A stroke, often called a “brain attack,” occurs when blood flow to a part of the brain is interrupted, leading to cell damage. While high blood pressure is typically a major risk factor for stroke, there are specific situations after certain types of stroke where temporarily elevated blood pressure can be beneficial. This article explains the reasons behind this temporary strategy and how it helps protect brain tissue.
Maintaining Brain Blood Flow
When an ischemic stroke occurs, caused by a blockage in a blood vessel that supplies the brain, some brain tissue loses its direct blood supply. Around the core area of irreversible damage, there is often a surrounding region known as the “ischemic penumbra.” This penumbra is brain tissue that is at risk but not yet permanently damaged, as it receives some blood flow from collateral vessels. The cells in this vulnerable area are struggling but can still be saved if blood supply is restored quickly.
Brain cells require a continuous supply of oxygen and nutrients. After an ischemic stroke, the brain’s normal ability to regulate its own blood flow, a process called cerebral autoregulation, becomes impaired. Under normal circumstances, cerebral autoregulation keeps blood flow to the brain constant despite fluctuations in overall blood pressure. However, in an ischemic brain, this protective mechanism is often compromised, making blood flow directly dependent on systemic blood pressure.
In this compromised state, maintaining a temporarily higher blood pressure helps to “push” blood through the narrowed or partially blocked vessels and through existing collateral pathways to the ischemic penumbra. This increased pressure can augment blood flow to the threatened brain tissue, preventing further cell death and potentially reducing the overall size of the stroke. This response aims to preserve brain function.
Risks of Aggressive Blood Pressure Lowering
Lowering blood pressure too rapidly or aggressively after an acute ischemic stroke can have severe negative consequences. A sudden drop in blood pressure can significantly reduce the already compromised blood flow to the ischemic penumbra. This reduction in perfusion can expand the area of brain damage, leading to a larger infarct size.
Such an expansion of the damaged area could worsen neurological outcomes, potentially increasing disability or even leading to death. While high blood pressure generally poses long-term health risks, in the immediate aftermath of an ischemic stroke, the danger of reducing blood pressure too much can outweigh the immediate risks of the temporary elevation. The goal during this acute phase is to support the struggling brain tissue, and aggressive lowering might inadvertently starve it further.
Brain tissue damaged by lack of blood flow is particularly sensitive. Lowering blood pressure too much can lead to insufficient blood supply to vulnerable cells, hindering recovery and potentially causing new injury. Medical professionals must carefully balance preventing further complications with ensuring adequate brain blood flow.
Managing Blood Pressure After Stroke
Medical professionals manage blood pressure in the acute phase after an ischemic stroke with careful consideration, tailoring treatment to each patient. Specific blood pressure targets are set to maintain adequate cerebral perfusion without causing other complications. For patients not receiving clot-busting medications, blood pressure is generally not lowered unless it exceeds 220/120 mmHg. If it is above this level, a gradual reduction of about 15% within the first 24 hours is often recommended.
For patients receiving intravenous thrombolytic therapy, blood pressure targets are stricter. Before administering these medications, blood pressure is usually lowered to below 185/110 mmHg. After treatment, it is maintained below 180/105 mmHg for at least 24 hours to minimize the risk of bleeding in the brain. Close monitoring of blood pressure is essential, often every 15 minutes initially, then every 30 minutes, and hourly for the first 24 hours.
This elevated blood pressure target is usually temporary. Once the acute phase of the stroke passes and the brain stabilizes, typically after the first 24 to 72 hours, blood pressure management shifts. The long-term goal then becomes to gradually reduce blood pressure to healthier levels, usually below 140/90 mmHg, or even lower for some individuals. This long-term management is important for preventing future strokes and other cardiovascular events.