Initial Prehospital Rapid Emergency Medicine Score (REMS) as a Predictor of Patient Outcomes

Background: A standardized objective measure of prehospital patient risk of hospitalization or death is needed. The Rapid Emergency Medicine Score (REMS), a validated risk-stratification tool, has not been widely tested for prehospital use. This study's objective was to assess predictive characteristics of initial prehospital REMS for ED disposition and overall patient mortality. Methods: This retrospective analysis used linked prehospital and hospital data from the national ESO Data Collaborative. All 911 responses from 1/1/2019-12/31/2019 were included. REMS (0-26) was calculated using age and first prehospital values for: pulse rate, mean arterial pressure, respiratory rate, oxygen saturation, and Glasgow Coma Scale. Non-transports, patients <18 and cardiac arrests prior to EMS arrival were excluded. The primary outcome was ED disposition, dichotomized to discharge versus admission, transfer, or death. The secondary outcome was overall survival to discharge (ED or inpatient). Transfers and records without inpatient disposition were excluded from the secondary analysis. Predictive ability was assessed using area under the receiver operating curve (AUROC). Optimal REMS cut points were determined using test characteristic curves. Univariable logistic regression modeling was used to quantify the association between initial prehospital REMS and each outcome. Results: Of 579,505 eligible records, 94,640 (16%) were excluded due to missing data needed to calculate REMS. Overall, 62% (n = 298,223) of patients were discharged from the ED, 36% (n = 175,212) were admitted, 2% (n = 10,499) were transferred, and 0.2% (n = 931) died in the ED. A REMS of 5 or lower demonstrated optimal statistical prediction for ED discharge versus not discharged (admission/transfer/death) (AUROC: 0.68). Patients with initial prehospital REMS of 5 or lower showed a three-fold increase in odds of ED discharge (OR: 3.28, 95%CI: 3.24-3.32). Of the 457,226 patients included in overall mortality analysis, >98% (n = 450,112) survived. AUROC of initial prehospital REMS for overall mortality was 0.79. A score 7 or lower was statistically optimal for predicting survival. Initial prehospital REMS of 7 or lower was associated with a five-fold increase in odds of overall survival (OR:5.41, 95%CI:5.15-5.69). Conclusion: Initial prehospital REMS was predictive of ED disposition and overall patient mortality, suggesting value as a risk-stratification measure for EMS agencies, systems and researchers.