analysis of failed intubation: intubator experience

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Summary of findings 1. Macintosh‐style videolaryngoscopy compared to direct laryngoscopy for adults undergoing tracheal intubation

Outcomes	*Anticipated absolute effects^ (95% CI)**		Relative effect (95% CI)	№ of participants (studies)	Certainty of the evidence (GRADE)	Comments
Macintosh‐style videolaryngoscopy compared to direct laryngoscopy for adults undergoing tracheal intubation
Patient or population: adults undergoing tracheal intubation Setting: hospital and out‐of‐hospital; international Intervention: Macintosh‐style videolaryngoscopy Comparison: direct laryngoscopy
Outcomes	Risk with direct laryngoscopy	Risk with Macintosh‐style videolaryngoscopy	Relative effect (95% CI)	№ of participants (studies)	Certainty of the evidence (GRADE)	Comments
Failed intubation	Study population		RR 0.41 (0.26 to 0.65)	4615 (41 RCTs)	⊕⊕⊕⊝ Moderate^a
Failed intubation	65 per 1000	27 per 1000 (17 to 42)	RR 0.41 (0.26 to 0.65)	4615 (41 RCTs)	⊕⊕⊕⊝ Moderate^a
Hypoxaemia	Study population		RR 0.72 (0.52 to 0.99)	2127 (16 RCTs)	⊕⊕⊕⊝ Moderate^a
Hypoxaemia	106 per 1000	76 per 1000 (55 to 105)	RR 0.72 (0.52 to 0.99)	2127 (16 RCTs)	⊕⊕⊕⊝ Moderate^a
Successful first attempt	Study population		RR 1.05 (1.02 to 1.09)	7311 (42 RCTs)	⊕⊕⊝⊝ Low^a,b
Successful first attempt	813 per 1000	854 per 1000 (830 to 887)	RR 1.05 (1.02 to 1.09)	7311 (42 RCTs)	⊕⊕⊝⊝ Low^a,b
Oesophageal intubation	Study population		RR 0.51 (0.22 to 1.21)	2404 (14 RCTs)	⊕⊕⊝⊝ Low^a,c
Oesophageal intubation	29 per 1000	15 per 1000 (6 to 36)	RR 0.51 (0.22 to 1.21)	2404 (14 RCTs)	⊕⊕⊝⊝ Low^a,c
Dental trauma	Study population		RR 0.68 (0.16 to 2.89)	2297 (18 RCTs)	⊕⊝⊝⊝ Very low^a,d
Dental trauma	4 per 1000	2 per 1000 (1 to 10)	RR 0.68 (0.16 to 2.89)	2297 (18 RCTs)	⊕⊝⊝⊝ Very low^a,d
Cormack‐Lehane grade	Study population		RR 0.38 (0.29 to 0.48)	4368 (38 RCTs)	⊕⊕⊕⊝ Moderate^a,b	Data presented for frequency of Cormack‐Lehane grade 3 and 4 views
Cormack‐Lehane grade	196 per 1000	75 per 1000 (57 to 94)	RR 0.38 (0.29 to 0.48)	4368 (38 RCTs)	⊕⊕⊕⊝ Moderate^a,b
Time for tracheal intubation	See comment	See comment	‐	4061 (35 RCTs)	⊕⊝⊝⊝ Very low^a,e	High level of statistical heterogeneity between studies; therefore meta‐analysis not completed
*The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: confidence interval; RCT: randomized controlled trial; RR: risk ratio
GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of effect.
^aWe downgraded by one level for risk of performance bias due to the lack of blinding. ^bWe downgraded by one level for inconsistency because we noted considerable statistical heterogeneity. ^cWe downgraded by one level for imprecision because the confidence intervals indicated possible benefits as well as harms. ^dWe downgraded by two levels for imprecision because the frequency of events was small and the confidence intervals indicated possible benefits as well as harms. ^eWe downgraded by two levels for inconsistency because we noted extremely high statistical heterogeneity (I² = 96%).

