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Anesth Analg 2001;92:1331-1336
© 2001 International Anesthesia Research Society

GENERAL ARTICLES

The Disposition of the Cervical Spine and Deformation of Available Cord Space with Conventional- and Balloon Laryngoscopy-Guided Laryngeal Intubation: A Comparative Study

Spyros D. Mentzelopoulos, MD, Maria J. Tzoufi, MD, and Evangelos P. Papageorgiou, MD, PHD

Department of Anesthesiology, Egion General Hospital, Egion, Greece

Address correspondence and reprint requests to Spyros D. Mentzelopoulos, MD, 2A Kypseli Str., 11362, Athens, Greece. Address e-mail to sdm{at}hol.gr


   Abstract
Top
 Abstract
Introduction
 Methods
 Results
 Discussion
 References
 
Orotracheal intubation causes cervical spine (C-spine) extension and potential (hypothetical) space available for the cord (SAC)-deformation. In the present study, we determined and compared the changes induced by conventional- and balloon laryngoscopy-guided orolaryngeal intubation in the upper C-spine’s osseous unit-orientation, segmental angulation, segmental SAC-sagittal surface areas (SSAs), segmental/total posterior SAC-aspect, and segmental SAC-width. Eight healthy volunteers were enrolled. A set of neutral head position (baseline)- and two sets of intubation-lateral C-spine radiographs were obtained. Relative to baseline, both intubation techniques induced significant changes in the occiput (OCC)-, third cervical vertebra (C3)-, C4-, and C5-orientation, the OCC-C1-segmental angulation, all the segmental SAC-SSAs, and the OCC-C1-, and C1-2-posterior SAC-aspect (P < 0.05 to < 0.001); conventional intubation caused additional significant changes in C2-orientation, total (OCC through C5)-posterior SAC-aspect, and OCC-C1-SAC-width (P < 0.05 to < 0.001). Relative to conventional intubation, balloon-assisted intubation caused less change in C3-orientation and C2-3-SAC-width (P < 0.05), and less reduction in OCC-C1-, C1-2-, and C4-5-SAC-SSAs (P < 0.05 to < 0.01). Orotracheal intubation should be cautiously performed in patients with space-occupying upper-C-spine-SAC lesions, even if there is no concomitant osseous/ligamentous pathology. In such cases, balloon laryngoscopy may be chosen over the conventional technique, because it causes less SAC deformation.

Implications: This study shows that direct laryngoscopy-guided orotracheal intubation causes deformation of the upper cervical space available for the cord, even in the absence of cervical spine instability. These effects are attenuated with balloon laryngoscopy, and thus, its use is recommended in patients with space-occupying lesions within the spinal canal.


   Introduction
Top
 Abstract
 Introduction
Methods
 Results
 Discussion
 References
 
The direct laryngoscopy-induced upper cervical spine (C-spine) extension is maximized on laryngeal intubation (1,2). During extension, the spinal cord folds like an accordion (3) and its width increases, resulting in compression risk if the space available for the cord (SAC) is already narrowed by space-occupying lesions (e.g., epidural hematoma) (4).

We theorized that conventional- and balloon laryngoscopy-guided (5,6) orotracheal intubation can cause upper-C-spine-SAC (occiput [OCC] through 5th cervical vertebra [C5])-deformation even in adults with intact C-spines, and that the potential SAC deformation is less with balloon-assisted intubation; the intubation-associated C-spine-osseous-rotation (1,2) and SAC-posterior contour changes (1–3) were determined and compared between the above techniques as well.


   Methods
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 Abstract
 Introduction
 Methods
Results
 Discussion
 References
 
After institutional approval, eight consenting, nonobese, healthy volunteers (male/female ratio: 5/3) aged 39, 19–50 yr (mean, range) were enrolled. Volunteer-median simplified airway risk index score (7) was 0 (range: 0–1). The participants were positioned supine on a parallel-to-floor operating table (8) with a 1-cm thick rigid board placed under the shoulders and OCC. Anesthesia and neuromuscular blockade were induced with midazolam (0.08 mg/kg), fentanyl (5 µg/kg), propofol (2.5 mg/kg), and rocuronium (1.2 mg/kg) respectively. A portable machine was used to expose a cross-table lateral-C-spine view as previously described (3,9).

