Validation of field assessment stroke triage for emergency destination for prehospital use in a rural EMS system

Abstract

Background: Field Assessment Stroke Triage for Emergency Destination (FAST-ED) is a simple and accurate prehospital stroke severity scale that has been shown to have comparable accuracy to the gold standard National Institutes of Health Stroke Scale (NIHSS) but requires further field validation for use by emergency medical services (EMS), particularly in rural systems. FAST-ED scores ≥4 are considered high probability for large vessel occlusion (LVO) strokes, while scores <4 are low to moderate probability for LVO. The objective of this study was to assess inter-rater reliability of the EMS FAST-ED (EMS) score to the emergency department FAST-ED (ED-MD) scores.

Methods: EMS calculated FAST-ED scores prior to transport to the emergency department (ED) on patients with a positive prehospital stroke screen. EDMD calculated FAST-ED scores for the same patients upon arrival to the ED. Interrater reliability and test characteristics were calculated.

Results: A total of 95 patients were included in this study and 14 were subsequently diagnosed with an LVO. EMS assigned 34 patients (35.8%) a FAST-ED score of ≥4. EDMD assigned 25 patients (26.3%) a FAST-ED score of ≥4. Using the clinical cut-points of FAST-ED scores <4 and ≥ 4, a linearly weighted Cohen's kappa coefficient showed moderate interrater reliability when comparing EMS and EDMD scores (k_w 0.44, 95% CI 0.25-0.63). At ≥4, EMS FAST-ED scores had a sensitivity 0.48, specificity 0.75, PPV 0.62, NPV 0.62 for predicting an LVO, while EDMD FAST-ED scores had a sensitivity 0.36, specificity 0.82, PPV 0.64, NPV 0.60. Comparable receiver operator curve area under the curve values were obtained.

Conclusions: EMS and EDMD FAST-ED scores were moderately comparable in a rural EMS system. Similar NPVs compared to EDMD suggest the use of FAST-ED as an appropriate screening tool for EMS to predict the probability of LVO in the prehospital setting and make destination determinations regarding primary transport to a thrombectomy-capable stroke center.

Keywords: Acute ischemic stroke; Field assessment stroke triage for emergency destination; Large vessel occlusion; Prehospital emergency care; Rural emergency medicine; Stroke scale.