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Abstract |
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We conducted a randomized, controlled, crossover study to determine cervical spine motion for six airway management techniques in human cadavers with a posteriorly destabilized third cervical (C-3) vertebra. A destabilized C-3 segment was created in 10 cadavers (6–24 h postmortem). Cervical motion was recorded by continuous lateral fluoroscopy. The following airway management techniques were performed in random order on each cadaver with manual in-line stabilization applied: face mask ventilation (FM), laryngoscope-guided orotracheal intubation (OETT), fiberscope-guided nasal intubation (FOS-NETT), esophageal tracheal Combitube® (Kendall-Sheridan, Neustadt, Germany) insertion (ETC), intubating laryngeal mask insertion with fiberscope-guided tracheal intubation (ILM-OETT), and laryngeal mask airway insertion (LMA). Afterward, maximum head-neck flexion (FLEX-MAX) and maximum head-neck extension (EXT-MAX) without manual in-line stabilization was performed to determine maximum motion. The maximum posterior displacement of C-3 and the maximum segmental sagittal motion of C2-3 were determined. There was a significant increase in posterior displacement for the FM (1.9 ± 1.2 mm, P < 0.01), OETT (2.6 ± 1.6 mm, P < 0.0001), ETC (3.2 ± 1.6 mm, P < 0.0001), ILM-OETT (1.7 ± 1.3 mm, P < 0.01), LMA (1.7 ± 1.3 mm, P < 0.01), FLEX-MAX (3.7 ± 1.9 mm, P < 0.0001), EXT-MAX (1.8 ± 1.7, P < 0.01), however, not for FOS-NETT (0.1 ± 0.7 mm). Posterior displacement was less for the ILM-OETT and LMA than for the ETC (both P < 0.04). There were no significant increases in segmental sagittal motion with any airway manipulation other than with FLEX-MAX (-4.5 ± 4.0°, P < 0.01). Posterior displacement was similar to FLEX-MAX for the OETT and ETC; however, it was less for the FM, FOS-NETT, ILM-OETT, and LMA (all P < 0.01). Posterior displacement was similar to EXT-MAX for all airway manipulations other than for FOS-NETT (P < 0.001). For cervical motion and the techniques tested, the safest method of airway management in a patient with a posteriorly destabilized C-3 segment is FOS-NETT. LMA devices may be preferable to the ETC.
Implications: In the cadaver model of a destabilized third cervical vertebrae, significant displacement of the injured segment occurs during airway management with the face mask, laryngoscope-guided oral intubation, the esophageal tracheal Combitube® (Kendall-Sheridan, Neustadt, Germany), the intubating and standard laryngeal mask airway; but not with fiberscope-guided nasal intubation. For cervical motion and the techniques tested, the safest airway technique with this injury is fiberscope-guided nasotracheal intubation. Laryngeal mask devices are preferable to the esophageal tracheal Combitube®.
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Introduction |
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Cervical spine (C-spine) injuries occur in 1.5%–3% of all major trauma cases and are associated with major morbidity and mortality (1,2). There is anecdotal evidence that airway management can result in catastrophic neurologic injury (3); however, the kinetics of the unstable C-spine during airway management are poorly understood. Different approaches may be required, depending on the nature of the cervical instability (4); however, there are few data to guide the anesthesiologist in selecting the appropriate technique. Donaldson et al. (5) investigated the effect of airway management on the unstable C1-2 and C5-6 (6) segments in cadavers and showed that both oro/nasotracheal intubation and chin lift/jaw thrust cause diminution of space available for the cord at the affected segment. Lennarson et al. (7) investigated the effect of direct laryngoscopy on the unstable C4-5 segment and showed that the predominant motion changed from extension to flexion after the injury; however, the degree of motion was small. Our group has shown that the intubating laryngeal mask airway (ILM) can produce posterior displacement of the stable third cervical vertebrae in cadavers (8) and anesthetized patients (4). In the following randomized, controlled, crossover study, we determined C-spine motion for six airway management techniques in human cadavers with posteriorly destabilized C-3 segment during the application of manual in-line stabilization.