The volunteers were ventilated manually until the train-of-four response-abolishment (6), their heads were placed in the neutral position (8), and baseline radiographs were taken. Subsequently, laryngoscopy was performed in random order (always by the same experienced operator) (8) with a number 4 Macintosh blade and a Fogarty catheter blade (5,6) ( Fig. 1). Glottic exposure was limited to that allowing visual laryngeal intubation confirmation with a semirigid stylet-equipped 7.0–7.5-mm endotracheal tube. Balloon laryngoscopy technique (5,6) included modified blade tip insertion into the vallecula, Fogarty catheter balloon inflation with 2.0–2.4 mL of air, and subsequent blade elevation.



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  		Figure 1. One of the modified number 4 curved blades used in the present study. A 7F Fogarty catheter is attached on the midline of the blade concave surface. The elliptically shaped Fogarty catheter balloon is inflated with 2.0 mL of air, resulting in a sagittal diameter (height) (thin black line) of 1.0 cm.

 
Before each laryngoscopy, the neutral head position was resumed. After laryngeal intubation, the laryngoscopist’s handle-grasping hand was immobilized (6), the time to intubation (10) was recorded, the endotracheal tube was withdrawn, and a radiograph was taken (4–5 s after intubation). Volunteer head-to-head rest contact maintenance (1), and consequently, avoidance of excessive, head-elevating, laryngoscopic lifting force, and "ideal intubation" (11) with both blades were prerequisites for volunteer data analysis inclusion.

The radiographs were scanned in Photoshop 5.0 (Adobe Systems Inc., San Jose, CA); resolution was 1000 pixels/in. Dimensional corrections for the apparent radiograph magnification (based on the actual blade-tip-to-light source distance) were performed, and the scans were encoded and saved on hard disk. Image areas (of identical size/shape) containing/"corresponding to" a laryngoscope blade (laryngoscopy/baseline radiographs, respectively) were removed to achieve observer blinding.

The following anatomic landmarks were drawn on separate scan copy sets by two radiologists: 1) Chamberlain’s line (1) ( Fig. 2); 2) the posterior odontoid-cortex and its most cephalad point ( Fig. 3); 3) the most anterior anterior-C1 tubercle’s point and the posterior-C1-tubercle base’s midpoint, and most cephalad/caudal points (Figs. 2,3); and 4) the midpoints and most cephalad/caudal points of the subatlantal (C2-5) posterior vertebral body-cortexes and spinous process bases (Figs. 2,3). Each C-spine segment was taken to consist of two adjacent osseous units and connecting tissue (1).



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  		Figure 2. Cervical spine osseous-unit-orientation/segmental-angulation with corresponding reference lines and anatomic landmarks (white dots) presented on a lateral radiograph scan. OCC = occiput/Chamberlain’s line, C1-5 = cervical vertebrae/corresponding reference lines, HRL = horizontal reference line, OP = opisthion, HP = most posterior point of hard palate; the highlighted landmarks also include the most anterior point of the anterior C1-tubercle, the midpoint of the posterior C1-tubercle, and the midpoints of the C2-5 posterior-vertebral-body-cortexes/spinous-process-bases. The osseous unit orientation was determined by electronically measuring the highlighted angles formed between the OCC-C5-reference lines and the HRL. Segmental angulation was defined as the difference between two consecutive relative-to-HRL orientation line angles (caudal always subtracted from cephalad).

 


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  		Figure 3. The five upper cervical, sagittal surface areas of the space available for the cord (SAC1-SAC5) as determined by their perimeters and corresponding anatomic landmarks (white and black dots, cross, and asterisk) on a lateral radiograph scan. OCC = occiput, C1-5 = cervical vertebrae. SAC1-SAC5: the black dots highlight the most cephalad/caudal points of the C2-5-posterior-vertebral-body-cortexes/C1-posterior-tubercle/C2-5-spinous-process-bases, while the white dots highlight the respective midpoints. POC = posterior odontoid cortex; the asterisk highlights its most cephalad point, and the cross highlights its point of intersection by the caudal SAC1-aspect (which is part of the C1-orientation line of Fig. 2). OCA = occipital aspect of SAC1 drawn as parallel-to-the-caudal SAC-1-aspect; OCA extends between the points (hollow dots) of OCC-cortex intersection by a vertical-to-the-caudal SAC-1-aspect line at the posterior C1-tubercle’s midpoint and a parallel-to-the-latter vertical drawn from the asterisk.

 
Determined variables included C-spine osseous unit-orientation and segmental angulation (Fig. 2), segmental SAC-sagittal surface areas (SSAs) (Fig. 3) (subsequently measured with Autocad 2000 [Autodesk Inc., San Rafael, CA]), and segmental/total posterior SAC-aspect length and segmental SAC width ( Fig. 4). The scans’ codes were broken after measurement completion, and the means of the values provided by the two observers were analyzed.



