Original Article. Summary. Introduction

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1 Original Article doi: /anae A prospective randomised controlled trial comparing tracheal intubation plus manual in-line stabilisation of the cervical spine using the Macintosh laryngoscope vs the McGrath â Series 5 videolaryngoscope S. Ilyas, 1 J. Symons, 2 W. P. L. Bradley, 2 R. Segal, 3 H. Taylor, 4 K. Lee, 3 M. Balkin, 2 C. Bain 2 and I. Ng 3 1 Provisional Fellow, 3 Staff Consultant, 4 Registrar, Department of Anaesthesia and Pain Management, Royal Melbourne Hospital and University of Melbourne, Melbourne, Victoria, Australia 2 Senior Anaesthetic Consultant, Department of Anaesthesia and Perioperative Medicine, The Alfred and Monash University, Melbourne, Victoria, Australia Summary Cervical spine immobilisation can make direct laryngoscopy difficult, which might lead to airway complications. This randomised control trial compared the time to successful intubation using either the Macintosh laryngoscope or the McGrath â Series 5 videolaryngoscope in 128 patients who had cervical immobilisation applied. Intubation difficulty score, Cormack & Lehane laryngoscopic view, intubation failures, changes in cardiovascular variables and the incidence of any complications were recorded. The mean (SD) successful intubation time with the Macintosh laryngoscope was significantly shorter compared with the McGrath laryngoscope, 50.0 (32.6) s vs 82.7 (80.0) s, respectively (p = ), despite the McGrath laryngoscope s having a lower intubation difficulty score and a superior glottic view. There were five McGrath laryngoscope intubation failures, three owing to difficulty in passing the tracheal tube and two to equipment malfunction. Equipment malfunction is a major concern as a reliable intubating device is vital when faced with an airway crisis.... Correspondence to: I. Ng irene.ng@mh.org.au Accepted: 13 June 2014 Introduction Cervical spine immobilisation is required for trauma patients requiring tracheal intubation when cervical spine injury cannot be excluded either radiologically and/or clinically. Manual in-line stabilisation is the recommended method for maintenance of the neutral head position for laryngoscopy, but it is associated with a higher incidence of Cormack & Lehane scores 2, which are more likely to be associated with difficult or failed intubation [1 3]. This in turn can lead to major airway complications and significant morbidity and mortality [4, 5]. A number of optical laryngoscopes and videolaryngoscopes have become available in the last few years. They allow indirect laryngoscopy without alignment of the oral, pharyngeal and laryngeal axes. Some published data have shown that in patients with cervical spine immobilisation, videolaryngoscopy can improve laryngoscopic view [6 12] and reduce intubation difficulty [7, 10] compared with direct 2014 The Association of Anaesthetists of Great Britain and Ireland 1345

2 Ilyas et al. Tracheal intubation with Macintosh or McGrath laryngoscope laryngoscopy. On the other hand, some studies have shown that videolaryngoscopy does not reduce cervical spine motion [12, 13] and indeed prolongs intubation time [7, 13] compared with Macintosh laryngoscopy. The McGrath â Series 5 videolaryngoscope (Aircraft Medical Ltd, Edinburgh, UK) is a portable, lightweight unit with a disposable angulated acrylic blade. Due to the marked anterior bend in the blade design, it potentially does not require hyperextension of the neck to obtain an optimal glottic view and thus may avoid the need for cervical spine manipulation in trauma patients. The aim of this study was to compare conventional direct laryngoscopy using a Macintosh laryngoscope with the McGrath Series 5 videolaryngoscope for intubation in adult patients with manual in-line axial stabilisation of the cervical spine. We hypothesised that the McGrath videolaryngoscope would decrease the time to successful intubation by improving the grade of view of the larynx compared with the traditional Macintosh laryngoscope. Methods After obtaining approval from Alfred Health and Melbourne Health Human Research Ethics Committee, a total of 128 adult patients scheduled for elective surgery requiring tracheal intubation at the Alfred and the Royal Melbourne Hospital were recruited (Fig. 1). The inclusion criteria were age > 18 years, ASA physical status 1 3 and full upper dentition at the front. Patients who required an awake fibreoptic intubation, had known laryngeal pathology or were at risk of pulmonary aspiration were not studied. Group allocation was achieved using a computergenerated randomisation list and sealed envelopes. After obtaining written informed consent, each patient was allocated to have tracheal intubation performed using either the Macintosh laryngoscope or the McGrath Series 5 