Prehospital Stroke: Recognition, Time Window and Triage to the Stroke Unit

Why the prehospital phase is decisive

Acute ischaemic stroke is a time-critical emergency. Both reperfusion therapies depend on the time of symptom onset and on imaging: intravenous thrombolysis and mechanical thrombectomy for large vessel occlusion. Imaging only takes place in hospital. In the prehospital setting, ischaemic stroke cannot be reliably distinguished from intracranial haemorrhage. The task of the ambulance and emergency physician team is therefore clearly defined:

• recognise
• stabilise
• establish the time of onset
• select the right destination
• pre-alert

Specific thresholds and targets in stroke, for example for blood pressure, blood glucose or oxygen saturation, are outside the scope of this article. The current stroke guidelines of the neurological societies and regional protocols apply.

Stroke recognition: screening with a score

Simple screening tools

Short, standardised screening scores have become established for prehospital recognition:

• FAST (Face, Arm, Speech, Time): assesses facial palsy, arm weakness and speech disturbance, and serves as a reminder to record the time.
• BE-FAST adds Balance (balance, ataxia) and Eyes (visual disturbance, diplopia).

FAST captures posterior circulation symptoms inadequately. Acute vertigo, gait ataxia, diplopia, dysarthria or a sudden reduction in consciousness may indicate vertebrobasilar occlusion, even when FAST is unremarkable. A negative screen does not rule out stroke.

Scores for estimating large vessel occlusion

Scales intended to make an occluded artery in the anterior circulation more likely are increasingly used for destination decisions. Examples include RACE, LAMS and G-FAST. They mainly assess severity and cortical signs such as gaze deviation, aphasia or neglect.

• Diagnostic accuracy is limited.
• Which score applies, and with which threshold, is defined by regional triage protocols.
• What matters is consistent use of the tool agreed within the ambulance service area.

Level of consciousness and airway

The level of consciousness is documented using the Glasgow Coma Scale (3–15 points). At a score of ≤ 8, protective reflexes are at risk [Teasdale 1974]. Aspiration protection and airway management should then be considered.

For anaesthesia teams:

• Plan airway management to minimise haemodynamic compromise; avoid hypotension and hypoxia.
• Document the neurological findings before induction of anaesthesia, as they can no longer be assessed afterwards.

Consider stroke mimics

Several conditions can mimic stroke:

• hypoglycaemia
• epileptic seizure with postictal paresis
• migraine with aura
• intoxication
• sepsis with encephalopathy
• syncope
• functional disorders

Blood glucose measurement is therefore part of every initial assessment. Hypoglycaemia is treated on scene and the neurological findings are then reassessed. If the suspicion persists, the patient is managed as a stroke until imaging shows otherwise.

Establishing symptom onset: the key time point

"Last known well"

The relevant time point is when the person was last reliably seen without the current symptoms ("last known well"). The time of discovery is not relevant.

• Witnessed onset: ask for the exact time, ideally linked to an anchor event (phone call, television programme, meal).
• Wake-up stroke: the relevant time is when the person went to bed or last woke without symptoms.
• Fluctuating symptoms: if symptoms resolve completely and then recur, the reference time point may change. Document the course precisely.

According to the summary of product characteristics, intravenous thrombolysis with alteplase is intended within 4.5 hours of symptom onset and after exclusion of haemorrhage by CT or MRI [Fachinformation Alteplase].

An unknown or more remote onset is no reason to forgo triage to a stroke unit. Extended indications exist for thrombectomy and for imaging-based decisions when the time window is unclear. The specific time limits should be taken from current guidelines.

