Acute Stroke Management — Part 1: Prehospital Recognition, ED Evaluation & Neuroimaging

1. Stroke Classification and Pathophysiology

1.1 Ischemic Stroke (87% of All Strokes)

Ischemic stroke results from occlusion of a cerebral artery, leading to focal brain ischemia and infarction. The ischemic penumbra — tissue surrounding the infarct core that is hypoperfused but potentially salvageable — forms the basis for all acute reperfusion therapies.¹

Subtypes by Mechanism (TOAST Classification)

Large Vessel Occlusion (LVO)

Large vessel occlusions account for approximately 25-40% of acute ischemic strokes and produce the most devastating outcomes. LVO is defined as occlusion of the intracranial internal carotid artery (ICA), proximal middle cerebral artery (M1 or proximal M2 segment), or basilar artery. Identification of LVO is critical because these patients are candidates for endovascular thrombectomy.²

1.2 Hemorrhagic Stroke

Intracerebral Hemorrhage (ICH) — 10% of All Strokes

Spontaneous (non-traumatic) bleeding into the brain parenchyma, most commonly caused by hypertensive arteriopathy (affecting deep perforating arteries) or cerebral amyloid angiopathy (affecting cortical and leptomeningeal vessels). ICH carries a 30-day mortality of 30-50% and accounts for a disproportionate share of stroke-related disability.³

Subarachnoid Hemorrhage (SAH) — 3% of All Strokes

Bleeding into the subarachnoid space, most commonly from rupture of an intracranial saccular aneurysm (~85%). Presents with sudden-onset severe headache (“thunderclap headache”) with or without focal neurological deficits. SAH carries an overall mortality of approximately 25-50%, with an additional 30% of survivors experiencing significant morbidity.⁴

1.3 Transient Ischemic Attack (TIA)

TIA is defined as a transient episode of neurological dysfunction caused by focal brain, spinal cord, or retinal ischemia, without acute infarction on imaging. The tissue-based definition (absence of infarction on diffusion-weighted MRI) has replaced the older time-based definition (symptoms lasting < 24 hours). Approximately 10-15% of patients with TIA will have a stroke within 90 days, with the highest risk in the first 48 hours.⁵

2. Prehospital Recognition and Stroke Scales

2.1 EMS Activation and Stroke System of Care

Prehospital recognition of stroke is the critical first link in the chain of acute stroke care. The major professional societies recommend:^{1 6}

• Public education campaigns emphasizing stroke warning signs
• 9-1-1 activation for any suspected stroke symptom
• EMS dispatch protocols that prioritize stroke calls
• Prehospital stroke screening using validated scales
• Prehospital notification of the receiving stroke center
• Transport to the highest-level stroke center within a reasonable transport time
• Goal: EMS scene time < 15 minutes for suspected stroke

2.2 Prehospital Stroke Screening Scales

Cincinnati Prehospital Stroke Scale (CPSS)

The most widely used prehospital screening tool. Assesses three items; any single abnormality has a sensitivity of approximately 66-80% and specificity of 85-90% for stroke.⁷

Interpretation: Any single abnormality = positive screen → activate stroke protocol.

Los Angeles Motor Scale (LAMS)

A brief motor examination tool validated for identifying both stroke and LVO in the prehospital setting.⁸

Total score: 0-5

Rapid Arterial oCclusion Evaluation (RACE) Scale

A more comprehensive prehospital scale designed specifically to identify LVO candidates for direct transport to endovascular-capable centers.⁹

Total score: 0-9

Field Assessment Stroke Triage for Emergency Destination (FAST-ED)

Total score: 0-10. Score ≥ 4 suggests LVO (sensitivity ~60%, specificity ~90%).¹⁰

Vision, Aphasia, Neglect (VAN) Assessment

A cortical function screen designed to detect LVO by identifying cortical signs rather than motor deficits alone. The VAN assessment is performed only if a basic motor screen (face, arm, speech) is positive.¹¹

Interpretation: Positive motor screen + any VAN positive = high probability of LVO → consider direct transport to comprehensive stroke center.

