Recognizing Stroke: The FAST Test and Prehospital Time Management

Every minute counts – in the context of acute stroke, this phrase is not a cliché but a harsh neurobiological reality. For every minute a large vessel remains occluded, an estimated 1.9 million neurons, 14 billion synapses, and 12 kilometers of myelinated fibers are destroyed. The prehospital phase is the segment of the care chain with the greatest potential for time savings – and simultaneously where the most time is lost. For you as an emergency physician, paramedic, or emergency department nurse, this means: structured, rapid stroke recognition and consistent time documentation are the most effective "medications" you can administer during this phase.

Pathophysiological Background: Why Every Minute Counts

The concept of the ischemic penumbra is the key to understanding why time is so critical. Surrounding the infarct core – the already irreversibly damaged tissue – lies a zone of hypoperfused but still viable brain tissue. This tissue is functionally silent but structurally intact and potentially salvageable. With every passing minute, penumbra converts into infarct core.

The consequences for clinical outcome are dramatic:

• "Time is Brain": Estimates suggest that every 30-minute delay in reperfusion reduces the probability of a good functional outcome by approximately 10%.
• Thrombolysis time window: Intravenous thrombolysis with alteplase is approved under current guidelines within 4.5 hours of symptom onset, though the benefit decreases with every passing minute. The number needed to treat (NNT) rises from approximately 4–5 when treatment is given within the first 90 minutes to over 14 when treatment is given between 3 and 4.5 hours.
• Thrombectomy time window: Mechanical thrombectomy for large vessel occlusion (LVO) can be performed in selected patients even in extended time windows when salvageable tissue is demonstrated on imaging. Nevertheless, earlier is always better.

The FAST Test: Simple, Quick, Effective

The FAST test is the most widely used screening instrument for acute stroke in the prehospital setting worldwide. It was originally developed for public awareness but has also proven effective as a structured initial assessment tool in emergency medical services.

The Four Components

• F – Face: Ask the person to smile or show their teeth. A unilateral facial droop (drooping corner of the mouth, flattened nasolabial fold) is positive.
• A – Arms: Ask the person to hold both arms with eyes closed for 10 seconds at 90° (sitting) or 45° (lying down). Drift or pronation of one arm (pronator drift) is positive.
• S – Speech: Ask the person to repeat a simple sentence (e.g., "The sun is shining"). Slurred speech (dysarthria), word-finding difficulties, or language comprehension deficits (aphasia) are positive.
• T – Time: If any finding in F, A, or S is positive → immediate emergency call (144 in Austria or 112) and documentation of symptom onset.

Test Accuracy

In validation studies, the FAST test achieves a sensitivity of approximately 79–85% and a specificity of about 79% for acute stroke. This means: the FAST test is good, but not perfect. Approximately 15–20% of strokes are missed by FAST – particularly vertebrobasilar infarcts presenting with dizziness, visual disturbances, or ataxia as the leading symptom.

Extended Scales: BE-FAST and Other Screening Tools

To close the diagnostic gap of the classic FAST, extended scales have been developed. The most relevant extension for clinical practice is BE-FAST.

BE-FAST in Detail

• B – Balance: Sudden dizziness, gait instability, coordination deficits. This item specifically captures cerebellar and brainstem infarcts.
• E – Eyes: Sudden visual disturbances – diplopia, visual field deficits, monocular vision loss (amaurosis fugax). This item addresses infarcts in the posterior circulation as well as retinal ischemia.
• F – Face: Same as FAST.
• A – Arms: Same as FAST.
• S – Speech: Same as FAST.
• T – Time: Same as FAST.

By adding Balance and Eyes, sensitivity increases to over 95%. For you in practice, this means: BE-FAST is the FAST test with a built-in safety net for vertebrobasilar strokes that might otherwise be easily misinterpreted as "positional vertigo" or "eye problems."

Scales for LVO Detection

Beyond pure stroke recognition, it is becoming increasingly important to identify a large vessel occlusion (LVO) in the prehospital setting, since these patients benefit from thrombectomy and should ideally be transported directly to a neurovascular center (Comprehensive Stroke Center). Relevant scales include:

• RACE (Rapid Arterial oCclusion Evaluation): Assesses facial palsy, arm motor function, leg motor function, head/gaze deviation, and aphasia/agnosia. Score 0–9, a cut-off ≥ 5 suggests LVO.
• LAMS (Los Angeles Motor Scale): A simple 3-item scale (facial asymmetry, arm drift, grip strength), score 0–5, cut-off ≥ 4 for suspected LVO.
• G-FAST: Adds "Gaze" (gaze deviation) to FAST as a strong indicator of LVO.

