All patients sustaining blunt injuries to the head, face, neck, or upper thorax should be treated as if they would have an unstable cervical spine injury until proven otherwise . Cervical spine injuries occur in up to 6% of all major trauma cases . The management of trauma patients with a suspected or proven cervical spine injury necessitates immobilization of the cervical spine and in case of intubation meticulous airway management with maintenance of the alignment and approximate continuous cervical immobilization. Even though the overall risk of neurological deterioration following intubation has been estimated to be low [3,4] it should be the main goal to minimize cervical spine movement during intubation. Several techniques for non-invasive measurements of cervical range of motion have been undertaken in the past. Of the various computer-aided systems the ultrasound-based device resulted in precise and reproducible measurements .
The major goal of the present study was to evaluate the cervical spine movement using an ultrasonic device CMS 70P (Zebris Medizintechnik GmbH, Isny, Germany) that allows the detection of a three-dimensional motion during intubation. Specialized laryngoscopes and other airway equipment have been designed with the objective of minimizing head movement during tracheal intubation. The Bullard™ laryngoscope (Circon, ACMI, Stamford, CT, USA) is an anatomically shaped, rigid laryngoscope that uses fibreoptic technology to view the larynx. The oral, pharyngeal, and tracheal axes do not have to be aligned to view the larynx and it may result in less extension of the head and less flexion of the cervical spine during laryngoscopy and tracheal intubation . The intubation Bonfils fiberscope is also a rigid optic device, which was first commercialized in 1991. It is a visual, oral method for intubation.
The laryngeal mask airway is a well-established device, which is used widely in the management of failed intubation . It has been claimed that placement of the conventional laryngeal mask is best achieved when the neck is flexed and the head extended . In contrast, the intubating laryngeal mask airway is claimed to be best placed without flexing the neck and without extending the head .
After approval of the local ethics committee, 63 adult patients were evaluated preoperatively. Fifteen patients were excluded as a result of one or more exclusion criteria. Forty-eight American Society of Anesthesiologists (ASA) I-III adult patients without exclusion criteria gave written consent to take part in the study. Exclusion criteria were any medical history of cervical spine injury, cervical spine disease or abnormality, full stomach, gastroesophageal reflux disease, hiatus hernia, chronic headache, and neurological, oropharyngeal or vocal cord problems, any neck pain during evaluation, and any limitation in normal cervical motion. Cervical range of motion was evaluated in flexion, extension, lateral bending, and rotation. All patients were starved and scheduled to undergo elective surgery during which the trachea was to be intubated.
Patients were to be excluded when preoperative head and neck mobility was found to be clinically restricted. Cervical range of motion was tested on the day before surgery by physical examination and by use of the ultrasound-based system. The relative ease of direct laryngoscopy and orotracheal intubation for all subjects was predicted by using the classification scheme described by Mallampati and colleagues .
The patient was placed supine on the operating table with the occiput resting in the neutral position. Patients were continuously monitored using an electrocardiogram, finger pulse oximeter, automatic non-invasive arterial blood pressure device (Siemens Sirecust 1280, Erlangen, Germany), capnometer, and inspired oxygen analysis (Dräger PM 8050, Lübeck Germany) as well as relaxometer (TOF-Guard®, Organon Teknika, The Netherlands). After institution of full monitoring and pre-oxygenation for 3 min by facemask, anaesthesia was induced with fentanyl and thiopental in a dose sufficient to abolish the eyelash reflex. After assessment of possible ventilation, atracurium was administered. During introduction of anaesthesia patients were ventilated manually using a Sulla 808 V circuit with 100% oxygen. After the loss of all four twitches from the train-of-four (TOF) obtained by ulnar nerve stimulation at the wrist, patients were intubated according to the randomization using a Macintosh laryngoscope, a Bullard laryngoscope, a Bonfils fibrescope, or an intubating laryngeal mask airway. Orotracheal intubation was accomplished with an appropriate cuffed endotracheal tube. All tracheal intubations were performed by an experienced faculty anaesthesiologist. The anaesthesiologist was experienced with the use of all intubation techniques (Fig. 1).
