Cohort selection of obstetric patients. Automated electronic screening criteria were documentation of any of the following: observed or labeled difficult tracheal intubation, direct or video laryngoscopy Cormack–Lehane view of 3 or higher, three or more intubation attempts, fiberoptic intubation, laryngeal mask airway placement, surgical airway, documentation of neuromuscular blockade administration without concurrent documentation of endotracheal tube placement, or any documented attempt at direct or video laryngoscopy without concurrent documentation of endotracheal tube placement.