The intubating laryngeal mask airway (ILM) can be used to facilitate tracheal intubation without manipulation of the head and neck (1–4), and it has been used successfully in patients with cervical pathology (5–7). However, the ILM exerts a pressure greater than 150 cm H2O against the posterior pharyngeal mucosa in anesthetized humans (8), and posterior displacement of the C2-3 cervical vertebrae in cadavers with normal necks (9). In the following study, we quantify the extent and distribution of segmental cervical movement produced by the ILM during manual in-line stabilization in anesthetized human subjects with cervical pathology undergoing cervical spine surgery.
With ethical committee approval and informed consent, we studied 20 consecutive ASA physical status class I or II patients undergoing cervical spine surgery. Patients were excluded if they had cardiorespiratory or cerebrovascular disease or were at risk of aspiration. Premedication was diazepam 5 mg per os and roxatidine 75 mg per os approximately 1.5 h preoperatively. An electrocardiograph, pulse oximeter, gas analyzer, noninvasive blood pressure monitor, and peripheral nerve stimulator were applied before the anesthesia induction. Patients were in the supine position. Neck supports were removed, and patients adjusted themselves so that their head and neck were in the neutral position and resting on a standard firm pillow 7 cm in height. Manual in-line traction was applied by a neurosurgeon 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 and neck (10).
Oxygen was administered via a face mask for 5 min. Lidocaine 0.5 mg/kg was given IV, and anesthesia was induced 30 s later with fentanyl 2 μg/kg IV and propofol 2.5 mg/kg IV. When the jaw was relaxed and the eyelash reflex had disappeared, the ILM was inserted by an experienced ILM user (SK, >300 insertions) using a one-handed rotation technique as recommended by the manufacturer (11). A size 3 ILM was used for women and a size 4 or 5 for men. The cuff was inflated with air (size 3: 20 mL; size 4: 30 mL; size 5: 40 mL), and an anesthesia circuit was connected. Once adequate ventilation was confirmed, vecuronium 0.1 mg/kg IV was administered to facilitate intubation. Anesthesia was maintained with 50% nitrous oxide and 2% sevoflurane in oxygen until the train-of-four count was zero and tracheal intubation was attempted. Intubation was assisted with a lightwand (LW)-guided technique, as previously described (3,12). A lubricated straight silicone tracheal tube was mounted on a LW (Trachlight™; Laerdal Medical Corporation, Wappingers Falls, NY) without the inner metal guide. The soft, luminous tip of the LW was positioned 0.5 cm beyond the distal tip of the tracheal tube, and the tracheal tube with the LW was inserted through the ILM. Room illumination was reduced, and signs of the light were observed at the anterior neck. The detection of a distinct central point of light without a halo at the cricothyroid membrane was taken as evidence that the ILM cuff was correctly placed at around the laryngeal inlet. If correct transillumination was not observed, if resistance was felt through the tracheal tube, or if the light point was seen moving laterally when advanced, the tracheal tube was withdrawn to 1 cm beyond the epiglottic elevator bar and the following adjusting maneuvers were applied in sequence before each additional intubation attempt: 1) pulling the handle back toward the intubator; 2) withdrawal of the ILM by 5 cm followed by reinsertion; 3) ventilation commenced and the position of the ILM adjusted until the optimal seal was obtained; and 4) changing the size of ILM. If no resistance was felt, the tube was advanced by 8 cm, the cuff was inflated, and the circuit was reconnected. During ILM insertion and subsequent intubation, great care was taken to avoid pressing the handle posteriorly. Correct placement was confirmed by capnography. Once tracheal placement was confirmed, the cuff volume was adjusted so that no air leakage was obtained at 30 cm H2O inspiratory pressure. The ILM was removed 3 min after successful tracheal intubation by using a stabilizing rod. If intubation via the ILM could not be accomplished after all maneuvers above, intubation proceeded with a fiberscopic bronchoscope. Manual in-line stabilization was only released when the ILM had been removed.
