Patients with possible or confirmed cervical spine (c-spine) instability who require endotracheal intubation are a challenge for the anesthesiologist. Although in this type of case the causal nature of reported associations between direct laryngoscopy and adverse neurological outcomes is not determined,1 awake intubation with the flexible fiberoptic bronchoscope (FOB) is preferred by many anesthesiologists.2,3 However, awake FOB intubation has some disadvantages. It may be difficult or impossible in unconscious/sedated4 or uncooperative patients, and the risk of coughing during intubation, which can generate large c-spine movements, can be reduced but not completely eliminated when performing intubation in an awake patient. Another often-used technique for airway control of patients with c-spine instability is intubation using the FOB after inducing general anesthesia.5 This technique aims tocombine the advantages of the FOB with the total immobility afforded by unconsciousness and neuromuscular blockade. An interesting alternative for intubation of patients with c-spine instability is the Trachlight® (TL, Laerdal medical, NY). The TL is small, portable, inexpensive, fast, has a low complication rate, demands little maintenance, and has a high success rate.6–8 A continuous cinefluoroscopic comparison of the TL versus the McIntosh laryngoscope showed a reduction of c-spine movement when intubating with the TL.9 Although both the TL and the FOB are in routine use, no comparison of the c-spine movement produced by these two techniques has been published. We therefore performed a prospective, randomized, crossover, controlled trial comparing c-spine movement measured with continuous cinefluoroscopy, whereas performing orotracheal intubation with the FOB and the TL. Our hypothesis was that endotracheal intubation using the TL would not cause more c-spine movement than intubation with the FOB in patients under general anesthesia with neuromuscular blockade and manual in-line stabilization (MILS) of the c-spine. Secondary endpoints included the time needed to intubate and success rates with each technique.
After study approval from our Institutional Ethics Board, we prospectively enrolled 20 adult patients undergoing neuroradiologic examination or treatment requiring general anesthesia and orotracheal intubation between October 2006 and February 2007 at the Centre hospitalier de l’Université de Montréal. Exclusion criteria included patient refusal or inability to consent, gastroesophageal reflux, emergency intubation, known difficult intubation, c-spine abnormalities, body mass index greater than 35, upper airway tumor, trauma or infection, ASA Class IV or V, or those presenting contraindication to neuromuscular blockade.
After oral and written informed consent, the patient was questioned and examined, and epidemiologic and anthropometric data were collected. Vertical mouth opening (incisor to incisor), neck circumference, thyrosternal and thyromental distance, neck extension and flexion measuring distance from chin to manubrium, and the Mallampati grade10 were evaluated. Presence of snoring, sleep apnea, beard, moustache, and dentures was also noted.
Before the beginning of each procedure, a 7.0 mm internal diameter Parker Flex-Tip tracheal tube (Parker Medical, Englewood, CO) was verified and installed on both intubating devices. The TL was coated with lubricating gel, whereas silicone spray was used to lubricate the FOB. Patients were placed on a rigid radiologic table without pillow, and standard monitoring plus an arterial line were installed. Patients were administered 100% O2 for 3–4 min. The medications given for anesthetic induction were left to the attending anesthesiologist’s discretion but had to include a neuromuscular blocking drug. Once asleep, the patient’s lungs were ventilated by mask until complete neuromuscular blockade was confirmed by neurostimulation of the ulnar nerve at the wrist. With the c-spine in the neutral position, the occiput and shoulders resting directly on the firm horizontal surface of the fluoroscopy table and the head in the anatomical position, the cinefluoroscope (Axiom Artis biplane digital system, Siemens, Erlangen, Germany) was adjusted to include the base of the cranium (C0) and the fifth cervical vertebra (C5) in the lateral view. Once the positioning was deemed appropriate, neither the table nor the fluoroscopy camera was allowed to move. During each intubation attempt, a respiratory therapist continuously applied MILS.11 Each patient was sequentially intubated using both devices in an order determined by a computer-generated randomization table. For each patient, successful intubation using the first technique was confirmed by capnography, the patient’s lungs were ventilated and, when judged ready by the attending anesthesiologist, extubated then reintubated with the second device.
