DÄ internationalArchive26/2018Video Versus Direct Laryngoscopy for Inpatient Emergency Intubation in Adults

Original article

Video Versus Direct Laryngoscopy for Inpatient Emergency Intubation in Adults

A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Dtsch Arztebl Int 2018; 115(26): 437-44; DOI: 10.3238/arztebl.2018.0437

Rombey, T; Schieren, M; Pieper, D

Background: Emergency intubation carries a higher risk of complications than elective airway management. Video laryngoscopy (VL) could potentially improve patient safety. The goal of this study was to determine whether VL is superior to direct laryngoscopy for the emergency intubation of adults in the inpatient setting.

Methods: Pertinent studies were retrieved by a systematic literature search in the MEDLINE, Embase, and CENTRAL databases. The selection of studies, data extraction, and assessment of the potential for bias were carried out independently by two of the authors. Effect sizes were reported as odds ratios (OR) or mean differences (MD). The primary endpoint was successful intubation at the first attempt. Further variables were considered as secondary endpoints.

Results: 1098 titles and abstracts were retrieved, and the full texts of 43 articles were examined. Eight randomized and controlled trials, with a total of 1796 patients, were analyzed. VL was not found to confer any statistically significant advantage with respect to successful intubation at the first attempt (OR 0.72, 95% confidence interval [0.47; 1.12]) or with respect to the time to successful intubation (MD −8.99 seconds [−24.00; 6.01]). On the other hand, the use of VL was significantly associated with a lower number of intubation attempts (MD −0.17 [−0.31; −0.03]) and with a lower frequency of esophageal intubation (OR 0.27 [0.10; 0.75]).

Conclusion: The routine use of VL for airway management in emergency medicine might improve patient safety, as VL is associated with a lower number of intubation attempts and with a lower frequency of esophageal intubation. Further randomized controlled trials are needed before any definitive conclusions can be drawn about the advantages of video laryngoscopy.

LNSLNS

Airway management is a life-saving measure for severely injured and critically ill patients. According to the German Trauma Surgery Society (Deutsche Gesellschaft für Unfallchirurgie), 22% of severely injured patients admitted to hospitals via the emergency room in 2016 were intubated at the site of injury and a further 15% in the emergency room itself. Of the patients transferred to the intensive care unit, 39% were intubated and mechanically ventilated (1). There are no recent data revealing the absolute number of emergency intubations in the hospital setting in Germany.

The standard procedure for securing the airway is endotracheal intubation by means of conventional direct laryngoscopy (DL). Despite the unpredictability and urgency of emergency intubation, the success rate of DL usually exceeds 85% (2, 3). However, intubation safety may be affected by the short preparation time, the possible lack of control over events in the vicinity, the varying degree of training of the persons performing the intubation, and the patient’s unstable state and lowered cardiorespiratory reserves. Compared with elective intubation, emergency intubation is therefore associated with an elevated risk of procedure-related complications and severe adverse events such as aspiration, a fall in oxygen saturation, or even death.

There are indications of a strongly positive correlation between the number of intubation attempts and the rate of complications (4, 5). To increase the safety of intubation, therefore, the number of intubation attempts should be minimized and the first-pass success rate maximized. Video laryngoscopy (VL) may be advantageous in this regard because it visualizes the vocal cord level indirectly by means of an inbuilt camera and a video screen, thus significantly improving the view of the glottis (6). For this reason, VL has proved to be particularly beneficial for less experienced users and in patients with difficult airways (7). Moreover, VL can be used in the event of failure to achieve intubation with DL (8).

Recent systematic reviews of the use of VL in emergency airway management have concerned themselves with studies from one of two areas: out-of-hospital emergency medicine (9) or intensive care (1012). There are no systematic reviews based on randomized controlled trials from the emergency room or a combination of the two hospital settings (emergency department and intensive care unit). Therefore, in order to accurately reflect the complex clinical reality of hospital emergency intubation, characterized by heterogeneity of settings, devices, and levels of training, we included studies from both the emergency room and the intensive care unit in our review.

The results of the three recent systematic reviews point to superiority of VL. The difference is not statistically significant, however, as only three (10), five (11), and four (12) randomized controlled trials were included. Some of these studies excluded patients with difficult airways and are therefore not representative of clinical practice.

Our aim was to determine whether or not video laryngoscopy is superior to direct laryngoscopy for emergency intubation of adults in the hospital setting.