The following data were collected by an unblinded observer: grade of face mask ventilation (easy, Guedel airway not required; moderate, Guedel airway required; difficult, Guedel airway plus jaw thrust required; failed, failure to ventilate, alternative technique required); number of attempts required to place the ILM; number of adjusting maneuvers; and frequency of mucosal trauma (blood detected on the ILM following removal), lip or dental injury and hypoxia (Spo2 < 95%). A neurosurgeon familiar with the patients’ neurological status preoperatively scored any improvement/deterioration in neurological status 1 wk after surgery as considerable, moderate, slight, or nil.
Sequential lateral radiographic images of the patients’ necks were taken from a fixed position by a radiographer at the following times: 1) immediately preinduction (baseline); 2) toward the end of ILM insertion as the cuff was being rotated from the mouth into the pharynx (insertion); 3) when transillumination was first seen at the cricothyroid membrane (intubation A); 4) when the tube was being advanced into the trachea (intubation B); and 5) during ILM removal as the ILM cuff was being rotated from the pharynx into the mouth (removal). The timing of the films was determined by the radiographer. A 24-mm diameter coin was placed on the neck just below the chin for the purposes of distance calibration. All radiographic images were scanned, digitized, and downloaded to a computer. The following data were obtained by two independent investigators using a drawing software package (Canvas v 5.0; Deneba software, Miami, FL):
The cervical vertebrae nearest to the ILM shaft.
The degree of flexion/extension (13). On each radiographic image, reference lines were drawn to mark the positions of the occiput (C0), the atlas (C1), the axis (C2), and the third to fifth cervical vertebras (C3-5) (Fig. 1). The reference line of C0 was a line from the mandibular fossa to the most dorsal and caudal portion of the occiput. For the atlas, the reference line was the tangent between the anterior and posterior arches. The reference lines for C2 to C5 were lines drawn from the anterior basal plate to the caudal portion of the spinal process of each vertebrae. The change in angulation was compared with the preinduction values.
The extent of posterior movement. On each radiographic image, a reference line was drawn between the anterior surface of C1 and that of C6. The length of each line was calibrated by using the coin of known diameter. Changes of the distances from this line to C2-5 (midpoint of the anterior surface of each vertebra) were measured (Fig. 2).
Statistical analysis was with analysis of variance repeated measures and Bonferroni-Dunn test. Data is presented as mean ± sd. Significance was taken as P < 0.05.
Patient, airway assessment, surgical, and motor/sensory outcome data are presented in Table 1. The mean (range) duration of anesthesia was 266 (192–395) min. All patients had neurological symptoms (both sensory and motor) preoperatively. There was no deterioration in neurological symptoms in any patient on moving the head and neck into the neutral position or applying manual in-line stabilization. Face mask ventilation was graded as easy in all patients. ILM insertion was successful at the first attempt in all patients. All patients were successfully intubated by using the ILM-LW technique, but four patients required two adjusting maneuvers, four patients required three adjusting maneuvers, and two patients required four adjusting maneuvers. The image analysis software facilitated quantification of displacement of a given bony element with a resolution of 0.01 degrees and 0.1 mm. Interobserver variability averaged 0.17 ± 0.08 degrees (range 0.0–0.5) for flexion/extension movement and averaged 0.2 ± 0.1 mm (range 0.0–0.8) for posterior displacement.
The nearest vertebrae to the ILM shaft during insertion was C2 (17 of 20) and C3 (3 of 20), during intubation A was C2 (18 of 20) and C3 (2 of 20), and during intubation B was C2 (18 of 20) and C3 (2 of 20). The degree of segmental flexion/extension of the cervical vertebrae are shown in Table 2. During ILM insertion, C0 to C5 were flexed by an average of 1–1.6 degrees (all P < 0.05). During intubation A/B, C0-4 were flexed by an average of 1.4–3.0 degrees (all P < 0.01), but C5 was unchanged. During ILM removal, C0-3 were flexed by an average of 1 degree (all:P < 0.05), but C3-5 were unchanged. The extent of segmental posterior movement are showing in Table 3. During insertion and intubation A/B, C2-5 were displaced posteriorly by an average of 0.5–1.0 mm (all:P < 0.05). During removal, there was no change at C1-5. Three patients had unstable cervical spines (all at C7 and secondary to metastatic disease) and the degree of segmental flexion/extension and posterior movement was similar to patients with stable cervical spines. Lateral neck films at the end of surgery revealed no pharyngeal or epiglottic edema. The neurological symptoms of all patients improved following the surgery. Three patients had a mucosal injury, but there was no dental or lip trauma or hypoxia. There were no airway problems at extubation.
