5.3 Stroke Care: Hemorrhagic vs. Ischemic Thrombectomy Candidates

Stroke Care: Hemorrhagic vs. Ischemic Thrombectomy Candidates

Pathophysiology and Clinical Differentiation

Stroke is a time-critical neurological emergency characterized by the sudden disruption of cerebral blood flow, leading to cellular ischemia and rapid neuronal death. It is divided into two primary classifications: ischemic and hemorrhagic. Ischemic stroke (accounting for ~87% of cases) is caused by thrombotic or embolic arterial occlusion. Hemorrhagic stroke (~13% of cases) results from intracerebral hemorrhage (ICH) or subarachnoid hemorrhage (SAH).

In critical care transport, distinguishing between these two entities is crucial but impossible without neuroimaging. Therefore, immediate management focuses on screening for Large Vessel Occlusion (LVO), controlling blood pressure, and ensuring rapid transport to a capable facility. Every minute of cerebral ischemia results in the loss of approximately 1.9 million neurons, highlighting the flight paramedic's role in the "time is brain" continuum.

Large Vessel Occlusion (LVO) and Mechanical Thrombectomy

LVO refers to the occlusion of major proximal intracranial arteries, most commonly the internal carotid artery (ICA) or the M1 segment of the middle cerebral artery (MCA). These patients are candidates for mechanical thrombectomy, a catheter-based endovascular treatment.

• Time Windows: The standard window for mechanical thrombectomy is within 6 hours of symptom onset. However, based on the DAWN and DEFUSE 3 trials, mechanical thrombectomy can be performed up to 24 hours in selected patients who demonstrate salvageable brain tissue (ischemic penumbra) on advanced perfusion imaging (CT perfusion or MRI mismatch).
• Clinical Screening (LAMS & FAST-ED): Flight paramedics must use screening tools to predict LVO. The Los Angeles Motor Scale (LAMS) scores facial droop (0-1), arm drift (0-2), and grip strength (0-2). A LAMS score of >= 4 indicates a high likelihood of LVO. Similarly, a FAST-ED score of >= 4 predicts LVO. Patients meeting these criteria should be transported directly to a Comprehensive Stroke Center (CSC) bypass-permitting, rather than a Primary Stroke Center (PSC).

Hemodynamic Management: Ischemic Stroke

Blood pressure (BP) control in ischemic stroke is highly dependent on whether the patient is receiving thrombolytic therapy (Alteplase [tPA] or Tenecteplase [TNK]).

1. Thrombolytic Candidates

In patients scheduled for or currently receiving thrombolytics, strict blood pressure control is required to minimize the risk of hemorrhagic transformation (bleeding into ischemic brain tissue).

• Pre-treatment Limit: BP must be lowered to <185 mmHg systolic and <110 mmHg diastolic before administering the thrombolytic.
• Intra- and Post-treatment Target: BP must be maintained <180 mmHg systolic and <105 mmHg diastolic during the infusion and for 24 hours post-infusion.
• First-line Pharmacotherapy:
  • Nicardipine: IV infusion at 5 mg/h, titrating by 2.5 mg/h every 5–15 minutes to a maximum of 15 mg/h.
  • Clevidipine: IV infusion at 1–2 mg/h, doubling the dose every 90 seconds until the target BP is achieved, up to 21 mg/h. Clevidipine is highly preferred in transport due to its ultra-short half-life (~1-2 minutes) and rapid titration.
  • Labetalol: 10–20 mg IV bolus over 1–2 minutes, which may be repeated once.

2. Non-Thrombolytic Candidates (Permissive Hypertension)

For patients who are not candidates for thrombolytics or thrombectomy, the brain relies on collateral vessels to perfuse the ischemic penumbra (the salvageable tissue surrounding the core infarct). Because cerebral autoregulation is lost in these zones, cerebral perfusion pressure (CPP) is directly dependent on mean arterial pressure (MAP).

• Permissive Limits: Do not treat hypertension unless the systolic BP exceeds 220 mmHg or the diastolic BP exceeds 120 mmHg.
• Treatment Goal: If BP exceeds 220/120 mmHg, or if the patient has other compounding emergencies (e.g., acute coronary syndrome, aortic dissection, acute pulmonary edema), reduce the BP by a cautious 15% over the first 24 hours. Avoiding precipitous drops is critical to prevent expanding the infarct area.

Absolute Contraindications to Thrombolytic Therapy

When evaluating an ischemic stroke patient for thrombolytic candidate eligibility, flight paramedics must review the absolute contraindications for alteplase/tenecteplase. These include:

1. Active bleeding or bleeding diathesis: Platelet count <100,000/mm³, current anticoagulant use with INR >1.7 or PT >15 seconds, or therapeutic heparin within 48 hours with an elevated aPTT.
2. Structural intracranial pathology: History of prior intracranial hemorrhage, known structural cerebral vascular lesion (e.g., arteriovenous malformation or aneurysm), or intracranial neoplasm.
3. Recent trauma or surgery: Head trauma or ischemic stroke within the past 3 months, or major surgery/serious trauma within the past 14 days.
4. Severe uncontrolled hypertension: Systolic blood pressure >185 mmHg or diastolic blood pressure >110 mmHg that is unresponsive to emergency antihypertensive therapy.

Hemodynamic Management: Hemorrhagic Stroke

In hemorrhagic stroke (ICH and SAH), blood pressure control is aggressive and directed at minimizing hematoma expansion and reducing the rate of rebleeding.

• Hemodynamic Target: Guidelines recommend lowering the systolic blood pressure to a target of 130–140 mmHg if the presenting SBP is between 150 and 220 mmHg. Lowering the BP to <140 mmHg is safe and limits the hematoma volume, but dropping SBP <120 mmHg should be avoided due to the risk of renal injury and systemic hypoperfusion.
• ICP Control: Elevate the head of the bed (HOB) to 30 degrees (if spine is cleared) to optimize venous drainage and lower intracranial pressure. Ensure the neck is kept in a neutral midline position to prevent jugular venous compression.
• Osmotherapy for Elevated ICP: In patients showing signs of brain herniation (Cushing's Triad: bradycardia, hypertension, irregular respirations) or rapid pupillary changes, administer osmotic agents:
  • Hypertonic Saline (3%): 250–500 mL IV over 20 minutes (preferred in hemodynamically unstable patients).
  • Mannitol (20%): 0.5–1.0 g/kg IV over 20 minutes. Maintain adequate hydration as mannitol acts as an osmotic diuretic.

Transport and Aviation Considerations (CAMTS)

Critical care transport teams must manage physiological stressors during flight:

• Oxygenation: Maintain oxygen saturation >= 94%. Avoid high-flow oxygen in normoxic patients, as hyperoxia causes cerebral vasoconstriction, which worsens ischemic penumbral blood flow.
• Ventilation: Target normocapnia (ETCO2 35–45 mmHg). Hyperventilation causes cerebral vasoconstriction, reducing cerebral blood flow (CBF). Temporary mild hyperventilation (ETCO2 30–35 mmHg) is reserved strictly as a short-term bridge for impending herniation.
• Aviation Stressors: Ensure smooth flight paths to avoid rapid accelerations/decelerations, which can cause transient changes in intracranial pressure.