Anesth Analg 2001;93:799-801
© 2001 International Anesthesia Research Society
LETTERS TO THE EDITOR
Experimental Cervical Spine Injury and Airway Management Methods
Michael M. Todd, MD, and
Vincent C. Traynelis, MD
Department of Anesthesia, University of Iowa, Iowa City, IA
Department of Surgery (Neurosurgery), University of Iowa, Iowa City, IA
To the Editor: We read with interest the paper by Brimacombe et al. (1) concerning cervical spine motion during various airway management maneuvers, including the insertion of the intubating laryngeal mask airway (ILMA). Although they have provided a great deal of valuable data, we have some concerns about the injury model used and about the interpretation of their results.
The authors created a C3 injury in cadavers. Their previous work had shown that during ILMA insertion, the highest pressures were generated against the anterior body of C3 (2). Nevertheless, it is not clear that this is clinically relevant; human injuries at this level (and of the nature described) are exceptionally unusual, and the biomechanics of this model do not appear to have been previously described. There are also some unusual characteristics of the injury. The authors note that "posterior destabilization" was produced by sharp dissection of the C2-3 and C3-4 intervertebral spaces, followed by hitting the anterior surface of C3 with a metal rod and a 5-kg weight. It is not clear how this lesion can be classified as a "posterior injury" when all of the damaged structures are anterior. Of greater concern is the fact that it may not have resulted in instability in all cadavers. The authors do not describe direct disruption of the anterior or posterior longitudinal ligaments (although their sharp dissection would presumably have cut the anterior longitudinal ligament), the facet ligaments, facet capsules, or other structures that contribute to stability. They did not dislocate/relocate the facets to verify instability (3) nor do they provide radiologic evidence, in the absence of such "visual verification," confirming instability before airway manipulation in each cadaver. Extension/flexion radiographs were obtained at the end of the experiment, and it is clear that instability was present in at least some cadavers. For example, their Table 1 indicates several situations in which the maximal anterior-posterior displacement was >4 mm—a value typically considered indicative of translational instability. Nevertheless, instability may not have been present in all cadavers; the low range of maximum displacement with flexion was only 0.8 mm (1.3 mm with extension). In addition, motion with maximal flexion-extension was apparently less than that seen during some intubation maneuvers, again suggesting that instability was not achieved in all cadavers. The authors also did not separately describe motion at the two unstable segments (C2-3 and C3-4). Finally, manual axial traction (as distinct from simply manual stabilization) was used in all cases, but the authors provide no information regarding the traction force applied. Our own work suggests that traction does not reduce motion during direct laryngoscopy at the C4-5 interspace after a complete C4-5 injury (3). In fact, traction, by distracting the unstable structures, may actually increase anterior-posterior translational motion.
The other issue concerns the authors’ conclusion that "the safest method.... is (fiberscope-guided nasal intubation)" and "LMA devices may be preferable to the (esophageal tracheal Combitube®)." This is based on the observation that a maximal displacement of 1.7 mm was noted for fiberoptic intubation, versus maximal displacements of 4.2 mm for direct laryngoscopy, 6.2 mm for Combitube® insertion, and 5.2 mm for ILMA placement. However, the authors do not present the results of a statistical comparison between motion produced by the various airway interventions. The only statistical notations given in Table 1 are for a within-group comparison versus the preinjury state with the same airway management method. In the text, the authors state "Posterior displacement was similar to (maximal extension) for all airway manipulations other than for (fiberoptic intubation)." It hence appears difficult to conclude that any method (other than fiberoptic intubation) is "preferable" or even different from another. In addition, if complete instability was not present in all cadavers, comparisons between the groups might be misleading; different results might have been seen if verified instability was present in all cadavers. Similarly, different results might have been seen with a more relevant injury. For example, the greatest anterior-posterior motion in C spine injuries is generally seen with complete fractures of the base of the odontoid process of C2.
