6.1 Stroke Recognition & Out-of-Hospital Assessment

Stroke Recognition & Out-of-Hospital Assessment

Introduction to Acute Ischemic Stroke

Acute ischemic stroke is a profound, time-critical medical emergency that occurs when arterial blood flow to a specific region of the brain is suddenly obstructed. This obstruction is typically caused by either a localized thrombus forming on a ruptured atherosclerotic plaque or an embolus traveling from the heart or proximal vasculature. The sudden cessation of oxygenated blood flow immediately induces localized cerebral ischemia. If this ischemia is not rapidly reversed, the affected brain tissue undergoes irreversible infarction, leading to permanent neurological deficits or death.

The overarching, defining principle in all of modern stroke care is "Time is Brain." Research indicates that for every single minute that cerebral blood flow is interrupted, approximately 1.9 million neurons and 14 billion synapses are destroyed. Therefore, the early recognition of stroke symptoms and the immediate, unhesitating activation of emergency medical services (EMS) are paramount. The stroke chain of survival begins not in the hospital, but in the community, relying heavily on public awareness and the swift actions of first responders.

Stroke Warning Signs and Public Awareness

Educating the public and healthcare professionals to be hyper-vigilant for the warning signs of a stroke is a major public health initiative. The most commonly taught and widely recognized mnemonic for stroke recognition is FAST. This simple tool empowers bystanders to identify a potential stroke and take immediate action.

• Face drooping: One side of the face may suddenly droop or become numb. The person's smile may appear uneven or lopsided.
• Arm weakness: One arm may suddenly become weak or numb. When the person attempts to raise both arms, one arm may drift downward.
• Speech difficulty: The person may suddenly exhibit slurred speech, use inappropriate words, or be entirely unable to speak or understand conversation (aphasia).
• Time to call 9-1-1: If any of these signs are observed, even if they fluctuate or seem to resolve, emergency services must be contacted immediately.

Beyond the FAST mnemonic, other sudden symptoms warrant immediate emergency evaluation. These include sudden, unexplained numbness or weakness of the face, arm, or leg (especially if isolated to one side of the body); sudden confusion or altered mental status; sudden trouble seeing in one or both eyes (such as amaurosis fugax or hemianopsia); sudden trouble walking, severe dizziness, or a profound loss of balance and coordination; and a sudden, extremely severe headache with no known cause, often described by patients as "the worst headache of my life."

Out-of-Hospital Screening Tools

Emergency Medical Services (EMS) personnel are the critical first link in the medical response to a stroke. Because the presentation of a stroke can be heterogeneous, several prehospital stroke screening tools have been developed. These tools are designed to be highly sensitive, allowing paramedics and EMTs to quickly and accurately identify potential stroke patients in the field, even in chaotic environments.

Cincinnati Prehospital Stroke Scale (CPSS)

The Cincinnati Prehospital Stroke Scale (CPSS) is arguably the most widely utilized and easily administered screening tool in the prehospital setting. Derived from the NIH Stroke Scale, it requires no specialized equipment and can be performed in under a minute. It evaluates three specific physical findings:

• Facial Droop: The provider asks the patient to smile broadly or show their teeth. An abnormal finding occurs when one side of the face does not move symmetrically with the other, indicating unilateral facial nerve weakness.
• Arm Drift: The patient is instructed to close their eyes and hold both arms straight out in front of them with palms facing upward (supinated) for 10 seconds. An abnormal finding is recorded when one arm does not move at all, or if one arm drifts downward relative to the other. Pronation of the hand (the palm turning inward) is also a subtle sign of weakness.
• Abnormal Speech: The provider asks the patient to repeat a standard, simple phrase, such as "You can't teach an old dog new tricks." The provider listens for slurred words (dysarthria), the use of incorrect words, or an inability to speak entirely (expressive aphasia).

If any one of these three signs is abnormal, the probability that the patient is experiencing an acute ischemic stroke is highly significant—reported in literature as up to a 72% probability.

