Why Were Rigid and Semirigid Fiberoptic- and Video-Laryngoscopes Developed?
Macewan originally performed endotracheal intubation with his fingers.1 In 1913 Janeway used a speculum very similar to the laryngoscopes introduced by Miller and Macintosh in 1941 and 1942.2 And until recently, we’ve remained largely dependent on the line-of-sight technique exemplified by direct laryngoscopy (DL). It was proposed that “the sniffing position” aligns the axes of the mouth, pharynx, and trachea, yet the incisors, the tongue, the epiglottis, and occasionally the position of the larynx itself, often conspire against a clear view. Studies on conscious adults with normal airway features, in neutral, sniffing, and simple extension demonstrate that positioning alone does not align the axes3 and there was little difference between the sniffing position and simple extension in a large series of patients undergoing DL.4 If positioning does not align these axes, how do we accomplish intubation by DL? We apply force, displacing and compressing the tongue, mandible, and frequently the larynx itself. Yet even among adults with seemingly normal airways, it is not possible to view the larynx by direct means in approximately 6% to 10%.5-7 Despite attempts to do so, we frequently fail to identify patients in whom DL will prove difficult or worse.8 Studies suggest that when DL fails, all too frequently we try harder and more often,9 sometimes with adverse consequences.9-11
Instruments that are more or less anatomically shaped can overcome the anatomical barriers that may make DL difficult or impossible. Rigid and semirigid fiberoptic, optical, and video-laryngoscopes are designed specifically for this purpose.
Another significant limitation of DL is that the experience is difficult to share.12,13 Since only the laryngoscopist can visualize the procedure, this reduces the ability of an assistant to anticipate our needs, complicates the teaching and recording of laryngoscopy, limits clinical documentation and the possibilities for quality improvement as well as the conduct of airway research. Video-laryngoscopy circumvents many of these limitations but generally relies upon alternative devices. Visualizing the anatomy and the procedure of intubation can be achieved using a conventional laryngoscope. The Airway Cam®, developed by Dr. Richard Levitan, is a head-mounted camera which captures the laryngoscopist's view through an eye-level pentaprism and conveys the image to a video monitor and/or a recording device.14,15 This device enables a student and mentor to simultaneously view the same object, capturing the image and playing it back at a pace and time conducive to and appropriate for teaching, documentation, and research. While these achievements are clearly worthwhile, this technology does not improve laryngeal exposure.
Flexible endoscopes have greatly expanded our ability to diagnose and manage problems in previously inaccessible body parts. These devices are versatile but complex. For tracheal intubation, flexible fiberoptic and video-endoscopes demand a different skill set than DL. Nonetheless, ...