On the basis of these limitations, we would urge great caution in the interpretation of these results and in their extrapolation to any clinical setting. Fiberoptic intubation is often impractical in emergency settings, and we are concerned that the conclusions regarding differences among the Combitube®, LMA/ILMA, and even direct laryngoscopy may be incorrect. Until further work is completed, all airway management methods (other than perhaps flexible fiberoptic intubation) must be considered as having the potential for inducing spinal cord damage in patients with severe, unstable cervical spine injuries. If fiberoptic intubation is impractical, the choice of intubation method must be based on factors other than the possible—but unproven—differences in spine movement described by the authors (e.g., the anesthesiologist’s familiarity and comfort with a technique).
References
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Brimacombe J, Keller C, Kunzel KH, et al. Cervical spine motion during airway management: a cinefluoroscopic study of the posteriorly destabilized third cervical vertebrae in human cadavers. Anesth Analg 2000; 91: 1274–8.[Abstract/Free Full Text]
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Keller C, Brimacombe J, Keller K. Pressures exerted against the cervical vertebrae by the standard and intubating laryngeal mask airways: a randomized, controlled, cross-over study in fresh cadavers. Anesth Analg 1999; 89: 1296–300.[Abstract/Free Full Text]
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Lennarson PJ, Smith D, Todd MM, et al. Segmental cervical spine motion during orotracheal intubation of the intact and injured spine with and without external stabilization. J Neurosurg 2000; 92: 201–6.[Web of Science][Medline]
Response
Joseph Brimacombe, MD,
Christian Keller,
Karl H. Künzel,
Othmar Gaber,
Michael Boehler, and
Friedrich Pühringer
University of Queensland, Department of Anesthesia and Intensive Care, Cairns Base Hospital, Cairns, Australia
Department of Anesthesia and Intensive Care Medicine, Institute of Anatomy, Leopold-Franzens University, Innsbruck, Austria
In Response: We thank Drs. Todd and Traynelis for their interest in our article and will respond to each of their many points.
First, in addition to our previous findings for the intubating laryngeal mask and other airway devices (1,2), we studied the motion of the C3 injury because some work had already been conducted by others on cervical motion of injuries to the C1-2 (3), C4-5 (4), and C5-6 (5) segments.
Second, we disagree that the C3 injury we studied is "exceptionally unusual," at least in our institutes. We reviewed all cases of patients having cervical spine injuries admitted to our hospitals over the last 12 mo and found that 6% (10 of 155) had a C3 injury that involved posterior instability. Perhaps the snow-covered mountains surrounding Innsbruck or the rainforest-covered mountains and Great Barrier Reef surrounding Cairns somehow increase the risk of this type of injury.
Third, we used the term "posterior destabilization" to describe the direction of the instability rather than the location of the damaged structures.
Fourth, the biomechanical model we used was based on a flexion-compression injury. This is the most common mechanism for a posteriorly destabilized C3 injury in young adults.
Fifth, the injury was performed under direct vision and fluoroscopic guidance by an experienced anatomist (KK). Postinjury, we demonstrated radiologically a posterior instability greater than 4 mm during flexion in 9 of 10 cadavers and greater than 4 mm during extension in 8 of 10 cadavers. The remainder had flexion/extension instability greater than 3.0 mm. Thus, 9 of 10 cadavers had values typically indicative of translational instability, and one almost reached this value.
Sixth, Drs. Todd and Traynelis appear to be confused by the contents of Table 1 in our article. This has led them to underestimate the total amount of posterior displacement we found. Table 1 described the maximum posterior displacement for flexion, extension, and the six airway management techniques compared with postinjury, not preinjury, baseline values. The postinjury comparative values are lower than the preinjury comparative values because the injury produced a mean (SD, range) posterior displacement of 2.8 (0.8, 1.3–4.2) mm, as originally stated. The mean (SD, range) for maximum posterior displacement compared with preinjury baseline values were as follows: flexion, 6.5 (1.9, 2.0–9.3) mm; extension, 4.6 (1.7, 1.5–8.0) mm; face mask and chin lift/jaw thrust, 4.7 (1.2, 2.0–7.0) mm; laryngoscope-guided oral intubation, 5.4 (1.6, 3.0–9.0) mm; fiberscope-guided nasal intubation, 2.9 (0.7, 2.1–4.5) mm; esophageal tracheal Combitube® insertion, 6.0 (1.7, 3.0–9.0) mm; intubating laryngeal mask airway insertion/intubation, 4.5 (1.3, 2.0–8.0) mm; and laryngeal mask airway insertion, 4.5 (1.3, 2.0–7.0) mm.
