To the Editor:
We express our condolences to Epaud et al. and to their patient with ankylosing spondylitis who experienced a C5–C6 cervical spine fracture in association with a difficult videolaryngoscopic intubation. Their image report adds to existing reports of intubation-mediated cervical spine injury in patients with ankylosing spondylitis and conveys several important clinical messages.
The first message is neither glottic visualization nor intubation success are guaranteed with videolaryngoscopy. Clinical studies in which cervical spine mobility is artificially restricted—using either manual in-line stabilization or cervical collars—indicate that compared to conventional direct laryngoscopy, videolaryngoscopy: (1) improves glottic view with most but not all videolaryngoscopes and (2) increases first-attempt intubation success with only a few (n = 5) videolaryngoscopes but is not 100%. In two reports of 20 and 30 patients with ankylosing spondylitis in whom the GlideScope (Verathon, USA) was used for intubation, it was not possible to visualize the glottis in 13 to 15% or intubate in 7 to 15%.
The second message is that techniques intended to limit cervical spine motion during intubation can have adverse effects. Epaud et al. reported use of “in-line traction” during intubation. In the presence of cervical spine instability, axial traction can cause severe axial distraction.5 Consequently, manual inline stabilization, which does not utilize axial traction, is the method commonly used to reduce intubation-mediated cervical spine motion. Nevertheless, in two cadaver intubation studies, when compared with conventional laryngoscopy, manual inline stabilization did not change the motion of unstable cervical segments and in one study, it increased pathologic motion (subluxation). Increased pathologic motion with manual in-line stabilization is most likely explained as follows: first, by decreasing cervical spine motion, this technique impairs glottic visualization second, when glottic visualization is impaired, anesthesiologists may apply greater laryngoscope force, either with or without manual in-line stabilization and third, in the presence of an unstable segment, greater laryngoscope force application may result in greater segmental motion.
The third message is that clinicians should not assume that videolaryngoscopes always apply less force than conventional laryngoscopy. In patients predicted to be easy to intubate, videolaryngoscopes apply less force than conventional direct laryngoscopy. However, in a study of patients who had risk factors for difficult direct laryngoscopy, peak intubation forces did not differ between conventional direct (Macintosh) laryngoscopy and GlideScope laryngoscopy. In this latter study, failed intubation occurred in 5 of 20 (25%) of the Macintosh patients and 3 of 24 (12%) GlideScope patients and, in both groups, peak intubation forces were greater in patients in whom intubation failed. In their report, Epaud et al. state that there were “difficulties in exposing the epiglottis” and a bougie was utilized. Therefore, because of impaired glottic visualization, it is likely Epaud et al. applied a greater amount of force with the videoscope than they would have normally, causing the fracture.
Based on the aforementioned points, the fourth message is that there continues to be a role for fiberoptic intubation in airway management of patients who have ankylosing spondylitis and other forms of cervical spine disease. Epaud et al. state “…both videolaryngoscopy and fiberoptic intubation were considered…[but]…videolaryngoscopy was preferred because the operator was more familiar with this technique.” Because there are case series of patients with ankylosing spondylitis who were safely intubated with videolaryngoscopes the decision of Epaud et al. to use videolaryngoscopy instead of fiberoptic intubation was understandable. However, when performed well, fiberoptic intubation secures the airway with little to no force applied to the cervical spine; for patients with ankylosing spondylitis, that is vitally important. Accordingly, fiberoptic intubation continues to be an essential airway management technique with which anesthesiologists should maintain expertise.