Glidescope® video-laryngoscopy versus direct laryngoscopy for endotracheal intubation: a systematic review and meta-analysis
- First Online:
- Cite this article as:
- Griesdale, D.E.G., Liu, D., McKinney, J. et al. Can J Anesth/J Can Anesth (2012) 59: 41. doi:10.1007/s12630-011-9620-5
- 3.8k Views
The Glidescope® video-laryngoscopy appears to provide better glottic visualization than direct laryngoscopy. However, it remains unclear if it translates into increased success with intubation.
We systematically searched electronic databases, conference abstracts, and article references. We included trials in humans comparing Glidescope® video-laryngoscopy to direct laryngoscopy regarding the glottic view, successful first-attempt intubation, and time to intubation. We generated pooled risk ratios or weighted mean differences across studies. Meta-regression was used to explore heterogeneity based on operator expertise and intubation difficulty.
We included 17 trials with a total of 1,998 patients. The pooled relative risk (RR) of grade 1 laryngoscopy (vs ≥ grade 2) for the Glidescope® was 2.0 [95% confidence interval (CI) 1.5 to 2.5]. Significant heterogeneity was partially explained by intubation difficulty using meta-regression analysis (P = 0.003). The pooled RR for nondifficult intubations of grade 1 laryngoscopy (vs ≥ grade 2) was 1.5 (95% CI 1.2 to 1.9), and for difficult intubations it was 3.5 (95% CI 2.3 to 5.5). There was no difference between the Glidescope® and the direct laryngoscope regarding successful first-attempt intubation or time to intubation, although there was significant heterogeneity in both of these outcomes. In the two studies examining nonexperts, successful first-attempt intubation (RR 1.8, 95% CI 1.4 to 2.4) and time to intubation (weighted mean difference −43 sec, 95% CI −72 to −14 sec) were improved using the Glidescope®. These benefits were not seen with experts.
Compared to direct laryngoscopy, Glidescope® video-laryngoscopy is associated with improved glottic visualization, particularly in patients with potential or simulated difficult airways.
Le vidéolaryngoscope Glidescope® comparé à la laryngoscopie directe pour l’intubation trachéale : revue systématique de la littérature et méta-analyse
Le vidéolaryngoscope Glidescope® semble procurer une meilleure visualisation de la glotte que la laryngoscopie directe. Il n’est toutefois pas certain que cela se traduise par une meilleure réussite des intubations.
Nous avons fait une recherche systématique dans les bases de données électroniques, parmi les résumés de congrès et les références d’articles. Nous avons inclus les études chez l’homme comparant le vidéolaryngoscope Glidescope® à la laryngoscopie directe pour ce qui concerne la visualisation de la glotte, la réussite de l’intubation au premier essai et le délai d’intubation. Nous avons généré un risque relatif global ou des différences moyennes pondérées entre les études. Une métarégression a permis d’explorer l’hétérogénéité en fonction de l’expertise de l’opérateur et de la difficulté d’intubation.
Nous avons inclus 17 études incluant un total de 1998 patients. Le risque relatif (RR) global d’une laryngoscopie de grade 1 (contre une laryngoscopie de grade ≥ 2) avec le Glidescope® a été de 2,0 (intervalle de confiance [IC] à 95 % : 1,5 à 2,5). L’hétérogénéité significative a été expliquée en partie par la difficulté d’intubation en utilisant l’analyse par métarégression (P = 0,003). Le RR global pour les intubations non difficiles de grade 1 à la laryngoscopie (contre les grades ≥ 2) a été de 1,5 (IC à 95 % : 1,2 à 1,9) et le RR pour les intubations difficiles a été de 3,5 (IC à 95 % : 2,3 à 5,5). Il n’y a pas eu de différence entre le Glidescope® et la laryngoscopie directe pour ce qui concerne l’intubation réussie au premier essai ou pour le délai d’intubation, bien qu’une hétérogénéité significative ait été observée pour ces deux critères d’évaluation. Dans les deux études impliquant des non-experts, la première tentative réussie d’intubation (RR: 1,8; IC à 95 % : 1,4 à 2,4) et le délai d’intubation (différence de moyenne pondérée −43 sec; IC à 95 % : −72 à −14 sec) ont été améliorés par l’utilisation du Glidescope®. Ces avantages n’ont pas été retrouvés chez les experts.
