Mobile Stroke Units Linked to Reduced Stroke Disability

Erik Greb

September 09, 2021

Treatment in a mobile stroke unit (MSU) is associated with better functional outcomes, compared with treatment by emergency medical services (EMS), among patients with acute ischemic stroke, a newly published study suggests.

In an observational study of patients who were eligible for thrombolysis, the mean score on the utility-weighted modified Rankin scale (mRS) at 90 days was 0.72 among patients treated in an MSU and 0.66 among patients treated by EMS, indicating better outcomes in the former group.

"Our results show that in the areas served by the trial, patients who received emergency care within 4.5 hours after stroke onset had less disability on a utility-weighted scale at 90 days with MSU management than with management by EMS," conclude researchers led by James C. Grotta, MD, Memorial Hermann Hospital–Texas Medical Center in Houston, Texas.

The findings were published online September 8 in the New England Journal of Medicine. Interim findings of this study were presented at the International Stroke Conference (ISC) 2021 in February 2021 and reported at that time by Medscape Medical News.


The standard of care for patients with stroke is transportation by ambulance to an emergency department and, for eligible patients, the administration of tissue plasminogen activator (tPA). Patients with intracerebral large-vessel occlusion may be candidates for endovascular thrombectomy (EVT).

The MSUs studied in this trial consisted of an ambulance with an on-board CT scanner and laboratory testing. MSU personnel are trained to diagnose stroke, administer tPA, and triage for EVT en route to the hospital.

The investigators conducted the prospective, observational BEST-MSU study to examine whether MSUs affect outcomes of ischemic stroke. Patients within 4.5 hours of ischemic stroke onset who met screening criteria for tPA were enrolled in Houston and six other cities. MSU and EMS were available on alternating weeks, and patients were allocated to treatment based on their week of presentation.

The study's primary outcome was the score on the utility-weighted mRS. This score ranges from 0 to 1, and higher scores indicate better outcomes according to a patient value system based on scores on the mRS. The mRS score itself ranges from 0 to 6, and higher scores indicate greater disability.

In all, the investigators enrolled 1515 patients, and 1047 were eligible to receive tPA. Of the latter group, 617 patients received care by MSU, and 430 received care by EMS.

In the MSU group, the median time from onset of stroke to tPA administration was 72 minutes, compared with 108 minutes in the EMS group. Among patients eligible for tPA, 97.1% in the MSU group received it, compared with 79.5% in the EMS group.

At 90 days, the mean score on the utility-weighted mRS in patients eligible for tPA was 0.72 in the MSU group and 0.66 in the EMS group. The adjusted odds ratio (aOR) of a score of at least 0.91 was 2.43 (P < .001), favoring the MSU group.

Among participants who were eligible for tPA, 55.0% in the MSU group and 44.4% in the EMS group had a score of 0 or 1 (indicating a favorable outcome) on the mRS at 90 days.

Among all enrolled patients, the mean score on the utility-weighted mRS at discharge was 0.57 in the MSU group and 0.51 in the EMS group. The aOR for a score of at least 0.91 was 1.82 (P < 0.001). The rate of mortality at 90 days was 8.9% in the MSU group and 11.9% in the EMS group.

Population Benefit Uncertain

These findings are reassuring, but certain aspects of the trial's design limit the conclusions that can be drawn from them, writes Kennedy R. Lees, MD, of the University of Glasgow in Glasgow, Scotland, in an accompanying editorial.

The investigators limited their patient population to people who were eligible for tPA. This group represents about 69% of patients, which prevents the researchers from evaluating the population benefit of MSUs, Lees notes. The imbalance in the sizes of the treatment groups may have resulted from an active search for cases for the MSUs and limited data collection for controls, he added.

"Each of the compromises in trial design had a logical and well-intentioned justification, but independent replication of the benefit of MSUs is essential, particularly to guard against overestimation of the effect size," Lees writes.

An independent and contemporaneous European trial found that the dispatch of MSUs was associated with less disability at 3 months, compared with the dispatch of ambulances. It seems reasonable to conclude that MSUs improve outcomes for patients with acute cerebral ischemia, particularly among those who are eligible for and receive thrombolysis, Lees concluded.

The study was funded by a grant from the Patient-Centered Outcomes Research Institute. Grotta has received compensation for consulting for Frazer on the design and implementation of MSUs. Lees has disclosed no relevant financial relationships.

N Engl J Med. 2021;385:971-81,1043-44. Abstract, Editorial

Follow Erik Greb on Twitter: @MedscapeErik.

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