Management of the airway during elective intubation in the patient with upper cervical spine disease affords the practitioner several options, including awake flexible fiberoptic intubation with awake positioning and serial neurologic assessments. However, fiberoptic intubation is impractical due to the longer time required for intubation in emergency situations.28 In addition, patient cooperation is usually required for awake fiberoptic intubation, and, as such, patients requiring emergency intubation may offer far fewer alternatives for the safe management of the airway.
Occasionally, rapid and effective advanced airway management must be completed in the patient with known or suspected upper cervical spine instability in the prehospital setting. Neurologic injury may occur due to mechanical disruption at the unstable segments, but care must also be taken to not compromise global perfusion and oxygen delivery with multiple prolonged intubation attempts or failed intubation, which could also exacerbate neurologic injuries. Therefore, consideration for speed and success of intubation must be weighed heavily due to the likely harm from failed intubation, with resultant hypoxia, hypercarbia, risk of aspiration, and unrecognized esophageal intubation.1–6
We have shown that the LW technique created the least flexion-extension and rotational motion at C1-2 during advanced airway management with in-line stabilization whereas the ILMA and MAC produced the most movement. Progression of neurologic injury in patients with upper cervical spine disease is common, but the exact cause of the deterioration remains unclear. Expert opinion, in general, recommends minimizing cervical spine movement. Previous investigations considered a 10% to 30% reduction in motion to be a clinically significant result.29,30 In cadavers with a simulated type II odontoid fracture, the LW technique resulted in >3° less extension than with the ILMA and MAC, which is more than a 40% reduction in extension over the ILMA and MAC techniques. Whether just over 1° less rotation is clinically relevant between the LW and the ILMA and MAC is less certain. The correlations between the time required and magnitude of movement were low and of questionable clinical relevance.
Direct visualization from the oropharynx to the glottis with techniques such as the MAC typically requires the patient to assume the “sniffing position,” with extension of the upper cervical spine and flexion of the lower cervical spine.31 Therefore, there are theoretical benefits to devices that facilitate intubation without direct visualization, such as the LW, AT, and ILMA. A number of studies have evaluated cervical spine motion using various techniques. The reported extent to which each cervical segment is displaced is variable, depending on which segment is measured, how the displacement is measured, and which population is studied. In the published literature, the range of reported cervical spine extension created by direct visualization with techniques such as the MAC at the C1-2 segment is as low as 4° and as high as 13.5°.20,32–39 Techniques such as the LW have been reported to produce approximately 2° of extension at the C1-2 segment.37 With indirect visualization techniques, such as the AT, Bullard, and GlideScope, the range of reported cervical spine extension at C1-2 is 3° to 10.4° with the AT, 2.6° to 4.5° with the Bullard, and 4° to 7° with the GlideScope.35–40 The impact of the ILMA technique on cervical spine extension at C1-2 has also been reported from <1° to 5°.41–43
Our results lie within these ranges for all techniques, except for the ILMA, with which we found a mean degree of extension of 7.43°. This difference highlights the strengths and weaknesses of our study methods. We used electromagnetic motion analysis to assess motion at the unstable segment and were able to directly and simultaneously track displacement in 3 dimensions. The previously cited studies only used lateral fluoroscopic images to measure motion in 2 dimensions. Fluoroscopy has a number of significant limitations, most notably the interobserver variation in measurements. In addition, the Polhemus device is extremely accurate and able to detect differences in angular motion to 0.3°. We used cadavers with a created global instability at C1-2 whereas most other investigations used normal adult patients undergoing elective surgical procedures. The use of cadavers allowed us to repeatedly study the worst possible instability under the same patient conditions, thus limiting the variability in motion due to the variable airway anatomy among patients. Although the use of cadavers may be considered a weakness due to tissue degradation and rigor, we used only lightly embalmed cadavers to attempt to make the situation as close to in vivo as possible. The range of motion before the creation of instability was similar to that reported in normal geriatric adults. Another limitation of our study is the variability introduced by the heterogeneity in the experience and background of our practitioners. We included 5 providers, 2 attending anesthesiologists, and 3 emergency medical technician paramedics who used the same techniques to intubate. These groups have significant differences in levels of academic accomplishment, training, and experience; however, these practitioners may be representative of those called upon to provide advanced airway support to the patient with a known or suspected unstable cervical spine. Practitioners will have broad differences in experience with different techniques. Furthermore, the prehospital use of these and other similar airway devices, such as the AT, GlideScope, C-MAC, LW, and supraglottic airways like the ILMA, used by emergency medical technicians and other types of providers has been documented.44–53 Therefore, we believe the results recorded in our study may reflect the care provided to a patient with a known or suspected unstable spine. The variance imparted by the practitioners’ differing backgrounds in airway management and cadavers in an unbalanced, repeated-measures design was managed through the use of mixed models. Unfortunately, we discarded the data of 3 unsuccessful intubations with the ILMA before analysis. The data analyzed in this study were only from successful intubations.
This is the first study to evaluate the AT in subjects with C1-2 instability and compare the use of the AT with other devices in a controlled, reproducible manner. These 4 devices were selected for study because they are amenable for use in a wide array of settings, including the prehospital setting, because they are simple, inexpensive, and portable. Each technique was shown to have some advantages over the others in terms of speed, success rate, and cervical spine motion. It must be recognized that although the ILMA required the most time to complete by our practitioners, intermittent ventilation could continue during the procedure, and, although it had a lower success rate for our providers when using the blind technique, an improved success rate would be expected if a flexible fiberoptic scope was used to facilitate ILMA intubation, although that was not tested.
In conclusion, during intubation of the cadavers with created global instability at C1-2 (simulated type II odontoid fracture), the LW technique resulted in significantly less extension and axial rotation at C1-2 than with the ILMA and MAC techniques.
a Airtraq® Guided Video Intubation. Available at: http://www.airtraq.com/airtraq/portal.portal.action. Accessed September 15, 2011.
b Instruction Manual, LMA Fastrach Reusable & LMA Fastrach Single Use, revised 2006. San Diego, CA: LMA North America; Revised 2006. Available at: http://www.lmana.com/docs/LMA_Fastrach_manual.pdf. Accessed September 15, 2011.
c Liem EB. Lighted Stylet Intubation. The Virtual Airway Device. Intubation Techniques and Tutorials. Gainesville, FL: The University of Florida Center for Simulation, Advanced Learning and Technology. Available at: http://vam.anest.ufl.edu/airwaydevice/lightedstylet/index.html. Accessed September 15, 2011.
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