Methods Randomisation and sample size Our sample size calculation was based on an adjustment for the stratification and the cluster randomized design [20, 21]. Since there are no previous records of the trial's primary outcome measure, "unanticipated difficult intubation" a baseline study was conducted based on data from the Danish Anaesthesia Database (DAD). In order to reject or detect a 30 % relative risk reduction in the proportions of unanticipated difficult intubation between the intervention group and the control group approximately 30 departments were required in a 15 months period. Calculations were based on a maximum risk of type 1 error of 5% and risk of type 2 error of maximum 20 % (80 % power).