Prehospital Stroke Care Part 2: On-Scene Evaluation and Management by Emergency Medical Services Practitioners

Abstract

The prehospital phase is a critical component of delivering high-quality acute stroke care. This topical review discusses the current state of prehospital acute stroke screening and transport, as well as new and emerging advances in prehospital diagnosis and treatment of acute stroke. Topics include prehospital stroke screening, stroke severity screening, emerging technologies to aid in the identification and diagnosis of acute stroke in the prehospital setting, prenotification of receiving emergency departments, decision support for destination determination, and the capabilities and opportunities for prehospital stroke treatment in mobile stroke units. Further evidence-based guideline development and implementation of new technologies are critical for ongoing improvements in prehospital stroke care.

I. Introduction

Acute stroke care is demonstratively time sensitive; “minutes matter” when acute reperfusion is a treatment option for acute ischemic stroke (AIS) and when hematoma expansion mitigation therapies are considered in hemorrhagic stroke (HS). To facilitate efficient diagnosis and treatment, focus has turned to the prehospital phase of acute stroke care. Accurate stroke screening, including severe stroke syndromes indicative of HS or AIS from a large vessel occlusion (LVO) amenable to endovascular therapy (EVT), can lead to rapid treatment at an appropriately-resourced stroke center.^1,2 Emerging technologies tailored for out-of-hospital use can help optimize the prehospital phase of acute stroke care (Figure). Ultimately, however, clinical and technological advances that lead to universally high-quality prehospital stroke care depend on reliable implementation of evidence-based guidelines.

Critical actions for on-scene and in-transit prehospital stroke care, with current state practices and future innovations. EMS = emergency medical services, CT – computed tomography, CTA – CT angiography, GPS – global positioning system, IR – interventional radiology, MSU = mobile stroke unit.

This article is the second in a two-part topical review series on the current state of the science in prehospital stroke care. The companion article discussed the prehospital phase of stroke systems of care.³ This article presents detailed considerations related to the prehospital evaluation and management of patients with suspected stroke.

II. On-Scene Screening for Acute Stroke

Prehospital Stroke Identification

To maximize opportunities for acute stroke treatment, several prehospital stroke screening (PSS) tools have been developed to aid stroke recognition by emergency medical services (EMS) practitioners. PSSs typically include a combination of physical exam components that can be performed quickly and reliably to identify a localizing neurological deficit. Additionally, some PSSs incorporate glucose measurement, patient demographic information (e.g., age), and historical features (e.g., seizure history) to improve the predictive value of a positive PSS.

A Cochrane review identified 16 EMS-based validation studies of 8 existing PSSs.⁴ PSSs generally have favorable positive predictive values (34-58%) and sensitivity (64%) for stroke, and their use is associated with improved EMS stroke recognition.^5,6 Among commonly used PSSs, the Cincinnati Prehospital Stroke Scale (11 included studies) appeared to have the highest sensitivity for stroke, whereas the Los Angeles Prehospital Stroke Screen (5 studies) and the Melbourne Ambulance Stroke Screen (3 studies) had higher specificity.⁴

While identifying favorable performance of PSS, this review noted important limitations in published research, including significant selection bias and inconsistent reporting of how and when PSSs were used during patient encounters.⁴ Additionally, local stroke prevalence affects PSS test characteristics. Despite widespread use and demonstrated prehospital utility, most PSSs screen for anterior circulation AIS syndromes. In contrast, newer PSSs, such as the Balance Eyes Face Arm Speech Time tool, include posterior circulation screening, though in-field validation has not demonstrated improved accuracy.^7,8

Despite their limitations, PSSs help EMS practitioners identify the presence of stroke, and their routine use is recommended by international guidelines.^1,9 In fact, documentation of the use of a PSS is the only stroke quality measure currently endorsed by the National EMS Quality Alliance.¹⁰

Prehospital Stroke Severity Screening

Following the publication of trials demonstrating clear benefit of EVT for select patients with LVO,¹¹ significant attention has been directed to identifying patients eligible for EVT as early as possible in their clinical course. The benefits of EVT are time-dependent,¹² yet only 64% of the United States population has access to an EVT-capable hospital within 60 minutes.¹³ Furthermore, interfacility transfers are associated with significant delays in treatment, which may even preclude the opportunity for reperfusion.¹⁴ Therefore, beyond simply screening for the presence or absence of stroke with basic PSSs, there has been increasing interest in equipping EMS practitioners with the tools and knowledge to assess the severity of stroke symptoms in order to identify patients most likely to benefit from direct transport to a stroke center capable of treating HS and providing EVT.