Further history relevant to reperfusion

The history should specifically ask about contraindications to thrombolysis [Fachinformation Alteplase]:

• previous intracranial haemorrhage or stroke of unknown cause
• CNS damage, CNS tumour or arteriovenous malformation
• recent major trauma, surgery or head injury
• active bleeding, known bleeding tendency
• signs of aortic dissection, such as chest or back pain and pulse differential
• in addition, the indication-specific criteria in the summary of product characteristics

The following information is also relevant:

• Anticoagulation: agent and time of last dose; bring the medication list.
• ACE inhibitors: angioedema may occur during stroke thrombolysis, particularly in patients taking ACE inhibitors [Fachinformation Alteplase].
• Body weight: ask rather than estimate whenever possible, as the thrombolysis dose is weight-based.
• Pre-existing functional status: for example care dependency, as a basis for treatment decisions.

For context: in acute ischaemic stroke, alteplase is dosed in hospital at 0.9 mg/kg i.v., to a maximum of 90 mg. Of this, 10 % is given as a bolus over 1 min and the remainder over 60 min [Fachinformation Alteplase]. In large vessel occlusion, thrombectomy must not be delayed by thrombolysis.

Secure witnesses

Relatives or eyewitnesses are often the only source for the time of symptom onset.

• Allow them to accompany the patient to hospital, or at least document a telephone number.
• Queries from the neurology team are routine in thrombolysis and thrombectomy decisions.

Prehospital management: what to do, what to avoid

Measures

• ABCDE assessment, monitoring, blood glucose measurement
• Venous access without delay on scene; no delay to transport for repeated attempts
• 12-lead ECG if possible without delay (atrial fibrillation as embolic source, concomitant cardiac disease)
• Nil by mouth until swallowing has been assessed, because of aspiration risk with dysphagia
• Positioning according to clinical condition; evidence for a specific head-of-bed position is limited

To avoid

• Antiplatelet agents or anticoagulants before imaging, as haemorrhage cannot be excluded prehospital
• Intramuscular injections, which may be problematic if thrombolysis follows
• Indiscriminate blood pressure lowering; targets and intervention thresholds follow current guidelines and local protocols
• Loss of time due to non-essential measures on scene

Stroke unit triage: the right destination

Basic principle

Every suspected acute stroke should primarily be taken to a hospital with a stroke unit and immediately available imaging. Transport to a hospital without these facilities usually costs time that is then lacking for reperfusion.

Thrombolysis centre or thrombectomy centre?

When large vessel occlusion is strongly suspected, two strategies are discussed:

• Drip and ship: first to the nearest stroke unit with thrombolysis capability, followed by secondary transfer for thrombectomy
• Mothership: direct transport to a thrombectomy-capable centre

Which strategy is advantageous in the individual case depends on several factors:

• transport times and availability of air ambulance services
• structures of telestroke networks
• regional agreements

Evidence for general superiority of either strategy is limited. Regional triage algorithms that combine score results and transport times are decisive.

Pre-alert: structured and complete

The telephone pre-alert allows the receiving hospital to have the stroke team and imaging ready before arrival. A fixed sequence has proven useful:

1. Suspected diagnosis and score result (screening, and large vessel occlusion score if applicable)
2. Symptom onset or "last known well" with time and source
3. Key symptoms and Glasgow Coma Scale
4. Vital signs and blood glucose
5. Anticoagulation (agent, last dose) and relevant contraindications
6. Body weight (reported or estimated – state which)
7. Estimated time of arrival and accompanying persons or contactable relatives

Handover ideally takes place directly to the stroke team, if necessary directly at the imaging suite. Documentation should include all times: symptom onset, alert, arrival on scene, departure and handover.

Practical conclusions

• Recognise: structured screening with a score increases the detection rate. Posterior circulation symptoms and stroke mimics remain pitfalls.
• Establish the time point: "last known well" is the key information for all reperfusion decisions.
• Triage: stroke unit triage follows the regional algorithm; suspected large vessel occlusion influences the choice of destination hospital.
• Pre-alert: a structured pre-alert shortens in-hospital processes.

References

• Teasdale G, Jennett B. Assessment of coma and impaired consciousness. Lancet 1974;2:81–4.
• Fachinformation Alteplase (rt-PA), Boehringer Ingelheim – aktuelle Fassung.

This article does not replace clinical judgement in the individual case or the current summary of product characteristics and guidelines.