8.1.1 What Is the History and Evolution of Direct Laryngoscopy and Tracheal Intubation?
In the modern era, direct laryngoscopy is almost exclusively associated with tracheal intubation, even though the procedure was initially developed for diagnosing and treating laryngeal pathology. Following the development of mirror laryngoscopy in the 1800s (Czermark and others), Kirstein reported the first direct laryngoscopy in 1895.1 Over the next 20 years the basic tenets of the procedure were refined by surgeons interested in laryngeal examination and surgical exposure.
A step-wise approach, the focus on epiglottoscopy, recognition of posterior laryngeal landmarks, optimal positioning for laryngeal exposure, and the benefits of external laryngeal manipulation and head elevation, etc are all detailed by Chevalier Jackson in his 1922 text, Bronchoscopy and Esophagoscopy, A Manual for Peroral Endoscopy and Laryngeal Surgery.2
With the evolution of modern anesthesia, the original straight laryngoscope designs by ENT surgeons gave way to instruments specifically designed for tracheal intubation, such as the straight Miller blade (1941)3 and the curved Macintosh blade (1943).4 It was also in this time period that the modern design of a detachable blade and battery handle became commonplace.
Between the 1930s and 1970s many different laryngoscope blades were designed to facilitate intubation (eg, Wisconsin, Phillips, Guedel, etc), but the Miller and Macintosh models (albeit with some modifications) remain universally used, and in most settings, are the only laryngoscope blades available.
The development of flexible fiberoptics, subsequent attachment of fiberoptics to rigid blades (Bullard laryngoscope, Wu Scope, etc), and more recently video laryngoscopes (Glidescope, McGrath, Video MAC, etc) have narrowed the clinical role of standard, line-of-sight, direct laryngoscopy, and now there is a wide array of indirect visual devices for both diagnostic imaging of the larynx and tracheal intubation. Direct laryngoscopy remains the predominant method of tracheal intubation. Alternative devices, however, are being increasingly deployed for both routine and anticipated difficult laryngoscopy.
8.2.1 What Are the Principal Design Components of Laryngoscopy Blades and How Do They Work to Facilitate Endotracheal Intubation?
Laryngoscope blade design, light, and battery systems affect procedural performance since they impact on illumination, laryngeal exposure, and endotracheal tube (ETT) delivery. This holds true for both straight and curved laryngoscope blade designs, but because these designs function differently, there are different considerations (see below).
The principal components of a laryngoscope blade are the spatula (that passes over the lingual surface of the tongue) and the flange that is used to direct the tongue (Figure 8-1), a fluid-filled noncompressible structure, to the side of the mouth and into the mandibular space (the space below the tongue). This concept of mandibular space volume is particularly important in clinical practice as the practitioner evaluates for difficult laryngoscopy and intubation (see Chapter 1).