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Meta-analysis: the importance of a proper search strategy

Lu, Yi; Jiang, Hong

European Journal of Anaesthesiology: June 2012 - Volume 29 - Issue 6 - p 300
doi: 10.1097/EJA.0b013e32834f5edc

From the Department of Anaesthesiology, Shanghai Ninth People's Hospital Affiliated to Shanghai Jiao Tong University, School of Medicine Shanghai, China

Correspondence to Hong Jiang, MD, PhD, Department of Anaesthesiology, Shanghai Ninth People's Hospital Affiliated to Shanghai Jiao Tong University, School of Medicine, Shanghai, China Tel: +86 21 23271699; e-mail:

Published online 16 January 2012


Su et al.1 have recently published a meta-analysis that compared video laryngoscopes with direct laryngoscopy for tracheal intubation. The results showed that the video laryngoscopes achieved a better view of the glottis and a shorter time for tracheal intubation when difficulty is encountered but no difference of success rate between the two kinds of laryngoscopy. However, we have received several comments on this meta-analysis.

First, there might be some defects in the search strategy. As a previous meta-analysis shows,2 the keywords of the search strategy should include each video laryngoscope (e.g. ‘Glidescope’, ‘Pentax-AWS’, ‘McGrath’, ‘Bullard’, ‘WuScope’, etc.) and each direct laryngoscopy (e.g. ‘Macintosh’, ‘Miller’). Owing to the defects of the search strategy, the author might miss several randomised controlled trials that compare video laryngoscopes with direct laryngoscopy. For example, the study by Malik et al.3 that compares several video laryngoscopes with Macintosh laryngoscope in predicted difficult intubation and the study by Parichehr et al.4 that compares the Glidescope with Macintosh in novices were not included. The incomprehensive data might cause totally different results in a meta-analysis.

Second, we think it is more proper to analyse different devices separately instead of pooling the results of different kinds of video laryngoscopes together because each video laryngoscope has its own advantages and characteristics. Pooling them together might render the results of less value. For example, a similar meta-analysis5 indicated that the Glidescope video laryngoscope prolongs the intubation time when compared with direct laryngoscope, and another recently published meta-analysis6 showed a significant improvement in the success rate of intubation when Airtraq was used by novices. These different results of single-device-based meta-analysis are great threats to this article.

In summary, a meta-analysis is a data-based analysis that requires a comprehensive data collection and a well designed analysis strategy. Lack any of these elements may limit the certainty of the results and as a result may be misleading.

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None of the authors have any conflicts of interest with the original article. This correspondence is free of any financial interest.

Su et al. did not respond to the Editors invitation to reply to this letter.

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1. Su YC, Chen CC, Lee YK, et al. Comparison of video laryngoscopes with direct laryngoscopy for tracheal intubation: a meta-analysis of randomised trials. Eur J Anaesthesiol 2011; 28:788–795.
2. Mihai R, Blair E, Kay H, Cook TM. A quantitative review and meta-analysis of performance of nonstandard laryngoscopes and rigid fibreoptic intubation aids. Anaesthesia 2008; 63:745–760.
3. Malik MA, Subramaniam R, Maharaj CH, et al. Randomized controlled trial of the Pentax AWS, Glidescope, and Macintosh laryngoscopes in predicted difficult intubation. Br J Anaesth 2009; 103:761–768.
4. Parichehr NS, Mark S, Harald G. Laryngoscopy via Macintosh blade versus GlideScope: success rate and time for endotracheal intubation in untrained medical personnel. Anesthesiology 2009; 110:32–37.
5. Griesdale DE, Liu DD, McKinney J, et al. Glidescope Vs. Direct laryngoscopy for endotracheal intubation: a systematic review and meta-analysis. Am J Respir Crit Care Med 2011; 183:A4115.
6. Lu Y, Jiang H, Zhu YS. Airtraq laryngoscope versus conventional Macintosh laryngoscope: a systematic review and meta-analysis. Anaesthesia 2011; 66:1160–1167.
© 2012 European Society of Anaesthesiology