Force and torque vary between laryngoscopists and laryngoscope blades

Several studies have examined the effects of patient characteristics on force of laryngoscopy, but little attention has been paid to the importance of technique and equipment. This study investigated whether force, torque, head extension, and view varied significantly between laryngoscopists and compared force and torque using Macintosh 3 and Miller 2 blades. The study population consisted of ASA grade I and II patients requiring general anesthesia and endotracheal intubation for elective surgery. Force, torque, head extension, and laryngeal view were highly reproducible when laryngoscopy was repeated by the same individual, Force and torque showed great variation between laryngoscopies performed by different anesthetists, For example, peak force varied over a range of 56 newtons among patients, but could also vary as much as 30 newtons between different anesthetists repeating laryngoscopy in the same patient. Force and head extension were 30% less with Miller laryngoscope compared to the Macintosh. Thus, laryngoscopic force and torque depend on technique and equipment. Further studies of force and torque may lead to improved techniques. The force-measuring laryngoscope could be a useful tool in teaching laryngoscopy.