Methods

This systematic review was performed in line with the recommendations of the Cochrane Handbook for Systematic Reviews of Interventions (Cochrane Handbook) (13) and the PRISMA Statement (14). It was registered with PROSPERO (CRD42017065015) (15).

Inclusion criteria

We included randomized controlled trials that compared video laryngoscopy and direct laryngoscopy for urgent intubation of adults in the hospital setting and reported data for at least one of the predefined endpoints. Our primary endpoint was successful intubation at the first attempt. The following variables were used as secondary endpoints: overall success of intubation, number of attempts at intubation, time to successful intubation, and complications or serious adverse events.

Literature survey

The databases MEDLINE, Embase, and CENTRAL (Cochrane Central Register of Controlled Trials) were searched for relevant studies. The search strategy (eTable 1) was formed of relevant keywords and trade names and an RCT filter (RCT, randomized controlled trial) provided by the Cochrane Collaboration (16). No restrictions were imposed on language, publication date, or publication type. All searches were last updated in November 2017. Additional information on screening and other sources of data can be found in eBox 1.

Other sources and literature screening
Other sources and literature screening
eBox 1
Other sources and literature screening
Search strategies for database search
Search strategies for database search
eTable 1
Search strategies for database search

Data extraction and assessment of risk of bias

Two authors (TR, DP) independently recorded data on study characteristics and results using standardized data extraction sheets. The risk of bias for the included studies was evaluated by means of the Cochrane Collaboration’s tool for assessing risk of bias in randomized trials (13), and any disagreements were resolved by face-to-face discussion. If further information was needed, the authors of the study concerned were contacted by e-mail.

Data synthesis and analysis

All statistical analyses (for detailed information see eBox 2) were carried out with the Review Manager software (RevMan, version 5.3; Copenhagen: The Nordic Cochrane Centre, The Cochrane Collaboration, 2014).

Statistical analysis
Statistical analysis
eBox 2
Statistical analysis

The effect sizes for dichotomous endpoints were expressed as odds ratios (OR; Mantel–Haenszel method) and continuous endpoints as mean differences (MD; inverse variance method).

Results

Study selection and characteristics

Figure 1 presents the systematic literature search and study selection process. The electronic database search identified 2379 records; no further records were retrieved from other sources. After removal of duplicates, we screened the titles/abstracts of the remaining 1098 records and assessed 43 full texts. Of these 43 publications, 33 articles and 2 abstracts (Janz D, Semler M, Lentz R, et al.: Randomized trial of video laryngoscopy for endotracheal intubation of critically ill adults. Crit Care Med 2015; 43 (12 Suppl. 1): 212–3; Silverberg M, Li N, Kory P: Efficacy of video laryngoscopy vs. direct laryngoscopy during urgent endotracheal intubation: a randomized controlled trial. Chest 2013; 144 [4 meeting abstract], no pagination) were excluded for various reasons (e1e33), leaving 8 randomized controlled trials (1724) with a total of 1796 patients for analysis. All study authors were contacted, but not all ambiguities could be resolved. As a result, one study that did not provide absolute numbers of patients analyzed per group had to be excluded from the meta-analysis (24).

PRISMA flow chart
PRISMA flow chart
Figure 1
PRISMA flow chart

One half of the studies were performed in emergency departments, the other half in intensive care units. The intubators’ experience ranged from novices to experienced anesthesiologists, and the indications for intubation also varied among the studies. Some studies excluded patients who were known or could be anticipated to have difficult airways, an immobilized cervical spine, maxillofacial trauma, or cardiac arrest (19, 2224). The patients were given sedatives or hypnotics in all studies. In all but one study (22) muscle relaxants were administered. No study was industrially sponsored, but most of them were funded by their institution or by national funding bodies. Apart from one study (18), they were all registered with ClinicalTrials.gov. Detailed information on study characteristics can be found in Table 1.

Study characteristics
Study characteristics
Table 1
Study characteristics

Risk of bias

Overall, the risk of bias of the included studies was moderate (eFigure 1). In one study the randomization sequence was not properly generated and group allocation was not concealed (22). However, randomization was carried out correctly in all other studies, so altogether the risk of selection bias was low. Owing to the nature of the intervention, it was not possible to blind the intubators or other study personnel. Hence, the risk of performance bias was high for all studies and all endpoints. The risk of detection bias was also high, unless waveform capnography was used to determine the endpoints objectively. Given the short time spans between randomization, intubation, and endpoint measurement, no or only very little information regarding endpoints or study discontinuation was missing. The risk of attrition bias was therefore low, except in one study that reported relatively high rates of missing data (24). The risk of reporting bias was low for all studies for which a study protocol was provided (20, 21, 23); it remained unclear for the remaining studies (1719, 22, 24). Other sources of bias were not found.