videolaryngoscope. Physical characteristics and airway assessment were recorded pre-operatively. Standard monitoring of ECG, non-invasive blood pressure, end-tidal carbon dioxide and pulse oximetry, as well as bispectral index â (BIS) monitoring (Aspect Medical Systems, Norwood, MA, USA) and a nerve stimulator on the ulnar nerve were applied. Five minutes before induction, each patient received fentanyl lg.kg 1 and the nerve stimulator was calibrated. Manual in-line stabilisation of the cervical spine was performed by an experienced person by holding the sides of the patient s neck and mastoid processes to prevent flexion, extension or rotational movement of the head and neck. A specialist anaesthetist then undertook the induction of anaesthesia. A propofol target-controlled infusion was titrated aiming for a BIS < 60, and this was continued for maintenance of anaesthesia. Once the BIS was < 60, rocuronium bromide 1 mg.kg 1 was administered. The lungs were ventilated by mask with 100% oxygen. Once there were no twitches visible to a train-of-four nerve stimulation, laryngoscopy was performed. The anaesthetists Enrolment Assessed for eligibility (n = 131) Excluded n = 0 Surgery cancelled n = 1 Declined to participate n = 2 Randomisation (n = 128) Allocation Macintosh intubation (n = 64) McGrath intubation (n = 64) Follow-up Lost to follow-up (n = 0) Lost to follow-up (n = 0) Analysis Analysed (n = 64) Excluded from analysis (n = 0) Analysed (n = 64) Excluded from analysis (n = 0) Figure 1 CONSORT recruitment diagram The Association of Anaesthetists of Great Britain and Ireland

3 Ilyas et al. Tracheal intubation with Macintosh or McGrath laryngoscope Anaesthesia 2014, 69, performing intubation had a minimum of 10 years experience and were employed in major tertiary trauma centres. They were all clinically familiar with both devices and had undergone training in the use of the McGrath Series 5 before the start of the trial. For patients allocated to the Macintosh intubation group, the McGrath instrument was first used to record the laryngoscopic view according to Cormack & Lehane [14]. The McGrath was then exchanged for the Macintosh; the view was recorded and then intubation performed. Details including time to successful intubation, intubation difficulty score [15], physiological changes (heart rate, blood pressure, BIS score, endtidal carbon dioxide) and complications were recorded at baseline, intubation and 5 min after intubation. Effect-site propofol concentrations were recorded at the same time points. For patients allocated to the McGrath intubation group, the Macintosh was used first followed by the McGrath. Tracheal intubation was with a pre-shaped styletted tracheal tube of size for women and for men. If tracheal intubation with the allocated laryngoscope was unsuccessful, the anaesthetist could use any appropriate rescue devices and/or remove in-line cervical stabilisation to maintain oxygenation and ventilation of the patient s lungs. After successful intubation, anaesthesia was maintained with propofol target-controlled infusion and a mixture of 50% oxygen and air. No other medication was administered until the last cardiovascular variable was recorded 5 min after intubation. At this time the study was completed and the anaesthetist continued the anaesthetic as appropriate. The primary outcome was the time taken for successful intubation, defined as the time from when the allocated laryngoscope entered the mouth to when the first capnographic square wave was completed. Secondary outcomes included the intubation difficulty score, the Cormack & Lehane glottic view, physiological changes during intubation, and the incidence of complications such as dental damage, blood on the laryngoscope blade, mucosal laceration or other airway trauma. Based on a previous study [16], we determined an expected mean (SD) intubation time for the Macintosh laryngoscope in patients with restricted neck mobility of 50 (20) s. Power analysis showed that to show a 20% reduction to 40 s to intubate with the McGrath laryngoscope, a study including 128 patients would be required with a power of 80% and an alpha error of The Mann Whitney U-test was used to analyse the time to successful intubation, intubation difficulty score and the Cormack & Lehane view at laryngoscopy. The chi-squared test was used to analyse the number of successful and failed intubations, and the incidence of complications. For the analysis of physiological responses to intubation, repeated measures ANOVA was used. Statistical analysis was performed using Stata 11.0 (Statacorp, College Station, TX, USA). Results The baseline characteristics of the patients were similar in both groups (Table 1). The mean (SD) time taken to perform successful intubation was significantly shorter in the Macintosh group, although the intubation