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Methods |
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We studied 10 fresh cadavers (6–24 h postmortem). The specimens were not frozen, but were kept cool in a refrigerated morgue to better simulate the elasticity of tissue in the in vivo situation. Research and ethical committee approval was obtained and all patients or their relatives consented to postmortem research. Cadavers were excluded if they had oropharyngeal or C-spine pathology, or restricted range of head-neck movement. Cadavers were placed supine on a fluoroscopy table with the head supported by a pillow 5 cm in height. Lateral cinefluoroscopy (Philips BV 300, Philips Medical Systems, Vienna, Austria) was performed with a fixed 98-cm length beam, as follows: before the posterior destabilization (baseline); after the posterior destabilization with manual in-line stabilization applied (control); during each airway manipulation with manual in-line stabilization applied; and with the head and neck flexed and extended maximally without manual in-line stabilization (to determine maximum segmental movement). A metallic scale was placed on the neck for the purposes of distance calibration. The posteriorly destabilized C-3 segment was created by using a transoral approach and fluoroscopic guidance as follows: the intervertebral spaces between C2-3 and C3-4 were loosened by sharp dissection; the neck was flexed maximally; a steel rod was applied to the anterior surface of C-3; and a 5-kg weight applied in one fast hit. The following airway management techniques were performed in random order with each cadaver in the neutral position with manual in-line traction: 1) the application of a size 4 face mask (FM) with chin lift/jaw thrust; 2) orotracheal intubation with a size 3 Macintosh blade and a 7.5-mm tracheal tube (OETT) (Mallinckrodt Medical, Lo-Contour, Athlone, Ireland); 3) fiberscope-guided (FB 15 X; Pentax, Hamburg, Germany) nasotracheal intubation with a 7.5-mm tracheal tube (FOS-NETT); 4) insertion of a size 41FG esophageal tracheal Combitube® (ETC) (Kendall-Sheridan, Neustadt, Germany) and inflation of the proximal cuff with 85 mL air and the distal cuff with 10 mL air; 5) insertion of a size 4 intubating laryngeal mask (Laryngeal Mask Company Ltd, Henley-on-Thames, UK), inflation of the cuff with 15-mL air and fiberscope-guided intubation with a 7.5-mm straight silicone tracheal tube (ILM-OETT) (Euromedical Industries, Penang, Malaysia); and 6) insertion of a size 4 standard laryngeal mask airway and inflation of the cuff with air 15 mL (LMA). The ETC (9), ILM-OETT (10), and LMA (11) were inserted in accordance with the manufacturer’s recommendations. All airway management techniques were performed by a single anesthesiologist experienced with all techniques (30 to >1500 uses per technique). The anesthesiologist did not watch the fluoroscopy screen during airway management. Manual in-line stabilization was applied by a trained assistant who placed his hands on either side of the patient’s head and pulled the head in the caudal to cephalad direction as strongly as he felt would be necessary to stabilize the head-neck (12). When these airway manipulations were complete, the head-neck was flexed (FLEX-MAX) and extended (EXT-MAX) maximally in random order.
The fluoroscopic images were stored directly onto a hard drive and transferred into a picture archiving and communication system (Tiani Medgraph GMBH, Vienna, Austria). The cinefluoroscopic images were analyzed by two independent observers to determine the maximum anteroposterior displacement and maximum sagittal rotation of the C-3 segment relative to the adjacent vertebrae. To determine the anteroposterior position of the C-3 segment relative to the adjacent vertebrae, a reference line was drawn between the posterior border of the C-2 and C-4 segments, a parallel reference line was drawn on the posterior border of the C-3 segment, and the distance between these lines was noted (Figure 1). To determine the degree of segmental sagittal motion of C-3 relative to C-2, a reference line was drawn on the C-2 segment between the vertex of the angle formed by the anterior cortex of the vertebral body and the inferior vertebral endplate and the tip of the spinous process. An identical reference line was drawn on the C-3 segment (Figure 1). The degree of angulation in the sagittal plane of the C-3 reference line relative to the C-2 reference line was noted. Baseline measurements for position and angulation were made before and after the destabilized segment was created. The maximum displacement and maximum segmental sagittal motion (flexion/extension (13)) was the difference between the postdestabilization position and the maximum position observed during airway management. Multiple measurements were made where there was uncertainty about the point of maximal position or angulation. The phase of the airway management technique at which maximum motion occurred was also noted.
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The distribution of data was determined by using Kolmogorov-Smirnov analysis (14). Statistical analysis was by analysis of variance with post hoc test (Bonferroni) for multiple comparison. Unless otherwise stated, data are presented as mean (SD, range). Significance was taken as P < 0.05. Statistical analysis was performed on an IBM computer by using SYSTAT 7.0 (SPSS, Chicago, IL).
