The value of a diagnostic test is usually presented as sensitivity and specificity. We have chosen (1 - total accuracy) i.e. the proportion of unanticipated difficult intubations (False Negative, FN) and the proportion of unanticipated easy intubations (False Positive, FP). Both scenarios are of clinical relevance since the FN are at risk of hypoxia, increased morbidity and even death, while the FP are at risk of being imposed unnecessary discomfort by e.g. awake intubation. At the same time, both the FN and FP can take up unnecessary resources. Sensitivity and specificity are more difficult to interpret intuitively. Consequently, we chose to present more transparent primary outcomes. Using proportions of unanticipated difficult intubation allowed us to perform a baseline cohort study, on which we based our sample size and power calculations.