difficulty score was higher (Table 2). There were no failed intubations in the Macintosh group and five in the McGrath group. Two of them were a result of the videolaryngoscope screen s becoming blank during intubation. The remaining three were due to difficulties passing the tracheal tube. Table 1 Physical characteristics and airway assessment in 128 patients whose tracheas were intubated using either the Macintosh or the McGrath â laryngoscope. Values are mean (SD) or number (proportion). Macintosh (n = 64) McGrath (n = 64) Age; years 42.5 (13.1) 42.3 (14.0) Male 25 (39%) 35 (55%) BMI; kg.m (6.0) 28.5 (5.0) ASA physical status 1 23 (36%) 21 (33%) 2 39 (61%) 37 (58%) 3 2 (3%) 6 (9%) Mallampati score 1 24 (38%) 30 (47%) 2 34 (53%) 26 (41%) 3 6 (9%) 7 (11%) (2%) Thyromental distance; cm 6.9 (1.6) 7.1 (1.8) Inter-incisor distance; cm 4.6 (0.8) 4.7 (0.9) Neck circumference; cm 37.8 (3.7) 39.4 (4.2) BMI, body mass index The Association of Anaesthetists of Great Britain and Ireland 1347

4 Ilyas et al. Tracheal intubation with Macintosh or McGrath laryngoscope Table 2 Comparison of time to intubation, intubation difficulty score, intubation success and complications in 128 patients whose tracheas were intubated using either the Macintosh or McGrath â laryngoscope. Values are mean (SD), median (IQR [range]) or number (proportion). Macintosh (n = 64) McGrath (n = 64) p value Intubation 50.0 (32.6) 82.7 (80.0) time; s Intubation 2(0 3 [0 7]) 0 (0 3 [0 7]) difficulty score Successful 64 (100%) 59 (92.2%) intubation Mucosal 8 (12.5%) 4 (6.5%) NS bleeding Sore throat 25 (39.1%) 24 (35.9%) NS Hoarse voice 23 (35.9%) 22 (34.4%) NS Dental damage 0 NS Table 3 Difference in laryngoscopic view between the Macintosh and McGrath â instruments in 127 patients. Values are number or number (proportion). Grade using McGrath Grade using Macintosh 1 2 Total (29%) (48%) (23%) Total 117 (92%) 10 (8%) 127 The majority of patients had a worse laryngoscopic view with the Macintosh videolaryngoscope when compared with the McGrath laryngoscope, although two patients showed a grade-1 view with the Macintosh and grade-2 with the McGrath (Table 3). One patient in the McGrath group demonstrated a grade-1 glottic view with the Macintosh; when the McGrath was inserted, the videolaryngoscope screen failed and the laryngoscopic view could not be recorded, but the trachea was intubated under direct vision. There was no systematic difference in laryngoscopic view depending on which instrument was used first. There was no significant difference in physiological variables between the two groups. There was also no significant difference in the incidence of complications between the two groups. There was one case of minor dental damage in the McGrath group that required no further management. Discussion Our study showed a faster time to intubation with the Macintosh laryngoscope compared with the McGrath videolaryngoscope, despite better laryngoscopic views and a more favourable intubation difficulty score obtained with the latter. Cervical spine immobilisation has been employed in many studies to simulate a difficult airway. In contrast to our results, controlled trials evaluating either intubation success rate, duration of laryngoscopy or the ease of intubation as calculated by the intubation difficult score have shown that the Airtraq â [17], Pentax AWS â or the Glidescope â [7, 8, 11, 16, 18, 19] may outperform direct laryngoscopy. In our study, 85 (67%) cases showed a better view with the McGrath than the Macintosh, and 26 (20%) of these showed an improvement from grade 3 to grade 1. However, the overall success rate and intubation time were significantly worse in the McGrath group compared with the Macintosh group. Taylor et al. [20] performed a similar comparison of the Macintosh and McGrath laryngoscopes. They defined a primary outcome of 50% improvement in laryngoscopic view, whereas we used the time to successful intubation; we would argue that ours is a more clinically relevant outcome. The two studies found a similar distribution between good (grades 1 and 2) and poor (grades 3 and 4) views obtained using the McGrath. However, Taylor et al. found almost twice the incidence of poor views when using the Macintosh, 49% vs 23%. Both studies found that intubation time was shorter when using the Macintosh laryngoscope. The numerical differences in time to intubate may relate to different definitions; Taylor et al. used removal of the laryngoscope as the endpoint of the attempt, whereas we used the first complete end-tidal carbon dioxide square wave. The longer intubation time required with the McGrath videolaryngoscope was attributed to difficulty with manipulating the tracheal tube between the vocal cords. Sharp-angled, non-channelled videolaryngoscopes such as the McGrath usually require a stylet to aid positioning of the tracheal tube at the glottic outlet, but then the stylet must be partially The Association of Anaesthetists of Great Britain and Ireland