With the TL the ambient light was not dimmed, and the TL was used as described by Hung et al.6 and Agro et al.12 Jaw lift was used with the minimal force necessary to allow intubation. Time to intubate was calculated using the time stamp of the cinefluoroscope from the opening of the mouth to introduce the TL to the complete removal of the light wand from the endotracheal tube. Before intubation with the FOB (Pentax FB-15BS, 4.8 mm diameter), the introduction of an oropharyngeal airway (Williams Airway Intubator, Calgary, Canada) was recorded and timed with the cinefluoroscope. The FOB was then introduced and, if the glottic entrance was masked by collapsed pharyngeal tissues, a jaw thrust was performed by the attending anesthesiologist. The force was applied at first minimally and only increased as requested by the operator of the FOB. When the glottis was visualized, the FOB was advanced through the vocal cords until the carina was visualized. The endotracheal tube was then advanced to the correct position, and the FOB was removed followed by the oropharyngeal airway. For the FOB technique, the fluoroscopy and chronometer were restarted when the tip of the FOB crossed the entrance of the oropharyngeal airway and stopped after removal of the oropharyngeal airway. All intubations were executed by the same senior anesthesiology resident (BJH) who had previously performed 20 asleep FOB and 35 TL intubations. Three attempts were permitted for each technique. An attempt was stopped either by desaturation below 94% or time to intubate more than 100 s, the longest possible continuous recording time of the cinefluoroscope. Between attempts or techniques, the patient’s lungs were ventilated, the head replaced in anatomical position, cervical MILS reapplied, and a new baseline image was recorded. The Jones grading scale was used to quantify endotracheal tube hang-up.13 Any laryngeal maneuvers or external help was noted. The cinefluoroscope screen was not visible to the person performing the intubation. If multiple attempts were needed to successfully intubate a patient with a given technique, all of the attempts were recorded and examined, and the frames in which the greatest range of motion was present were used for further analysis.
Radiologic Measurements and Data Analysis
Digital cinefluroscopic recordings of each intubation at three frames per second were analyzed offline frame-by-frame on the Leonardo Workstation (Siemens, Erlangen, Germany). Intubation was divided into four stages for comparison between the two techniques. The first stage was the “baseline,” an image of the c-spine immediately before the introduction of the intubating device into the oropharynx. The second stage was the “introduction,” which included insertion of the endotracheal tube and its guiding device until the glottic aperture was reached (this stage also included introduction of the oropharyngeal airway for the FOB). The third stage, “intubation,” began when the endotracheal tube crossed the vocal cords. The fourth stage, “removal” recorded the withdrawal of the intubating device (including removal of the oropharyngeal airway in the case of FOB intubation) from the patient. Film for the last three stages was systematically reviewed frame-by-frame to determine peak c-spine displacement for each stage compared with the “baseline” image of each technique. The movement of all six osseous elements (occiput to C5) in the three frames thus selected was compared with the “baseline” position of each element. An additional frame representing peak movement during oropharyngeal airway introduction was also selected in the FOB group.
The 180 frames thus selected (20 patients, nine frames each) were analyzed by a senior radiology resident, together with an attending neuroradiologist. The measurements of angular movement from the cranium to C5 were made using the eFilm Workstation software version 1.9 (Merge Healthcare, Milwaukee, WI), using the same osseous landmarks as previously described by Robitaille et al.14 to represent the position of the cranium and vertebrae. If these landmarks were not visible, alternative ones were determined by the neuroradiologist on a case-by-case basis. For each patient, the same landmarks were used for all frames. Baseline position of the occiput and of each cervical vertebra was measured in every patient and for both techniques. The degree of rotation was assessed by measuring the angle formed by the intercept of the vertebral line and the reference line parallel to the angiosuite table. For each vertebra and each step of the intubation, rotation in the vertical plane was measured to calculate variation from the baseline value. Movement of the c-spine was described in a manner similar to Sawin et al.15 (by following segments defined by adjacent osseous units). An increase in the angle between two units compared with the baseline value, corresponding to an extension, was given a positive value; a decrease in the angle, corresponding to a flexion, was given a negative value.
