Predictors of difficult intubation when using a videolaryngoscope with an intermediate-angled blade during the first attempt: a prospective observational study

The curvature of a videolaryngoscope blade has been diversified from the standard macintosh-type to the hyperacute-angle-type, resulting in different performances. We aimed to determine the intubation success rate and identify predictors of difficult intubation when using an intermediate-angled videolaryngoscope in the first attempt of intubation under routine anaesthesia settings. We enrolled 808 patients between 19 and 79 years of age, scheduled for elective surgeries under general anaesthesia with orotracheal intubation from July 2017 to November 2018; patients who were candidates for awake intubation were excluded. We obtained patient demographic data and performed airway evaluation before induction of anaesthesia for elective surgeries. We used the UEScope for tracheal intubation with a hockey stick-shaped malleable stylet. The intubation time was defined as the total duration from the entry of the blade into the oropharynx to the detection of first end-tidal carbon dioxide capnogram; this duration was recorded along with the number of intubation attempts. Difficult intubation was defined as either > 60 s duration for tracheal intubation, or > 1 intubation attempt. The use of the UEScope demonstrated a 99.4% success rate for intubation; however, increased difficulties were observed in patients who were male, obese, had a short thyromental distance, limited mouth opening, and high upper-lip-bite test class. Despite the high intubation success rate using an intermediate-angled videolaryngoscope, we recommend preparing backup plans, considering the increased difficulty in patients with certain preoperative features.Clinical trial number and registry URL: Clinical Trials.gov Identifier: NCT03215823 (Date of registration: 12 July).restrictio