Pathophysiology paper: ischemic stroke from blocked artery to the ischemic penumbra

What happens in an ischemic stroke

An ischemic stroke occurs when a blood clot or narrowed artery blocks blood flow to part of the brain. The clot may form on a plaque in a cerebral or carotid artery (thrombotic stroke) or travel from elsewhere, often from the heart in atrial fibrillation (embolic stroke). Brain tissue has almost no energy reserve. It depends on a steady supply of oxygen and glucose, so injury begins within minutes.

The cellular cascade

1. Energy failure. Without oxygen, neurons can't make enough ATP, and the sodium–potassium pumps fail.
2. Cell swelling. Sodium and water flow into the cells (cytotoxic edema), and the neurons stop firing, which causes the sudden deficit.
3. Excitotoxicity. Damaged neurons release large amounts of the neurotransmitter glutamate, which opens channels that flood nearby cells with calcium.
4. Cell death. Calcium activates enzymes that break down cell membranes and proteins, and free radicals add to the damage.
5. Inflammation and edema. Over hours to days, the blood–brain barrier breaks down, and swelling can raise intracranial pressure.

The core and the penumbra

At the center of the blocked territory, blood flow is so low that tissue dies quickly: the ischemic core. Around it is the penumbra, tissue that has stopped working but is still alive because of some blood flow through collateral vessels. The penumbra is the target of emergency treatment. If blood flow returns in time, it can recover. If not, the core grows into it. This is why stroke care is built around time.

Recognizing a stroke

The FAST mnemonic (face, arm, speech, time) misses some strokes. Among 736 patients with ischemic stroke at one stroke center, 14.1% had no FAST symptoms when they arrived. Adding balance (gait imbalance or leg weakness) and eyes (visual symptoms) cut the proportion missed to 4.4% (Aroor et al., 2017). Posterior circulation strokes, which affect balance and vision, are the ones FAST is most likely to miss.

How treatment fits the pathophysiology

The American Heart Association/American Stroke Association guideline (Powers et al., 2019) recommends:

• Intravenous alteplase for eligible patients within 4.5 hours of when they were last known well, given as quickly as possible, with blood pressure below 185/110 mm Hg before treatment and below 180/105 mm Hg for 24 hours afterward.
• Mechanical thrombectomy for eligible patients with a large-vessel occlusion within 6 hours, and for selected patients up to 24 hours when imaging shows salvageable tissue.
• Dysphagia screening before the patient eats, drinks or takes oral medications, because stroke can impair swallowing and lead to aspiration pneumonia.

Nursing implications

Knowing the pathophysiology explains the nurse's priorities: recording the exact time last known well, recognizing balance and vision deficits as possible strokes, keeping blood pressure within the treatment limits, monitoring neurological status for signs of worsening or swelling, and keeping the patient nothing by mouth until a swallow screen is done.

References

Aroor, S., Singh, R., & Goldstein, L. B. (2017). BE-FAST (Balance, Eyes, Face, Arm, Speech, Time): Reducing the proportion of strokes missed using the FAST mnemonic. Stroke, 48(2), 479–481. https://doi.org/10.1161/STROKEAHA.116.015169

Powers, W. J., Rabinstein, A. A., Ackerson, T., Adeoye, O. M., Bambakidis, N. C., Becker, K., Biller, J., Brown, M., Demaerschalk, B. M., Hoh, B., Jauch, E. C., Kidwell, C. S., Leslie-Mazwi, T. M., Ovbiagele, B., Scott, P. A., Sheth, K. N., Southerland, A. M., Summers, D. V., & Tirschwell, D. L. (2019). Guidelines for the early management of patients with acute ischemic stroke: 2019 update to the 2018 guidelines for the early management of acute ischemic stroke: A guideline for healthcare professionals from the American Heart Association/American Stroke Association. Stroke, 50(12), e344–e418. https://doi.org/10.1161/STR.0000000000000211