Measurement of forces applied using a Macintosh direct laryngoscope compared with a Glidescope video laryngoscope in patients with predictors of difficult laryngoscopy: A randomised controlled trial

BACKGROUND In patients with predictive features associated with easy direct laryngoscopy, videolaryngoscoy with the GlideScope has been shown to require less force when compared with Macintosh direct laryngoscopy. OBJECTIVE The aim of this study was to compare forces applied with Glidescope vs. Macintosh laryngoscopes in patients with predictive features associated with difficult direct laryngoscopy. DESIGN A prospective randomised study. SETTING Toronto General Hospital, a university tertiary centre in Canada. PATIENTS Forty-four patients aged over 18 years, with one or more features of difficult intubation, undergoing elective surgery requiring single-lumen tracheal intubation. INTERVENTION We measured the force applied to oropharyngeal tissues by attaching three FlexiForce Sensors (A201-25) to the concave surface of Macintosh and GlideScope laryngoscope blades. Anaesthetists or experienced anaesthesia residents performed laryngoscopies with both devices in a randomised sequence. MAIN OUTCOME MEASURES The primary outcome was peak force. The secondary outcomes were average force and impulse force. The latter is the integral of the force over the time during which the force acted. RESULTS Complete data were available for 40 individuals. Peak and average forces decreased with GlideScope (17 vs. 21 N, P = 0.03, and 6 vs. 11 N, P 

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