Seventh, we did not use "manual axial traction," but rather "manual-in-line stabilization." We did not employ any traction force.
Eighth, the interdevice statistics for posterior displacement are as follows: fiberscope-guided nasal intubation produced significantly less than all other devices (all P < 0.01); esophageal tracheal Combitube® insertion produced significantly more than 1) the face mask and chin lift/jaw thrust (P = 0.01), 2) the intubating laryngeal mask airway insertion/intubation (P = 0.02), and 3) the laryngeal mask airway insertion (P = 0.01). There were no other significant differences.
Ninth, although we did not specifically describe the motion at C2-3 and C3-4, these segments were used in determining the motion at C3.
Tenth, we consider that our conclusions are entirely appropriate. Our first conclusion was that "in terms of cervical motion and the techniques tested, the safest method for airway management in a patient with a posteriorly destabilized C3 segment is fiberscope-guided nasal intubation." This was based on our finding that fiberscope-guided nasal intubation caused significantly less motion than all other airway devices. Our second conclusion was that "laryngeal mask airway devices may be preferable to the esophageal tracheal Combitube®." This was based on our finding that the esophageal tracheal Combitube® caused significantly more motion than both laryngeal mask devices. To this second conclusion we would add that the face mask and chin lift/jaw thrust might also be preferable to the esophageal tracheal Combitube®.
Eleventh, we agree that our data should be interpreted cautiously, but we strongly disagree that our findings have no clinical relevance. Our data suggest that in patients with a posteriorly destabilized C3 fracture, the best option in terms of cervical motion is nasal fiberoptic-guided intubation and that the face mask, laryngeal mask, and intubating laryngeal mask are preferable to the esophageal tracheal Combitube®.
Twelfth, we did not claim that our results applied to all cervical spine injuries, only to the specific injury we investigated.
Finally, many factors determine the choice of airway management in the unstable C-spine, not only the anesthesiologist’s familiarity and comfort with the technique, but also the time and equipment available, contraindications to particular airway devices, the conscious state of the patient, oropharyngeal bleeding, the level of risk of aspiration, patient preference, and the type/extent of cervical injury. A considerable amount of work is required to determine the best method of airway management for the myriad of cervical injuries that can occur. We hope that clinicians will factor in our findings when faced with a posteriorly destabilized C3 spine.
References
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Keller C, Brimacombe J. Pharyngeal mucosal pressures, airway sealing pressures and fiberoptic position with the intubating versus the standard laryngeal mask airway. Anesthesiology 1999; 90: 1001–6.[Web of Science][Medline]
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Keller C, Brimacombe J, Keller K. Pressures exerted against the cervical vertebrae by the standard and intubating laryngeal mask airway: a randomized, controlled crossover study in fresh cadavers. Anesth Analg 1999; 89: 1296–300.
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Donaldson WF, Heil BV, Donaldson VP, Silvaggio VJ. The effect of airway maneuvers on the unstable C1-C2 segment: a cadaver study. Spine 1997; 22: 1215–8.[Web of Science][Medline]
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Lennarson PJ, Smith D, Todd MM, Carras D, et al. Segmental cervical spine motion during orotracheal intubation of the intact and injured spine with and without external stabilization. J Neurosurg 2000; 92: 201–6.
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Donaldson WF, Towers JD, Doctor A, Brand A. A methodology to evaluate motion of the unstable spine during intubation techniques. Spine 1993; 18: 2020–3.[Web of Science][Medline]
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