Assessment of the risk of bias in the included studies. n.a., not applicable
Assessment of the risk of bias in the included studies. n.a., not applicable
eFigure 1
Assessment of the risk of bias in the included studies. n.a., not applicable

Results

There was no difference in first-pass intubation success rate between video laryngoscopy and direct laryngoscopy (p = 0.14); however, the data point to superiority of video laryngoscopy (OR 0.72, 95% confidence interval [CI] [0.47; 1.12], n = 1173 (1723), I2 = 49%) (Figure 2).

Meta-analysis of first-pass intubation success: studies divided by setting
Meta-analysis of first-pass intubation success: studies divided by setting
Figure 2
Meta-analysis of first-pass intubation success: studies divided by setting

Because the overall intubation success rate in four (19, 2123) of the five studies that reported this endpoint was 100% for either one of the two intubation techniques, the study results for this endpoint were not subjected to meta-analysis. In the remaining study (18), 92% of patients in the VL group and 96% in the DL group were intubated. The number of intubation attempts was lower for video laryngoscopy than for direct laryngoscopy in intensive care studies (MD −0.28 [−0.42; −0.14], n = 678, I= 25%), but not in emergency room studies (MD −0.04 [−0.13; 0.06], n = 345, I= 19%). Overall, however, the number of intubation attempts was lower for video laryngoscopy than for direct laryngoscopy (MD −0.17 [−0.31; −0.03], n = 1023 (17, 1923), I= 71%) (Figure 3). No effect of video laryngoscopy was observed on the time to successful intubation (MD −8.99 s [−24.00; 6.01], n = 975 (1823), I= 64%) (eFigure 2).

Meta-analysis of number of intubation attempts: studies divided by setting
Meta-analysis of number of intubation attempts: studies divided by setting
Figure 3
Meta-analysis of number of intubation attempts: studies divided by setting
Meta-analysis of time to successful intubation in seconds: studies divided by setting
Meta-analysis of time to successful intubation in seconds: studies divided by setting
eFigure 2
Meta-analysis of time to successful intubation in seconds: studies divided by setting

The following complications were reported in at least two studies: airway trauma, dental injuries, aspiration, cardiac arrest, death during intubation, esophageal intubation, hypoxemia, and hypotension (eTable 2). However, the number of studies with adequate reporting of data on airway trauma, dental injuries, aspiration, cardiac arrest, and death during intubation was not high enough for meta-analysis. Because the threshold values for the occurrence of hypoxemia and hypotension varied across studies, only the role of video laryngoscopy in esophageal intubation could be analyzed. Video laryngoscopy lowered the incidence of this complication (OR 0.27 [0.10; 0.75], n = 782 [18, 20–22], I= 0%) (Figure 4).

Meta-analysis of esophageal intubation: studies divided by setting
Meta-analysis of esophageal intubation: studies divided by setting
Figure 4
Meta-analysis of esophageal intubation: studies divided by setting
Endpoint results of included studies (video laryngoscopy vs. direct laryngoscopy)
Endpoint results of included studies (video laryngoscopy vs. direct laryngoscopy)
eTable 2
Endpoint results of included studies (video laryngoscopy vs. direct laryngoscopy)

No differences for any endpoint were found among different video laryngoscopy devices (C-MAC, GlideScope, McGrath; data not shown) or among intubators with differing amounts of experience (eFigures 3–5).

Subgroup analysis of first-pass intubation success: studies divided by intubators’ level of training
Subgroup analysis of first-pass intubation success: studies divided by intubators’ level of training
eFigure 3
Subgroup analysis of first-pass intubation success: studies divided by intubators’ level of training
Subgroup analysis of number of intubation attempts: studies divided by intubators’ level of training
Subgroup analysis of number of intubation attempts: studies divided by intubators’ level of training
eFigure 4
Subgroup analysis of number of intubation attempts: studies divided by intubators’ level of training
Subgroup analysis of time to successful intubation: studies divided by intubators’ level of training
Subgroup analysis of time to successful intubation: studies divided by intubators’ level of training
eFigure 5
Subgroup analysis of time to successful intubation: studies divided by intubators’ level of training

In the course of the planned sensitivity analysis, one study was excluded from meta-analysis because it had a high risk of selection bias and was also the only study in which patients did not routinely receive muscle relaxants and for which the first-pass intubation success rate of direct laryngoscopy was strikingly low (22). Exclusion of this study had no impact on statistical significance (not shown), but the heterogeneity of first-pass intubation success rate was reduced to I= 0%.

