SGEM#354: Everybody Walk the Dinosaur and Not Take the MSU

Date: December 21st, 2021

Guest Skeptic: Dr. Howard “Howie” Mell began his career as a firefighter / paramedic in Chicago. He became double board certified in Emergency Medicine (EM) and Emergency Medical Services (EMS). Howie also has a Master of Public Health.

Reference: Grotta JC et al. Prospective, multicenter, controlled trial of mobile stroke units. NEJM 2021

Case: The Mayor of your community consults you as an expert in public health, EMS and as an EM physician on whether they should purchase a mobile stroke unit (MSU) ambulance.

Background: No one who has listened to the SGEM will be surprised we are covering another paper looking at stroke. We have often discussed the use of thrombolysis for acute ischemic stroke (AIS) with or without endovascular therapy (EVT). However, the SGEM has also looked at secondary stroke prevention on previous episodes (SGEM#24, SGEM#303).

The SGEM has looked at pre-hospital stroke care using early administration of nitroglycerin by paramedics to see if it would improve neurologic outcome in patients with a presumed acute stroke (SGEM#269). The results from the RIGHT-2 trial reported no statistical difference in functional outcome as measured by the modified Rankin Scale (mRS) score at 90 days.

The SGEM bottom line was that very early application of transdermal nitroglycerin by paramedics in the pre-hospital setting cannot be recommended at this time in patients with a suspected stroke.

Mobile Stroke Unit

The issue of having a MSU has also been discussed on  SGEM#330. A systematic review and meta-analysis which included seven randomized controlled trials and four observational studies including 21,297 patients was critically appraised.  The primary outcomes reported better neurologic outcome at seven days but not at one day post treatment by a MSU compared to conventional care (Fatima et al Int J Stroke 2020).

The SGEM bottom line from that episode was we cannot recommend the use of MSU based on the available evidence.

Clinical Question: Should mobile stroke units be purchased and deployed in your community?

Reference: Grotta JC et al. Prospective, multicenter, controlled trial of mobile stroke units. NEJM 2021

Population: Patients calling EMS with a history and physical/neurological examination consistent with acute stroke who is last seen normal (LSN) possibly within 4 hours and 30 minutes and who had no definite tPA exclusions per guidelines, prior to CT scan or baseline labs. Daytime hours and mostly weekdays.
Intervention: Care by a mobile stroke unit (MSU)
Comparison: Care by traditional EMS referred to as standard management (SM)
Outcome:

Primary Outcome: Score on the utility-weighted modified Rankin scale (uw-mRS) at 90 days in patients who were adjudicated to be eligible to receive tPA on the basis of subsequent blinded review
Secondary Outcomes: There were twelve secondary endpoints in their final protocol listed in hierarchical sequence of importance

Agreement between on-board vascular neurologists (VN) and the remote VN
Exploratory cost-effectiveness analysis (CEA)
Outcomes comparing patients found eligible for tPA on MSU weeks compared to patients on SM weeks

Ordinal (shift) analysis of mRS at 90 days, and
Proportion of patients achieving 90 day mRS 0,1 vs 2-6
30% improvement from baseline to 24hr NIHSS

Outcomes comparing all patients treated with tPA (whether or not adjudicated as tPA eligible) on MSU weeks compared to patients on SM weeks.
Uw-mRS at 90 days

Ordinal (shift) analysis of mRS at 90 days, and
Proportion of patients achieving 90 day mRS 0,1 vs 2-630%
Improvement from baseline to 24hr NIHSS

Outcomes of those treated within 60 min LSN compared to those treated from 61 to 270 minutes

Change in uw-mRS from baseline at 90 days
Ordinal shift analysis of MRS at 90 days
Proportion of patients achieving 90 day mRS 0,1 vs 2-6