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Which parameters influence the grade of laryngeal visualization?

Last post 01 Jan 2019, 8:52 AM by Narcis Ungureanu. 1 replies.
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  •  15 Aug 2018, 1:28 PM 2630

    Which parameters influence the grade of laryngeal visualization?

    I read with interest the article  ‘’ A randomised clinical trial comparing the ‘sniffing’ and neutral position using channelled (KingVision) and non-channelled (C-MAC) videolaryngoscopes’’ by Mendoca et al. (1). I read through the article carefully and found some questions about their study.

    Notice to particulars pending placing is significant in prevention the little technical mistakes that may influence the outgoing apperance and many different parameters interact to influence the eventual grade of laryngeal visualization. For instance lifting force during the laryngoscopy (2). However, the authors only checked the glottic opening score among the sniffing position and neutral position, without considering the attempt throughout the laryngoscopy.

    Another factor affecting the degree of laryngeal visualization is the type and size of the  laryngoscope blade (3). We are of the opinion that it is not very appropriate to compare the SP with the neutral position using the channelled King Vision laryngoscopes, which are different in size and angle, with non-channelled C-MAC (4,5).

    Based on these considerations, in order to make a comparison between SP and neutral position during laryngoscopy, I think that the above two factors should be considered.

    O. Onal

    M. Sari

    H. H. Bayram

    Selcuk University School of Medicine,

    Konya, Turkey.

    Email: drozkanonal@selcuk.edu.tr


    No external funding and no conflicts of interest declared.



    1.      Mendonca C, Ungureanu N, Nowicka A, Kumar P. A randomised clinical trial comparing the 'sniffing' and neutral position using channelled (KingVision® ) and non-channelled (C-MAC® ) videolaryngoscopes. Anaesthesia 2018; 73: 847-55.

    2.      Duggan JE, Syndercombe A, Haig T, Thompson R. Can force be used as a surrogate measure for difficult laryngoscopy? Anaesthesia 2008; 63: 318-9

    3.      Arino JJ, Velasco JM, Gasco C, Lopez-Timoneda F. Straight blades improve visualization of the larynx while curved blades increase ease of intubation: a comparison of the Macintosh, Miller, McCoy, Belscope and Lee-Fiberview blades. Canadian Journal of Anaesthesia 2003; 50: 501-6.

    4.      https://www.ambu.com/products/airway-management/video-laryngoscopes/product/king-vision-ablade

    5. https://www.karlstorz.com/iq/en/website-search.htm?chunk=2

  •  01 Jan 2019, 8:52 AM 2706 in reply to 2630

    Re: Which parameters influence the grade of laryngeal visualization?

    We thank Drs Onal, Sari and Bayram for their interest in our paper [1]. We agree that there are many variables influencing the laryngeal inlet visualisation during videolaryngoscopy. As they mentioned, the lifting force is only one of them [2] and this also featured along other optimisation manoeuvres for the two studied videolaryngoscopes in our paper. The successful placement of the tracheal tube during videolaryngoscopy may depend on several other factors, including the head and neck position [3].

    It is true that we recorded the percentage of glottic opening (POGO) scores as a secondary outcome, but the primary outcome in our study was the modified intubation difficulty scale (mIDS) score. The POGO score was only one element of this modified intubation difficulty scale (mIDS) along the lifting force, external laryngeal pressure and a number of other optimisation manoeuvres [1]. The mIDS was a modification of a previously validated score by Adnet et al [4] and reflects the complexities and dynamic nature of not only videolaryngoscopy and visualisation of the laryngeal inlet, but also of the subsequent insertion of the tracheal tube which ultimately is the aim of the procedure.

    We agree that the size and type of the videolaryngoscope blade influences the way the airway is approached, oropharyangeal tissues displacement and how the tracheal intubation is performed with a particular device. We therefore allocated our patients into four groups called KingVision 'sniffing', KingVision neutral, C-MAC 'sniffing' and C-MAC 'neutral' to reflect the type of the device and the respective position it was used for. The primary outcome, the modified intubation difficulty scale (mIDS) was then compared between the two positions for the same device [1]. Perhaps this part of the methodology was not very clear to Onal and colleagues. We did not compare the two types of videolaryngoscopes in one position but rather the same type of videolaryngoscope  (either channelled KingVision or non-channelled C-Mac) in the two different positions. Accordingly, we presented our results in four groups (KingVision 'sniffing', KingVision ‘neutral’, C-MAC 'sniffing' and C-MAC ‘neutral’) in the figures and tables of our paper [1].


    N. Ungureanu

    University Hospitals Birmingham,

    Birmingham, UK.


    C. Mendonca

    A. Nowicka

    P. Kumar

    University Hospital Coventry and Warwickshire,

    Coventry, UK

    Email: unarcis@doctors.org.uk

    No external funding and no conflicts of interest declared.



    1. Mendonca C, Ungureanu N, Nowicka A, Kumar P. A randomised clinical trial comparing the 'sniffing' and neutral position using channelled (KingVision® ) and non-channelled (C-MAC® ) videolaryngoscopes. Anaesthesia 2018; 73: 847-55.

    2. Duggan JE, Syndercombe A, Haig T, Thompson R. Can force be used as a surrogate measure for difficult laryngoscopy? Anaesthesia 2008; 63: 318-9.

    3. Aziz MF, Bayman EO, Van Tienderen MM, et al. Predictors of difficult videolaryngoscopy with GlideScope® or C-MAC® with D-blade: Secondary analysis from a large comparative videolaryngoscopy trial. British Journal of Anaesthesia 2016; 117: 118-23.

    4. Adnet F, Borron SW, Racine SX, et al. The intubation difficulty scale (IDS): proposal and evaluation of a new score characterizing the complexity of endotracheal intubation. Anaesthesia 1997; 87: 1290-7.  

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