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  		Figure 4. Posterior aspect (bold gray line) and segmental width (white lines) of the upper cervical space available for the cord (SAC) drawn on a lateral radiograph scan; the contours of SAC1-SAC5 of Figure 3 are highlighted by the dotted, thin black line. OCC = occiput, C1-5 = cervical vertebrae. The bold gray line extends from the OCC-cortex (cephalad-posterior hollow dot determined as in Fig. 3) to the C5-spinous-process-base-midpoint (most caudal white dot) and passes through the midpoints of the posterior-C1-tubercle/C2-4-spinous process bases (consecutive intermediate white dots). In SAC1 (see also Fig. 3), the white line is the midparallel between its cephalad (occipital) and caudal aspect; the caudal-to-C1 white lines (or their extensions) bisect the respective segments of the bold gray line as well as the distances between the anterior SAC2-SAC5-aspects’ cephalad and caudal endpoints (highlighted in Fig. 3).

 
The Kolmogorov-Smirnov-test (12) revealed that all acquired data sets were normally distributed. The times to intubation and conventional/balloon-assisted orolaryngeal intubation and baseline/intubation technique radiographic variable-values were compared with the paired t-test (13,14). Data were presented as mean (SD). Significance was set at P < 0.05; SPSS 8.0 (SPSS Inc., Chicago, IL) was used.


   Results
Top
 Abstract
 Introduction
 Methods
 Results
Discussion
 References
 
All volunteer data were analyzed. Conventional/balloon-assisted intubation times were 14.3 (3.1) s/13.8 (3.3) s, respectively (P = 0.75), and glottic exposure always exceeded the posterior vocal cords’ third. The osseous unit orientation/segmental angulation, segmental SAC-SSAs, and segmental/total posterior-SAC aspect-length/segmental SAC width were determined consistently within 1°, 0.02 cm2, and 0.1 cm, respectively. Table 1 provides a detailed data presentation.


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  		Table 1. Cervical Spine Radiographic Variables
 
Relative to baseline, conventional/balloon-assisted intubation induced significant changes in OCC-, C3-, C4-, and C5-orientation, OCC-C1-segmental angulation, all segmental SAC-SSAs, and OCC-C1- and C1-2-posterior-SAC-aspect length (P < 0.05 to < 0.001). Conventional intubation caused an additional significant C2-orientation-change (P < 0.05), and additional significant reductions in OCC-C1-SAC width/total posterior-SAC-aspect length (P < 0.05/< 0.001, respectively).

Relative to conventional intubation, balloon-assisted intubation caused less change in C3-orientation (P < 0.05) and less reduction in the OCC-C1-, C1-2-, and C4-5-SAC-SSAs (P < 0.01, < 0.05, and < 0.05, respectively) (respective proportional reductions: 6.5% [2.5%] vs 16.7% [5.0%], 18.1% [10%] vs 25.1% [10%], and 3.5% [2.8%] vs 6.0% [3.1%], balloon vs conventional intubation), and resulted in greater C2-3-SAC-width (P < 0.05) (by 5.4% [4.4%]).


   Discussion
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
References
 
Apart from osseous rotation (1,2), orolaryngeal intubation (performed in the neutral head position) narrows all the intact-upper-C-spine’s segmental SAC-SSAs. Thus, in patients with stable C-spines and space-occupying SAC lesions, such as intradural spinal cysts (15), extradural tumors (16), and epidural/subdural hematomas (4,17–20), there is a potential risk of intubation-associated spinal cord compression. In such cases, balloon-assisted intubation may provide an "extra margin of safety" by attenuating SAC deformation.

During balloon laryngoscopy (6), the Fogarty catheter balloon inflation (Fig. 1) induces an initial epiglottis-lifting/glottic-exposure by displacing upwardly solely the hyoid/tongue-base; thus, in this stage, there is probably no tongue-upper surface compression. In the modified blade elevation stage, tissue displacement is still restricted mainly in the hyoid/tongue-base area (especially if full glottic visualization is not sought) ( Fig. 5A). On the contrary, any epiglottis lifting with a balloon-lacking Macintosh blade causes concomitant whole-tongue compression (6) (Fig. 5B).



