This study was performed to identify variables potentially associated with failure of the first intubation attempt in an out-of-hospital emergency setting, considering all aspects of tracheal intubation. This observational prospective multicenter study was performed over 17 months and involved 10 prehospital emergency medical units. After each tracheal intubation, the operator was required to provide information concerning operator and patient characteristics, as well as the environmental conditions during intubation, by completing a data collection form. The primary endpoint was failure of the first intubation attempt. During the study period, 1546 patients were analyzed, of whom 59% were in cardiac arrest; 486 intubations failed on the first attempt (31.4% [95% confidence interval = 30.2-32.6]). Multivariate analysis revealed that the following 7 of 28 factors were associated with an increased risk of a failed first intubation attempt: operator with fewer than 50 prior intubations (odds ratio [OR] = 1.8 [1.4-2.4]), small inter-incisor space (OR = 2.3 [1.7-3.2]), limited extension of the head (OR = 1.6 [1.1-2.1]), macroglossia (OR = 2.3 [1.6-3.2]), ear/nose/throat (ENT) tumor (OR = 4.4 [1.4-13.4]), cardiac arrest (OR = 1.8 [1.3-2.6]), and vomiting (OR = 1.7 [1.3-2.3]). The frequency of adverse events among non-cardiac arrest patients was 17.6%; it increased with each additional intubation attempt. The first intubation attempt failed in more than 30% of cases, and seven variables were associated with increased risk of failure. Most of these factors could not be predicted.Read less <