Direct versus indirect epiglottis elevation during McGrath MAC videolaryngoscopy: a randomized trial of glottic visualization and the hemodynamic response

Videolaryngoscopy is widely used for tracheal intubation. With Macintosh-geometry videolaryngoscopes such as the McGrath MAC, the epiglottis can be elevated indirectly by placing the blade tip in the vallecula, or directly by advancing it beneath the epiglottis. Their relative effects on the glottic view and on the haemodynamic response to laryngoscopy are unclear. In this prospective, randomized, controlled, single-centre trial, 82 adults (American Society of Anesthesiologists physical status I–III, body mass index 25–30 kg/m²) with normal airways undergoing elective surgery were allocated 1:1 to direct (sub-epiglottic; Group D) or indirect (vallecular; Group I) epiglottis elevation during McGrath MAC videolaryngoscopy. The same videolaryngoscope and the same blade type were used in both groups; the groups differed only in the final position of the blade tip. Here “direct” and “indirect” denote the method of epiglottis elevation and not direct versus video laryngoscopy. The primary outcome was the percentage of glottic opening (POGO) score. Secondary outcomes were the Cormack–Lehane grade, the use of facilitating maneuvers, intubation characteristics, and haemodynamic variables (heart rate, mean arterial pressure, and bispectral index) recorded before induction (T1), after induction (T2), and immediately after intubation (T3). Between-group comparisons are reported with effect sizes and 95% confidence intervals, and the nine haemodynamic comparisons were corrected for multiplicity by the Holm–Bonferroni method. All 82 randomized patients completed the trial and were analysed, and tracheal intubation succeeded in every patient. Baseline characteristics were comparable. The POGO score did not differ between Group D and Group I (median 80%, interquartile range 70–90, in both groups; Hodges–Lehmann median difference 0%, 95% confidence interval − 10 to 0; p = 0.547), nor did the Cormack–Lehane grade ( p = 0.638); no patient had a grade 3 or 4 view. Time to glottic visualization, intubation time, the number of attempts, and the use of facilitating maneuvers did not differ significantly. Heart rate immediately after intubation was nominally lower with the direct technique (80 versus 84 beats/min; difference − 6 beats/min, 95% confidence interval − 12 to 0; unadjusted p = 0.023), but this did not survive correction for multiple comparisons (Holm-adjusted p = 0.159) and was not reproduced when the change from baseline was analysed (T3 − T1, p = 0.176). Mean arterial pressure did not differ between the groups at any time point. Bispectral index values differed between the groups at the two time points preceding laryngoscopy, a small difference that lay within the awake range at T1 and within the protocol-specified target range at T2, but not immediately after intubation ( p = 0.061). In adults with normal airways, direct and indirect epiglottis elevation with the McGrath MAC provided closely comparable glottic visualization and intubation conditions, with a confidence interval that excludes any difference in POGO score greater than 10% points. No difference in the haemodynamic response withstood correction for multiple comparisons. In routine practice the choice between the two techniques can reasonably be left to operator preference. ClinicalTrials.gov NCT05967338. Registered retrospectively on 1 June 2023.