In an additional sensitivity analysis, the study excluded due to persisting ambiguities (24) was included in the meta-analysis under the assumption of even distribution of the missing data. However, the overall results were not significantly altered (OR for first-pass intubation success rate 0.79 [0.55; 1.13], MD of time to successful intubation −2.49 s [−14.48; 9.49]).

Because fewer than 10 studies were analyzed, publication bias was assessed only by visual evaluation of the funnel plot (eFigure 6). The distribution of results for the primary endpoint seemed to be relatively symmetrical, but nevertheless the risk of publication bias remains unclear.

Funnel plot of study results with regard to successful first-pass intubation; studies divided by setting
Funnel plot of study results with regard to successful first-pass intubation; studies divided by setting
eFigure 6
Funnel plot of study results with regard to successful first-pass intubation; studies divided by setting

Discussion

We evaluated the results of eight randomized controlled trials that compared video laryngoscopy to direct laryngoscopy in adult patients who required emergency airway management in the emergency room or intensive care unit. These studies included a total of 1796 patients, in most of whom there was no reason to expect difficult airways. The risk of bias was moderate.

No statistically significant difference was found between video laryngoscopy and direct laryngoscopy with regard to the primary endpoint of this systematic review, the first-pass success rate for intubation. However, video laryngoscopy reduced the number of intubation attempts and the rate of esophageal intubation: in every sixth patient, an additional intubation attempt was avoided. The number of treatments needed to prevent one esophageal intubation was 24.

Strengths and limitations

One strength of our review is its systematic, predetermined nature. Clinical heterogeneity among the studies as a result of different settings or use of different devices for video laryngoscopy was assessed in subgroup analyses. With regard to the primary endpoint, however, the effect size for emergency room studies (OR 0.75) scarcely differed from that for studies in the intensive care unit (OR 0.69). Furthermore, the calculated effect sizes were not decisively altered by supplementary sensitivity or subgroup analyses, which speaks for their robustness.

Despite our extensive literature search, we found only a small number of relevant randomized controlled trials. Moreover, no ongoing or not yet published studies were registered at ClinicalTrials.gov. The risk of bias of the eight studies included was elevated by the fact that it would hardly have been feasible to blind the study personnel to the type of laryngoscope used. While the risk of other forms of bias was relatively low, the risks of performance bias and detection bias were classed as high for most of the endpoints. Given the particularly critical circumstances in the case of emergency intubation, despite the lack of blinding it is unlikely that the patients were treated dissimilarly or the endpoints systematically measured differently. Apart from the training level of the operator, the setting, and the type of video laryngoscopy device used, there were also other differences among the studies for which no adjustment was possible. Therefore, the findings of our analysis may have been influenced by differences in intubation practice (e.g, in preoxygenation or neuromuscular blockade), by the indication for intubation, or by the definitions of the endpoints. Furthermore, the patients’ basic characteristics were comparable only to a limited degree. The proportion of patients with difficult airways, for instance, was not reported by all studies, which prevented systematic comparison of this variable. Among the studies that reported it, however, there was no difference between the VL and DL groups.

Only one study (24) reported how long video laryngoscopy had already been in use in the authors’ institution. In common with regular airways training, however, duration of use is a factor that may influence individual performance, but could not be considered in our analysis because the available data did not permit quantification. Furthermore, the meta-analyses included no correction for multiple testing, because there is currently no established standard method for tackling this problem. Possible solutions are being debated (25).

Comparison with other systematic reviews

Huang et al. (11) and Zhao et al. (12) have recently published meta-analyses of randomized controlled trials carried out in intensive care units. Their results are in accordance with ours: the first-pass intubation success rate was not significantly improved (p = 0.35 and 0.27) or the time to successful intubation shortened (p = 0.08 and 0.69) by video laryngoscopy, but the incidence of esophageal intubation was reduced (p = 0.03 in both meta-analyses). Neither study investigated the effect of video laryngoscopy on the overall intubation success rate or the number of intubation attempts.