All results are presented as a mean ± 1 standard deviation unless stated otherwise. Mean values of angular change for each segment, during each stage, and with each of the two techniques were calculated using the absolute value of the angles. For each intubating device, the average maximal segmental motion observed in every patient at any stage or cervical segment was calculated and compared using Student’s t-test. A t-test was also used to compare the mean time needed to intubate with both techniques. Based on previous studies,14,16,17 it was calculated that 16 patients would allow detection of a 5° difference in segmental motion between the two groups (α error 0.05, β error 0.2, two-sided test and estimated standard deviation 5°).
Characteristics of the 20 patients included in the study are presented in Table 1. Intubation took 34 ± 17 s in group TL, versus 60 ± 15 s in group FOB (P < 0.001). All intubations required only one attempt, except for one patient in whom intubation with the TL necessitated three attempts. When performing FOB intubation, every patient required some jaw thrust to visualize the glottis. All 40 intubations were rated 0 on the Jones scale, meaning that no manipulation of the tube or laryngeal maneuver was needed to pass through the vocal cords. Figure 1 illustrates segmental motion during intubation for each device. No data were missing for any patient for both intubating devices, during all stages and at every cervical level.
Overall, the FOB resulted in an average maximal segmental motion of 11° ± 5° and the TL 12° ± 6° (P = 0.5). For both the TL and the FOB, maximal segmental motion was observed during the introduction stage in 18 patients, during the intubation stage in one patient, and during the removal stage in one patient. For all three stages using both devices, most of the movement took place at the C0–1 segment. At C0–1 during introduction, the mean extension was 10.5° ± 5° for the FOB and 11.5° ± 6° for the TL. Movements at other segments were far less than at C0–1. During the intubation and removal stages, the spine generally tended to return to the baseline position. No complications related to the study protocol were noted.
In patients under general anesthesia, including neuromuscular blockade and MILS of the head and neck, we found no significant difference in the segmental c-spine motion produced during endotracheal intubation using either the FOB or the TL.
With both the FOB and the TL, every effort was made to minimize cervical movement. The MILS was used to steady every patient’s c-spine. In addition to the MILS, with both devices, only the minimal amount of jaw thrust or lift necessary to successfully intubate the trachea was applied. Also, an endotracheal tube shown to reduce resistance to passage into the trachea helped eliminate the need for rotation of the tube or external laryngeal maneuver,18 which could have caused cervical displacement. In addition, with the FOB, the oropharyngeal airway used in the study was chosen for the better glottic visualization19,20 it affords when compared with competing devices. The orotracheal intubation technique used in this study is similar to nasotracheal intubation in terms of c-spine motion.21,22 To reduce impingement against the epiglottis or arytenoids, the largest available flexible FOB was used with the smallest size tube in routine use for adults in our institution,23 and as soon as the FOB passed the cords, jaw thrust was released to decrease the likelihood of difficult tube advancement.23
Despite those precautions, intubation with both the TL and the FOB produced cervical movements, mostly during introduction of the device. In the present study, movement was concentrated at the atlantooccipital articulation and to a lesser extent at the atlantoaxial level. The distribution of c-spine movement in this study is in agreement with a previous study examining c-spine movement produced by the TL.9 When the present work is examined in the light of a previous study which also examined c-spine movement during intubation with MILS,14 it appears that the TL, FOB, Glidescope and MacIntosh blade may induce about the same magnitude of cervical segmental spine motion at the same level (principally the occipitoatlantal and atlantoaxial articulations). As has been previously observed,6,12,13,19,24–26 the introduction stage necessitated some jaw thrust for the FOB and jaw lift for the TL in every patient to permit visualization of the glottic aperture in the former or passage of the tube into the trachea for the latter. Knowing that basic airway maneuvers, such as jaw thrust, have previously been shown to cause cervical motion in unstable segments equal to or greater than the movements produced by direct laryngoscopy,16,21,22 we surmise that these maneuvers may explain the similar degree of cervical motion produced by the FOB and TL. This may also mean that there is a minimum amount of cervical displacement necessary to gain access to the trachea, whatever the device used, to perform endotracheal intubation under general anesthesia. This displacement may be the result of the anteriorly directed force vector applied to the jaw that every technique requires in the anesthetized patient. The decision to intubate a given patient awake or asleep then becomes a question of balancing the risk of coughing or other uncontrolled movements inherent to awake intubation versus the nonzero movements necessary to provide basic airway management and intubation in asleep patients. The actual device used for intubation could be determined by considerations, such as the urgency of the case and airway morphology, pathology, or trauma, as long as basic precautions, such as MILS, are applied and the selected device can be used in an expert manner.