The choice of scale depends on regional protocols. What matters most is that you use a standardized instrument at all and actively communicate the suspicion of LVO so that the disposition decision – Primary Stroke Center vs. Comprehensive Stroke Center – can be made correctly.

The Prehospital Chain of Care: From Symptom Onset to Hospital

The survival and outcome chain in stroke can be divided into clearly defined time intervals. Each interval offers potential for optimization.

1. Onset-to-Call Time (Symptom Onset to Emergency Call)

This is typically the longest interval and is most strongly influenced by patient and bystander education. Median values in registry data are 60–90 minutes – an enormous time loss. Common reasons:

• Symptoms are not recognized as stroke (especially with atypical presentations)
• "Wait and see if it gets better" mentality
• Symptom onset during sleep (wake-up stroke) → unclear time of onset

2. Dispatch-to-Scene Time (Dispatch to Arrival on Scene)

Influenced by dispatch center disposition. It is critical that the dispatch center recognizes the suspicion of stroke and sends the appropriate resource. Standardized dispatch protocols with stroke screening questions improve accuracy.

3. On-Scene Time (Time Spent at the Scene)

This is a major lever for EMS. The target on-scene time for a clear stroke suspicion should be under 15 minutes. What needs to happen during this time?

• Clinical assessment: BE-FAST or FAST, LVO screening scale if applicable
• Establish symptom onset: When were the symptoms last noticed? When was the person last symptom-free ("last known well")? This time point is critical for the thrombolysis decision.
• Measure blood glucose: Hypoglycemia is the most important and most common stroke mimic that is immediately treatable. A blood glucose < 60 mg/dL must be corrected and the stroke suspicion re-evaluated.
• Vital signs: Blood pressure, heart rate, SpO₂, temperature, ECG (atrial fibrillation?)
• Establish IV access: Preferably on the non-paretic arm, 18 G or larger
• No delays from unnecessary interventions: No comprehensive neurological exam, no unnecessary repositioning, no waiting for the emergency physician if transport would be delayed

4. Transport and Pre-notification

• Destination hospital: Stroke unit with 24/7 thrombolysis capability; if LVO is suspected, directly to a Comprehensive Stroke Center with thrombectomy capability per regional agreement.
• Pre-notification: Advance notification of the destination hospital is a critical factor. Studies show that structured pre-notification can reduce door-to-needle time by 15–20 minutes. The pre-notification should include the following information:
  • Suspected diagnosis: Acute stroke
  • Symptom onset or "last known well" time
  • Brief symptom description (side, which deficits)
  • Suspected LVO yes/no
  • Relevant concomitant medications (especially anticoagulants!)
  • Estimated time of arrival (ETA)

5. Door-to-Needle Time (Hospital Arrival to Thrombolysis)

The target time is ≤ 60 minutes, though high-performance centers achieve values under 30 minutes. During this interval, the following must occur: initial physician assessment, CT/CTA, laboratory analysis (at minimum blood glucose and INR if anticoagulation is known), thrombolysis decision, and bolus administration.

The Importance of Time Documentation

Accurate time documentation is not a bureaucratic obligation – it is a therapeutic tool. Without reliable time data, no thrombolysis decision can be made.

What Must Be Documented

Time Point	Why Is It Relevant?
Symptom onset or "last known well"	Defines the thrombolysis time window
Time of emergency call	System performance analysis
Arrival at scene	Calculation of on-scene time
Departure from scene	Calculation of on-scene time
Arrival at destination hospital	Start of door-to-needle calculation
Blood glucose measurement (time and value)	Exclusion of stroke mimic

Special Cases in Time Determination

• Wake-up stroke: Symptoms are noticed upon waking. The time the patient was last known to be symptom-free (e.g., going to bed) is documented as "last known well." Using MRI-based tissue selection (DWI/FLAIR mismatch), thrombolysis can be considered even with an unclear time window – but the in-hospital imaging must be capable of providing the relevant information.
• Fluctuating symptoms: Document the onset of the current episode AND whether there were previous episodes (crescendo TIA as a high-risk constellation).
• Unwitnessed onset: The patient is found unresponsive. "Last known well" is the last time point at which someone verifiably saw the person symptom-free. When in doubt, this is the last documented interaction.