2.3 Prehospital LVO Triage — Scale Comparison

3. Emergency Department Evaluation

3.1 Time Targets

The fundamental principle of acute stroke care is minimizing time from symptom onset to definitive treatment. The following benchmarks are recommended by the major stroke and cardiovascular professional societies:^{1 6}

3.2 Initial Assessment

Airway, Breathing, Circulation

• Assess airway patency; intubate if GCS ≤ 8 or inability to protect airway
• Monitor oxygen saturation; supplemental O2 if SpO2 < 94%
• Do NOT administer supplemental oxygen if SpO2 ≥ 94% (no benefit, potential harm)¹
• Establish IV access; avoid dextrose-containing fluids (hyperglycemia worsens outcomes)
• Cardiac monitoring — stroke and cardiac events share risk factors; acute MI and arrhythmias can coexist with or cause stroke

Focused History — “LAST KNOWN WELL” is Critical

The last known well (LKW) time is the single most important historical data point, as it determines eligibility for time-based reperfusion therapies. LKW is defined as the last time the patient was observed at their neurological baseline — NOT the time symptoms were discovered.¹

3.3 Laboratory Evaluation

Only blood glucose is required before initiating IV thrombolysis. Other labs should be drawn but should NOT delay treatment unless there is clinical suspicion of a specific abnormality.¹

4. National Institutes of Health Stroke Scale (NIHSS) — Complete Reference

The NIHSS is a 15-item neurological examination scale that provides a quantitative measure of stroke-related neurological deficit. It is the standard tool for assessing stroke severity, determining treatment eligibility, and monitoring neurological status over time. The scale is performed by trained clinicians and takes approximately 5-8 minutes to complete.¹²

4.1 General Scoring Rules

• Score what the patient does, not what you think they can do
• Score the first response, not the best response (except where noted)
• Do not coach the patient
• Record each item independently — do not allow knowledge of one item’s result to influence another
• Score items in the order listed
• For items where left/right is tested, score the worse side unless otherwise specified
• A total NIHSS score of 0 indicates no measurable deficit; maximum score is 42

4.2 Complete NIHSS Scoring Table

4.3 NIHSS Score Interpretation

4.4 Important NIHSS Caveats

• The NIHSS is heavily weighted toward anterior (carotid) circulation deficits, particularly left hemisphere (language items contribute significantly to total score)
• Posterior circulation strokes (basilar artery occlusion, cerebellar stroke) may present with low NIHSS scores despite devastating pathology — vertigo, ataxia, diplopia, and dysphagia are poorly captured
• A “minor stroke” by NIHSS (score 1-4) may still be disabling if the deficit involves the dominant hand, speech, or gait
• NIHSS can fluctuate — serial examinations are essential; a worsening NIHSS of ≥ 4 points suggests clinical deterioration
• An NIHSS of 0 at presentation does not exclude acute ischemic stroke; approximately 10-15% of patients with acute infarction on DWI have an NIHSS of 0

5. Neuroimaging

5.1 Non-Contrast CT (NCCT) — The First-Line Study

Non-contrast CT of the head is the essential first imaging study in all patients with suspected acute stroke. Its primary role is to exclude hemorrhage and identify other stroke mimics (mass lesion, subdural hematoma). NCCT is rapid, widely available, and has near-100% sensitivity for acute hemorrhage.^{1 13}

NCCT Findings in Acute Ischemic Stroke

5.2 Alberta Stroke Program Early CT Score (ASPECTS)

ASPECTS is a 10-point quantitative scoring system applied to NCCT (or CT angiography source images) to assess the extent of early ischemic changes in the middle cerebral artery territory. It is a critical tool for patient selection in endovascular thrombectomy.¹⁴