We found that ILM insertion causes flexion and posterior displacement of the cervical spine in patients with cervical pathology during manual in-line stabilization. Although the ILM shaft only presses against the anterior surfaces of C2-3, movement occurs from C0-5, suggesting that the posterior force is transmitted to adjacent vertebrae. Both stages of intubation were associated with increases in segmental movement. After insertion, the ILM is moved in the pharynx to align the cuff with the glottis. This probably causes a change in the vector and the level of the force exerted by ILM against the cervical vertebrae. There was no difference in the extent of segmental movement between intubation phase A and B. This is probably because, once the ILM is aligned for intubation, the position is held steady until intubation is accomplished. During removal, there was a reduction in the degree of flexion, and the posterior displacement returned to near-baseline levels. The handle is elevated slightly as it is rotated out of the pharynx. It has been shown that handle elevation reduces the pressure exerted against the cervical vertebrae (9). Our findings are consistent with Keller et al. (9), who showed that ILM insertion and intubation could cause posterior displacement of the cervical vertebrae in cadavers.
Sawin et al. (13), using real-time cinefluoroscopy, showed that direct laryngoscopy produces extension in each cervical segment, with the most significant motion being 5–7 degrees at C0-2 (13). We found that segmental movement with the ILM was most significant at C0-3, but was approximately 50% lower. Also, the direction of movement was flexion and posterior displacement rather than extension. This is not surprising, because the force vectors for the ILM and laryngoscope are opposite. Our results probably represent the minimal movement of the cervical spine, because we used a single-frame technique, and the moment of maximum motion may have been missed, particularly during insertion where the pressure against C2-3 is briefly 3 times greater than when the ILM is already in position (9). The fact that movement was similar during insertion and intubation (despite the increased posterior force during insertion) suggests that the point of maximum motion was not seen in our study.
Manual in-line stabilization did not prevent movement of the cervical spine in our patients. It has been shown that manual in-line stabilization reduces cervical movement in patients undergoing laryngoscopy (14). However, it is likely that segmental motion in our study would have been greater if manual in-line stabilization had not been applied. We had no problems inserting the ILM in patients with manual in-line stabilization. This supports the findings of Asai et al. (4) who showed that ILM insertion is easier that the standard LMA with manual in-line stabilization in patients with normal necks.
In a cadaver study, Keller et al. (9) showed that the ILM exerted greater pressure against the cervical vertebrae than direct laryngoscopy. The authors recommended that the ILM should only be used in the unstable cervical spine if difficulties were anticipated or encountered with established techniques. Although we found that neurological symptoms improved in all patients, only three patients had an unstable cervical spine, making it difficult to comment on the safety aspects of the technique in this situation. In addition, the unstable cervical spine segment of all three patients was C7, and this could not have been seen radiologically. Nakazawa et al. (7) reported the use of the ILM as a guide to blind intubation in 40 patients with cervical pathology undergoing cervical spine surgery, but made no comment about neurological outcome. However, the authors noted that severe pharyngeal edema (6 times increase in thickness of posterior pharyngeal wall at C1-3) commonly occurred if the ILM was left in situ during surgery. This complication is probably related to the high pressure exerted by the ILM against the pharyngeal mucosa (8). Interestingly, no patient developed pharyngeal edema in our series when the ILM was removed before surgery. This adds further support to the recommendation that the ILM should be removed after its use as an airway intubator (8). Finally, our data confirms previous studies (3,12) showing that the ILM-LW technique has a high success rate.
Finally, Sawin et al. (13) speculated that direct laryngoscopy may be more hazardous to patients with cervical instability that is exacerbated by head and neck extension rather than by flexion maneuvers. We similarly speculate that the ILM technique may be more hazardous to patients with cervical instability exacerbated by flexion maneuvers.
We conclude that the ILM produces segmental motion of the cervical spine, despite manual in-line stabilization in patients with cervical spine pathology undergoing cervical spine surgery. This motion is in the opposite direction to direct laryngoscopy, suggesting that different approaches to airway management may be more appropriate, depending on the nature of the cervical instability.
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