Summary of findings 1. Macintosh‐style videolaryngoscopy compared to direct laryngoscopy for adults undergoing tracheal intubation

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Summary of findings 2. Hyperangulated videolaryngoscopy compared to direct laryngoscopy for adults undergoing tracheal intubation

Outcomes	*Anticipated absolute effects^ (95% CI)**		Relative effect (95% CI)	№ of participants (studies)	Certainty of the evidence (GRADE)	Comments
Hyperangulated videolaryngoscopy compared to direct laryngoscopy for adults undergoing tracheal intubation
Patient or population: adults undergoing tracheal intubation Setting: hospital and out‐of‐hospital; international Intervention: hyperangulated videolaryngoscopy Comparison: direct laryngoscopy
Outcomes	Risk with direct laryngoscopy	Risk with hyperangulated videolaryngoscopy	Relative effect (95% CI)	№ of participants (studies)	Certainty of the evidence (GRADE)	Comments
Failed intubation	Study population		RR 0.51 (0.34 to 0.76)	7146 (63 RCTs)	⊕⊕⊕⊝ Moderate^a
Failed intubation	56 per 1000	29 per 1000 (19 to 43)	RR 0.51 (0.34 to 0.76)	7146 (63 RCTs)	⊕⊕⊕⊝ Moderate^a
Hypoxaemia	Study population		RR 0.49 (0.22 to 1.11)	1691 (15 RCTs)	⊕⊕⊝⊝ Low^a,b
Hypoxaemia	44 per 1000	22 per 1000 (10 to 49)	RR 0.49 (0.22 to 1.11)	1691 (15 RCTs)	⊕⊕⊝⊝ Low^a,b
Successful first attempt	Study population		RR 1.03 (1.00 to 1.05)	8086 (66 RCTs)	⊕⊕⊝⊝ Low^a,c
Successful first attempt	854 per 1000	879 per 1000 (854 to 896)	RR 1.03 (1.00 to 1.05)	8086 (66 RCTs)	⊕⊕⊝⊝ Low^a,c
Oesophageal intubation	Study population		RR 0.39 (0.18 to 0.81)	1968 (14 RCTs)	⊕⊕⊕⊝ Moderate^a
Oesophageal intubation	26 per 1000	10 per 1000 (5 to 21)	RR 0.39 (0.18 to 0.81)	1968 (14 RCTs)	⊕⊕⊕⊝ Moderate^a
Dental trauma	Study population		RR 0.51 (0.16 to 1.59)	3497 (30 RCTs)	⊕⊝⊝⊝ Very low^a,d
Dental trauma	4 per 1000	2 per 1000 (1 to 7)	RR 0.51 (0.16 to 1.59)	3497 (30 RCTs)	⊕⊝⊝⊝ Very low^a,d
Cormack‐Lehane grade	Study population		RR 0.15 (0.10 to 0.24)	6058 (54 RCTs)	⊕⊕⊕⊝ Moderate^a,c	Data presented for frequency of Cormack‐Lehane grade 3 and 4 views
Cormack‐Lehane grade	189 per 1000	28 per 1000 (19 to 45)	RR 0.15 (0.10 to 0.24)	6058 (54 RCTs)	⊕⊕⊕⊝ Moderate^a,c
Time for tracheal intubation	see comment	see comment	‐	6644 (59 RCTs)	⊕⊝⊝⊝ Very low^a,e	High level of statistical heterogeneity between studies; therefore meta‐analysis not completed
*The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: confidence interval; RCT: randomized controlled trial; RR: risk ratio
GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of effect.
^aWe downgraded by one level for risk of performance bias due to the lack of blinding. ^bWe downgraded by one level for imprecision because the confidence intervals indicated possible benefits as well as harms. ^cWe downgraded by one level for inconsistency because we noted considerable statistical heterogeneity. ^dWe downgraded by two levels for imprecision because the frequency of events was small and the confidence intervals indicated possible benefits as well as harms. ^eWe downgraded by two levels for inconsistency because we noted extremely high statistical heterogeneity (I² = 99%).