Numerous stroke severity screening tools have been developed through modification and simplification of the National Institutes of Health Stroke Scale (NIHSS). A 2018 review demonstrated moderately high sensitivity and specificity of the Los Angeles Motor Scale, Cincinnati Stroke Triage Assessment Tool (formally known as the Cincinnati Prehospital Stroke Severity Score), and the 3-Item Stroke Scale; however, only 2 included studies were conducted in the prehospital environment.¹⁵ Since this review, several prehospital-based studies have reported the performance of new prehospital stroke severity screens, including Field Assessment Stroke Triage for Emergency Destination (FAST-ED), Los Angeles Motor Scale , Cincinnati Prehospital Stroke Scale (based on quantifying the three elements), Cincinnati Stroke Triage Assessment Tool, Vision Aphasia Neglect scale, Rapid Arterial Occlusion Evaluation, Austrian Prehospital Stroke Scale, and Ventura Emergent LVO Score.^16,17 Prevalence of LVO was highly variable in these studies (5-30%), as some included all patients with EMS-suspected stroke while others studied patients with confirmed AIS. Three studies have directly compared multiple scales, but none has identified a clearly superior scale.^16–18 Ultimately, stroke severity screens demonstrate moderately high sensitivity and specificity (60-80%), but none are diagnositc.^16,17 However, future innovations hold the potential for enhanced stroke severity screening, adjusting an individual’s pretest probability based on patient-level factors and point-of-care biomarkers.^19,20

An additional challenge in interpreting and implementing prehospital stroke severity screening for routine use by EMS practitioners is determining the optimal diagnosis for which a stroke severity screen is designed to detect. In Part 1 of this series, the authors describe at length the considerations of direct transport to a higher level of stroke center based on prehospital stroke severity screening.³ Often, stroke severity screens are conceptualized and described as “LVO screens.” However, if the destination hospital changes based on the result of the stroke severity screen, then conceptually the diagnosis of interest should be matched with the capabilities of the receiving stroke center. This is an important distinction in current stroke care wherein two levels of advanced stroke center are recognized by most stroke center certifying bodies – thrombectomy capable stroke centers (TSC) that can offer ready access to EVT and comprehensive stroke centers (CSC) that provide EVT as well as ready access to neurosurgical and neurointensive care for HS patients.² Because there is overlap in how LVO and HS present clinically, particularly in terms of exam elements included in stroke severity screens, distinguishing LVO from HS exclusively using stroke severity screens may not be possible. Additionally, nearly 20% of patients with LVO have an NIHSS score <6, which is the current guideline severity indication for EVT.^1,21 Of course, patients with lower NIHSS with LVO may still be eligible for EVT based on clinical judgement and in the context of clinical trials, but to build systems of care around exceptions to current guideline recommendations is imprudent.

Lastly, even if severe stroke (i.e., LVO or HS) is identified using severe stroke screening, the most appropriate receiving hospital remains a question of open inquiry. Currently, the American Heart Association/American Stroke Association (AHA/ASA) recommends that patients with a severe stroke syndrome be transported to a CSC if the additional transport time is not prohibitive.² However, this strategy may result in a delay to and lower rate of thrombolysis.²² Additionally, patients with HS may benefit from airway stabilization, blood pressure management, and anticoagulant reversal at a primary stroke center prior to transfer. Understanding the optimal destination for stroke patients is an area of active research, and implementing differential destination protocols requires a broader interpretation of stroke severity screening as more than simply LVO screens.

Emerging Technology for On-Scene Patient Evaluation

Artificial Intelligence Assisted Clinical Assessments

Accurate and precise stroke screening using PSSs and stroke severity screens alone is inherently limited because of several factors, including the dynamic nature of stroke, challenges to detailed on-scene neurological examinations, and the overall low prevalence of stroke compared with all EMS dispatches. Emerging technologies hold the promise of improving the accuracy of prehospital stroke screening by assisting EMS practitioners during their clinical evaluation of suspected stroke patients.²³ One innovation is leveraging artificial intelligence (AI) to detect subtle physical exam findings of stroke that may not be detected by most EMS practitioners. Proof-of-concept studies of facial weakness exist, but this technology currently remains in its infancy.²⁴ A future vision of this applied technology could have EMS practitioners use a handheld camera with AI visual recognition software.

Portable Diagnostic Technologies

Portable technology holds the promise of expanding from prehospital stroke screening to stroke diagnosis. Emerging technologies have focused on distinguishing stroke from non-stroke diagnoses as well as differentiating types of acute stroke using portable platforms. Devices using myriad technologies, including electroencephalogram (EEG), somatosensory evoked potentials, transcranial doppler (TCD), volumetric impedance phase shift spectroscopy, microwaves, and accelerometers, are currently in development for the out-of-hospital setting.

EEG-based devices use a limited number of lead tracings to detect asymmetry, producing a binary output indicating a high or low likelihood of AIS. Brainscope One has shown a sensitivity of 91.7% but low specificity of 50.4%.²⁵ Alphastroke uses EEG and somatosensory evoked potentials with 80% sensitivity and specificity for LVO detection.²⁶

TCD is a well-established technology that has a high sensitivity and specificity to detect LVO.²⁷ Robotic TCD technology has facilitated its application in the prehospital setting. One such device, the Lucid M1 Robotic TCD System, uses a machine learning algorithm to interpret TCD signals with a sensitivity and specificity of 90.9% and 87.9%.²⁸

Volumetric impedance phase shift spectroscopy uses electromagnetic waves of diverging frequencies directed through the patient’s skull, detecting patterns of modification by brain tissue fluid and electrical properties. The most tested device, Cerebrotech Visor, can identify large AIS and HS with 93% sensitivity and 87% specificity.²³

The StrokeFinder MD100 is a helmet with an array of antennae that emits microwaves, using a spectrum analyzer to determine asymmetry. Proof-of-principle studies have demonstrated the ability to distinguish between AIS and HS in up to 65% of patients.²⁹

Accelerometer-based technologies, like Head Pulse and BrainPulse, temporally correlate pulsatile blood flow in the brain with a simultaneous electrocardiogram, and lack of expected correlation indicates abnormal cerebral blood flow. Head Pulse has demonstrated 73% sensitivity and 87% specificity in detecting LVO.³⁰

These innovations hold the promise of improving the ability of EMS practitioners to discern among stroke mimics, AIS, LVO, and HS beyond a degree of accuracy that clinical screening scales would be expected to achieve. As the accuracy of new devices improve and as devices are designed specifically for use in an ambulance, further clinical evaluation and implementation testing is expected. Once device performance is optimized, additional challenges to implementation, including device approval, EMS practitioner education, and incorporation into routine EMS workflow, will need to be addressed to facilitate widespread adoption.

Virtual On-Scene Decision Support through Ambulance-Based Telestroke

“Telestroke” is the evaluation of a patient with suspected stroke by a remote stroke specialist using a real-time audio-visual connection and has been a mainstay of acute stroke care in hospitals without access to real-time in-person stroke specialist consultation. Ambulance-based telestroke (ABT) is an innovation with the potential to facilitate rapid stroke treatment by enabling stroke specialist evaluation prior to hospital arrival. In fact, an AHA/ASA scientific statement suggested that ABT holds promise as a novel solution to improving the accuracy of prehospital stroke screening, facilitate prehospital stroke diagnosis, and shorten time to treatment.³¹

The Improving Treatment with Rapid Evaluation of Acute Stroke via Mobile Telemedicine study deployed a tablet device, 4G LTE modem, externally mounted antennae, and an encrypted videoconference application in standard ambulances of two EMS agencies. EMS practitioners initiated notification to the receiving hospital’s stroke physician who had access to a high-quality tablet-based endpoint unit to perform a patient assessment with assistance from local EMS practitioners.^32,33 This early ABT research demonstrated clinical value with high inter-rater reliability, but transmission instability via second generation cellular technology was common and limited effective implementation.³⁴ However, with improvements in high-capacity bandwidths and prioritization of emergency broadband communication, more recent studies have demonstrated significant improvements in wireless reliability.^{32,33,35–39}

Several additional limitations exist to wide-spread implementation of ABT. Beyond connectivity, technological challenges included unscheduled software updates, uncharged batteries, and use of non-compatible equipment.^33,36,37 As technology has improved, other studies have identified modifiable human and operational barriers to effective ABT implementation, including usability of software and equipment, end user perceptions, and additional workload.^33,38–42 One study revealed that mount location, camera design, and paramedic seat size were factors that interfered with effective ABT.⁴³ More broadly, an ABT hub must have a well-established telemedicine system with technical support to facilitate high-quality ABT. Additional logistical considerations include cost of implementation, effect of over-activation on stroke specialists, and reimbursement eligibility. Integration of ABT into existing EMS systems, including the interaction among ABT stroke specialists, EMS medical directors, and online medical control for EMS practitioners, continues to be nascent.

Ultimately, however, any innovation that improves the accuracy of prehospital stroke screening or diagnosis should be expected to have a discernable positive impact on patients’ overall clinical course because of their potential to extend prehospital time. This downstream impact could be myriad, including faster emergency department evaluation, changes to prehospital management, and changes in hospital destination. However, if an innovation adds time to the prehospital phase of care without positively influencing any downstream action, implementation may be counterproductive.

III. On-Scene and In-Transit Interventions for Acute Stroke Patients in Conventional EMS Systems

Prehospital Medications and Interventions

In most EMS systems, even when EMS practitioners accurately identify stroke, prehospital stroke treatment is typically supportive. For example, one critical component of prehospital stroke care is close monitoring for neurological decompensation. If necessary, paramedics can intervene to secure a patient’s airway through advanced procedures such as endotracheal intubation. However, for EMS systems with emergency medical technicians (EMTs) only, airway management strategies are more limited, as EMTs typically can only use non-invasive airway management procedures.

Medications for blood pressure management, such as metoprolol, hydralazine, and diltiazem, may be available depending on local protocols, though medications to treat blood pressure are typically limited.⁴⁴ However, in the absence of confirmatory imaging to establish a diagnosis of AIS or HS, even when antihypertensive agents are available, aggressive blood pressure management should be deferred.¹ A broader range of medications is available to critical care paramedics and nurses performing interfacility critical care transport in mobile intensive care units after stroke has been diagnosed.

Conceptually, there exist opportunities for EMS practitioners in conventional EMS systems to treat a patient with stroke very early in their clinical course while still agnostic to the final stroke diagnosis, and several clinical trials of prehospital stroke inventions have completed or are currently enrolling. These interventions include magnesium, lisinopril, nitroglycerin, nerinetide, and remote ischemic conditioning.^45–49 To date, completed studies have not shown clinical benefit, and in fact enrollment in the Multicentre Randomised Trial of Acute Stroke Treatment in the Ambulance with a Nitroglycerin Patch was stopped early because of safety concerns for patients with HS.⁵⁰ Lastly, although the Head Positioning in Acute Stroke Trial did not define optimal head positioning for acute stroke patients, elevation of the patient’s head to 30 degrees during transport may be reasonable to facilitate airway protection and monitoring during transport.⁵¹

Prearrival Notification of the Receiving Stroke Center

To facilitate rapid diagnosis and treatment in the emergency department, a smooth and efficient transition from the prehospital to hospital setting is critical. In most EMS systems, this process starts with stroke-specific prearrival notification of the receiving hospital by EMS practitioners (i.e., “prenotification”). In response to prenotification, emergency departments can ensure that staff and equipment are immediately available upon patient arrival. With sufficiently accurate information, downstream processes for patients with LVO can be initiated prior to patient arrival, including summoning the endovascular team or planning for rapid interfacility transfer at hospitals without EVT capability. Prenotification has been associated with reduced in-hospital mortality.⁵²

Effective stroke prenotification includes the patient’s age, PSS and stroke severity screen findings, vital signs, blood glucose measurement, any obvious contraindications to thrombolysis, last known well (LKW) time, and symptom discovery time. While typical prenotification is performed via non-encrypted radio, if secured channels are available, communicating patient identifiers and power of attorney contact information can facilitate prearrival registration and review of the patient’s electronic medical record. In some EMS systems, prenotification can also help to determine hospital destination. For example, in New York City, patients with a positive stroke severity screen are transported to a TSC or CSC, but only after discussion with online medical direction.⁵³

Emerging Technology for Assisting Prehospital Communication and Destination Decisions

To optimize efficient and accurate information transfer during prenotification, a number of applications have been developed, including Twiage, Stop Stroke (Pulsara), CodeStroke Alert, and Join (Allm Inc Japan).²³ These apps have the benefit of utilizing an encrypted connection between the ambulance and hospital for communicating real-time patient information.

The proliferation of global positioning systems (GPS) in hand-held devices has enabled the possibility for technology-assisted destination algorithms to identify the closest appropriate stroke center. A proof-of-concept study using Google Maps AI has modeled how dynamic routing can incorporate time of day and learned traffic patterns.⁵⁴ The FAST-ED app maps locations of TSC and CSCs in a geographic region to facilitate GPS-enabled navigation.⁵⁵ An overarching platform, however, remains on the horizon.

IV. Mobile Stroke Units as an Emerging Innovation for Prehospital Diagnosis and Treatment

Diagnostics and Therapeutics in a Mobile Stroke Unit

Even in the highest performing EMS systems, prehospital transport time comprises a significant portion of the duration from ambulance dispatch to revascularization for patients with acute stroke.⁵⁶ Mobile stroke units (MSUs) are licensed ambulances equipped with neuroimaging technology, stocked with advanced therapeutics (including thrombolytics), and staffed with trained personnel. The goal of MSUs is to enable rapid diagnosis and treatment of patients with neurovascular emergencies in the prehospital setting by eliminating prehospital transport time and bringing diagnostics and therapeutics directly to the patient, namely thrombolytics for patients with AIS.^57,58 Fassbender and colleagues proposed the modern MSU concept in 2003, later implementing the first MSU in Saarland, Germany, in 2008.^59,60 Since that time, MSUs now exist on all inhabited continents except Africa.⁶¹

Non-contrast head computed tomography (CT) capability is universal to all MSUs, with most using an 8-slice portable head CT scanner.⁵⁷ The first MSU to use a 16-slice total body CT scanner was deployed in 2016 with the capability for aortic arch, neck, and head CT angiography (CTA).⁶² The technical capability to perform CT perfusion (CTP) exists in MSUs with CTA, provided CTP processing software is available. However, routine use of MSU CTP has not been reported for a variety of reasons, including that CTP may not be necessary to determine if EVT is indicated for most patients evaluated in the MSU during the hyperacute phase of AIS. Additionally, its utility in early pilots has been tempered by image acquisition time, contrast load, and limited opportunities to influence arrival destination based on the MSU CTP. The future may even see the use of small, rapid magnetic resonance imaging devices capable of acquiring stroke-specific sequences within 20 minutes.⁶³ Routine repeat non-contrast CT imaging upon hospital arrival is not recommended for MSU CT images with adequate quality, as this slows time to definitive EVT in patients with LVO, thereby reducing the potential benefit of MSUs.⁶⁴ However, like any patient receiving thrombolysis, repeat imaging in patients transported via MSU is prudent in patients with neurological decline and as part of routine post-thrombolysis surveillance.

Staffing fulfills the dual mission of MSUs as a fully licensed transport ambulance and a site of advanced stroke care.⁵⁷ MSU vehicle operators are typically EMTs that can competently and safely operate the MSU, including vehicle leveling during CT acquisition. Image acquisition requires a licensed CT technologist on board the MSU. General patient care is typically performed by a paramedic and/or nurse. Some programs use an on-board physician or advanced neurovascular nurse practitioner to direct acute stroke management.^57,62,65,66 Other MSU programs replace the on-board stroke specialist with ABT, allowing the stroke specialist to be available for consultations other than from the MSU.⁶⁷ Some MSUs are fully-integrated into local EMS operations, allowing MSU personnel to use local EMS protocols for non-stroke emergencies, while taking direction for acute stroke management from the stroke specialist.⁶⁵

Several stroke-specific treatments are available to patients in an MSU. Tissue plasminogen activator treatment was first reported on an MSU in 2008.⁶⁰ In addition to thrombolytics, several acute therapeutics unique to MSUs can also be administered because CT imaging is performed in the prehospital setting, including antihypertensives for rapid blood pressure control. Most MSUs also carry anticoagulant-specific reversal agents for treatment of coagulopathic HS, including 4-factor prothrombin complex concentrate, andexanet alfa, and idarucizumab. The Recombinant Factor VIIa for Hemorrhagic Stroke Treatment at Earliest Possible Time trial is studying the effect of recombinant factor VIIa when administered in an ultra-early time window from stroke onset in non-coagulopathic HS patients, and MSUs participating as enrolling sites are expected to facilitate increased enrollment.⁶⁸

Impact of Mobile Stroke Units on Patient Outcomes

Since the first report of successful thrombolysis in an MSU, numerous studies support the safety of MSU thrombolytic administration and have consistently reported significantly faster treatment times than in conventional EMS systems.^{60,62,69–71} A meta-analysis of early MSU experience demonstrated a 30-minute reduction in LKW to thrombolysis and a signal toward improved clinical outcomes, with a 65% increased odds of an excellent clinical outcome for patients treated in an MSU.⁷¹ Two large prospective non-randomized controlled trials have since demonstrated improved clinical outcomes for patients with AIS receiving thrombolysis in MSUs compared with standard care. The Berlin Pre-hospital Or Usual Delivery of stroke care (B_PROUD) and Benefits of Stroke Treatment Using a Mobile Stroke Unit (BEST-MSU) studies showed that MSU treatment resulted in increased thrombolysis rates, shortened LKW to treatment time, and improved functional outcomes at 90 days without increased safety concerns.^69,70

Successful MSU implementation requires close collaboration with EMS medical directors and local EMS practitioners. Typically, MSUs are dispatched simultaneously with local EMS. Some models also permit a secondary request by on-scene EMS practitioners and allow for rendezvous models wherein the MSU meets a transporting local EMS crew en route to the hospital. Because of the time-sensitive nature of the response, accurate stroke identification during the 9-1-1 call facilitates optimized utilization of the MSU, and on-going training of emergency medical dispatchers, EMS practitioners, and MSU personnel facilitates teamwork and timely patient treatment and transport. With the proliferation of MSU programs internationally, many examples of successful incorporation into existing EMS systems exist.^72,73

While MSUs effectively facilitate thrombolysis compared to standard care, their superiority for patients with LVO remains unproven. A recent meta-analysis demonstrated an overall neutral effect of MSUs on the time from ambulance dispatch to EVT arterial access for all MSU-transported patients with LVO.⁷¹ However, a positive effect has been demonstrated for patients diagnosed with LVO in the MSU who subsequently receive EVT.^64,74 Therefore, standardization of MSU protocols to include expanded appropriate use of CTA may be a strategy to ensure direct transport of patients with LVO to EVT-capable hospitals and rapid EVT through direct transport to the angiography suite. Ultimately, however, the decision to pursue CTA in the MSU may also be dependent on the capabilities of the MSU CT and receiving hospital imaging protocols. For example, if vessel imaging at an individual TSC or CSC is routinely deferred to the angiography suite for patients with high suspicion for LVO, MSU CTA imaging may not provide additional benefit.

Despite the proven clinical benefits of MSUs, one barrier to wide-spread implementation of MSUs has been the significant financial investment and operational costs of MSU programs.^75–77 However, both B_PROUD and BEST-MSU demonstrated cost-effectiveness of MSUs, with a reported incremental cost-effectiveness ratio of €41,000 and $34,000 per Quality Adjusted Life Year , respectively. Cost effectiveness of MSUs appears to be affected by stroke prevalence in the MSU catchment area, MSU thrombolysis rate, and baseline functional status of treated patients.⁶¹ Lastly, MSU-specific reimbursement models acknowledging the unique care provided in MSUs do not currently exist and do not sufficiently reflect the complex patient care performed in MSUs.

V. Stroke Guideline Implementation in EMS Protocols

Certain challenges limit immediate, effective implementation of scientific advances into EMS clinical care and operations.⁷⁸ First is the awareness of individual EMS medical directors, administrators, and EMS practitioners about advances in recommended management strategies and associated metrics to incorporate into EMS protocols and quality improvement initiatives. The rapid publication pace of new scientific literature on stroke, which may or may not be targeted directly toward EMS practitioners, makes dissemination and incorporation of this knowledge challenging for individual EMS systems. Implementation efforts, including EMS practitioner education, must not only consider new science and guideline recommendations but interpret these advances in the context of local EMS system operations.

Evidence-based guidelines (EBGs) represent a structured synthesis of all available literature relevant to a clinical or operational topic, with recommendations based on acceptable scientific evidence and often with input from multi-disciplinary experts.⁷⁹ EBGs aim to facilitate the dissemination and incorporation of new knowledge and to limit unwarranted variations in patient care. Highest-quality EBGs provide recommendations based on a systematic review of the literature and use a structured approach to evidence evaluation to grade the quality of included evidence and strength of individual care recommendations.^80,81 Furthermore, following the National Model for Prehospital EBGs, sample protocols and other implementation tools should be created in tandem with EBG publication to facilitate timely dissemination and implementation into individual EMS systems.⁸²

Multiple EBGs have been published addressing the prehospital evaluation and management of patients with suspected stroke.^{1,2,9,83–89} These EBGs have been developed and/or supported by international organizations, including the AHA/ASA, the Heart and Stroke Foundation (Canada), the European Academy of Neurology, the European Stroke Organization, the Chinese Stroke Association, and the Stroke Foundation (Australia). Most stroke-related guidelines incorporate prehospital care recommendations into broader guidelines addressing inpatient and post-acute care.^1,83–88 However, several guidelines have a specific focus on prehospital stroke care.^2,9,58,89

Such EBGs have addressed a wide range of important topics pertinent to prehospital stroke care. Several guidelines have addressed layperson education to better recognize stroke and to activate EMS^{1,2,9,83,85,86,89} and subsequent ambulance dispatch.^1,85,86,88 There has also been a focus on how EMS practitioners evaluate potential stroke patients, including performance of PSSs,^{1,9,83,85–87,89} stroke severity screening,^{1,9,83–85,89} and transport recommendations, including air versus ground transport from a scene.^{1,2,9,83–85,88,89} Finally, some guidelines have focused on specific aspects of stroke care, including assessing patients potentially eligible for EVT,⁸⁹ prehospital pediatric stroke care,⁸⁷ and care of suspected stroke patients during the COVID-19 pandemic. EMS medical directors and administrators are well-served to consider high-quality EBGs when updating and implementing prehospital care protocols and EMS practitioner education.

VI. Conclusion

Prehospital care has the potential to significantly impact overall acute stroke care. Prehospital screening for stroke and severe stroke, determining hospital destination based on screening information and stroke center availability, and notifying the receiving stroke center are patient care practices that EMS systems currently utilize to facilitate rapid care of stroke patients. Emerging technology is allowing for more advanced prehospital evaluation and treatment of patients, currently through MSU programs and in the future through expanded use of telestroke and other technology-enabled modalities. However, implementation of current and future innovations in EMS systems requires high-quality EBGs and implementation strategies. Ultimately, prehospital care provides continued promise for coordinated hyperacute treatment of patients experiencing stroke.

Non-standard Abbreviations and Acronyms

ABT

Ambulance-Based Telestroke

AHA/ASA

American Heart Association/American Stroke Association

AI

Artificial Intelligence

AIS

Acute Ischemic Stroke

B_PROUD

Berlin Pre-Hospital or Usual Delivery of Stroke Care

BEST-MSU

Benefits of Stroke Treatment Using a Mobile Stroke Unit

CSC

Comprehensive Stroke Centers

CT

Computed Tomography

CTA

Computed Tomography Angiography

CTP

Computed Tomography Perfusion

EBG

Evidence-Based Guideline

EEG

Electroencephalogram

EMS

Emergency Medical Services

EMT

Emergency Medical Technician

EVT

Endovascular Therapy

FAST-ED

Field Assessment Stroke Triage for Emergency Destination

GPS

Global Positioning Systems

HS

Hemorrhagic Stroke

LKW

Last Known Well

LVO

Large Vessel Occlusion

MSU

Mobile Stroke Unit

NIHSS

National Institutes of Health Stroke Scale

PSS

Prehospital Stroke Screening

TCD

Transcranial Doppler

TSC

Thrombectomy Capable Stroke Centers