This study is the first to record oral FOB intubation with MILS using cinefluoroscopy and evaluate movements based on changes in the angulation of adjacent osseous elements.15 Hauswald et al.21 performed cinefluoroscopic recording in eight fresh cadavers submitted to eight airway procedures, including oral and nasal FOB and light stylet intubation, without MILS. They measured maximal c-spine displacement in millimeters and reported that these three techniques produced the least displacement. Brimacombe et al.16 studied c-spine motion using cinefluoroscopy in cadavers with a posteriorly destabilized third cervical vertebrae: nasal FOB produced less motion than other devices used in their research, but neither oral FOB nor TL intubation were examined.
On an average, intubation with the TL was faster than with the FOB. One patient required three attempts before being successfully intubated with the TL, whereas all patients were successfully intubated on the first attempt with the FOB. Saha et al.8 compared nasal FOB and oral TL intubation in 38 awake patients presenting for cervical stabilization and concluded that the TL was faster and produced less epistaxis and sore throat. Differences in the definition of intubation times, the progressive application of jaw lift in the present study in an attempt to minimize c-spine motion, and relatively limited intubator experience with the TL may have contributed to the slightly longer intubation times with the TL in this study compared with previous results.6,7,9,24
The following limitations apply to the current study. A larger sample size may have permitted statistically significant differences in the movements generated by each technique to emerge from the data, although the clinical relevance of what appears from our sample to be very small differences would be debatable. The order in which the intubations were performed could have affected the results, although randomization minimized this problem and post hoc testing did not show any significant difference because of the order of intubation. The person performing the intubation and the radiologists analyzing the images could not be blinded to the intubation technique (however, the radiological team was not made aware of the study hypothesis until their analysis was completed). Even though every effort was made to optimize the intubation technique, the previous experience of the person that performed the intubations may have influenced the results, because the number of intubations needed to achieve maximum performance with each of these devices is not known. Another limitation is the recording of images only in the sagittal plane, although force vectors generated by FOB and TL are principally in that plane. As in other studies,14,15,25,26 only motion from the occiput to C5 was examined. Also, the patients in the present study had normal c-spines; whether the present results can be generalized to patients with c-spine abnormalities is unknown.
There is no threshold of c-spine movement established as predicting damage to the spinal cord. The existence of such a threshold is debatable, as it is likely that individual anatomy and different pathologies have a strong influence on the degree of c-spine motion that will produce neurological deterioration. The c-spine movements measured in studies such as this one may therefore appear difficult to translate into clinical terms. We believe that, in the absence of other data, attempting to minimize c-spine movement in the presence of significant c-spine pathology appears to be the most prudent management strategy. Within its limitations, the results of this study demonstrate that the FOB and TL are equivalent in this respect.
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© 2009 International Anesthesia Research Society
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