Summary of findings 2. Hyperangulated videolaryngoscopy compared to direct laryngoscopy for adults undergoing tracheal intubation

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Summary of findings 3. Channelled videolaryngoscopy compared to direct laryngoscopy for adults undergoing tracheal intubation

Outcomes	*Anticipated absolute effects^ (95% CI)**		Relative effect (95% CI)	№ of participants (studies)	Certainty of the evidence (GRADE)	Comments
Channelled videolaryngoscopy compared to direct laryngoscopy for adults undergoing tracheal intubation
Patient or population: adults undergoing tracheal intubation Setting: hospital and out‐of‐hospital; international Intervention: channelled videolaryngoscopy Comparison: direct laryngoscopy
Outcomes	Risk with direct laryngoscopy	Risk with channelled videolaryngoscopy	Relative effect (95% CI)	№ of participants (studies)	Certainty of the evidence (GRADE)	Comments
Failed intubation	Study population		RR 0.43 (0.30 to 0.61)	5367 (53 RCTs)	⊕⊕⊕⊝ Moderate^a
Failed intubation	44 per 1000	19 per 1000 (13 to 27)	RR 0.43 (0.30 to 0.61)	5367 (53 RCTs)	⊕⊕⊕⊝ Moderate^a
Hypoxia	Study population		RR 0.25 (0.12 to 0.50)	1966 (15 RCTs)	⊕⊕⊕⊝ Moderate^a
Hypoxia	42 per 1000	10 per 1000 (5 to 21)	RR 0.25 (0.12 to 0.50)	1966 (15 RCTs)	⊕⊕⊕⊝ Moderate^a
Successful first attempt	Study population		RR 1.10 (1.05 to 1.15)	5210 (47 RCTs)	⊕⊕⊝⊝ Very low^a,b,c
Successful first attempt	826 per 1000	909 per 1000 (868 to 950)	RR 1.10 (1.05 to 1.15)	5210 (47 RCTs)	⊕⊕⊝⊝ Very low^a,b,c
Oesophageal intubation	Study population		RR 0.54 (0.17 to 1.75)	1756 (16 RCTs)	⊕⊕⊝⊝ Low^a,d
Oesophageal intubation	34 per 1000	19 per 1000 (6 to 60)	RR 0.54 (0.17 to 1.75)	1756 (16 RCTs)	⊕⊕⊝⊝ Low^a,d
Dental trauma	Study population		RR 0.52 (0.13 to 2.12)	2375 (29 RCTs)	⊕⊝⊝⊝ Very low^a,e
Dental trauma	3 per 1000	2 per 1000 (0 to 7)	RR 0.52 (0.13 to 2.12)	2375 (29 RCTs)	⊕⊝⊝⊝ Very low^a,e
Cormack‐Lehane grade	Study population		RR 0.14 (0.09 to 0.21)	3955 (40 RCTs)	⊕⊕⊕⊝ Moderate^a,b	Data presented for frequency of Cormack‐Lehane grade 3 and 4 views
Cormack‐Lehane grade	194 per 1000	27 per 1000 (17 to 41)	RR 0.14 (0.09 to 0.21)	3955 (40 RCTs)	⊕⊕⊕⊝ Moderate^a,b
Time for tracheal intubation	see comment	see comment	‐	5676 (57 RCTs)	⊕⊝⊝⊝ Very low^a,f	High level of statistical heterogeneity between studies; therefore meta‐analysis not completed
*The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: confidence interval; RCT: randomized controlled trial; RR: risk ratio
GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of effect.
^aWe downgraded by one level for risk of performance bias due to the lack of blinding. ^bWe downgraded by one level for inconsistency because we noted considerable statistical heterogeneity. ^cWe downgraded by one level for suspicion of publication bias. ^dWe downgraded by one level for imprecision because the confidence intervals indicated possible benefits as well as harms. ^eWe downgraded by two levels for imprecision because the frequency of events was small and the confidence intervals indicated possible benefits as well as harms. ^fWe downgraded by two levels for inconsistency because we noted extremely high statistical heterogeneity (I² = 98%).