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Results |
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The mean (range) for age, height, and weight was 79 (69–87) yr, 168 (152–189) cm, and 66 (42–93) kg, respectively. The male/female ratio was 7:3. All of the data for the displacement and segmental sagittal motion were normally distributed. The image analysis software facilitated quantification of displacement and angulation with a resolution of 0.1 mm and 0.05 degrees, respectively. The mean (range) for measurement discrepancies between observers was 0.23 (0–2.68) mm for position and 0.24 (0–2.5) degrees for angulation. Data for the maximum posterior displacement, the maximum segmental sagittal motion of C2-3, and the phase of maximum motion are given in Table 1. Compared with baseline values, the posterior displacement and segmental sagittal motion after destabilization was 2.8 (0.8, 1.3–4.2) mm and 1.2 (3.5, -6.0–8.0) degrees, respectively. There was a significant increase in posterior displacement for the FM (P < 0.01), OETT (P < 0.0001), ETC (P < 0.0001), ILM-OETT (P < 0.01), LMA (P < 0.01), FLEX-MAX (P < 0.0001), and EXT-MAX (P < 0.01), however, not for FOS-NETT (0.1 ± 0.7 mm). Posterior displacement was less for the ILM-OETT and LMA than the ETC (both P < 0.04). There were no significant increases in segmental sagittal motion with any airway manipulation other than with FLEX-MAX (-4.5 ± 4.0°, P < 0.01). Posterior displacement was similar to FLEX-MAX for the OETT and ETC; however, it was less for the FM, FOS-NETT, ILM-OETT, and LMA (all P < 0.01). Posterior displacement was similar to EXT-MAX for all airway manipulations other than for FOS-NETT (P < 0.001). For all airway manipulations, sagittal rotation was less than FLEX-MAX (all P < 0.0001) and similar to EXT-MAX. In all cadavers, the point of maximum displacement and maximum segmental sagittal motion occurred during chin lift (FM), exposure of the glottis (OETT), advancing the tube (FOS-NETT), cuff inflation with 85 mL air (ETC), intubation (ILM-OETT), and insertion (LMA). There was no displacement or segmental sagittal motion for the FOS-NETT.
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Discussion |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Several groups have attempted to determine the safest method of airway management in the unstable C-spine. Bivins et al. (15) examined four trauma patients with various C-spine instabilities undergoing laryngoscope-guided oral intubation with axial traction applied to reduce subluxation and found that it produced distraction. The authors recommended nasal intubation without traction and cricothyrotomy, if nasal intubation was contraindicated. Aprahamian et al. (16) looked at airway maneuvers with and without a collar after ligamentous release at C5-6 in cadavers and showed that chin lift/jaw thrust, the esophageal obturator airway, and oro/nasotracheal intubation can cause extension, widening, and anterior subluxation. They noted that nasal intubation seemed to cause less motion and that the application of a soft or rigid collar did little to prevent movement. Donaldson et al. (6) studied cadavers with an instability created at the C5-6 space and showed that oral techniques of intubation caused more motion than nasotracheal techniques, and that preintubation maneuvers, such as chin lift/jaw thrust caused as much motion as some of the intubation techniques. In a similar follow-up study, Donaldson et al. (5) quantified the amount of motion that occurs at an unstable C1-2 spinal segment and showed that oro/nasotracheal intubation caused similar motion; however, the chin lift/jaw thrust caused more motion than either nasal or oral intubation. The authors suggested that great care should be taken while performing the chin lift/jaw thrust maneuvers in preparation for intubation. Recently, Lennarson et al. (7) investigated the effect of laryngoscope-guided orotracheal intubation after posterior destabilization of the C4-5 segment in cadavers. They showed that the predominant motion of the unstable segment changed from extension to flexion after the injury; however, the degree of motion was small and unaffected by the application of traction. Kihara et al. (4) measured C-spine movement in three patients with unstable C-7 segments from metastatic disease who were tracheally intubated through the ILM. They found that the degree of segmental flexion/extension and posterior movement of the C0-6 segments was similar in patients with stable C-spines.
