How does cerebral steal affect blood flow in ischemic regions when vasodilators are administered?

Cerebral steal refers to the phenomenon where the administration of vasodilators leads to an increase in blood flow to areas of the brain that are already well-perfused (non-ischemic regions) while simultaneously diverting blood flow away from ischemic regions. When vasodilators are introduced, they widen the blood vessels in well-perfused areas, allowing for increased blood flow. However, in regions that are ischemic — meaning they are deprived of adequate blood supply — the perfusion mechanism is impaired due to already compromised blood flow.

As the vasodilators cause the blood vessels in non-ischemic areas to dilate, these vessels can accommodate more blood than before. This leads to a situation where the increased blood flow in non-ischemic regions occurs at the expense of reduced perfusion in ischemic areas. Essentially, the physiological response of the brain prioritizes areas that are already receiving adequate blood supply, thereby reducing the overall blood flow to the ischemic areas, which may exacerbate the tissue hypoxia and damage in those regions.

Understanding this concept is crucial in clinical settings where managing tissue perfusion is critical, especially in conditions involving stroke or other types of cerebral ischemia.