Comparée à la laryngoscopie directe, la vidéolaryngoscopie avec le Glidescope® est associée à une amélioration de la visualisation de la glotte, en particulier chez les patients avec des voies aériennes difficiles potentielles ou simulées.
Anesthesiologists perform endotracheal intubation (ETI) in the operating room under controlled circumstances, and the procedure carries a low risk of complications.1 Although laryngoscopy is difficult in 6-10% of intubations,2-4 difficult or failed intubations are much less frequent, occurring in 1.8-5.8% and 0.13-0.30%, respectively.2,5-8 Unfortunately, physical findings on examination of the airway discriminate poorly between potentially easy and difficult intubations.9 Thus, anesthesiologists need to be prepared for the unanticipated difficult airway, as many of these patients have had a “reassuring” airway physical examination. In addition to the unanticipated difficult airway, there are circumstances that lend themselves to a high risk of difficult laryngoscopy and tracheal intubation. In particular, emergent ETI outside of the operating theatre is associated with a much higher risk of difficult laryngoscopy and intubation.10-13 As such, techniques that may improve successful intubation may be especially beneficial in these emergent environments. Laryngoscopy with the Glidescope® video-laryngoscope (Verathon Medical, Bothell, WA, USA) appears to be associated with improved glottic visualization.14,15 Whether the improved visualization translates into increased success at ETI, when compared to direct laryngoscopy, remains unclear.14,16 Given this uncertainty, our goal was to perform a systematic review and meta-analysis of randomized and quasi-randomized trials comparing Glidescope® video-laryngoscopy to direct laryngoscopy regarding glottic visualization, successful first-attempt intubation, and time to intubation. In addition, we explored the heterogeneity in these outcomes based on operator expertise and according to the difficulty of the intubation.
This article reports our meta-analysis of controlled trials of Glidescope® video-laryngoscopy compared to direct laryngoscopy in accordance with the Preferred Reporting Items for Systematic reviews and Meta-analyses (PRISMA) statement.17 A review protocol was not published for this study.
We systematically searched MEDLINE (1966 to June 13, 2011), EMBASE (1977 to June 13, 2011), and The Cochrane Central Register of Controlled Trials (CENTRAL) (1948 to June13, 2011) for randomized and quasi-randomized trials comparing Glidescope® video-laryngoscopy to direct laryngoscopy regarding the glottic view, successful first-attempt intubation, and time to intubation. We included non-English publications. We hand-searched abstracts of selected conferences from 2000 to 2010, including those of the American Society of Anesthesiologists, the Canadian Anesthesiologists’ Society, and the International Anesthesia Research Society. We also hand-searched bibliographies of all relevant trials and review articles.
For the bibliographic review, we constructed search filters for the concepts “Glidescope video-laryngoscope” and “clinical trials” using a combination of exploded Medical Subject Heading (MeSH) terms and text words all combined with the Boolean operator “OR.” The Glidescope® video-laryngoscope filter contained the text words glidescope and video-laryngoscope. The clinical trials filter included the MeSH terms clinical trials [publication type], clinical trials as topic, placebos with text words trial*, random* or placebo. A similar search strategy was used for both EMBASE and CENTRAL.
Selection criteria, data abstraction, and methodological quality
In duplicate and independently, two authors (D.G., D.L.) screened all articles and abstracts, which were included if they 1) were randomized or quasi-randomized controlled trials, 2) compared direct laryngoscopy to Glidescope® video-laryngoscopy, 3) addressed adult patients, and 4) contained any outcome of interest (Cormack-Lehane view,18 successful first-attempt intubation, time to intubation).
