Stroke, defined as a sudden loss of brain function resulting from an interference with the blood supply to the brain, is a major and growing problem in the United States. A stroke can be either ischemic or hemorrhagic in origin. Acute ischemic stroke represents the majority (85 percent) of the 600,000 strokes that occur in the United States each year, with a mortality rate of 20 to 50 percent. Lewandowski and Barsan review the pathophysiology and management of persons with acute ischemic stroke.
Acute vascular occlusion is the central event in acute ischemic stroke and precipitates injury by limiting the flow of oxygen and glucose. Occlusion is rarely complete. The amount of injury is proportional to the duration and severity of the ischemia. In the area of ischemia there is a central core with marked diminution in cerebral blood flow and a surrounding area of marginal blood flow called the “ischemic penumbra.” Any decrease in systemic blood pressure can extend the area of ischemia and infarction.
Diagnosis of acute ischemic stroke includes a characteristic history of sudden onset of focal neurologic deficit that can wax and wane over the first few hours. Risk factors are similar to those of coronary artery disease and may include a history of transient ischemic attacks, previous stroke or atrial fibrillation. The time of onset is a critical element of treatment decisions. The neurologic examination can determine whether a focal neurologic deficit in a characteristic vascular distribution exists. Noncontrast computed tomographic (CT) scan of the brain is the major imaging study required. Because fresh blood is hyper-dense, intracranial hemorrhage can be accurately detected. CT sensitivity for ischemic stroke is low (30 percent) within three hours of the event and increases to 100 percent by day 7. Initial scan results may also reveal a hyperdense middle cerebral artery thought to be caused by a fresh clot or embolus. Magnetic resonance imaging (MRI) can reveal edema and mass effect better than CT and is more useful when imaging the posterior fossa and brain stem, but the ability to detect intracranial hemorrhage is limited. Noncontrast CT scan of the brain remains the imaging technique of choice because it is available, fast, reliably visualizes intracranial hemorrhage and provides prognostic information.
Acute supportive care includes cautious treatment of patients with hypertension. In fact, treatment should not be initiated for hypertension because it normally resolves over a period of hours to days. Patients with hypotension should be treated more aggressively, with fluids, inotropic agents or vasopressors as indicated to maintain perfusion and prevent extension of the infarct. Hyperglycemic patients should be treated with insulin. Patients with hyperthermia should be treated with antipyretics to achieve euglycemia. Oxygenation should be optimized. Aspirin should be given early in the episode unless the patient is considered a candidate for thrombolytic therapy.
Therapy consists of rapid reperfusion through intravenous thrombolysis. Intravenous recombinant tissue plasminogen activator (rtPA) is useful in patients with ischemic strokes when therapy is started within three hours of symptom onset, although there is an increased risk of intracranial hemorrhage. Appropriate patient selection for intravenous thrombolysis is founded on close adherence to the inclusion and exclusion criteria that have been adapted from the experience gained in the major thrombolytic trials (see accompanying table).
The authors conclude that with the development of care paths and the use of flow charts in assessing patients who present with acute stroke, treatment of acute ischemic stroke could be more effective. Unfortunately, most patients present to the hospital more than three hours after symptom onset. Public education, more efficient evaluation protocols, safer and more effective thrombolytic techniques and development of neuroprotective agents may improve treatment efficacy and prolong the therapeutic window for treatment of patients with acute ischemic stroke.