To the Editor: 

Fiadjoe et al.  1should be applauded for their efforts in comparing the performance of the GlideScope Cobalt® video laryngoscope (GCV) (Verathon Medical, Bothell, WA)‡with the Miller laryngoscope (Heine, Dover, NH) for tracheal intubation in neonates and infants with a normal airway. Quite rightly, the primary outcomes of this study are intubation time and success rate with the two devices. However, there are several issues of the study that need to be clarified.

The authors did not indicate how many of the neonates aged younger than 1 month and the infants aged 1–12 months were included in each group. Is a size 1 Miller blade the best selection for all patients in the direct laryngoscopy group? In our experience, a size 0 Miller blade is more useful than a size 1 Miller blade in the neonates. In the GCV group, a size 2 blade of the GCV was selected. However, an important issue ignored by the authors is bodyweight range of patients. The GCV is a single-use version of the original GlideScope® video laryngoscope. The most important improvement in the GCV is the availability of a 10-mm blade, compared with 14.5 mm in original models.2As yet, there are five disposable blades of the GCV available. In the manufacturer's description, the blade choice of the GCV is based on bodyweight of patients. The recommended blade sizes are size 0 for patients weighing less than 1.5 kg, size 1 for patients weighing 1.5–3.6 kg, size 2 for patients weighing 1.8–10 kg, size 3 for patients weighing 10 kg, or adults, and size 4 for patients weighing 40 kg, or morbidly obese patients. Because each blade covers a wide bodyweight range and the infant's airway is typically 3 or 4 mm in diameter, the laryngoscopic view of the GCV may vary with the size of the blade.

The authors compared the percentage of glottic opening score obtained by the two devices, and demonstrated that the GCV yielded a better laryngoscopic view than the Miller laryngoscope. We were also very interested in the use of maneuvers to aid laryngoscopy in this study, especially for the use of optimum external laryngeal manipulation. It is generally recommend that optimum external laryngeal manipulation should be used with a poor laryngoscopic view in order to improve visualization with direct laryngoscopy.3Benumof and Cooper4demonstrated that optimum external laryngeal manipulation may improve the laryngoscopic view by at least one whole grade in adults. Smilarly, this maneuver has proved effective for direct laryngoscopy in pediatric patients.5In the clinical studies comparing performance of Glidescope® video laryngoscope with direct laryngoscope for tracheal intubation in pediatric patients with normal and difficult airways,6,7optimum external laryngeal manipulation has also been shown to provide improved laryngoscopic view. In methods, we do not feel that the authors clearly described if they had adopted an optimal-best attempt at laryngoscopy when evaluating the best views obtained with the two laryngoscopes.

Fiadjoe JE, Gurnaney H, Dalesio N, Sussman E, Zhao H, Zhang X, Stricker PA: A prospective randomized equivalence trial of the GlideScope Cobalt® video laryngoscope to traditional direct laryngoscopy in neonates and infants. ANESTHESIOLOGY 2012; 116:622–8
Holm-Knudsen R: The difficult pediatric airway–A review of new devices for indirect laryngoscopy in children younger than two years of age. Paediatr Anaesth 2011; 21:98–103
Hagberg CA, Benumof JL: The American Society of Anesthesiologists' management of difficult airway algorithm and explanation–analysis of the algorithm. In: Hagberg CA, ed. Benumof's Airway Management. 2nd ed. Philadelphia: Mosby; 2007:245
Benumof JL, Cooper SD: Quantitative improvement in laryngoscopic view by optimal external laryngeal manipulation. J Clin Anesth 1996; 8:136–40
Podraza AG, Ansari-Winn D, Salem MR, Heyman JH, Mahdi M: Tracheolaryngeal cephalad displacement facilitates tracheal intubation in pediatric patients. Anesth Analg 1995; 80:S377
Kim JT, Na HS, Bae JY, Kim DW, Kim HS, Kim CS, Kim SD: GlideScope video laryngoscope: A randomized clinical trial in 203 paediatric patients. Br J Anaesth 2008; 101:531–4
Armstrong J, John J, Karsli C: A comparison between the GlideScope Video Laryngoscope and direct laryngoscope in paediatric patients with difficult airways–a pilot study. Anaesthesia 2010; 65:353–7