What is a stroke?

A stroke¹ is where the blood supply of an area of brain is cut off, either by a blood clot (thrombotic stroke)blocking the blood vessel or by the vessel bleeding (haemorrhagic stroke). That piece of brain dies and this causes a loss of function, the function depending on which part of the brain is affected. There is an area around the dead brain tissue called the penumbra with reduced blood supply which can still be salvaged with treatment. Diffusion-perfusion magnetic resonance imaging that demonstrates swelling and blood flow of the brain is the scan that shows the penumbra best.

The dying cells in the area of stroke release various chemicals² that affect the penumbra - for example increasing its oxygen needs, and so making the blood supply even more critical. Therefore treatments for stroke look at reducing these harmful effects (neuroprotective agents).

Current treatment of stroke

Good stroke care includes general measures to prevent any further damage to the brain by maximising the blood supply of the penumbra. This includes good hydration, maintaining the patient's blood pressure³ and normal blood sugar, and oxygen if required. Until recently there was no treatment to reduce the amount of brain affected, but now treatment can be given to reopen the vessel by dissolving any clot. This is only given when an early CT⁴ scan rules out a haemorrhagic stroke. The CT scan must be performed in the first three hours and interpreted by a suitably experienced radiologist. Specialists have renamed stroke "brain attack" to emphasis the need for speedy assessment. However very few centres in the UK have the necessary personnel and procedures to provide this treatment.

The drug , tissue plasminogen activator (tPA), is given either intravenously or intraarterially and reduces the disability suffered but slightly increases the death rate. The treatment cannot be offered without clinicians and radiologists experienced in its use. The treatment is only suitable for a small proportion (around 5% or less) of stroke victims anyway.

Areas of research

Many areas of promising research have not produced equally promising results in clinical trials. The critical area for neuroprotective agents is the timing of administration. NMDA receptor ⁵ blockers have been trialled but the results so far have been disappointing. The window for benefit seems to be 1-2 hours after the artery being blocked. Free radical scavengers also have failed to realise the benefit shown in animal models.

Prevention

Prevention is very important since brain tissue doesn't regenerate for practical purposes (with current treatment anyway). Picking up high blood pressure and treating it, treating other cardiovascular risk factors (high cholesterol, smoking) and giving blood thinners for those at risk of thrombosis (irregular heart rhythm) all reduce strokes.