Mobile Stroke Units Tied to Better Acute Stroke Outcomes at 90 Days

stroke, TIA, hemorrhagic stroke, hematoma
In an observational study, researchers assessed outcomes from mobile stroke units or emergency medical services within 4.5 hours after onset of acute stroke symptoms.

Mobile stroke units (MSU) improved care for patients with acute stroke long-term compared with standard emergency medical services (EMS), according to a study published in The New England Journal of Medicine.

Every second counts in response to acute ischemic stroke. Prior research has found that delivery of tissue plasminogen activator (tPA) within the first hour of stroke onset is optimal. MSU are ambulances that bring computed tomography (CT), laboratory testing, tPA and personnel trained in their use and triage for endovascular thrombectomy (EVT) to patients, rather than at their arrival at an emergency department. Researchers sought to determine the difference MSU would make on 90-day outcomes for patients who experienced a stroke.

In the trial, researchers enrolled patients from 7 cities who met screening criteria for tPA treatment on MSU or EMS arrival at the scene, which included having acute stroke within the previous 4.5 hours. MSU and EMS were alternated in each city site in alternating shift schedules. Both units were dispatched on each call.

If they encountered each other, they jointly evaluated the patient. MSU obtained intravenous access, determined National Institutes of Health Stroke Scale (NIHSS) score regarding neurologic deficits, non-contrast CT of head, blood-pressure control, and tPA initial bolus and start of infusion if applicable. Patients were then rushed to the emergency department of a stroke center EMS judged suitable during triage.

When EMS was assigned, an MSU nurse met the patient and EMS at the emergency department EMS selected. NIHSS score at the hospital and data EMS obtained at first contact prompted extrapolated NIHSS score.

Of the 1,515 patients enrolled in the trial (58.5% MSU group), 617 patients cared for via MSU, and 430 patients cared for via EMS were eligible for tPA. A total of 97.1% and 79.5% of those groups received it, respectively.

The median time from onset of stroke to administration of tPA was 36 minutes fewer in the MSU group compared with the EMS group (72 vs 108 minutes respectively).

After 3 months, utility-weighted mean modified Rankin scale scores were higher in the MSU group (0.72±0.35) compared with the EMS group (0.66±0.36), as was survival (8.9% mortality in MSU group 11.9% in EMS group). At that time, the portion of patients eligible for tPA who had a score of 0 or 1 on the modified scale was higher in the MSU group (55% vs. 44.4%).

Mean scores at discharge were 0.57±0.37 in the MSU group and 0.51±0.36 in the EMS group. Seventy-five percent of patients in the MSU group and 67.8% in the EMS group experienced a 30% reduction in NIHSS score 24 hours after baseline (adjusted odds ratio, 1.45). NIHSS scores at 0 improved by arrival at the emergency department in more MSU group individuals (5.5%) compared with EMS group individuals (3.3%).

Study limitations included possible bias in group assignment and generalization due to limited enrollment at non-Houston sites due to delayed start-up and COVID-19. EMS squads alerted MSU squads of discovery of stroke outside of dispatch during MSU weeks but not on EMS weeks.


Grotta JC, Yamal JM, Parker SA, et al. Prospective, multicenter, controlled trial of mobile stroke units. N Engl J Med. Published online September 9, 2021. doi: 10.1056/NEJMoa2103879