Summary

Video laryngoscopy seems to reduce the number of intubation attempts and the rate of esophageal intubation, so its use in emergency airway management could potentially increase patient safety. Video laryngoscopy also tended to be superior to direct laryngoscopy in terms of first-pass intubation success rate, but the difference was not statistically significant. Moreover, this finding was for patients who in most cases exhibited no evidence of difficult airways. Consequently, no conclusions can be drawn with regard to patients with difficult airways. Neither can routine use of video laryngoscopy be definitively recommended for urgent intubation of adults in the hospital setting, at least until future research, e.g., randomized controlled trials, provides unequivocal evidence.

Acknowledgment

The authors thank Kirsten Hüllebrand for her expert clinical advice.

Conflict of interest statement

The authors declare that no conflict of interest exists.

Manuscript submitted on 13 September 2017, revised version accepted on 21 February 2018

Translated from the original German by the authors and David Roseveare

Corresponding author
Tanja Rombey
Institut für Gesundheitsökonomie und Klinische Epidemiologie
Universität zu Köln
Gleueler Str. 176
50935 Köln, Germany
tanja.rombey@uni-wh.de

Supplemantary material
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eTables, eBox and eFigures:
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Sulser S, Ubmann D, Brueesch M, et al.: The C-MAC videolaryngoscope compared with conventional laryngoscopy for rapid sequence intubation at the emergency department: study protocol. Scand J Trauma Resusc Emerg Med 2015; 23: 38 CrossRef MEDLINE PubMed Central
e26.
Teoh WH, Saxena S, Shah MK, Sia AT: Comparison of three videolaryngoscopes: pentax airway scope, C-MAC, glidescope vs the Macintosh laryngoscope for tracheal intubation. Anaesthesia 2010; 65: 1126–32 CrossRef MEDLINE
e27.
Truszewski Z, Bogdanski L, Kurowski A, et al.: Does the venner A.P. advance video laryngoscope improve success of first intubation attempt of trauma patient? Am J Emerg Med 2016; 34: 315–6.
e28.
Woo CH, Kim SH, Park JY, et al.: Macintosh laryngoscope vs. Pentax-AWS video laryngoscope: comparison of efficacy and cardiovascular responses to tracheal intubation in major burn patients. Korean J Anesthesiol 2012; 62: 119–24 CrossRef MEDLINE PubMed Central
e29.
Xue FS, Yang GZ, Li HX, Liu YY: Comparing direct and video laryngoscopy for urgent intubation during chest compression. Resuscitation 2017; 111: e1 CrossRef MEDLINE
e30.
Xue FS, Yang GZ, Sun C: Comparing video and direct laryngoscopy in critically ill patients: rational study design is important. Crit Care Med 2017; 45: e326 CrossRef PubMed Central
e31.
Yanik BG, Yolcu S, Aydinok G, et al.: The quickest and easiest endotracheal intubation device in difficult airway for emergency residents: video laryngoscope, the easiest laryngoscope for emergency residents. Am J Emerg Med 2014; 32: 807–9 CrossRef MEDLINE
e32.
Yeatts D, Grissom T, Dutton R, Hu P, Chang YW, Scalea T: Video laryngoscopy does not improve outcomes in emergency intubation. Crit Care Med 2009; 37: A455.
e33.
Yu JH, Wang Y: [Clinical study of SMT- video laryngoscope with difficult airway intubation in emergency department]. Zhonghua Wai Ke Za Zhi 2017; 55: 549–53 MEDLINE
Institute for Health Economics and Clinical Epidemiology of the University of Cologne: Tanja Rombey
Department of Anesthesiology and Intensive Care Medicine, Medical Center Cologne-Merheim, Witten/Herdecke University: Dr. Mark Schieren
Department of Evidence-based Health Services Research, Institute for Research in Operative Medicine, Chair of Surgical Research, Faculty of Health, School of Medicine, Witten/Herdecke University: Dr. Dawid Pieper
PRISMA flow chart
PRISMA flow chart
Figure 1
PRISMA flow chart
Meta-analysis of first-pass intubation success: studies divided by setting
Meta-analysis of first-pass intubation success: studies divided by setting
Figure 2
Meta-analysis of first-pass intubation success: studies divided by setting
Meta-analysis of number of intubation attempts: studies divided by setting
Meta-analysis of number of intubation attempts: studies divided by setting
Figure 3
Meta-analysis of number of intubation attempts: studies divided by setting
Meta-analysis of esophageal intubation: studies divided by setting
Meta-analysis of esophageal intubation: studies divided by setting
