A stroke is caused by a disruption in the supply of blood to the brain, which leads to cell death as oxygen is required. There are two types: ischaemic (where a clot cuts off blood supply to an area of the brain by blocking an artery) or haemorrhagic (when a blood vessel ruptures and leaks blood instead of delivering it to tissue). The most common cause of a stroke is a clot that made its way up to carotid arteries into the brain until it wedges in small vessel. There are many risk factors for blood clots, such as smoking, high cholesterol levels, atrial fibrillation and long distance flights.
Because the brain is always in high demand of oxygen (taking 20% of the total oxygen available), strokes can produce devastating effects within minutes. 5 minutes of oxygen deprivation can lead to irreversible cell death, a principle that is also used in cases of shock, where the blood pressure is too low to supply organs, or cardiac arrest. Therefore, it is crucial to recognise a stroke early so that an ambulance may arrive and deliver clot-busting medication such as streptokinase.
The FAST mnemonic is an effective way of remembering the common signs of a stroke. It is also useful in reminding people to respond fast.
- F - Facial weakness: Is the person’s smile crooked? Disrupted brain function causes facial weakness on the opposite side. The weakness is usually seen around the mouth or eyes.
- A - Arm weakness: Can the person keep both arms outstretched? This is related to motor function of the brain.
- S - Speech difficulty: Is the person’s speech slurring or are they having problems understanding speech? This is a combined result of impaired motor function and speech centres of the brain.
- T - Time to act: Call an ambulance. NOW.