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  		Figure 5. Laryngoscope blade-containing parts of scanned cervical spine cross-table-lateral view radiographs taken 4–5 s after the confirmation of laryngeal intubation in one of the study-participants (see Methods). A, Balloon laryngoscopy. B, Conventional laryngoscopy. The intubationist reported that "more than the posterior third of glottis" was exposed with both techniques. T = tongue, HB = hyoid body, E = epiglottis, BL = 7F Fogarty catheter balloon inflated with 2.0 mL of air. The arrows indicate directions of upper airway tissue lifting. The elliptically shaped BL selectively lifts the HB/T-base; its sagittal diameter (height) (thin white line) is slightly reduced relative to Figure 1 (0.92 vs 1.0 cm, respectively) as a result of compression between the posterior HB and the modified blade’s distal concave surface and tip. During conventional laryngoscopy, an additional blade elevation of 0.92 cm (and consequently additional T compression) relative to balloon laryngoscopy was required for the achievement of a similar laryngoscopic view (in this particular volunteer).

 
Similar and submaximal hyoid/tongue-base/epiglottis lifting and laryngeal visualization were sought and achieved with both blades; lifting force exertion duration was similar as well. Consequently, the proportional, monoexponential peak force decrease (21) should also be similar on laryngeal intubation radiographs’ obtainment. However, during balloon-assisted intubation, the conventional intubation’s OCC-C5-SAC-posterior contour line-shortening (3) and the C2-orientation-change were not observed, while the C3-anterior rotation was less (Table 1).

Despite the lack of lifting force data (21), we postulate that balloon laryngoscopy constrains the laryngotracheal intubation-associated upper airway tissue-lifting/compression to the tongue-base/posterior-hyoid-body (6), resulting in reduced operator lifting effort relative to the conventional technique; consequently, the corresponding rotational/lifting torque applied on the C-spine’s osseous/ligamentous elements and SAC should be reduced as well.

We obtained solely static radiographs (and not cinefluoroscopic images) (1,2), because C-spine motion is maximized on laryngeal intubation (1,2). Head/neck stabilization was not used, because we have already shown that balloon-assisted, full glottic visualization under rigid Philadelphia collar stabilization results in approximately 40% less head extension relative to the conventional technique (8).

Radiographic biases were eliminated by electronically removing the laryngoscopes’ images from the radiographs’ scans; however, to eliminate the present study’s potential operator bias risk as well, a videographic laryngoscopic view-assessment (22,23) by two blinded-to-intubation technique observers (6) would be required.

According to our experience (6), the operator-based, visual laryngeal intubation confirmation should have required exposure of more than the posterior vocal cords’ third (Cormack-Lehane-grade I view). The subsequent subjective (as a result of lack of laryngoscopist-to-blade-type blinding) laryngoscopic view-assessment was performed under laryngoscopist’s handle-grasping-hand immobilization that was begun on intubation confirmation. Accordingly, any potential operator bias (e.g., preferentially reporting grade I glottic views with one of the blades used when grade II/III views are actually present) would have affected intubation confirmation as well. However, especially in patients with probable easy glottic visualization (7), it seems unlikely (although theoretically possible) for an experienced and motivated (24) operator to systematically misjudge laryngeal intubation achievement with either blade. In addition, intubation times (unbiased measurement) (10) and difficulty degree (determined both subjectively and objectively) (11) were nearly identical with both blades.

We conclude that even in the absence of any segmental-C-spine instability, orotracheal intubation should be cautiously performed in patients with upper cervical SAC pathology, because it causes significant SAC deformation. In such cases, balloon laryngoscopy may be chosen over the conventional technique, because it causes less SAC deformation.


   Acknowledgments
 
The authors wish to thank Mr. G. Grilis, Mr. N. Nikolaides, and the staff members of the Departments of Radiology and Anesthesiology of Egion General Hospital for their invaluable support.


   References
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 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 