To perform laryngoscopy with the Bullard laryngoscope, an endotracheal tube was mounted on the intubating stylet and it was inserted in the patient's mouth with the long axis of the laryngoscope handle oriented horizontally. Once the blade and tube had passed the tongue, the laryngoscope handle was rotated to an upright position, and the blade was dropped into the posterior pharynx. A scooping motion was used to lift the blade up against the posterior surface of the tongue, retracting the epiglottis anteriorly. Gentle upward traction was used to obtain the view of the glottis (Fig. 2).
To perform laryngoscopy with the Bonfils fibrescope, an endotracheal tube was first mounted on the stylet. The Bonfils fibrescope is a non-flexible fibrescope device. Laryngeal view was obtained by retromolar insertion of the stylet combined with a chin-lift manoeuvre.
Intubation of patients using the intubating laryngeal mask was performed according to the manufacturer's guidelines. The mask was held by its handle between the thumb and fingers. The mask tip was positioned so it was flat against the hard palate just inside the mouth, immediately posterior to the upper incisor teeth. The mask was slid backwards following the curve of the rigid tube, so that the tube curvature closely followed the anatomical curve of the palate and posterior pharyngeal wall. After that the mask was inflated. The intubation was performed immediately after insertion of the device, grasping the device handle with one hand, gripping the handle firmly to draw the larynx forwards a few millimetres and gently passing the endotracheal tube into the trachea. After intubation had been accomplished, the mask was removed.
Ventilation in all patients was assessed by end-tidal carbon dioxide, bilateral chest auscultation, bilateral chest movement, expired tidal volume of greater than 7 mL kg−1 and auscultation over the epigastrium for sounds suggestive of stomach inflation. Three intubation attempts were allowed with ventilation and oxygenation interposed. Attempted tracheal intubation was terminated if the patient showed signs of oxygen desaturation or if it was felt by the anaesthesiologist that further attempts would be unsafe and/or futile. The time to intubate during each attempt was defined as the time from the insertion of the device into the oral cavity to its removal. Total time to intubate was defined as the summation of time to intubate for all attempts. The total time to intubate and the number of attempts and failures were recorded. After extubation at the end of surgery the patients were asked for complaints of sore throat prior to discharge from the post-anaesthetic care unit and 24 h after surgery.
The Zebris CMS 70P system is an ultrasound-based device that allows the detection of three-dimensional motion. The measuring system consists of a convenient measuring sensor with a stand, a basic unit and the appropriate markers and application aids. The measuring procedure is based on the determination of the spatial co-ordinates of miniature ultrasound transmitters, which generate the ultrasound impulses. The measuring sensor is connected to the stand by means of a ball-and-socket joint and can be brought into any desired position. A marker pin and one triple marker are used. The triple marker, which establishes the reference plane, is attached to the subject in a fixed position. The ultrasound triple markers work with a frequency of 35 kHz. The system has been developed for three-dimensional motion analysis and position finding, which allow millimetre-accurate tracking of measuring markers. The measuring sensor mounted on a tripod detects the travel time of the ultrasound signals and transmits the results to the basic unit. The sensor allows the registration of movement in all degrees of freedom. The sound pulse time between the transmitters and the three microphones integrated in the measuring sensor is measured. In accordance with the scanning rate, measuring areas of 1.5 mm × 3 mm × 3 mm to 2 mm × 4 mm × 4 mm can be implemented. The basic unit is connected to the parallel printer port of a computer. The cinematic data are transmitted synchronously with the analogue data. The movements investigated comprised lateral bending, flexion/extension, axial rotation, and translation. The measuring system generates curves for all movement patterns; a diagram is presented for each main direction movement. Reliability and validity of this system was tested by Castro and colleagues with the Zebris CMS 50 System, which is structurally identical with the CMS 70P . The system provides precise reproducible measurements of range of motion of the cervical spine in all three planes. The measuring system generates curves for flexion/extension, lateral bending, rotation, and translation.
During the first evaluation the patients were instructed to sit straight with fixed chest and the measuring transducers were placed laterally next to the patient's cervical spine. The examiner asked the patient to move his or her head as far as possible in each tested direction. During intubation the patients were in the supine position with chest and head in contact with a rigid board. The measuring transducers were placed laterally next to the patient cervical spine. The triple ultrasound markers were attached to the patient's head by non-slip tape. In the resting position the system was calibrated. The motion of the cervical column was measured continuously during the intubation procedures and index marks were set four times. First, in the neutral position; second during opening of the mouth, third during insertion of the laryngoscope, fourth while positioning the laryngoscope for an optimal view on glottic structures and during removal of the device while inserting the endotracheal tube.
