Acta Anaesthesiol Scand 2002; 46: 1003–1009 Copyright C Acta Anaesthesiol Scand 2002 Printed in Denmark. All rights reserved ACTA ANAESTHESIOLOGICA SCANDINAVICA 0001-5172 Design evaluation of commonly used rigid and lever laryngoscope blades I. Z. Y ARDENI 1 , A. G EFEN 2 , V. S MOLYARENKO 1 , A. Z EIDEL 1 and B. B EILIN 1 1 Department of Anesthesiology, Rabin Medical Center, Golda-Hasharon Campus, Sackler Faculty of Medicine, and 2 Department of Biomedical Engineering, Faculty of Engineering, Tel Aviv University, Tel Aviv, Israel Background: The shape of a laryngoscope blade affects the ex- position 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 neu- tral 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 Eng- lish and Standard Macintosh .3. Although the Miller and the Flexiblade in a straight position afford a nearly ideal view line, S UCCESSFUL direct laryngoscopy requires the fulfilmentof two essentialconditions:(a) elev- ation of the epiglottis by compression of the laryngo- scope blade tip,and (b)a clear view into the vocal cords.Intubating conditions, apart from varying ana- tomic structures, are highly dependent on the shape and length ofthe laryngoscope blade. A Macintosh blade is generally regarded as the preferred blade whenever there is a little upper airway room, and a Miller blade is considered convenient for use in pa- tients with small mandibular space, large incisors, or a long and floppy epiglottis (1, 2). During difficult endotracheal intubation with a Ma- cintosh laryngoscope, the application of increased lift- ing force combined with a levering movement of the blade is inevitable. In this case, the patient is exposed to potential damage, and the upper teeth may be in- advertently used as a fulcrum (3). The engineering de- sign of the McCoy levering laryngoscope was one of the first attempts to address these difficulties. Having its fulcrum at a lower point within the pharynx, it was 1003 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 distalportion of a large- sized curved blade is more effective than the full length ofa shorter blade. The .4 English Macintosh is a better choice for routine clinical use. The Flexiblade performs as a multiblade de- vice and can therefore be used for both routine and difficult intubations. Received 18 October 2001, accepted for publication 15 April 2002 Key words: English-Macintosh; Flexiblade;levering blades; McCoy; Miller; rigid blades; Standard Macintosh. c Acta Anaesthesiologica Scandinavica 46 (2002) expected to simplify the elevation of the epiglottis and the exposure of the larynx, reducing contact with the upper incisor teeth (4). The ‘Flexiblade’is a new laryngoscope with the same concept of an internal levering blade but with a wider range of movements (5, 6) (Fig. 1F). Marks et al.(1993)suggested criteria for laryngo- scope evaluation (7). This criteria is based upon meas- urements of two angular parameters representing (a) the eye line deviation from the straight ideal line of view to the laryngealinlet,and (b) the amountof space occupied by the blade behind the mandible (Fig. 2). The availablespace behind the mandiblewas shown by several investigators to be correlated with the difficulty of laryngoscopy and tracheal intubation (8–10). If the tongue is not compressible, there may be difficulty in exploring the vocal cords. It follows that the amount of space the laryngoscope blade itself oc- cupies behind the mandible is an important factor when space is already limited. Failure of a blade tip to put tension on the hyoepiglottic ligament when