ASPECTS Regions

ASPECTS divides the MCA territory into 10 regions across two standardized axial CT levels:

Ganglionic Level (basal ganglia level):

Supraganglionic Level (above the basal ganglia):

ASPECTS Scoring

• Start with 10 points (normal CT)
• Subtract 1 point for each region showing early ischemic change (hypoattenuation, loss of gray-white differentiation, or sulcal effacement)
• Score of 10 = normal CT, no early ischemic changes
• Score of 0 = ischemic changes in all 10 MCA regions

ASPECTS Limitations

• Interrater reliability is moderate (kappa 0.5-0.7); automated ASPECTS software improves consistency
• ASPECTS applies only to the MCA territory — not validated for ACA, PCA, or posterior circulation strokes
• Early ischemic changes may be subtle or absent in the first 3-6 hours, leading to overestimation of the ASPECTS score
• CT angiography source images may improve sensitivity for early ischemic changes compared to NCCT alone

5.3 CT Angiography (CTA)

CTA of the head and neck (arch to vertex) should be obtained in all patients with suspected acute ischemic stroke who are potential candidates for endovascular therapy. CTA should NOT delay IV thrombolysis if the patient is otherwise eligible.^{1 2}

Key CTA Findings

CTA Collateral Assessment

5.4 CT Perfusion (CTP)

CT perfusion provides a tissue-level assessment of cerebral hemodynamics and is the primary imaging modality for selecting patients in the extended time window (6-24 hours) for endovascular thrombectomy. CTP generates parametric maps that distinguish the ischemic core (irreversibly damaged tissue) from the penumbra (at-risk but potentially salvageable tissue).^{15 16}

CTP Parameters

Perfusion Mismatch for Treatment Selection

5.5 MRI in Acute Stroke

MRI with diffusion-weighted imaging (DWI) is the most sensitive imaging modality for detecting acute ischemic stroke, with sensitivity > 95% within minutes of symptom onset. However, MRI is not routinely used as the first-line imaging study in acute stroke due to longer acquisition time and limited availability.^{1 17}

Key MRI Sequences in Acute Stroke

DWI-FLAIR Mismatch for Wake-Up Stroke

In patients who awaken with stroke symptoms (unknown time of onset), the DWI-FLAIR mismatch concept identifies patients whose stroke likely occurred within the thrombolysis treatment window:¹⁸

• DWI positive + FLAIR negative = likely onset within 4.5 hours → may be eligible for IV thrombolysis (supported by the WAKE-UP trial)
• DWI positive + FLAIR positive = likely onset > 4.5 hours → thrombolysis eligibility depends on perfusion imaging and extended-window criteria

6. Door-to-Imaging Workflow

6.1 Recommended Acute Stroke Imaging Algorithm

Patient with suspected acute stroke
│
├─ ALL PATIENTS: Non-contrast CT head (door-to-CT ≤ 20 min)
│   ├─ Hemorrhage present → ICH or SAH pathway
│   └─ No hemorrhage → Acute ischemic stroke pathway
│       │
│       ├─ LKW 0–4.5 hours: Evaluate for IV thrombolysis
│       │   └─ CTA head/neck (do not delay tPA for CTA)
│       │       └─ LVO identified → Evaluate for thrombectomy
│       │
│       ├─ LKW 4.5–24 hours (or unknown/wake-up):
│       │   ├─ CTA head/neck → LVO identified?
│       │   ├─ CT perfusion or MRI DWI/PWI → Mismatch analysis
│       │   └─ If mismatch criteria met → Evaluate for thrombectomy
│       │       (DAWN 6-24h or DEFUSE-3 6-16h criteria)
│       │
│       └─ Wake-up stroke with unknown onset:
│           ├─ MRI: DWI-FLAIR mismatch → If present, consider IV thrombolysis
│           │   (WAKE-UP trial criteria)
│           └─ CTP: Perfusion mismatch → If present, consider EVT

References