The same two authors abstracted the data and assessed the study quality in duplicate and independently. Disagreement was resolved by discussion and arbitrated if necessary by a third author (P.C.). We abstracted the year of publication, sample size, country of origin, operator training and experience, physical examination of the airway, anticipated or history of difficult intubation, application of manual in-line stabilization, Cormack-Lehane grade, successful first attempt at intubation, and time required to intubate. We contacted investigators for missing data as necessary.
We used relative risk (RR) as the summary measure for dichotomous outcomes (glottic view and successful first intubation attempt) and the weighted mean difference (WMD), in seconds, as the summary measure for time to intubate. We applied a half-integer continuity correction to all four cells if the event rates were zero. The random effects method of DerSimonian and Laird was used to generate a pooled RR or WMD across studies.19 Random effects analysis yields a more conservative estimate than the fixed-effects model in the presence of between-study heterogeneity. We assessed statistical heterogeneity using Cochran’s Q statistic20 (with P < 0.10 considered significant) and expressed the quantity using the I2 statistic and 95% confidence interval (CI). The I2 statistic indicates the percentage of variation in study results that is due to between-study heterogeneity rather than sampling variability.21 We assessed for the following outcomes: Cormack-Lehane view grade 1 vs grade ≥ 2, successful first-attempt intubation, and time to intubate (in seconds).
Sources of potential heterogeneity identified a priori were the experience level of the operator (anesthesia or casualty consultants or house staff vs “other”) and potential difficulty. Intubations were considered difficult in studies that included patients with a known prior difficult intubation, physical examination features suggesting a difficult intubation, or in whom difficult intubation was simulated by providing manual-in-line stabilization. Random-effects meta-regression was used to evaluate the relation between these subgroups on the final pooled estimates.22 We evaluated the presence of publication bias by visual inspection of the funnel plot and by using Egger’s and Begg’s tests, with P < 0.05 considered statistically significant. All analyses were done using Stata 10.0 (2007) (StataCorp LP, College Station, TX, USA).
Characteristics of randomized and quasi-randomized trials comparing Glidescope® video-laryngoscopy to direct laryngoscopy
First author, year
Country of origin
No. of patients
Total no. patients randomized
Excluded MP III-IV or history of DI
Elective CABG surgery
Anesthesiologist consultants 39%
House staff 61%
Experienced (≥ 10 GS intubations) 39%
Excluded if history of DI
Elective dental or maxillofacial surgery
Anesthesiologists with varying experience with the GS
ASA I + II patients
Excluded patients with a potentially difficult airway or MP III/IV
Patients maintained in manual in-line stabilization
ASA I and II patients admitted for elective gynecological procedures
Truview EVO2 30
Anesthesiologists experienced with each device (≥ 20 clinical intubations)
Excluded if (1) history of DI or (2) features suggestive of DI (MP III/IV, TMD < 6.0 cm, IID < 3.5 cm)
Manual in-line stabilization applied
ASA I-III. Any surgical procedure requiring intubation
Anesthesiologists experienced with each device (≥ 50 clinical intubations)
At least two features of DI (TMD < 6 cm, MP III/ IV, IID < 4 cm)
ASA I-III. Any surgical procedure requiring intubation
All patients had examinations with both
No signs of predicted DI
ASA I-III patients
Each operator performed 5 intubations with each technique
Inexperienced trainees: 8 paramedics, 4 first-year house staff, 4 nurses, 4 medical students
No history of signs of DI
MP I or II, mouth opening > 4 cm
ASA I or II undergoing elective surgery requiring ETI
All 20 patients had laryngoscopy with DL and GS (in randomized order)