We found significant motion of the destabilized C-3 segment with the FM, OETT, ETC, ILM-OETT, and LMA, but not with the FOS-NETT. The quantity of motion was posterior displacement of between 1.7 and 3.2 mm and it is not known whether this would place the patient at risk. The maximum displacement with the FM occurred during chin-lift/jaw thrust, a similar finding to Donaldson et al. (5,6) for the unstable C1-2 and C5-6 segments. The maximum motion with the OETT occurred during exposure of the glottis, a similar finding to Sawin et al. (13) in anesthetized patients with normal C-spines. The maximum motion for the ETC was during inflation of the proximal cuff with 85 mL air. This may be related to the large cuff pressing against the posterior pharyngeal wall. There are no published data about C-spine movement with the ETC; however, Aprahamian et al. (16) noted substantial motion of the unstable C5-6 segment in cadavers for the esophageal obturator airway, a similar device. The maximum motion for the ILM-OETT was during intubation. This is surprising, because the ILM exerts a higher pressure against the C2-3 segment during insertion than during intubation (273 vs. 96 cm H2O) (8). However, in our study, the ILM handle was sometimes pressed posteriorly during intubation to align the ILM with the glottis and this can generate much higher pressures (394 cm H2O) (8). The maximum motion for the LMA was during insertion and this fits with the finding that the maximum pressure against the C2-3 space occurs during LMA insertion (8). We found that the ILM-OETT and LMA caused 1.7 mm of posterior displacement of the destabilized C-3 segment. This compares with a previous nonradiologic cadaver study in which the ILM and LMA could produce 1–3 mm of posterior displacement of the stable C-3 segment (8). Interestingly, we found that the maximum (as opposed to the mean) values for maximum cervical motion (other than posterior displacement for FOS-NETT) were similar between techniques. This suggests that any of the tested techniques can produce significant motion of the C-3 segment in individual patients. We studied the C-3 segment because of the motion we detected at this segment in a previous cadaver study (8).
We found that FOS-NETT produced no motion of the unstable C-3 segment. However, Donaldson et al. reported laryngoscope-guided nasal intubation produced motion at the unstable C1-2 and C5-6 segments. We postulate that fiberscope-guidance produces less motion than direct laryngoscopy during nasal intubation. There have been no formal assessments of C-spine movement with the FOS-NETT in the unstable C-spine. We suggest that for cervical motion and the techniques tested, the safest method of airway management in a patient with a posteriorly destabilized C-3 segment is FOS-NETT, provided the practitioner is skilled with the technique and the patient is suitable. Cervical motion was similar for the FM and LMA, suggesting that either technique would be suitable for preintubation airway management. Cervical motion was similar for the ILM-OETT and OETT, suggesting that either technique would be suitable to facilitate intubation whether FOS-NETT was unavailable or contraindicated.
Our study has a number of limitations. First, we did not compare C-spine motion with or without manual in-line traction. However, posterior displacement for all airway management techniques was similar to EXT-MAX and some were similar to FLEX-MAX, suggesting that manual in-line stabilization was generally ineffective in preventing motion. This supports Lennarson et al.’s (7) findings that manual in-line stabilization does not prevent movement of the unstable or stable subaxial cervical segments. Second, we did not compare C-spine motion for each airway management technique before and after the creation of the destabilized segment. However, our analysis reflects the clinical situation where airway management is conducted with manual in-line stabilization in the presence of an unstable C-spine. Third, our cadaveric findings should be extrapolated cautiously to living patients. Interestingly, the validity of the cadaver model for evaluating cervical motion in the stable and unstable states has been determined by Lennarson et al. (7). The authors showed that cadaveric C-spine motion accurately reflects previously reported motion in living anesthetized patients (13). Fourth, all airway management techniques were conducted by a single anesthesiologist. It is possible that the extent of manipulation and the degree of force exerted with each technique may not represent that of the average anesthesiologist. Also, although the anesthesiologist was experienced with all airway management techniques, it is possible that user bias may have influenced the results. Finally, the clinical significance of the C-spine motion we detected is unknown because there are no published studies relating C-spine motion to C-spine injury in patients.
We conclude that for cervical motion and the techniques tested, the safest method for airway management in a patient with a posteriorly destabilized C-3 segment is FOS-NETT. LMA devices may be preferable to the ETC.
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References |
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Kihara S, Watanabe S, Brimacombe J, et al. Segmental cervical spine movement with the intubating laryngeal mask during manual in-line stabilization in patients with cervical pathology undergoing cervical spine surgery. Anesth Analg 2000; 91: 195–200.
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