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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

Cordovani, Daniel; Russell, Twain; Wee, Wallace; Suen, Andrew; Cooper, Richard M.

European Journal of Anaesthesiology (EJA): March 2019 - Volume 36 - Issue 3 - p 221–226
doi: 10.1097/EJA.0000000000000901
Airway management

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 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 < 0.001, respectively). Laryngoscopy time increased with the GlideScope (30 vs. 18 s, P < 0.001), resulting in similar median impulse forces (206 vs. 175 N, P = 0.92).

CONCLUSION GlideScope laryngoscopy resulted in reduced peak and average forces, but as the laryngoscopy duration increased, the product of force and time (impulse force) was similar with both devices.

TRIAL REGISTRATION Identifier: NCT01814176.

From the Department of Anesthesia, McMaster University, Hamilton, Ontario, Canada (DC), The Department of Anesthesia, Sir Charles Gairdner Hospital, Hospital Ave, Nedlands, Western Australia, Australia (TR), The Edmonton Clinic Health Academy, Edmonton, Alberta (WW), The Department of Anesthesia, Pain Management and Perioperative Medicine, Dalhousie University, Halifax, Nova Scotia (AS), The Department of Anesthesia and Pain Management, Toronto General Hospital, Toronto, Ontario, Canada (RMC)

Correspondence to Daniel Cordovani, The Department of Anesthesia, McMaster University, 1280 Main Street West, Room HSC-2V9, Hamilton, ON L8S 4K1, Canada. Tel: +1 905 521 2100 x75171; fax: +1 905 523 1224; e-mail:

Published online 10 October 2018

© 2019 European Society of Anaesthesiology