Two senior anesthesiology house staff (≥ 30 GS intubations)
Patients maintained in manual in-line stabilization
Elective neuroradiological procedure
All 120 patients had laryngoscopy with each device (in randomized order)
Two anesthesiology consultants with ≥ 50 intubations with each device
At least one predictor of difficult airway (MP ≥ II, decreased atlantooccipital joint movement ≤ 15°, mouth opening ≤ 38 mm, TMD ≤ 65 mm)
ASA I-III elective patients
Nonanesthesia house staff
Elective dental surgery
Single anesthesiologist with ≥ 50 intubations with each device
Excluded patients with a history of anticipated/difficult airway, or MP III/IV
ASA I and II patients scheduled for elective surgery
5 Experienced anesthesiologists (> 10 years practice) and > 20 GS intubations)
No exclusions based on known or anticipated difficulty
ASA I-IV. Elective operating room patients
Pentax AWS 100
Experienced anesthesiologists with > 30 intubations with each device
Excluded patients with BMI > 40 and those with limited mouth opening
ASA I-III. Elective gynecological, orthopedic, breast, or esthetic surgery
All 18 patients had both GS and DL (in random order)
One anesthesiologist who performed > 50 intubations with each device
Excluded: BMI > 35, prior neck surgery, or difficult airway
ASA I-III elective noncardiac surgery
In-line stabilization maintained
Excluded: BMI > 35, prior difficult intubation
In-line stabilization maintained
One anesthesiologist experienced in GS and DL
Excluded patients with predicted difficult airways
ASA I patients for elective plastic surgery
Anesthesiology and emergency medicine house staff
Patients requiring emergent airway management at a level 1 trauma center
Most of the studies specifically excluded patients with a known or anticipated difficult airway.14,16,23,25,27,28,30-34 In contrast, two studies selected patients with clinical examination features suggesting a difficult intubation.24,26 Five studies attempted to increase the difficulty of laryngoscopy by applying manual in-line stabilization.23,28,29,31,34 Finally, three studies did not specify any exclusion or inclusion criteria based on prior or anticipated difficulty of laryngoscopy.15,35,36
Grade 1 glottic view
Outcomes of randomized and quasi-randomized trials comparing Glidescope® video-laryngoscopy to direct laryngoscopy
First author, year
Cormack-Lehane I/II/III/IV (no.)
Successful 1st intubation attempt (event/total patients)
Time to intubation (sec) (SD or IQR)
Gr 1 or 2: 37/39
Gr 1 or 2: 17/39
Successful first-attempt intubation
Time to intubation
In this meta-analysis of randomized trials comparing Glidescope® video-laryngoscopy to direct laryngoscopy, the former was associated with improved glottic visualization, particularly amongst studies that considered patients with potential or simulated difficult airways. Although there was an improved successful first intubation attempt and faster time to intubation with Glidescope® video-laryngoscopy, it was confined to studies of nonexpert operators. There was no benefit in either of these outcomes in studies with expert operators. Importantly, there was marked between-study heterogeneity in all three outcomes.
Improved glottic visualization (compared to that with direct laryngoscopy) is a consistent finding with nonstandard laryngoscopes, including video-laryngoscopes.37 Building on this, we have demonstrated that improvement in glottic visualization afforded by the Glidescope® is even greater in studies using patients with either simulated (via manual in-line stabilization) or physical examination predictors of difficult laryngoscopy. This is not surprising as the Glidescope® appears to be used often by clinicians in these situations. A large observation cohort study by Aziz and colleagues of 2,004 Glidescope® intubations showed that most were performed in patients with clinical examination predictors of a difficult direct laryngoscopy.38 Thus, clinicians are triaging patients to video-laryngoscopy when difficulty with endotracheal intubation is anticipated.
