Proposal of a simplified intubation difficulty scale for comparing techniques and devices

To the Editor Many techniques and devices for airway management have been proposed in the search for a simple, safe method to overcome the difficulties of tracheal intubation: a reliable standardised method is needed to compare these. While the predictors of difficult intubation are well known, the same cannot be said for the parameters that need to be measured to assess the actual difficulty of intubation. Because the intubation procedure depends strongly on the skill of the clinician, it is difficult to find objective assessment parameters that allow the comparison of different techniques and devices. In 1997, Adnet et al. introduced the intubation difficulty scale (IDS), which includes seven variables: 1) number of attempts made; 2) number of additional operators; 3) alternative techniques used; 4) Cormack-Lehane index (ICL); 5) force exerted on the laryngoscope; 6) manoeuvre facilitation; and 7) position of the vocal cords (1Adnet F Borron SW Racine SX Clemessy JL Fournier JL Plaisance P Lapandry The intubation difficulty scale (IDS): proposal and evaluationof a new score characterizing the complexity of endotracheal intubation.Anesthesiology. 1997 Dec; 87: 1290-1297Crossref PubMed Scopus (482) Google Scholar). This scale is very accurate and complete, but difficult to apply in practice, especially when one needs to perform many procedures to use a technique ordevice (2Malik M.A. Subramaniam R. Maharaj C.H. Harte1and B.H. Laffey J.G. Randomized controlled trial of the Pentax AWS®, Glidescope®, and Macintosh laryngoscopes in predicted difficult intubation.Br. J. Anaesth. 2009; 103: 761-768Abstract Full Text Full Text PDF PubMed Scopus (141) Google Scholar, 3Combes X. Dhonneur G. Difficult tracheal intubation.BJA. 2010; 104: 260-261Abstract Full Text Full Text PDF PubMed Scopus (13) Google Scholar). The IDS is intended for assessing the technical difficultiesinvolved in intubation, not the clinical efficiency or effectiveness of the technique or device used. It should be possible to simplify the IDS to devise a uniform evaluation system. Specifically, variables 1 to 3 from the IDS can be included in terms of the time taken: the total duration of attempts, ventilations, additional viewing, and introducing the tracheal tube. This duration can give an idea of the difficulties encountered in a specific procedure. Additionally, the Cormack-Lehane index (variable 4 from the IDS) can be incorporated to reflect the level of anatomical difficulty. Variables 5 and 6 from the IDS are not objective measures, as the perception of force exerted and manoeuvre facilitation may vary between operators. Finally, variable 7 from the IDS involves various pharmacological and muscular factors, and conditions may vary during different techniques. Therefore, the difficulty scale could be simplified to include only the time taken for the procedure and the Cormack-Lehane index. Reports about intubation always refer to the time taken, but it is not clear when the timing starts and stops. Adnet et al. defined the time of intubation as the period from when the blade is introduced into the oral cavity to when the endotracheal tube is inserted. Given the wide variety and type of devices available, timing could start at the removal of mask ventilation and end at the connection of the hose to the ventilation system with the verification of end-tidal CO2. Along with the time taken, evaluation should include the objective difficulty, which is reflected by the Cormack-Lehane index. For example, a technique or device that requires 48 seconds to intubate a Cormack-Lehane grade 4 individual can certainly be considered valid. Thousands of intubation reports are available. When evaluating the results, it is difficult to compare the times, in seconds, with the other parameters. Categorising cases using time intervals can simplify comparison. A simplified scale could include three grades: grade 1, < 1min; grade 2, 1-3 min; and grade 3, > 3 min. (Table 1). Relating this grading system with Cormack-Lehane classification canyield a measure of the effectiveness of the technique or device. (Fig. 1) We propose a simple, standardised system for data collection. Table and figure Conflict of Interest: