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Functional stroke outcomes after mobile
stroke unit deployment –the revised
protocol for the Berlin Prehospital Or Usual
Delivery of acute stroke care (B_PROUD)
part 2 study
Peter Harmel
1,2*
, Martin Ebinger
3
, Erik Freitag
1
, Ulrike Grittner
4,5
, Irina Lorenz-Meyer
1,2
, Ira Napierkowski
1,2
,
Christian H. Nolte
1,2,5,6,7
, Bob Siegerink
2,5
and Heinrich J. Audebert
1,2
Abstract
Background: Studies investigating the Mobile Stroke Unit (MSU) concept have shown increased thrombolysis rates,
reduced alarm-to-treatment times and improved prehospital triage. Yet, so far, there is no definite scientific proof of
better functional outcome after MSU deployment compared to regular ambulances.
Methods: We provide a revised protocol for the second part of the B_PROUD trial as organization of the MSU dispatch
did not meet the anticipated standards in the first part. B_PROUD is a pragmatic, prospective study comparing functional
outcomes of treatment candidates with or without MSU care. Treatment candidates are defined as patients with a final
diagnosis of ischemic stroke or transient ischemic attack, onset-to-dispatch-times ≤4 h, disabling symptoms not resolved
at time of ambulance arrival, and the ability to ambulate prior to the qualifying event. These patients are included if their
emergency call prompted a stroke alarm at the dispatch center during MSU operation hours (7 am–11 pm, Monday-
Sunday) and if the emergency is located within the MSU operation area in Berlin, Germany. The intervention group
consists of patients who are cared for by the MSU. When the MSU is already in operation for another emergency, MSU
dispatches are handled by regular ambulances (about 45%). These dispatches create the control group. Blinded stroke
physicians assess the modified Rankin Scale (mRS) score in recorded structured interviews 3 months after stroke. The
primary outcome is the degree of disability and death over the full range of the mRS. As a change to the previously
published protocol and only pertinent in case of more than 9% lost-to-follow-up, a co-primary outcome was introduced
consisting of the proportions of death, new institutional care or severe disability in patients with additional use of
information from registration offices.
Perspective: The results will inform parties involved in acute stroke care organization on the effectiveness of the MSU
concept.
(Continued on next page)
© The Author(s). 2019 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0
International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and
reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to
the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver
(http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
* Correspondence: peter.harmel@charite.de
1
Department of Neurology, Charité - Universitätsmedizin Berlin,
Hindenburgdamm 30, 12203 Berlin, Germany
2
Center for Stroke Research, Charité - Universitätsmedizin Berlin, Berlin,
Germany
Full list of author information is available at the end of the article
Neurological Researc
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Harmel et al. Neurological Research and Practice (2019) 1:18
https://doi.org/10.1186/s42466-019-0022-4
(Continued from previous page)
Trial registration: The protocol is registered in (NCT03931616) and has been approved by the ethical review committee
of the Charité –University Medicine Berlin (EA4/109/15) on September 2, 2015. The study protocol of B_PROUD part 1
had been published in the International Journal of Stroke as “Berlin Prehospital Or Usual Delivery of acute stroke care (B_
PROUD) –study protocol”(doi: https://doi.org/10.1177/1747493017700152)onMarch22,2017[1]previoustofirst
patient’s registration.
Keywords: Stroke, Prehospital, Mobile stroke unit, Thrombolysis, Endovascular thrombectomy, Functional outcome
Background
In the event of an acute ischemic stroke, fast recanalization
of the occluded vessel is crucial because of the rapid death
of neurons in ischemic brain tissue [2]. The only
evidence-based measures to achieve tissue reperfusion are
administration of tissue-type plasminogen activator and
endovascular thrombectomy. The Mobile Stroke Unit
(MSU) concept was first introduced in 2008 in Homburg,
Germany [3]. In 2011 the Stroke Emergency Mobile
(STEMO) was implemented in Berlin, Germany and
yielded clear improvements regarding thrombolysis rates
and onset-to-treatment times [4]. Additionally, ischemic
and hemorrhagic stroke patients have been more accurately
routed to hospitals with Stroke Units or neurosurgery de-
partments [5]. In the meantime, the MSU concept has been
implemented in many cities worldwide, and various groups
contribute their experiences to the Pre-hospital Stroke
Treatment Organization (PRESTO) [6]. Yet, despite a
non-significant trend for disability-free survival at 3 months
in favor of the MSU care group in a registry-based analysis
[7,8], definite scientific proof of a positive effect of MSU
treatment on functional outcome of stroke patients is still
lacking.Thus,westartedtheB_PROUDstudyonFebruary
1, 2017 [1]. In the meantime, the STEMO service in Berlin
was extended to three simultaneously operating STEMOs
covering almost the entire Berlin city area. Since logistical
problems occurred during almost the entire first study
period, we recognized the necessity of a revised study
protocol for an additional evaluation during the period
after resolving these challenges. The deviations from the
original STEMO setting during the PHANTOM-S trial [4]
included reduced accuracy of dispatching for stroke emer-
gencies, fewer STEMO dispatches for severe stroke cases
(because general emergency physicians were dispatched to
patients with impaired consciousness or instable vital pa-
rameters instead of the STEMO team), more frequent can-
cellations of the STEMO dispatch (thus leading to more
cross-overs and in-hospital thrombolyses), and longer dis-
tances to scene. These issues led to fewer and more delayed
STEMO interventions and thrombolytic treatments. After
adjustment of the STEMO dispatch organization, we ex-
pect that the use of the dispatch algorithm will be equiva-
lent to its use during the preceding PHANTOM-S trial.
Following the recommendation of the B_PROUD Data
Safety Monitoring Board and in agreement with the Berlin
Department of Internal Affairs, we decided to start a
second part of the B_PROUD study - with full reporting of
the first evaluation period.
Methods
Aim of the trial
Here, we describe a confirmatory trial to prove the effi-
cacy of the MSU intervention compared to regular care
using the modified Rankin Scale (mRS) score 3 months
after event.
Study description and study design
B_PROUD (Berlin Prehospital Or Usual Delivery of acute
stroke care) is a pragmatic, prospective, multicenter study
with blinded outcome assessment (PROBE design). Inclu-
sion of eligible patients is currently carried out in the
metropolitan area of Berlin, Germany, in cooperation with
all 15 stroke centers of various Berlin hospital owners. The
B_PROUD study makes use of the B-SPATIAL registry
(Berlin –specific acute therapy in ischemic or hemorrhagic
stroke with long-term follow-up, NCT03027453) that col-
lects 3 months follow-up assessment on an opt-out basis.
In line with German data-protection legislation and ap-
proval of the Berlin data protection representatives, patients
are informed beforehand about the planned follow-up and
can opt-out at any time before or during the telephone
interview or optional questionnaire based assessment.
Arms and intervention
The intervention group consists of patients for whom an
MSU is deployed by the dispatch center of the Berlin Fire
Department after stroke suspicion during emergency call
[9]. Based on the preceding PHANTOM-S trial [4], ap-
proximately 45% of the stroke alarms are expected to be
handled by regular ambulances because the MSU is already
in operation or undergoing service. Compared to regular
ambulances offering standard of care, the intervention by
MSU includes prehospital neurovascular expertise by a
neurologist staffing the MSU, computed tomography (CT)
based brain scanning including visualization of large vessel
occlusion by CT-angiography, and specific pre-notification
to endovascular treatment capable centers. Details of the
Harmel et al. Neurological Research and Practice (2019) 1:18 Page 2 of 5
STEMO equipment, staffing and operational proce-
dures have been published elsewhere [10,11]. After a
decision of the Berlin state government that STEMO
careshouldbeavailablefortheentirepopulationof
Berlin, two additional STEMOs have been implemented
and gone operational in 2017 and 2018 –under the
condition of an accompanying scientific evaluation on
outcome effects.
Eligibility criteria
All patients calling the emergency services and prompt-
ing a stroke alarm [9] at the dispatch center will be
screened for eligibility. Only treatment candidates de-
fined by the inclusion and exclusion criteria listed in
Table 1will be included in the primary study population
and thus compared for the primary outcome. Thereby,
the screening process is operationalized aiming at a
minimization of selection bias. Monitoring is carried out
continuously for all eligibility criteria. If ascertainment is
uncertain, the clinical documentation is submitted to an
independent adjudication committee for blinded judge-
ment. Additionally, patients with [1] stroke mimics re-
ceiving thrombolysis will be included in a sensitivity
analysis together with the primary study population, and
patients with [2] intracerebral hemorrhage presenting
within 6 h from symptom onset will be analyzed as a
companion study population.
Outcome measures
The primary outcome is the modified Rankin score
(mRS) 3 months after the acute event which is the most
common outcome measure in stroke trials [12]. Since
the type of intervention does not allow blinding of pa-
tients, the structured telephone interviews after 3
months are recorded and subsequently assessed by
stroke experts who are unaware of the treatment arm
allocation. For those patients who remain unreachable
via phone or mail, we use information from registration
offices regarding vital and residential status including
living address. This information allows assessment of
the co-primary outcome consisting of the following
Table 1 Inclusion and exclusion criteria for the study
population
Inclusion criteria:
1. Suspected acute stroke according to the dispatcher stroke
identification algorithm [8] during MSU hours and within
the MSU catchment area
2. Age ≥18 years
Inclusion criteria for the primary study population:
3. Final diagnosis of ischemic stroke (ICD-10: I63) or TIA
(G45 except G45.4)
4. Pre-stroke mRS ≤3 (able to ambulate without assistance)
5. Confirmed onset-to-alarm time ≤4h
Exclusion criteria:
1. Symptom remission until arrival of MSU or regular ambulance
a
2. Malignant or other severe primary disease with life
expectancy < 1 year
Exclusion criteria for the primary study population:
3. Major surgery within last 4 weeks
4. Confirmed stroke within last 3 months
5. Absolute contraindication for both thrombolysis and
endovascular treatment
ICD-10 International Statistical Classification of Diseases and Related Health
Problems 10th revision, mRS modified Rankin Scale, MSU Mobile Stroke Unit,
TIA transient ischemic attack,
a
no acute disabling neurological symptoms
described in emergency medical service (EMS) documentation
Table 2 Outcome measures
Primary outcome measure:
1. Primary outcome: assessment of functional outcome over the entire
range of the mRS
2. Co-primary outcome: assessment of functional outcome including
the following range of outcomes: mRS 0–3 if available, mRS 4–5or
(if mRS is missing) living in institution (information according
registration office at 4 months after stroke), and death
Secondary outcome measures:
1. Thrombolysis rate
2. Endovascular thrombectomy rate
3. Onset-to-treatment time
4. Onset-to-reperfusion time (for endovascular thrombectomy,
Charité centers only)
5. Alarm-to-imaging time
6. Alarm-to-treatment time
7. Imaging-to-treatment time
8. Cost effectiveness (additional costs due to implementation and
running of STEMO, duration of hospital stay regarding acute
treatment and rehabilitation, hospital related costs, costs of
long-term care, and combination of above mentioned)
9. Quality of life (EQ-5D)
10. Shift analyses for mRS ≤1 at 3 months in patients ≤80 years of
age living at home without disability and mRS ≤2 at 3 months in
patients > 80 years of age living at home with help or living in an
institution
11. Secondary ICH after thrombolysis or thrombectomy
12. Symptomatic secondary ICH according to the discharge letter
13. In-hospital mortality
14. Death rate over time (Kaplan-Meier plot)
15. Discharge status (including in-hospital mortality among patients
not included in the primary study population, especially patients
with ICH)
16. Functional outcome among patients with ICH
17. Rate of emergency medical service deliveries to specialized facilities
(patients with large vessel occlusion to endovascular thrombectomy
capable facility, patients with ICH to neurosurgery department)
EQ-5D EuroQol Group 5 dimensions, ICD-10 International Statistical
Classification of Diseases and Related Health Problems 10th revision, ICH
intracerebral hemorrhage, mRS modified Rankin Scale, MSU Mobile Stroke Unit,
TIA transient ischemic attack
Harmel et al. Neurological Research and Practice (2019) 1:18 Page 3 of 5
three categories: ‘1’able to ambulate (mRS 0–3) or (if
mRS not available) living at home, ‘2’living with severe
disability (mRS 4–5) or living in institutional care, and
‘3’death (mRS 6). We introduced this novel outcome
definition within a study protocol amendment during the
first part of the B_PROUD trial in order to use all available
information for the purpose of informing parties involved
in acute stroke care organization on the effectiveness of
the MSU concept. Only if the lost-to-follow-up rate is
higher than 9% in this community nested trial, this out-
come will be used as a co-primary outcome measure. .
Secondary outcomes include performance measures like
thrombolysis and endovascular treatment rates and process
times as well as clinical outcomes such as quality of life and
dichotomized three-months mRS. All outcome measures
are listed in in detail in Table 2.
A continuous reporting system for serious adverse events
of special interests (SAESI) is implemented to check rates
of symptomatic secondary intracerebral hemorrhages
(sICH) or deaths. In case of more than 10 deaths within 7
days (or at discharge, whatever comes first), or more than
10 symptomatic sICH per 100 treatment candidates in the
MSU group, the study has to be stopped after recommen-
dation by an external data safety monitoring board. To ad-
dress the intention-to-treat approach for outcome analyses,
we rigorously consider STEMO availability as determinative
and, for example, count cancellations of STEMO dispatches
to the MSU intervention group.
Sample size estimation
The proposed sample size to be analyzed is 1372 patients
–equal to the sample size of B_PROUD part 1. Sample
size calculation was originally performed in October 2015
based on outcomes seen in a registry-based comparison of
the first 193 patients with pre-hospital thrombolysis on
STEMO and 615 consecutive patients with in-hospital
thrombolysis of the Charité thrombolysis registry. Inclu-
sion of 1500 patients will be necessary, considering 9%
lost-to-follow-up. For the primary outcome, we expect the
following differences (STEMO vs. control group): mRS 0:
21/21%; 1: 21/15%; 2: 7/9%; 3: 20/12%; 4: 11/14%; 5: 5/9%;
6: 15/20%. The Mann-Whitney test with two-sided signifi-
cance level of 0.05 has 80% power to detect such a group
difference in at least 686 patients per group.
In case of more than 9% lost-to-follow-up, the study
will be seen as successful only if both co-primary end-
points (mRS, mRS in three categories: 0–3, 4–5, 6) show
significant better outcome for the intervention using a
two-sided significance level of α= 0.05.
The power calculation was conducted with the
R-Package sample size [13]. Since there is scarce informa-
tion on the possible effect size, an interim analysis for a
blinded sample size re-estimation is planned after primary
outcome assessment of 300 patients.
Contacts
B_PROUD is sponsored by Charité –University Medicine
Berlin, Berlin, Germany via the Center for Stroke Research
Berlin and the excellence cluster NeuroCure, Berlin,
Germany, and funded by German Research Foundation.
The B_PROUD MSU evaluation is conducted in close col-
laboration with the Berlin Fire Department and its medical
lead of EMS as well as with the 15 Berlin stroke centers.
Perspective
While scientific evaluations of the Berlin MSU imple-
mentation so far have shown that pre-hospital thromb-
olysis is safe and associated with a substantial shortening
in time to treatment [4,7], a definite proof of clinical
benefit has not yet been accomplished. The B_PROUD
trial was therefore designed to provide confirmatory
evidence that earlier (pre-hospital) stroke work-up and
treatment leads to better functional outcomes. Recruit-
ment to B_PROUD part 1 was started in February 2017
and is planned to be completed in 2019, concurrent with
a similar trial, the BEST-MSU trial [14]. Despite similar
inclusion criteria of the latter also ensuring the compari-
son of only treatment candidates, our study design al-
lows follow-up of the patients without written informed
consent which may to some extend limit external valid-
ity by introducing a selection bias.
In addition to the primary outcome, the B_PROUD
study will provide valuable information on effects of
earlier treatment (blood pressure lowering and anticoa-
gulation reversal) on hematoma volumes in intracerebral
hemorrhages.
While the time saving approach of the prehospital MSU
concept is intriguing, stakeholders of stroke care need reli-
able information on the effect size of clinical outcomes
and cost-effectiveness. The expected benefits in outcome
and potentially reduced costs for hospital and long-term
care need to be weighed against additional costs of imple-
mentation and running not only a single but three STE-
MOs. B_PROUD and parallel studies such as BEST-MSU
[14] are designed to provide the needed data and will
therefore support future decision making.
Abbreviations
B_PROUD: Berlin Prehospital Or Usual Delivery of acute stroke care; BEST-
MSU: Benefits of Stroke Treatment Delivered Using a Mobile Stroke Unit; B-
SPATIAL: Berlin - specific acute therapy in ischemic or hemorrhagic stroke
with long-term follow-up; CT: Computed tomography; EMS: Emergency
medical service; EQ-5D: EuroQol Group 5 dimensions; ICD10: International
Statistical Classification of Diseases and Related Health Problems 10th
revision; ICH: Intracerebral hemorrhage; mRS: Modified Rankin scale;
MSU: Mobile Stroke Unit; PHANTOM-S: Pre-Hospital Acute Neurological
Therapy and Optimization of Medical care in Stroke patients; PRESTO: Pre-
hospital Stroke Treatment Organization; PROBE: Prospective randomized
open blinded end-point; SAESI: Serious adverse events of special interests;
sICH: secondary intracerebral hemorrhage; STEMO: Stroke Emergency Mobile;
TIA: Transient ischemic attack
Harmel et al. Neurological Research and Practice (2019) 1:18 Page 4 of 5
Acknowledgements
We thank the Berlin Fire Department for the productive and long-lasting
cooperation.
Funding
B_PROUD is funded by the German Research Foundation (project number
EB 525/2–1).
Availability of data and materials
At individual level and adhering to the General Data Protection Regulation,
every patient has the right to get access to their personal data. Data are
available upon request.
Authors’contributions
PH: Design of database; drafted and revised the manuscript; performed
literature search; prepared tables. ME: Conceived and designed the study;
organized study funding; commented on the manuscript. EF: Coordinates
screening procedure; commented on the manuscript. UG: Planning of
statistical analysis; power calculation; reviewed and commented on the
manuscript. IL-M: Coordinates data entry; commented on the manuscript. IN:
Monitors data entry; supervises safety outcomes; critical revision to the
manuscript and tables. CHN: Contributed to the study design; critical revision
to the manuscript and tables. BS: Lead data acquisition; contributed to the
study design; revised the manuscript. HJA: Conceived and designed the
study; organized study funding; drafted and revised the manuscript. All
authors read and approved the final manuscript.
Ethics approval and consent to participate
The ethical review committee of the Charité –University Medicine Berlin
(EA4/109/15) has given ethics approval on September 2, 2015. B_PROUD is
embedded in the ‘Berlin - specific acute therapy in ischemic or hemorrhagic
stroke with long-term follow-up’(B-SPATIAL) registry that has been estab-
lished to assess process and outcome quality of hyperacute stroke care in
Berlin. Since B-SPATIAL constitutes a quality registry, all patients are automat-
ically included if they fulfill the inclusion criteria of the registry that also
covers all inclusion criteria of the B_PROUD trial. With regard to the follow-
up assessment process, an opt-out clause ensures the patient’s right to re-
tract participation at any time before contact, during follow-up or even after-
wards. Patients are informed with an information leaflet at discharge and
again approximately 4 weeks before telephone follow-up.
Consent for publication
As described above and due to quality assurance issues, no written
agreement from the patient is needed beforehand. However, patients are
contacted at discharge or postally, and informed about the use of their
anonymized data in scientific publications. Again, it is the patients’right to
opt-out at any time before contact, during follow-up or even afterwards.
Competing interests
The authors declare that they have no competing interests.
Publisher’sNote
Springer Nature remains neutral with regard to jurisdictional claims in
published maps and institutional affiliations.
Author details
1
Department of Neurology, Charité - Universitätsmedizin Berlin,
Hindenburgdamm 30, 12203 Berlin, Germany.
2
Center for Stroke Research,
Charité - Universitätsmedizin Berlin, Berlin, Germany.
3
Department of
Neurology, Medical Park Berlin Humboldtmühle, Berlin, Germany.
4
Institute of
Biometry and Clinical Epidemiology, Charité - Universitätsmedizin Berlin,
Berlin, Germany.
5
Berlin Institute of Health (BIH), Berlin, Germany.
6
German
Centre for Cardiovascular Research (DZHK), Partner Site, Berlin, Germany.
7
German Center for Neurodegenerative Diseases (DZNE), Partner Site, Berlin,
Germany.
Received: 24 January 2019 Accepted: 14 April 2019
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