The sample size calculation of the one-way analysis of variance is based on the significance level α = 0.05, the power of 80% and the effect size of Δ = 0.25. Effect size Δ is the variance of the means divided by the within-group variance. The number of groups to be studied was four. The resulting sample size per group was 12 and total sample size 48. Mean, standard deviation, minimum and maximum are given for age, weight, height, body mass index (BMI), and the doses of fentanyl, atracurium, and thiopental. For the intubation times and the cervical spine movement the median is given in addition. To analyse the median intubation times between the different intubation procedures, closed test procedures  were used. The simultaneous comparison between two, three, or four groups was done using the Kruskal-Wallis test. The evaluations of the partition hypotheses are due to the global Bonferroni test. To analyse the impact of the four intubation methods on the maximal flexion, rotation, and lateral bending as well as on the intubation times closed test procedures for each parameter were performed. Since four closed test procedures were performed the local significance level for each of the closed test procedures was set to 0.0125 to keep an overall significance level of 0.05. All the analyses were done using SPSS 10.0.
Patient characteristics are given in Table 1. Forty patients were classified as Mallampati Class I and eight as Mallampati Class II. For induction of general anaesthesia all patients received fentanyl, thiopental, and atracurium. Fentanyl doses were 0.157 ± 0.034 mg (range: 0.1-0.3 mg), atracurium 41.1 ± 6.7 mg (range: 25-50 mg) and thiopental 428 ± 63 mg (range: 300-550 mg). Cervical spine motion and intubation times are shown in Tables 2 and 3.
The quality of the laryngeal view depended on the laryngoscope. The laryngeal view was optimal in 11 of 12 patients when the Bullard laryngoscope and the Bonfils fibrescope were used. In two patients intubation was impossible because of mucus and saliva. In one patient intubation failed using the Bullard laryngoscope, whereas in another patient the Bonfils fibrescope was applied unsuccessfully. All other patients were intubated on the first attempt. In patients who were intubated using a Macintosh laryngoscope, the laryngoscopic view was classified according to Cormack and Lehane. Four patients had a Cormack and Lehane Grade I, six patients Grade II and in two patients Grade III.
No difference was found between the devices with respect to postoperative complaints with potential relationship to intubation.
The purpose of this study was to determine a noninvasive method for cervical range of motion measurement in different intubation techniques. We investigated the total range of motion of the cervical spine. The study design was conducted to build a prediction model that could be useful in evaluating the biomechanical status of the normal cervical spine during different intubation techniques; it could not explain the cervical segmental vertebral motion. The prediction model was developed from an asymptomatic population, a clinical generalization to symptomatic or asymptomatic cervical injured populations would be limited to the scope of this paper. Classical cervical ranges of motion analysis, which focus on total cervical range of motion, are rarely examined in a clinical context.
Levitan and colleagues conducted a National Survey of Emergency Medicine Residency Programme Directors to determine which alternative devices were available in their emergency departments for difficult airway management. They found that rigid fibreoptic devices, such as the Bullard laryngoscope are stocked in 6% as an alternative intubation device in their department . Many techniques, in addition to the Bullard laryngoscope, have been proposed for minimally invasive tracheal intubation of patients with cervical spine disease or injuries. Each technique requires additional training and has its own set of advantages and disadvantages.
Under conditions of the present study we were able to present convincing evidence that cervical spine movements are less with the Bullard laryngoscope, the Bonfils fibrescope and the intubating laryngeal mask airway than with the Macintosh laryngoscope. Successful laryngoscopy occurred with less extension, less flexion, and less rotation of the cervical spine when the three alternative devices were used compared to the Macintosh laryngoscope. Furthermore no significant differences between the intubation times from Bullard and Macintosh laryngoscopes were detected. Even though the use of the Bonfils fibrescope and the intubating larngeal mask airway resulted in less flexion/extension and rotation of the cervical column during intubation than did the Macintosh laryngoscope, time to secure the airway is significantly longer than using the Macintosh laryngoscope. The results of the present study give clear evidence that the intubation using the Bullard laryngoscope not only shows advantages with respect to the laryngeal view, but also results in less movement of the cervical column in flexion/extension and rotation as well as lateral bending in comparison to direct laryngoscopy.
