Association Between Dispatch of Mobile Stroke Units and Functional Outcomes Among Patients With Acute Ischemic Stroke in Berlin

Abstract

Importance: Effects of thrombolysis in acute ischemic stroke are time-dependent. Ambulances that can administer thrombolysis (mobile stroke units [MSUs]) before arriving at the hospital have been shown to reduce time to treatment.

Objective: To determine whether dispatch of MSUs is associated with better clinical outcomes for patients with acute ischemic stroke.

Design, setting, and participants: This prospective, nonrandomized, controlled intervention study was conducted in Berlin, Germany, from February 1, 2017, to October 30, 2019. If an emergency call prompted suspicion of stroke, both a conventional ambulance and an MSU, when available, were dispatched. Functional outcomes of patients with final diagnosis of acute cerebral ischemia who were eligible for thrombolysis or thrombectomy were compared based on the initial dispatch (both MSU and conventional ambulance or conventional ambulance only).

Exposure: Simultaneous dispatch of an MSU (computed tomographic scanning with or without angiography, point-of-care laboratory testing, and thrombolysis capabilities on board) and a conventional ambulance (n = 749) vs conventional ambulance alone (n = 794).

Main outcomes and measures: The primary outcome was the distribution of modified Rankin Scale (mRS) scores (a disability score ranging from 0, no neurological deficits, to 6, death) at 3 months. The coprimary outcome was a 3-tier disability scale at 3 months (none to moderate disability; severe disability; death) with tier assignment based on mRS scores if available or place of residence if mRS scores were not available. Common odds ratios (ORs) were used to quantify the association between exposure and outcome; values less than 1.00 indicated a favorable shift in the mRS distribution and lower odds of higher levels of disability.

Results: Of the 1543 patients (mean age, 74 years; 723 women [47%]) included in the adjusted primary analysis, 1337 (87%) had available mRS scores (primary outcome) and 1506 patients (98%) had available the 3-tier disability scale assessment (coprimary outcome). Patients with an MSU dispatched had lower median mRS scores at month 3 (1; interquartile range [IQR], 0-3) than did patients without an MSU dispatched (2; IQR, 0-3; common OR for worse mRS, 0.71; 95% CI, 0.58-0.86; P < .001). Similarly, patients with an MSU dispatched had lower 3-month coprimary disability scores: 586 patients (80.3%) had none to moderate disability; 92 (12.6%) had severe disability; and 52 (7.1%) had died vs patients without an MSU dispatched: 605 (78.0%) had none to moderate disability; 103 (13.3%) had severe disability; and 68 (8.8%) had died (common OR for worse functional outcome, 0.73, 95% CI, 0.54-0.99; P = .04).

Conclusions and relevance: In this prospective, nonrandomized, controlled intervention study of patients with acute ischemic stroke in Berlin, Germany, the dispatch of mobile stroke units, compared with conventional ambulances alone, was significantly associated with lower global disability at 3 months. Clinical trials in other regions are warranted.

Figure 1.. Participant Flowchart in the B_PROUD Study Population

^aThe list of the dispatch center does not provide reliable documentation of reasons for not matching with the Berlin Specific Acute Treatment in Ischemic and Hemorrhagic Stroke With Long-term (B-SPATiAL) registry except for when a patient is not transported to a hospital or is transported to a hospital that doesn’t have a stroke unit. Exclusion criteria included patients who were younger than 18 years, did not have a stroke or transient ischemic attack diagnosis, had no symptoms at the emergency department medical service or at hospital arrival, or arrived at the hospital more than 6 hours after symptom onset. ^bPatients taking oral anticoagulation who had no large vessel occlusion. ^cMissing information because of incomplete documentation in the B-SPATiAL registry because of expired access to electronic hospital records. ^dThe majority had a blinded rating (381 recorded interviews, 181 written questionnaires, and 52 dead), while the remaining 40 had unblinded rating by study nurses. ^eThe majority had a blinded rating (407 recorded modified Rankin Scale interviews, 165 written questionnaires, and 68 dead), while the remaining 43 had unblinded rating by study nurses. ^fFor the coprimary outcome, the level of disability among patients without an mRS score was based on residential status—no to moderate disability was assigned to those living at home and severe disability was assigned to those living in a nursing care facility.

Figure 2.. Map of Berlin, Germany, Showing the 3 Catchment Areas for the Mobile Stroke Units

The red line indicates the outer border of the city. The 3 overlapping mobile stroke unit catchments are indicated by green, blue, and orange boundary lines with corresponding shading. The yellow lines show highways (“Autobahnen”). Mobile stroke unit (MSU) 3600 started in February 2011 and has operated at the shown base station since February 2018. The MSU 6100 started in April 2017 and MSU 4390 in April 2018. The map shows the base stations of the 3 MSUs as well as the 56 base stations for the normal ambulances and the locations of the 15 hospital Stroke Units. The approximate population of Berlin is 3.8 million over 344 square miles. This map is modified from the EL Berliner Feuerwehr [Berlin Fire Brigade].

Figure 3.. Modified Rankin Scale Score Distribution at 3 Months, Unadjusted Only for Patients With Respective Follow-up

The modified Rankin Scale (mRS) score is a measure of disability ranging from 0, no neurological deficits, to 6, death. ^aThree-tier disability scale (none to moderate disability; severe disability; dead) with tier assignment were based on mRS scores if available and place of residence if the mRS scores were not available. None to moderate disability was considered present if the mRS score was 0 to 3 or when mRS score were not available, if the patient was residing at home. Severe disability was considered present if the mRS score was 4 to 5 or, when mRS score was not available, if the patient was residing in a nursing care facility.