We were interested to read the recent article by McElwain et al [1], which compared the C-MAC^® (Karl Storz Endoscopy, Tuttlingen, Germany), the Glidescope^® (Verathon, WA, USA) and Airtraq^® (Prodol Meditec S.A., Vizcaya, Spain) video-laryngoscopes in easy and difficult mannequin simulations. Video-laryngoscopes provide a method for indirect visualisation of the glottic inlet. The Glidescope and Airtraq employ a ‘hockey-stick' shaped laryngoscope blade, foregoing the need to align the oral, pharyngeal and laryngeal axes, which may be advantageous when direct laryngoscopy is difficult [2]. However, both of these video-laryngoscopes require the acquisition of new skills, and this has implications for training and skill retention. The C-MAC has a blade shape based upon the standard Macintosh laryngoscope, and so may be advantageous by offering a familiar technique to those trained in the use of direct laryngoscopy. However, during difficult laryngoscopy, the oral, pharyngeal and laryngeal axes must still be substantially aligned.

There is a learning curve for video-laryngoscopes previously described by these authors [3,4]. We believe this learning curve might account for the apparent decrease in intubation time and intubation attempts when the study participants (all anaesthetists experienced in direct laryngoscopy) attempted the difficult simulation. It appears from the paper that participants practised upon, then first attempted the easy simulation. This was most noticeable with the Glidescope; mean (SD) times for 1^st attempt laryngoscopy duration were 33 (20) s for the easy simulation and 25  (18) s for the difficult simulation. In the easy simulation, 7 participants required more than 1 attempt, compared with only 4 participants in the difficult simulation. The relatively high SD may have been due to 23% of participants having had previous Glidescope experience, whereas 77% were entirely new to its use.

Importantly, none of the participants in the study had previous experience of the C-MAC, yet all were able to achieve good views and rapid intubation in both easy and difficult scenarios. We believe this demonstrates the value of combining indirect video technology and familiar technique for successful intubation of the difficult airway.

There are video-laryngoscopes that may be fitted with either a standard Macintosh blade or a channelled difficult airway blade, the latter permitting a similar technique to that used with conventional laryngoscopy. Channelled devices such as the Airtraq, the Pentax AWS^® (Pentax Corporation, Tokyo, Japan), and the Venner AP Advance^®  (Venner Medical, Singapore) may provide better protection of airway structures, as they obviate the use of the styletted tube [5].

Ultimately, many difficult laryngoscopies are unexpected [6] and in routine practice are rare events. Timely resolution, airway control and intubation are often necessarily provided by less experienced or junior practitioners, who may have had only a limited exposure to these devices. A difficult airway device should ideally allow intuitive use without the need to learn and maintain a new skill set.

Angus. G. Butchart

Peter J. Young

Queen Elizabeth Hospital

King's Lynn, UK

E-mail: peteryoung101@googlemail.com; angusbutchart@doctors.org.uk

Dr Young is a co-inventor and patent holder (owned by Venner Medical) for the Venner AP Advance video laryngoscope, which is manufactured by Venner Medical, Switzerland. He has performed consultancy work for Venner Medical, Singapore and hopes to benefit from the patent held.

References

1.        McElwain J, Malik MA, Harte BH, Flynn NM, Laffey JG. Comparison of the C-MAC videolaryngoscope with the Macintosh, Glidescope, and Airtraq laryngoscopes in easy and difficult laryngoscopy scenarios in manikins. Anaesthesia 2010; 65: 483-9.

2.        Rose DK, Cohen MM. The Airway: problems and predictions in 18,500 patients. Canadian  Journal of  Anaesthesia 1994; 41: 372-83.

3.        Maharaj CH, Costello JF, Higgins BD, Harte BH, Laffey JG. Learning and performance of tracheal intubation by novice personnel: a comparison of the Airtraq and Macintosh laryngoscope. Anaesthesia 2006; 61: 671-7.

4.        Nasim S, Maharaj CH, Malik MA, O' Donnell J, Higgins BD, Laffey JG. Comparison of the Glidescope and Pentax AWS laryngoscopes to the Macintosh laryngoscope for use by Advanced Paramedics in easy and simulated difficult intubation. BMC Emergency Medicine 2009; 9: 9.

5.        Hsu WT, Hsu SC, Lee YL, Huang JS, Chen CL. Penetrating injury of the soft palate during Glidescope intubation. Anesthesia & Analgesia 2007; 104: 1609-10.

6.        Tse JC, Rimm EB, Hussain A. Predicting difficult endotracheal intubation in surgical patients scheduled for general anesthesia: a prospective blind study. Anesthesia and Analgesia 1995; 81: 254-8.

