Comparison of the ease of tracheal intubation using a McGrath Mac videolaryngoscope and a standard Macintosh laryngoscope in normal airways

Editor, The McGrath Mac videolaryngoscope (Covidien France SAS, Paris, France) is a recent device with a blade similar to the Macintosh blade; it has no specific channel to guide the advancement of the tube. The McGrath Mac has been reported to be better than the Macintosh laryngoscope for successful intubation in difficult airways.1 The question arises of the place of the videolaryngoscope for routine intubation compared with the standard Macintosh laryngoscope and this was the aim of this trial. The current monocentric randomised controlled trial was approved by the local Ethics Committee (No. 131060) and was registered on the ClinicalTrials.gov website (NCT02292901). Patients aged from 18 to 80 years undergoing elective surgery under general anaesthesia requiring standard endotracheal intubation were enrolled, whereas pregnant women, breastfeeding mothers, patients needing a rapid sequence induction, patients with ear–nose–throat surgery and with history of previous difficult intubation were excluded. Patients with potentially difficult intubation were also not included; this potential difficulty was defined as the presence of at least two of the following factors: diseases associated with difficulties in intubation or clinical symptoms of airway disease, snoring or obstructive sleep apnoea syndrome, short thick neck, limited mandibular protrusion, head and neck movement 80° or less, edentulous, thyromental distance less than 65 mm, interincisor gap less than 35 mm and Mallampati class more than II. At their admission in the operating room, patients were centrally randomised to one of the two study groups: conventional laryngoscopy for intubation (Macintosh group) or video-assisted laryngoscopy with a McGrath Mac videolaryngoscope (McGrath Mac group). After pre-oxygenation, induction was performed using sufentanil, propofol and atracurium. When train of four was 0/4, endotracheal intubation was performed according to the randomisation. The investigator could use a stylet, make external laryngeal pressure or change the technique (laryngeal mask, transtracheal ventilation or tracheostomy) in case of unexpected difficulty. The primary outcome was the intubation difficulty scale (IDS).2 The study hypothesis was that use of the videolaryngoscope would decrease the incidence of unanticipated difficult endotracheal intubations compared with a conventional laryngoscope. Based on previous studies, the incidence of unanticipated difficult endotracheal intubation defined as an IDS more than 5 was 10%.3 A decrease from 10 to 2% of unanticipated intubation using the McGrath Mac led to include 162 patients per group, with an 80% power and an alpha risk at 5%. An interim analysis was scheduled after the first 130 randomised patients. Normally distributed variables are presented as mean and SD and nonnormally distributed ones as median and interquartile range. The Student t test or the Wilcoxon test was used to analyse quantitative data, and Fisher's exact test was used to compare categorical data. P value less than 0.05 was considered significant. Between February and October 2015, 155 patients were eligible, and finally, 130 were randomised: 60 patients in the Mac group and 70 in the McGrath Mac group. An interim analysis was performed then as planned. Finally, 57 patients completed the study in the Mac group and 65 in the McGrath group (Fig. 1). The groups were similar for patient characteristics except for age: 53.5 ± 13.3 in the Mac group and 59.1 ± 13.2 in McGrath, P = 0.02. There was no difference in the incidence of unanticipated difficult intubation, defined by an IDS more than 5, between the two groups: 2 (3.5%) vs. 1 (1.5%) respectively; P = 0.59, whereas the Cormack and Lehane grade was lower in the McGrath Mac group (P = 0.04). The time to intubation was greater in the McGrath Mac group (P = 0.01). The number of oesophageal intubations was lower in the McGrath Mac group, but the difference did not reach statistical significance (Table 1). Few intra-operative events were recorded, especially one case of oxygen desaturation in the McGrath Mac group; the incidences of postoperative hoarseness and sore throat were similar in both groups (Table 1).Fig. 1: Study flow chart.Table 1: Intubation variables, intra-operative oxygen desaturation and postoperative hoarseness and sore throatOur study is the second to test the McGrath Mac in this indication. Wallace et al.4 compared a McGrath Mac videolaryngoscope group, a second McGrath Mac videolaryngoscope group using the device as a direct laryngoscope, and a control group using a standard Macintosh laryngoscope. Poorer IDS were observed when the McGrath Mac videolaryngoscope group was used as a direct laryngoscope. Our results are also consistent with a meta-analysis published in 2013 which did not show the benefit of videolaryngoscopes for patients with normal airway.5 Finally our findings are consistent with the recent literature on other devices: the C-MAC (Karl Storz, Tuttlingen, Germany)6 and the GlideScope videolaryngoscope.7 The most important limitation is that the study was stopped prematurely. A calculation made from our results about unanticipated difficult intubation showed that around 1900 patients were required to find a significant difference in IDS between both groups. In conclusion, our study did not find a real interest for the use of the McGrath Mac videolaryngoscope in normal airways among experts in laryngoscopy. However, our results questioned the choice of the primary outcome and the risk of an interim analysis. Acknowledgements relating to this article Assistance with the letter: we thank Elodie Feliot and Etienne Gayat, MD, PhD, for their help in statistical analysis and Polly Gobin for her linguistic help. Financial support and sponsorship: this work was supported by Hôpital Foch, Suresnes, France. Conflicts of interest: none.