Differential Diagnoses: Recognizing Stroke Mimics

Approximately 20–30% of patients initially admitted as stroke have a different diagnosis. This is acceptable – an over-triage system is intentional to avoid missing any true stroke. Nevertheless, you should know the most important mimics:

• Hypoglycemia: The most common reversible cause of focal neurological deficits. Therefore: blood glucose measurement is mandatory and takes priority.
• Epileptic seizure with Todd's paresis: Postictal paresis can perfectly mimic a stroke. Collateral history regarding seizure activity is crucial.
• Migraine with aura: Hemiplegic migraine can present dramatically. Typical features: symptom migration over minutes (march), known history of migraine, younger age.
• Functional neurological disorder: Inconsistent findings, Hoover's sign, discrepancy between examination findings and impairment.
• Intracranial mass lesion: Usually subacute onset, but can present acutely with hemorrhage into a tumor.
• Hypertensive encephalopathy: Extremely high blood pressure values (>220/120 mmHg), headache, altered consciousness, often bilateral.

The differentiation between ischemia and intracerebral hemorrhage (ICH) cannot be reliably made clinically in the prehospital setting. Both entities can present identically. Therefore, CT in the hospital is mandatory before any thrombolytic therapy. In EMS, the rule is: transport if stroke is suspected – differentiation occurs in the hospital.

Prehospital Blood Pressure Management

A common pitfall is the management of elevated blood pressure values. In acute stroke, blood pressure is reactively elevated and serves to maintain perfusion of the penumbra. Prehospital recommendations:

• No routine blood pressure lowering for values < 220/120 mmHg
• Intervene only at values > 220 mmHg systolic or in hypertensive emergency with end-organ damage (pulmonary edema, aortic dissection, acute coronary syndrome)
• If lowering is necessary: cautious titration with easily controllable agents (e.g., urapidil 10–25 mg IV bolus), target reduction of no more than 15–20% in the first hour
• Avoid hypotension: A systolic blood pressure < 120 mmHg worsens outcome in acute stroke. Consider volume administration with crystalloid solution.

Common Errors in Prehospital Stroke Care

• Failure to measure blood glucose: Every suspected stroke requires a blood glucose value. Period.
• Vague time information: "Sometime this morning" is not usable. Actively inquire: When did they last make a phone call? When did they last eat? When were they last seen?
• No pre-notification: Without advance notification, the stroke team will not be activated in time.
• Wrong destination hospital: If LVO is suspected and the transport time to a thrombectomy center is short, go to the right hospital, not the closest one. Follow regional protocols.
• Excessive on-scene time: Every minute at the scene that does not directly serve diagnostics or life-saving measures is lost time for the penumbra.
• Aggressive blood pressure lowering: Well-intentioned but harmful – the penumbra needs perfusion pressure.

Summary: The Prehospital Stroke Algorithm

1. Recognize suspicion → Perform BE-FAST screening
2. Measure blood glucose → Rule out/treat hypoglycemia
3. Document symptom onset / "last known well" → Exact time
4. LVO screening → Gaze deviation? Severe hemispheric symptoms? → Consider LVO transport if suspected
5. Vital signs + IV access → Do not lower blood pressure (unless > 220 mmHg systolic)
6. Choose destination hospital → Stroke Unit / Comprehensive Stroke Center per regional protocol
7. Pre-notification → Structured handoff: suspicion, time of onset, deficits, anticoagulation, ETA
8. Transport → Promptly, supine, 30° head-of-bed elevation
9. Hospital handover → Communicate exact times, findings, and all relevant information

Practical Training

Prehospital stroke recognition and management depends on routine application of structured algorithms under time pressure. In the emergency training courses offered by Simulation Tirol, you can practice exactly these scenarios in a realistic setting – from initial assessment with BE-FAST, through decision-making on destination hospital selection, to structured pre-notification and handover. Hands-on practice under simulated conditions reinforces procedural workflows so they can be recalled quickly and confidently in real emergencies. More information on current course offerings is available at simulationtirol.com.