We would like to thank Drs Butchart and Young for their interesting comments regarding our paper [1], and welcome the opportunity to respond to these comments. We agree with the authors that there is a learning curve in regard to the acquisition of skills with all laryngoscopes, and a decay curve in regard to loss of skills over time. However, these skills appear to be acquired more quickly, and lost less quickly, at least with the Airtraq® laryngoscope, when compared to the Macintosh laryngoscope [2-3].

With regard to our study, the authors are correct in that, while the participants used the devices in random order, the order in which the scenarios were attempted was not randomized. Tracheal intubation attempts with each device were first performed in the easy laryngoscopy scenario, followed by the difficult laryngoscopy scenario. Therefore, it is possible that a learning effect was seen when using the Glidescope laryngoscope. However, this was not seen when testing the other videolaryngoscopes, namely the C-MAC and Airtraq laryngoscopes.

We agree that there may be advantages to using videolaryngoscopes that incorporate the Macintosh laryngoscope blade, given its familiarity to anaesthetists, and our results in this study do provide some support for that premise [1]. However, these findings need to be replicated in clinical studies, both of easy and predicted difficult laryngoscopy. In addition, it must be remembered that other video laryngoscopes, which incorporate novel blade curvatures and structures, particularly the Airtraq [4-6] and Pentax laryngoscopes [7-9], have performed well in clinical studies of both easy and difficult laryngoscopy, and hold significant promise as alternatives or backup devices to the Macintosh Laryngoscope. We are not aware of the Venner AP Advance^® laryngoscope (Venner Medical, Singapore), and could find no published data regarding this device.

Ultimately, we believe that anaesthetists should be expert in the use of more than one type of laryngoscope, and should not limit themselves to the use of laryngoscopes based on the Macintosh blade. The optimal ‘secondary' laryngoscope (or ‘primary' laryngoscope, for that matter) that anaesthetists should use will depend on several issues, and remains an active area of investigation.

We wish to thank Drs Butchart and Young for their interesting comments, and for their interest in our paper.

J. McElwain

J. G. Laffey

National University of Ireland,

Galway, Ireland

E-mail: john.laffey@nuigalway.ie

No external funding and no competing interests declared. Previously posted at the Anaesthesia Correspondence website: http://www.anaesthesiacorrespondence.com.

References

1.        McElwain J, Malik MA, Harte BH, Flynn NM, Laffey JG. Comparison of the C-MAC videolaryngoscope with the Macintosh, Glidescope, and Airtraq laryngoscopes in easy and difficult laryngoscopy scenarios in manikins. Anaesthesia 2010; 65: 483-9.

2.        Maharaj CH, Costello J, Higgins B, Harte BH, Laffey JG. Learning and performance of Tracheal intubation by novice personnel: A comparison of the Airtraq® and Macintosh laryngoscope. Anaesthesia 2006; 61: 671-7.

3.        Maharaj CH, Costello J, Higgins BD, Harte BH, Laffey JG. Retention of tracheal intubation skills by novice personnel: A comparison of the Airtraq® and Macintosh laryngoscopes. Anaesthesia 2007; 62: 272-8.

4.        Maharaj CH, Buckley E, Harte BH, Laffey JG. Endotracheal Intubation in Patients with Cervical Spine Immobilization: A Comparison of Macintosh and Airtraq^TM Laryngoscopes. Anesthesiology 2007; 107: 53-9.

5.        Maharaj CH, Costello JF, Harte BH, Laffey JG. Evaluation of the Airtraq and Macintosh laryngoscopes in patients at increased risk for difficult tracheal intubation. Anaesthesia 2008; 63: 182-8.

6.        Maharaj CH, O'Croinin D, Curley G, Harte BH, Laffey JG. A comparison of tracheal intubation using the Airtraq or the Macintosh laryngoscope in routine airway management: a randomised, controlled clinical trial. Anaesthesia 2006; 61: 1093-9.

7.        Malik MA, Maharaj CH, Harte BH, Laffey JG. Comparison of Macintosh, Truview EVO2, Glidescope, and Airwayscope laryngoscope use in patients with cervical spine immobilization. British Journal of Anaesthesia 2008; 101: 723-30.

8.        Malik MA, Subramaniam R, Churasia S, Maharaj CH, Harte BH, Laffey JG. Tracheal intubation in patients with cervical spine immobilization: a comparison of the Airwayscope, LMA CTrach, and the Macintosh laryngoscopes. British Journal of Anaesthesia 2009; 102: 654-61.

9.        Malik MA, Subramaniam R, Maharaj CH, Harte BH, Laffey JG. Randomized controlled trial of the Pentax AWS, Glidescope, and Macintosh laryngoscopes in predicted difficult intubation. British Journal of Anaesthesia 2009; 103: 761-8.