Figure 4
Meta-analysis of esophageal intubation: studies divided by setting
Key messages
Study characteristics
Study characteristics
Table 1
Study characteristics
The clinical perspective
Other sources and literature screening
Other sources and literature screening
eBox 1
Other sources and literature screening
Statistical analysis
Statistical analysis
eBox 2
Statistical analysis
Assessment of the risk of bias in the included studies. n.a., not applicable
Assessment of the risk of bias in the included studies. n.a., not applicable
eFigure 1
Assessment of the risk of bias in the included studies. n.a., not applicable
Meta-analysis of time to successful intubation in seconds: studies divided by setting
Meta-analysis of time to successful intubation in seconds: studies divided by setting
eFigure 2
Meta-analysis of time to successful intubation in seconds: studies divided by setting
Subgroup analysis of first-pass intubation success: studies divided by intubators’ level of training
Subgroup analysis of first-pass intubation success: studies divided by intubators’ level of training
eFigure 3
Subgroup analysis of first-pass intubation success: studies divided by intubators’ level of training
Subgroup analysis of number of intubation attempts: studies divided by intubators’ level of training
Subgroup analysis of number of intubation attempts: studies divided by intubators’ level of training
eFigure 4
Subgroup analysis of number of intubation attempts: studies divided by intubators’ level of training
Subgroup analysis of time to successful intubation: studies divided by intubators’ level of training
Subgroup analysis of time to successful intubation: studies divided by intubators’ level of training
eFigure 5
Subgroup analysis of time to successful intubation: studies divided by intubators’ level of training
Funnel plot of study results with regard to successful first-pass intubation; studies divided by setting
Funnel plot of study results with regard to successful first-pass intubation; studies divided by setting
eFigure 6
Funnel plot of study results with regard to successful first-pass intubation; studies divided by setting
Search strategies for database search
Search strategies for database search
eTable 1
Search strategies for database search
Endpoint results of included studies (video laryngoscopy vs. direct laryngoscopy)
Endpoint results of included studies (video laryngoscopy vs. direct laryngoscopy)
eTable 2
Endpoint results of included studies (video laryngoscopy vs. direct laryngoscopy)
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e25. Sulser S, Ubmann D, Brueesch M, et al.: The C-MAC videolaryngoscope compared with conventional laryngoscopy for rapid sequence intubation at the emergency department: study protocol. Scand J Trauma Resusc Emerg Med 2015; 23: 38 CrossRef MEDLINE PubMed Central
e26.Teoh WH, Saxena S, Shah MK, Sia AT: Comparison of three videolaryngoscopes: pentax airway scope, C-MAC, glidescope vs the Macintosh laryngoscope for tracheal intubation. Anaesthesia 2010; 65: 1126–32 CrossRef MEDLINE
e27.Truszewski Z, Bogdanski L, Kurowski A, et al.: Does the venner A.P. advance video laryngoscope improve success of first intubation attempt of trauma patient? Am J Emerg Med 2016; 34: 315–6.
e28.Woo CH, Kim SH, Park JY, et al.: Macintosh laryngoscope vs. Pentax-AWS video laryngoscope: comparison of efficacy and cardiovascular responses to tracheal intubation in major burn patients. Korean J Anesthesiol 2012; 62: 119–24 CrossRef MEDLINE PubMed Central
e29. Xue FS, Yang GZ, Li HX, Liu YY: Comparing direct and video laryngoscopy for urgent intubation during chest compression. Resuscitation 2017; 111: e1 CrossRef MEDLINE
e30.Xue FS, Yang GZ, Sun C: Comparing video and direct laryngoscopy in critically ill patients: rational study design is important. Crit Care Med 2017; 45: e326 CrossRef PubMed Central
e31.Yanik BG, Yolcu S, Aydinok G, et al.: The quickest and easiest endotracheal intubation device in difficult airway for emergency residents: video laryngoscope, the easiest laryngoscope for emergency residents. Am J Emerg Med 2014; 32: 807–9 CrossRef MEDLINE
e32.Yeatts D, Grissom T, Dutton R, Hu P, Chang YW, Scalea T: Video laryngoscopy does not improve outcomes in emergency intubation. Crit Care Med 2009; 37: A455.
e33.Yu JH, Wang Y: [Clinical study of SMT- video laryngoscope with difficult airway intubation in emergency department]. Zhonghua Wai Ke Za Zhi 2017; 55: 549–53 MEDLINE