Design evaluation of commonly used rigid and levering laryngoscope blades

Background: The shape of a laryngoscope blade affects the exposition of the larynx. This study evaluates and compares some rigid and levering blade designs based on previous investigative X-ray laryngoscopic studies. Methods: Five rigid laryngoscope blades (Miller #3, Standard Macintosh #3, Classical Macintosh #4 and English-Macintosh #3 and #4) and two levering laryngoscope blades (McCoy in neutral and maximally elevated positions and Flexiblade in three basic positions: straight, neutral, and maximally curved) were evaluated. This study assesses two parameters derived from the depth of insertion: the eye line deviation from the ideal straight view line to the vocal cords, and the space occupied by the blade behind the mandible, which affects the contact of the blade tip with the base of the tongue. Results: The best results on larynx exposition were produced by the English-Macintosh #4 at all insertion depths between 5 and 14 cm. It surpassed the Classical Macintosh #4 and both the English and Standard Macintosh #3. Although the Miller and the Flexiblade in a straight position afford a nearly ideal view line, both blades reduce the space reserved for the tongue behind the mandible. The McCoy with its tip maximally elevated provides limited view, while activation of the Flexiblade provides various ranges of larynx exposition. Conclusion: The difference in shape and design of Macintosh blades affects their performance. The distal portion of a large-sized curved blade is more effective than the full length of a shorter blade. The #4 English Macintosh is a better choice for routine clinical use. The Flexiblade performs as a multiblade device and can therefore be used for both routine and difficult intubations.