Summary of findings 3. Channelled videolaryngoscopy compared to direct laryngoscopy for adults undergoing tracheal intubation

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Comparison 1. Macintosh‐style VL versus DL

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1.1 Failed intubation Show forest plot	41	4615	Risk Ratio (M‐H, Random, 95% CI)	0.41 [0.26, 0.65]

1.2 Hypoxaemia Show forest plot	16	2127	Risk Ratio (M‐H, Random, 95% CI)	0.72 [0.52, 0.99]

1.3 Successful first attempt Show forest plot	42	7311	Risk Ratio (M‐H, Random, 95% CI)	1.05 [1.02, 1.09]

1.4 Oesophageal intubation Show forest plot	14	2404	Risk Ratio (M‐H, Random, 95% CI)	0.51 [0.22, 1.21]

1.5 Dental trauma Show forest plot	18	2297	Risk Ratio (M‐H, Random, 95% CI)	0.68 [0.16, 2.89]

1.6 Cormack‐Lehane (CL) grade Show forest plot	38	13104	Risk Ratio (M‐H, Random, 95% CI)	0.90 [0.81, 1.00]

1.6.1 Cormack‐Lehane 1	38	4368	Risk Ratio (M‐H, Random, 95% CI)	1.50 [1.39, 1.63]
1.6.2 Cormack‐Lehane 2	38	4368	Risk Ratio (M‐H, Random, 95% CI)	0.62 [0.51, 0.76]
1.6.3 Cormack‐Lehane 3‐4	38	4368	Risk Ratio (M‐H, Random, 95% CI)	0.38 [0.29, 0.48]
1.7 Time for tracheal intubation Show forest plot	35		Mean Difference (IV, Random, 95% CI)	Subtotals only

1.8 Patient‐reported sore throat Show forest plot	17	1960	Risk Ratio (M‐H, Random, 95% CI)	0.85 [0.68, 1.07]

1.9 Number of attempts Show forest plot	31	6480	Risk Ratio (M‐H, Random, 95% CI)	1.03 [0.98, 1.08]

1.9.1 1 attempt	31	3240	Risk Ratio (M‐H, Random, 95% CI)	1.05 [1.01, 1.10]
1.9.2 2‐4 attempts	31	3240	Risk Ratio (M‐H, Random, 95% CI)	0.68 [0.46, 1.01]
1.10 Intubation Difficulty Scale (IDS) Show forest plot	4	801	Risk Ratio (M‐H, Random, 95% CI)	1.05 [0.88, 1.25]

1.10.1 IDS 0	4	267	Risk Ratio (M‐H, Random, 95% CI)	1.22 [0.87, 1.72]
1.10.2 IDS 1‐5	4	267	Risk Ratio (M‐H, Random, 95% CI)	1.04 [0.84, 1.28]
1.10.3 IDS > 5	4	267	Risk Ratio (M‐H, Random, 95% CI)	0.60 [0.25, 1.45]
1.11 POGO Score Show forest plot	5		Mean Difference (IV, Random, 95% CI)	Subtotals only

1.12 Mortality Show forest plot	3	719	Risk Ratio (M‐H, Random, 95% CI)	1.01 [0.82, 1.24]

1.13 Subgroup analysis of failed intubation: airway difficulty Show forest plot	37	3925	Risk Ratio (M‐H, Random, 95% CI)	0.40 [0.23, 0.68]

1.13.1 Predicted, known or simulated difficulty	12	1393	Risk Ratio (M‐H, Random, 95% CI)	0.37 [0.19, 0.74]
1.13.2 No difficulty	25	2532	Risk Ratio (M‐H, Random, 95% CI)	0.42 [0.16, 1.10]

Comparison 1. Macintosh‐style VL versus DL

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Comparison 2. Hyperangulated VL versus DL

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
2.1 Failed intubation Show forest plot	63	7146	Risk Ratio (M‐H, Random, 95% CI)	0.51 [0.34, 0.76]

2.2 Hypoxaemia Show forest plot	15	1691	Risk Ratio (M‐H, Random, 95% CI)	0.49 [0.22, 1.11]

2.3 Successful first attempt Show forest plot	66	8086	Risk Ratio (M‐H, Random, 95% CI)	1.03 [1.00, 1.05]

2.4 Oesophageal intubation Show forest plot	14	1968	Risk Ratio (M‐H, Random, 95% CI)	0.39 [0.18, 0.81]

2.5 Dental trauma Show forest plot	30	3497	Risk Ratio (M‐H, Random, 95% CI)	0.51 [0.16, 1.59]

2.6 Cormack‐Lehane (CL) grade Show forest plot	54	18174	Risk Ratio (M‐H, Random, 95% CI)	0.83 [0.74, 0.94]

2.6.1 Cormack‐Lehane 1	54	6058	Risk Ratio (M‐H, Random, 95% CI)	1.77 [1.56, 2.01]
2.6.2 Cormack‐Lehane 2	54	6058	Risk Ratio (M‐H, Random, 95% CI)	0.54 [0.46, 0.63]
2.6.3 Cormack‐Lehane 3‐4	54	6058	Risk Ratio (M‐H, Random, 95% CI)	0.15 [0.10, 0.24]
2.7 Time for tracheal intubation Show forest plot	59		Mean Difference (IV, Random, 95% CI)	Subtotals only

2.8 Patient‐reported sore throat Show forest plot	31	3725	Risk Ratio (M‐H, Random, 95% CI)	0.81 [0.66, 1.00]

2.9 Number of attempts Show forest plot	50	11004	Risk Ratio (M‐H, Random, 95% CI)	1.02 [0.99, 1.04]

2.9.1 1 attempt	50	5502	Risk Ratio (M‐H, Random, 95% CI)	1.02 [1.00, 1.05]
2.9.2 2‐4 attempts	50	5502	Risk Ratio (M‐H, Random, 95% CI)	0.84 [0.66, 1.08]
2.10 Intubation Difficulty Scale (IDS) Show forest plot	10		Risk Ratio (M‐H, Random, 95% CI)	Totals not selected

2.10.1 IDS 0	10		Risk Ratio (M‐H, Random, 95% CI)	Totals not selected
2.10.2 IDS 1‐5	10		Risk Ratio (M‐H, Random, 95% CI)	Totals not selected
2.10.3 IDS > 5	10		Risk Ratio (M‐H, Random, 95% CI)	Totals not selected
2.11 POGO Score Show forest plot	14		Mean Difference (IV, Random, 95% CI)	Subtotals only

2.12 Mortality Show forest plot	3	826	Risk Ratio (M‐H, Random, 95% CI)	1.15 [0.73, 1.79]

2.13 Subgroup analysis of failed intubation: airway difficulty Show forest plot	59	6607	Risk Ratio (M‐H, Random, 95% CI)	0.45 [0.30, 0.68]

2.13.1 Predicted, known or simulated difficulty	15	1520	Risk Ratio (M‐H, Random, 95% CI)	0.29 [0.17, 0.48]
2.13.2 No difficulty	44	5087	Risk Ratio (M‐H, Random, 95% CI)	0.64 [0.38, 1.06]

Comparison 2. Hyperangulated VL versus DL

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Comparison 3. Channelled VL versus DL

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
3.1 Failed intubation Show forest plot	53	5367	Risk Ratio (M‐H, Random, 95% CI)	0.43 [0.30, 0.61]

3.2 Hypoxaemia Show forest plot	15	1966	Risk Ratio (M‐H, Random, 95% CI)	0.25 [0.12, 0.50]

3.3 Successful first attempt Show forest plot	47	5210	Risk Ratio (M‐H, Random, 95% CI)	1.10 [1.05, 1.15]

3.4 Oesophageal intubation Show forest plot	16	1756	Risk Ratio (M‐H, Random, 95% CI)	0.54 [0.17, 1.75]

3.5 Dental trauma Show forest plot	29	2375	Risk Ratio (M‐H, Random, 95% CI)	0.52 [0.13, 2.12]

3.6 Cormack‐Lehane (CL) grade Show forest plot	40	11865	Risk Ratio (M‐H, Random, 95% CI)	0.70 [0.58, 0.85]

3.6.1 Cormack‐Lehane 1	40	3955	Risk Ratio (M‐H, Random, 95% CI)	2.01 [1.75, 2.31]
3.6.2 Cormack‐Lehane 2	40	3955	Risk Ratio (M‐H, Random, 95% CI)	0.24 [0.17, 0.35]
3.6.3 Cormack‐Lehane 3‐4	40	3955	Risk Ratio (M‐H, Random, 95% CI)	0.14 [0.09, 0.21]
3.7 Time for tracheal intubation Show forest plot	57		Mean Difference (IV, Random, 95% CI)	Subtotals only

