Pre-Hospital Early Warning Scores are Associated with Requirement for Medical Retrieval Services

Objective: Prehospital early warning scores (EWSs) can accurately identify patients at risk of clinical deterioration. We hypothesised that EWSs can identify patients during the prehospital phase who will subsequently require clinical escalation via medical retrieval. Methods: A retrospective observational study of adult patients attended in 2018 by Ambulance Victoria in rural regions was conducted. We calculated EWSs using National Early Warning Score 2 (NEWS2) and Rapid Emergency Medicine Score (REMS) methods. Primary outcome was activation of Adult Retrieval Victoria (ARV) within 24h of ambulance attendance. We evaluated sensitivity and specificity for each score, and used multivariable logistic regression analysis to assess the independent association between EWSs and ARV activation. Results: 71 401 patients were included, of which 607 (0.9%) required ARV activation within 24h. Sensitivity and specificity of NEWS2 were 0.484 (95% CI 0.444–0.525) and 0.806 (95% CI 0.803–0.809) respectively, compared with 0.552 (95% CI 0.511–0.592) and 0.508 (95% CI 0.504–0.512) respectively for REMS. After adjustment for remoteness, distance to hospital, sex, age and hospital service level, a medium/high risk score according to the NEWS2 (OR 4.12; 95% CI 3.50–4.85, p<0.001) and REMS (OR 2.92, 95% CI 2.26–3.77) was associated with ARV activation. Odds of ARV activation increased with remoteness and decreasing service level of the receiving hospital. Conclusions: Prehospital NEWS2 and REMS were associated with medical retrieval within 24h of ambulance attendance. EWSs may allow early identification of ambulance patients requiring medical retrieval, thus facilitating earlier activation and reduced time to definitive care.