A Novel Score for Procedural Difficulty During Videolaryngoscopic Intubation

Videolaryngoscopy improves the glottic view compared with direct laryngoscopy, but an adequate view does not guarantee easy delivery of the tracheal tube into the trachea. Existing classifications address either the laryngeal view (Cormack-Lehane grade, percentage of glottic opening) or the overall difficulty of the intubation episode (Intubation Difficulty Scale). The Video Classification of Intubation records blade type, glottic opening and the ease of tube passage as a descriptive label. None of these tools identifies which specific mechanism produced the difficulty encountered during a videolaryngoscopic intubation.

SCORE UNDER EVALUATION

The score comprises four components, each graded 0, 1 or 2, giving a total range of 0 to 8:

1. View-tube concordance: whether the tracheal tube can be advanced towards the glottic opening under the obtained view without additional manipulation.
2. Restricted epiglottic movement: whether epiglottic behaviour interferes with visualisation of the glottic opening.
3. Need for additional laryngoscopic manoeuvres: whether external laryngeal manipulation, blade repositioning or blade change was required to obtain the view.
4. Need for tube-shaping adjustment: whether the stylet had to be reshaped or an alternative device such as a bougie was required to direct the tube.

The components were derived from concepts described in the Video Classification of Intubation tube-delivery category and the videolaryngoscopic intubation and difficult airway classification, and were operationalised on a 0 to 2 ordinal scale.

OBJECTIVES

The primary objective is to examine whether the total score is associated with procedural outcomes of the intubation: intubation time, number of attempts and first-attempt success.

Secondary objectives are to examine the relationship of the total score with the Intubation Difficulty Scale, with the Video Classification of Intubation tube delivery category and with the percentage of glottic opening; to examine the association of each individual component with the procedural outcomes; to examine the association of preoperative airway assessment parameters (Mallampati classification, mouth opening, thyromental distance, neck extension, dental prosthesis, upper lip bite test, history of difficult intubation, body mass index) with the total score; and to examine whether operator experience is associated with the score and with the procedural outcomes.

The study does not aim to define a threshold for difficult videolaryngoscopic intubation and does not classify intubations as easy, moderate or difficult. Adult patients undergoing elective surgery under general anaesthesia requiring tracheal intubation will be assessed. All intubations will be performed with a Macintosh-blade videolaryngoscope. For each intubation the four score components, the Intubation Difficulty Scale, the Video Classification of Intubation, the percentage of glottic opening, the Cormack-Lehane grade, preoperative airway assessment parameters, operator experience, intubation time, number of attempts, first-attempt success, need for additional manoeuvres and oxygen desaturation below 90 percent will be recorded.

Continuous variables will be summarised as median with interquartile range. Internal consistency of the score will be assessed with Cronbach's alpha and corrected item-total correlations, and its dimensionality with principal component analysis. Associations will be examined with Spearman rank correlation, Mann-Whitney U and Kruskal-Wallis tests, and with regression models appropriate to the distribution of each outcome.