Los Angeles Prehospital Stroke Screen (LAPSS)

The Los Angeles Prehospital Stroke Screen (LAPSS) is another robust, validated tool that incorporates a brief patient history and a point-of-care blood glucose test alongside a physical assessment. It was designed to help exclude stroke mimics, such as hypoglycemia and seizures. The LAPSS criteria include:

• Patient age over 45 years.
• No prior history of seizures or epilepsy.
• Symptom duration of less than 24 hours.
• The patient is not wheelchair-bound or bedridden at their baseline.
• Blood glucose is between 60 and 400 mg/dL.

The physical examination component of the LAPSS checks for unilateral asymmetry in three areas: facial smile/grimace, grip strength, and arm strength. If all criteria are met and there is unilateral weakness, the screen is positive for a high likelihood of stroke.

NIH Stroke Scale (NIHSS) in the Prehospital Setting

While the full National Institutes of Health Stroke Scale (NIHSS) is a comprehensive, 15-item neurological examination used primarily in the hospital setting, abbreviated versions are increasingly being utilized by advanced EMS systems. These shortened scales help provide a quantitative measure of stroke severity in the field. Importantly, they are specifically designed to identify patients presenting with severe deficits that correlate with a potential Large Vessel Occlusion (LVO). Identifying an LVO in the field is critical because these patients often require mechanical thrombectomy and may benefit from direct transport to a Comprehensive Stroke Center.

The Critical Importance of Last Known Well (LKW) Time

Throughout the entire continuum of stroke care, perhaps the single most critical piece of historical information gathered is the Last Known Well (LKW) time, sometimes referred to as Time Zero. The LKW time is precisely defined as the exact time the patient was last witnessed or known to be at their normal, baseline neurological state, completely free of the current stroke symptoms.

Determining the LKW time can be complex, especially if the onset of symptoms was unwitnessed.

• If a patient goes to bed at 10:00 PM feeling completely normal, wakes up at 6:00 AM, and realizes they have right-sided weakness, their LKW time is 10:00 PM, not 6:00 AM. This is classified as a "wake-up stroke."
• If a patient is found unresponsive and aphasic on the floor by a family member at 2:00 PM, but the mail carrier spoke with the patient and noted they were completely normal at 11:30 AM, the LKW time is 11:30 AM.

The LKW time represents a hard boundary because it dictates the patient's eligibility for highly time-sensitive reperfusion therapies. Intravenous fibrinolytic therapy and mechanical thrombectomy have strict, unforgiving time windows. An inaccurate determination of the LKW time can have devastating consequences: it can either inappropriately exclude a patient from a life-saving, disability-preventing therapy, or it can expose a patient to dangerous interventions outside the safety window, leading to fatal hemorrhagic transformation.

EMS Pre-Notification and Routing to a Stroke Center

Once a stroke is suspected based on field assessment, EMS must act with immense urgency, minimizing scene time to the absolute essentials (ABCs, vital signs, glucose check, IV access if it doesn't delay transport) and initiating rapid transit. A critical, non-negotiable intervention during this transport phase is providing immediate pre-notification to the receiving hospital.

EMS pre-notification acts as a catalyst for the hospital's internal systems. When the hospital receives the alert, it can immediately activate its specialized Stroke Team, pre-register the patient in the electronic medical record, ensure the CT scanner is cleared and waiting, and alert the pharmacy to prepare potential fibrinolytic medications. Studies have consistently demonstrated that EMS pre-notification significantly decreases door-to-imaging and door-to-needle times, directly translating to improved functional outcomes for the patient.

Furthermore, EMS routing protocols are crucial. Paramedics should transport the patient to the closest appropriate stroke center—such as a Primary Stroke Center, Thrombectomy-Capable Stroke Center, or Comprehensive Stroke Center—rather than simply driving to the nearest hospital emergency department. Bypassing a non-stroke center to reach a specialized facility with advanced imaging and endovascular capabilities can dramatically improve outcomes, provided the transport time is not excessively prolonged.