Fig. 2. A receiver operating characteristic (ROC) curve evaluating the sensitivity and specificity of risk factors for grade 3 (difficult) or 4 (impossible) mask ventilation and difficult intubation (grade III or IV direct laryngoscopy view or 4+ intubation attempts by staff). Five independent predictors were observed: limited or severely limited mandibular protrusion, thick/obese neck anatomy, a history of sleep apnea, a history of snoring, and body mass index of 30 kg/m²or greater. A prediction score for difficult mask ventilation and intubation was based on how many of these risk factors a patient possessed. The area under the curve for the difficult mask ventilation ROC curve was 0.78.