Abstract WMP40: A Geospatial Information Services Assessment of Prehospital Bypass on Overtriage for Large Vessel Occlusion and Hemorrhagic Stroke

Abstract

Introduction: To increase the number of patients with large vessel occlusion (LVO) acute ischemic strokes (AIS) transported directly to Comprehensive Stroke Centers (CSCs), on December 1, 2021, the threshold score for our county EMS agency’s quantitative stroke severity scale (FAST-ED) for bypassing a non-CSC decreased from 7 to 6. The goal of this work was to evaluate the impact of and adherence to this change, and its effect on overtriage. Methods: Two large regional health systems and the county EMS agency collaborated on this study. Using latitude and longitude coordinates from our EMS agency’s database, we geocoded the pick-up location of all patients who had a FAST-ED score of ≥6 from September 2019 to December 2022. We used ArcGIS to calculate drive times to the closest facility among 2 CSCs and 7 non-CSCs, and linked EMS records to hospital records to determine LVO AIS involving the intracranial ICA, M1, M2 or basilar artery. For patients without a CSC as the closest destination facility, we defined overtriage as routing to a CSC for a non-LVO or non-hemorrhagic stroke patient. Results: Over our 40-month study period, among patients with a FAST-ED score performed (n=13,913), 824 had a score ≥6. Actual versus ArcGIS drive times in minutes [mean(SD)] compared favorably [14.8(8.5) vs 14.4(6.4), with an ICC of 0.68 (95% CI 0.64-0.72). For 799/824 patients (97%), one of the county’s two CSCs was not the closest destination facility, and among this group 99% (n=787/799) of EMS records were successfully linked to the hospital record. Among these patients, prior to December 1, 2021, 67% (n=219/326) patients with FAST-ED score ≥7 were bypassed to a CSC, with an overtriage rate of 49% (n=107/219), while after that date 88% (n=230/262) patients with a FAST-ED score ≥6 were bypassed to a CSC, with an overtriage rate of 55% (n=126/230). Conclusion: It is feasible to use drive times calculated from ArcGIS to evaluate the performance of EMS stroke triage and destination plans. Lowering our county’s FAST-ED score threshold for bypass increased adherence to the bypass protocol with a modest increase in overtriage. Future work will incorporate undertriage rates with the ultimate goal of optimizing our regional stroke and triage destination plan.