Evaluation of the discriminative performance of the prehospital National Advisory Committee for Aeronautics score regarding 48-h mortality

The National Advisory Committee for Aeronautics (NACA) score is used by many emergency medical services to assess the severity of prehospital patients. Little is known about its discriminative performance regarding short-term mortality. We retrospectively included adult missions between 2008 and 2014 in a Swiss ground and air-based emergency medical services. We excluded uninjured or dead-on-scene patients. Primary outcome was assessment of the discriminative performance of the NACA score to classify the 48-h vital status of patients. Overall discrimination was quantified using the area under receiver operating characteristic curve (AUC). We also explored the influence of epidemiological characteristics (age and sex), mechanism (trauma or nontrauma) and clinical parameters (respiratory rate, oxygen saturation, heart rate, systolic blood pressure, capillary refill time, and Glasgow Coma Scale) on its discriminative performance. We then assessed the incremental value of these variables in the classification accuracy of a rule based on these variables in addition to the NACA score. We included 11 567 patients out of 11 639 (72 exclusions for missing data). Overall AUC was 0.86. The score was more discriminant for trauma (AUC = 0.95 vs. 0.83), and for younger patients (AUC = 0.91 for 16-59 vs. 0.78 for 84-104 years). Adding age, sex, mechanism, and clinical parameters resulted in a classification rule with higher discriminative performance than NACA score alone (AUC of 0.92 vs. 0.86; P < 0.001). The NACA score is an efficient way to discriminate victims regarding short-term mortality. Its performance can be enhanced by also integrating epidemiological and clinical parameters into an extended classification rule.