Abstract Body: Introduction: Mobile Stroke Treatment Units (MSTU) are improving clinical outcomes by significantly shortening the time-to-treatment. On scene, the specialized staff, including a registered nurse and critical care paramedic, are able to rapidly assess the patient for acute stroke symptoms. This rapid treatment algorithm can potentially lead to missed strokes as compared to those patients transported via standard Emergency Medical Services (EMS). Therefore, we evaluated the rate of missed stroke diagnosis through MSTU assessment in the field as compared to the standard EMS-to-Emergency Department (ED) pathway.

Methods: A retrospective analysis of patients with potential stroke evaluated by the MSTU crew between 7/25/23 and 5/31/24 was performed. Admission criteria includes age 18 years or older, last known well within 24 hours, one or more cardinal signs of stroke, and exclusions of any other suspected diagnosis outside of stroke or neurological disorders. Our study evaluated patients who were excluded from MSTU admission based on failure to meet said admission criteria. These patients were transported to the hospital by standard EMS. Patient demographics, symptoms, and final hospital diagnoses were extracted to complete univariate and multivariable regression analyses.

Results: Our final analysis included 235 patients (mean age 66.3, 56.0% women) evaluated by the MSTU crew, but not admitted due to lower concern for stroke. In our study cohort, 11 had a final diagnosis of stroke that were missed upon initial MSTU evaluation. Patients with missed stroke were significantly older (OR 1.04 (95%CI 1.01 - 1.08), p=0.04) and had a nonsignificant trend towards female sex (OR 0.44 (95%CI 0.14 – 1.45), p=0.17). We did not see any differences among specific MSTU staff performing the evaluation or time of day and day of week. Of the 11 patients with a final stroke diagnosis, none received any acute interventions on arrival to the hospital.

Conclusion: Our MSTU admission criteria resulted in an overall low rate of true stroke misses with none of the “missed strokes” receiving an acute intervention at the hospital. Rapid patient evaluation on scene by an expert stroke crew adhering to a standardized admission criterion does not lead to acute stroke interventions being performed upon arrival to the ED. Older patients with stroke-like symptoms evaluated by a Mobile Stroke Treatment Unit are more likely to be misdiagnosed, which deserves further investigation.