3.8 Patient‐reported sore throat Show forest plot	18	1666	Risk Ratio (M‐H, Random, 95% CI)	0.91 [0.73, 1.14]

3.9 Number of attempts Show forest plot	38	8314	Risk Ratio (M‐H, Random, 95% CI)	1.05 [1.00, 1.10]

3.9.1 1 attempt	38	4157	Risk Ratio (M‐H, Random, 95% CI)	1.09 [1.04, 1.14]
3.9.2 2‐4 attempts	38	4157	Risk Ratio (M‐H, Random, 95% CI)	0.47 [0.33, 0.68]
3.10 Intubation Difficulty Scale (IDS) Show forest plot	16	3012	Risk Ratio (M‐H, Random, 95% CI)	0.84 [0.59, 1.19]

3.10.1 IDS 0	16	1004	Risk Ratio (M‐H, Random, 95% CI)	3.34 [2.43, 4.60]
3.10.2 IDS 1‐5	16	1004	Risk Ratio (M‐H, Random, 95% CI)	0.38 [0.27, 0.53]
3.10.3 IDS > 5	16	1004	Risk Ratio (M‐H, Random, 95% CI)	0.21 [0.12, 0.37]
3.11 POGO Score Show forest plot	5		Mean Difference (IV, Random, 95% CI)	Subtotals only

3.12 Subgroup analysis of failed intubation: airway difficulty Show forest plot	52	5287	Risk Ratio (M‐H, Random, 95% CI)	0.42 [0.29, 0.62]

3.12.1 Predicted, known or simulated difficulty	20	1433	Risk Ratio (M‐H, Random, 95% CI)	0.22 [0.10, 0.49]
3.12.2 No difficulty	32	3854	Risk Ratio (M‐H, Random, 95% CI)	0.53 [0.32, 0.88]

Comparison 3. Channelled VL versus DL

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Comparison 4. VL versus DL (all devices combined)

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
4.1 Failed intubation Show forest plot	139	16228	Risk Ratio (M‐H, Random, 95% CI)	0.44 [0.35, 0.56]

4.2 Hypoxia Show forest plot	41	5434	Risk Ratio (M‐H, Random, 95% CI)	0.61 [0.44, 0.85]

4.3 Successful first attempt Show forest plot	138	19797	Risk Ratio (M‐H, Random, 95% CI)	1.05 [1.03, 1.07]

4.4 Oesophageal intubation Show forest plot	40	5768	Risk Ratio (M‐H, Random, 95% CI)	0.47 [0.29, 0.77]

4.5 Subgroup analysis of failed intubation: theatre versus non‐theatre Show forest plot	141	16450	Risk Ratio (M‐H, Random, 95% CI)	0.46 [0.36, 0.59]

4.5.1 Theatre	130	14604	Risk Ratio (M‐H, Random, 95% CI)	0.41 [0.32, 0.54]
4.5.2 Non‐theatre	11	1846	Risk Ratio (M‐H, Random, 95% CI)	0.68 [0.42, 1.09]
4.6 Subgroup analysis of failed intubation: obesity Show forest plot	133	14881	Risk Ratio (M‐H, Random, 95% CI)	0.43 [0.32, 0.56]

4.6.1 Obese	13	1085	Risk Ratio (M‐H, Random, 95% CI)	0.25 [0.13, 0.46]
4.6.2 Non‐obese	120	13796	Risk Ratio (M‐H, Random, 95% CI)	0.47 [0.35, 0.62]
4.7 Subgroup analysis of failed intubation: airway difficulty Show forest plot	132	14999	Risk Ratio (M‐H, Random, 95% CI)	0.42 [0.32, 0.54]

4.7.1 Predicted, known or simulated difficulty	42	4100	Risk Ratio (M‐H, Random, 95% CI)	0.32 [0.23, 0.44]
4.7.2 No difficulty	90	10899	Risk Ratio (M‐H, Random, 95% CI)	0.54 [0.38, 0.78]
4.8 Subgroup analysis of failed intubation: intubator experience Show forest plot	115	13095	Risk Ratio (M‐H, Random, 95% CI)	0.44 [0.34, 0.58]

4.8.1 Expert	98	10939	Risk Ratio (M‐H, Random, 95% CI)	0.41 [0.33, 0.50]
4.8.2 Non‐expert	17	2156	Risk Ratio (M‐H, Random, 95% CI)	0.62 [0.32, 1.18]

Comparison 4. VL versus DL (all devices combined)

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