As in our current review, a prior systematic review demonstrated significant heterogeneity when comparing the Glidescope® results to those achieved with the direct laryngoscope.37 In contrast, we attempted to quantify and evaluate sources of heterogeneity by both operator expertise and potential difficulty of the intubation. Given that most of the studies were performed by airway management experts on patients without predictors of difficult intubation, it is not surprising that the Glidescope® did not result in improved first-attempt success. Aside from one trial with a markedly low rate of 63%, documented by Morello et al.,33 the rest of the studies with experts—and excluding difficult airways—had a first-attempt success rate of > 90%.15,16,27,32 This high rate of success with direct laryngoscopy by anesthesiologists is reflected in other clinical studies.6 Even in the unlikely scenario that Glidescope® video-laryngoscopy would improve the success rate in patients without difficult airways by experts, it would require a large sample of patients to prove it. Thus, potential benefits of Glidescope® video-laryngoscopy may lie with: 1) use in patients with clinical features indicating difficult laryngoscopy; 2) it being used as a rescue method following failed direct laryngoscopy; or 3) it being used by nonexpert providers. Indeed, the observational study by Aziz et al. demonstrated that the Glidescope® was successful in 96% of patients with predictors of difficult direct laryngoscopy and in 94% following failed direct laryngoscopy.38
Although our review did show increased first-attempt success and decreased time to intubation in studies of nonexperts with the Glidescope® compared to direct laryngoscopy, these results must be interpreted with caution given that there were only two studies in this subgroup.14,36 Rather, the possible benefit of Glidescope® video-laryngoscopy amongst nonexperts should be viewed as an area that requires further research.
This systematic review and meta-analysis highlights several areas that need to be addressed. How is expertise developed and defined, particularly when a new technology is introduced? What role should nonexperts play in airway management? Studies examining new technology are prone to proficiency bias. Despite this fact, anesthesiologists have incorporated the Glidescope® into their armamentarium with a high rate of success.39 Although it seems reasonable to assume that anesthesia consultants are experts, it remains less clear how, and at what point, this competence develops. When examining trainees, we have previously shown that anesthesia house staff were successful in 85% of their first attempts at intubating critically ill patients.40 This success rate is very respectable given that this is a population with a 6.6-22.0% risk of a difficult intubation.11,13,41 Furthermore, anesthesia house staff require fewer attempts to perform tracheal intubation compared to their nonanesthesia counterparts. Having an airway management expert at the bedside for each intubation may be advantageous, but there are many situations when this is not feasible. In many environments, there may be limited, if any, access to anesthesiologists, and airway management must be delivered by physicians from different speciality backgrounds. Endotracheal intubation remains a competence objective of the Royal College of Physicians and Surgeons of Canada in training for internal medicine.42 Also, use of an advanced airway (e.g., endotracheal tube) remains a fundamental skill in Advanced Cardiac Life Support according to the 2005 American Heart Association Guidelines.43 Thus, technologies that can improve the success of airway management, particularly in the hands of nonexperts, are desirable and should be studied. An example is Glidescope® use by prehospital paramedics.44
There are several limitations to our review. As previously stated, there was marked heterogeneity in all of our endpoints that was only partially explained by subgroup analysis. We attempted to account for this heterogeneity by performing a random-effects meta-regression, which yields a more conservative pooled estimate when between-study heterogeneity exists.45 In addition, we explored heterogeneity by a priori defined subgroups and presented these results when they were significant. As with all meta-analyses, our review is subject to information bias. We defined expertise and difficulty a priori, but there may be marked differences between studies with respect to subject or operator characteristics that we were unable to evaluate from the available information. Another limitation is the low number of studies that included nonexperts, which markedly limits the ability to evaluate the effect of video-laryngoscopy in this important subgroup. Finally, there was evidence of publication bias in our primary outcome of the glottic view, suggesting that small studies favouring direct laryngoscopy were not being published. However, tests of publication bias are subject to a high risk of a type I error in the presence of significant heterogeneity, limiting their interpretability.46
In conclusion, we have shown in our meta-analysis that, compared to direct laryngoscopy, Glidescope® video-laryngoscopy is associated with improved glottic visualization, particularly in studies that considered patients with potential or simulated difficult airways. In addition, there is marked heterogeneity in all of our outcomes that is partially explained by operator expertise or the difficulty of intubation. There is a need for further evaluation of potential improvements in successful first-attempt intubations or time to intubate among nonexperts.
We thank Dr. Seiji Ishikawa for translating the article published in Japanese.
Dr. Griesdale is supported by a Clinician Scientist Award from the Vancouver Coastal Health Research Institute.
This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.