5 Ilyas et al. Tracheal intubation with Macintosh or McGrath laryngoscope Anaesthesia 2014, 69, withdrawn to permit tube advancement beyond the posterior angle of the descending trachea [21]. The most important difference between the study by Taylor et al. and ours was the success rate for tracheal intubation; they found a statistically significant difference of 59% for the Macintosh and 100% for the McGrath, whereas we found a difference of 100% and 92%, respectively. We consider that their finding of a 41% failure rate for intubation with the Macintosh laryngoscope is surprisingly high and inconsistent with the rate quoted in the literature of about 10% [7, 10, 18]. Despite longer intubation times and more failures, we found that the McGrath laryngoscope provided significantly better intubation difficulty scores compared with the Macintosh. This may be attributed to the better laryngoscopic views obtained, which then obviate the need for increased lifting force or external laryngeal pressure; but as discussed, better views do not necessarily translate into easier intubation [22]. The complication rate was similar between the two groups. The majority of complications were due to hoarse voice and sore throat after intubation, which were in keeping with the previously reported incidence of 45.4% [23]. The McGrath laryngoscope has previously been reported as having a success rate in difficult airways between 92% and 98% [24 26], comparable to our findings even taking into account two episodes of screen failure. The distributors were alerted to these episodes. On three occasions, we were unable to pass the tracheal tube, probably related to impaction of the tip of the tube on the anterior wall of the subglottic space. Standard techniques such as withdrawing the stylet and rotating the tracheal tube were utilised, but did not help. We did not use other techniques such as reverse loading or using a Parker Flex-Tip â or a silicone LMA Fastrach â tube [27]. There were a few limitations to this study. Firstly, we were not able to blind the intubating anaesthetist or the observer, which may have led to bias. However, the primary outcome of intubation time and most of the secondary outcomes were well defined and objective. Secondly, a selected group of anaesthetists were involved in performing the laryngoscopy and therefore there may have been variations in the level of experience or skill in using the McGrath laryngoscope. However, this instrument was available in both our departments for a number of years before commencement of the study and all anaesthetists involved were experienced with the device. Thirdly, there was the potential for the second laryngoscopy to be rated differently depending on the findings of the first, although we did not find any systematic difference. Fourthly, the person performing the manual in-line stabilisation was not the same person each time, although we attempted to standardise for this using a specific technique and experienced trauma personnel. In conclusion, this study shows that although the McGrath Series 5 videolaryngoscope provides a better laryngoscopic view of the glottis and better intubation difficulty scores compared with the Macintosh laryngoscope when used in patients with manual in-line cervical stabilisation, it prolongs the intubation time and leads to more intubation failures in part because of equipment technical difficulties. This is a major concern for a device that is supposed to be used as a primary airway device or as a rescue device. Acknowledgements The McGrath Series 5 Videolaryngoscopes with the disposable blades were made available to the Royal Melbourne Anaesthetic department, during the study period, at no cost by Aircraft Medical Ltd and Ecomed Pty Ltd. The Alfred had already purchased its own devices. We would like to thank Dr Andrew Bjorksten and Dr Enjarn Lin for providing valuable assistance with the data analysis. Competing interests No competing interests and no external funding declared. References 1. Heath KJ. The effect on laryngoscopy of different cervical spine immobilisation techniques. Anaesthesia 1994; 49: Nolan JP, Wilson ME. Orotracheal intubation in patients with potential cervical spine injuries. An indication for the gum elastic bougie. Anaesthesia 1993; 48: Thiboutot F, Nicole PC, Trepanier CA, Turgeon AF, Lessard MR. Effect of manual in-line stabilization of the cervical spine in adults on the rate of difficult orotracheal intubation by direct laryngoscopy: a randomized controlled trial. Canadian Journal of Anesthesia 2009; 56: The Association of Anaesthetists of Great Britain and Ireland 1349

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