  1. Sawin PD, Todd MM, Traynelis VC, et al. Cervical spine motion with direct laryngoscopy and orotracheal intubation: an in vivo cinefluoroscopic study of subjects without cervical abnormality. Anesthesiology 1996; 85: 26–36.[Web of Science][Medline]
  2. 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]
  3. Panjabi MM, White AA 3rd . Basic biomechanics of the spine. Neurosurgery 1980: 76–93.
  4. Oliviero A, Insola A, Santili V, et al. Concomitant post-traumatic craniocervical junction epidural hematoma and pontomedullary junction infarction: clinical, neurophysiologic, and neuroradiologic features. Spine 2000; 25: 888–90.[Medline]
  5. Mentzelopoulos SD, Tsitsika MV, Karamichali EA. Difficult airway management with Fogarty catheter balloon inflation. Anesth Analg 2000; 91: 495.[Free Full Text]
  6. Mentzelopoulos SD, Romana CN, Corolanoglou DS, et al. Balloon versus conventional laryngoscopy: a comparison of laryngoscopic findings and intubation difficulty. Anesth Analg 2000; 91: 1513–9.[Abstract/Free Full Text]
  7. El-Ganzouri AR, McCarthy RJ, Tuman KJ, et al. Preoperative airway assessment: predictive value of a multivariate risk index. Anesth Analg 1996; 82: 1197–204.[Abstract]
  8. Mentzelopoulos SD, Tsitsika MV, Balanika MP, et al. Balloon laryngoscopy reduces head extension and blade leverage in patients with potential cervical spine injury. Crit Care 2000; 4: 40–4.[Web of Science][Medline]
  9. Papageorgiou E, Kokkinis K, Goumas P, et al. Objective evaluation of the difficulty of endotracheal intubation: a comparative study of two different laryngoscope blades. Anaesth Intensive Care 1997; 25: 655–8.[Medline]
  10. Watts ADJ, Gelb AW, Bach DB, Pelz DM. Comparison of the Bullard and Macintosh laryngoscopes for endotracheal intubation of patients with a potential cervical spine injury. Anesthesiology 1997; 87: 1335–42.[Web of Science][Medline]
  11. Adnet F, Borron SW, Racine CX, et al. The intubation difficulty scale (IDS): proposal and evaluation of a new score characterizing the complexity of endotracheal intubation. Anesthesiology 1997; 87: 1290–7.[Web of Science][Medline]
  12. Using explore to screen and describe subpopulations. In: SPSS Base 8.0 applications guide. Chicago: SPSS, 1998:37–63.
  13. Majernick TG, Bieniek R, Houston JB, Hughes HG. Cervical spine movement during orotracheal intubation. Ann Emerg Med 1986; 15: 417–20.[Web of Science][Medline]
  14. Hastings RH, Wood PR. Head extension and laryngeal view during laryngoscopy with cervical spine stabilization maneuvers. Anesthesiology 1994; 80: 825–31.[Web of Science][Medline]
  15. Fortuna A, Mercuri S. Intradural spinal cysts. Acta Neurochir (Wien) 1983; 68: 289–314.[Medline]
  16. Chakravarty K, Scott DG, Dick D, Visick J. Cervical spondylotic myelopathy with occult foramen magnum meningioma: a case for MRI? Postgrad Med J 1993; 69: 720–3.[Abstract/Free Full Text]
  17. Fukui MB, Swarnkar AS, Williams RL. Acute spontaneous spinal epidural hematomas. AJNR Am J Neuroradiol 1999; 20: 1365–72.[Abstract/Free Full Text]
  18. Pullarkat VA, Kalapura T, Pincus M, Baskharoun R. Intraspinal hemorrhage complicating oral anticoagulant therapy: an unusual case of cervical hematomyelia and a review of the literature. Arch Intern Med 2000; 160: 237–40.[Abstract/Free Full Text]
  19. Juvonen T, Tervonen O, Ukkola V, Klintrup HE. Widespread posttraumatic subdural hematoma-imaging findings with spontaneous resolution: case report. J Trauma 1994; 36: 262–4.[Medline]
  20. Rogers LA. Acute subdural hematoma and death following lateral cervical spinal puncture: case report. J Neurosurg 1983; 58: 284–6.[Medline]
  21. Hastings RH, Hohn ED, Nghiem C Wahrenbrock EA. Force, torque, and stress relaxation with direct laryngoscopy. Anesth Analg 1996; 82: 456–61.[Abstract]
  22. Levitan RM. Direct laryngoscopy imaging: teaching and research application. Am J Anesthesiology 1999; 26: 39–42.
  23. Ochroch EA, Levitan RM. A videographic analysis of laryngeal exposure comparing the articulating laryngoscope and external laryngeal manipulation. Anesth Analg 2001; 92: 267–70.[Abstract/Free Full Text]
  24. Hastings RH, Vigil CA, Hanna R, et al. Cervical spine movement during laryngoscopy with the Bullard, Macintosh, and Miller laryngoscopes. Anesthesiology 1995; 82: 859–69.[Web of Science][Medline]
Accepted for publication January 23, 2001.




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Lippincott, Williams & Wilkins Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins and Stanford University Libraries' HighWire Press®. Copyright 2001 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999 HighWire Press