Doubtless, the most important advantage of the intubating laryngeal mask airway is the possibility of ventilation and oxygenation before tracheal intubation is attempted. The efficacy of the intubating laryngeal mask airway as a ventilatory device and blind intubation guide has been previously reported in patients with normal [9,13-16] and abnormal [9,17-19] airways. These finding suggest that the Bonfils fibrescope and intubating laryngeal mask airway may be useful adjuncts to intubate patients with cervical spine injuries in the elective situation when time to intubation is not critical.
However, there were several limitations to our study. The relevance of the study for patients with cervical spine pathology or injuries may be limited because this study was performed in the operating room under ideal conditions. In contrast to the study patients, intubation of trauma patients is complicated by various factors. There might be the presence of injuries of varying degrees, the use of manual in-line stabilization and cricoid pressure during laryngoscopy and last but not least a greater sense of urgency. It is also questionable whether the results would apply to patients with cervical spine disease or injuries, compared to the patients with normal spines studied here. Furthermore, there were also certain limitations to our protocol, namely that the operator could not be blinded to the type of laryngoscope in use. However these problems are inherent in studies of this nature.
Various studies have been conducted to investigate the cervical spine movement during intubation. A comparison between Miller blade  and the Belscope  with the Macintosh blade did not show any significant reduction in the cervical spine movement. Furthermore, a study comparing the McCoy laryngoscope in the activated position and the standard Macintosh blade did not show a significant difference in cervical spine movement either . In contrast to MacIntyre and colleagues and in order not to expose patients to X-rays and to determine the overall three-dimensional motion of the cervical spine we used an ultrasonic guided motion analysis system. There is a great deal of evidence that normal cervical spine movement is influenced by age and gender [22-26], and consequently we stratified our patients during the randomization process. Richter and colleagues made us aware in their three-dimensional in vitro study of the normal and injured lower cervical spine, that the movement in the flexion/extension direction is the most sensitive load-direction for discoligamentous instabilities . Sawins and colleagues demonstrated with continuous lateral fluoroscopy that the greatest movement of the cervical spine during direct laryngoscopy occurred when lifting the epiglottis forward to expose the glottis .
The median time required for intubation with the Macintosh laryngoscope was similar to those reported in previous studies [28-30]. Watts and colleagues measured median intubation times of 15 s  and Nolan and Wilson used a median time of 20 s in patients with a simulated cervical spine injury . In the present study median time to intubation using the Bullard laryngoscope took 16 s and, therefore was similar to the times needed to intubate patients with the Macintosh laryngoscope. To intubate with the Bonfils fiberscope took a mean time of 52 s in our hands. Total time to intubation using the intubating laryngeal mask airway was 50 s and was similar to the other alternative methods described for endotracheal intubations in patients suffering from cervical spine injuries in previous studies [30-32]. Nolan and Wilson  described intubation over a 15-G gum elastic bougie with manual in-line stabilization in a simulated cervical spine injury and showed that the patients were intubated within 45 s (median 25 s) and consequently recommended the gum elastic bougie as an aid to the intubation of a patient with suspected cervical spine injury. Blind oral intubation with the Augustine device, was compared with direct laryngoscopy by Fitzgerald and colleagues . They demonstrated that the median time for intubation with this guide was 41 s compared with 22 s for direct laryngoscopy, but less extension occurred within the atlanto-occipital joint using the Augustine device. Those times are significantly longer compared to the gold standard. Normally the time limit for intubation is set to 30 s. Only sufficient pre-oxygenation allows such a time frame. With all these methods, there is inevitable compromise between the need for immediate airway control and the need for reduction of the movement in the occipito-atlanto-axial complex.
Many techniques have been proposed for minimally invasive tracheal intubation of patients with cervical spine disease or injuries. Each technique requires additional training and has its own set of advantages and disadvantages. However, the results of this study support the use of ultrasound to provide evaluation of angulation of the cervical spine. Further studies are needed to validate this model in different symptomatic and asymptomatic cervical spine injured populations. The use of dynamic magnetic resonance imaging could be a future direction for investigation .
We would like to thank all the theatre staff at the Johannes Gutenberg-University Hospital of Mainz for their assistance and Dr Andreas Faldum (Institute of Medical Biometry, Epidemiology and Informatics, Johannes Gutenberg-University of Mainz) for his statistical support.
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