Stroke Explained: From Interrupted Blood Flow to Neurological Deficit

FAST is useful because it helps us recognise a possible stroke quickly, but it does not explain what is actually happening inside the brain. To understand stroke properly, start with normal cerebral blood flow and then follow what changes.

The brain needs a continuous supply of oxygen and glucose. Neurones have a high metabolic demand and very limited energy reserves, so interruption of blood flow can affect neurological function within minutes. Which function changes depends on which part of the brain is affected. That is why stroke does not simply mean “weakness”: one patient may develop facial and arm weakness, another may lose language, vision or coordination, and another may become acutely dysphagic or less conscious.

From normal cerebral blood flow to a stroke

Blood reaches the brain through the carotid and vertebrobasilar arterial systems. Under normal conditions, cerebral circulation delivers enough oxygen and glucose for neurones to maintain adenosine triphosphate (ATP), ion gradients and normal electrical activity. A stroke occurs when this circulation is suddenly disrupted by either ischaemia or haemorrhage.

Most strokes are ischaemic. In an ischaemic stroke, an artery becomes occluded, commonly by a thrombus forming locally or an embolus travelling from elsewhere. Blood flow beyond the obstruction falls. The tissue with the most severe reduction in perfusion may progress rapidly towards irreversible infarction. Around this may be an area of hypoperfused tissue known as the ischaemic penumbra. Cells in the penumbra are not functioning normally, but some tissue may remain viable if blood flow can be restored in time.

This is the physiology behind the phrase “time is brain”. It does not mean every patient has the same treatment window or that all threatened tissue dies at the same rate. It means that delays can allow potentially salvageable brain tissue to become irreversibly injured.

At cellular level, reduced oxygen and glucose means less ATP can be produced. ATP-dependent ion pumps begin to fail, cell membranes depolarise and calcium enters cells. Excitatory neurotransmitter activity, oxidative stress, inflammation and cellular swelling contribute to further injury. If perfusion is not restored, cells within the affected region can die and the tissue becomes infarcted.

A haemorrhagic stroke is different. Here, a cerebral blood vessel ruptures and blood enters or surrounds brain tissue. The injury is therefore not caused by an arterial clot that needs dissolving or removing. Blood can directly damage tissue, increase local pressure and contribute to secondary brain injury. This distinction matters because treatment for an ischaemic stroke can be inappropriate or dangerous in intracranial haemorrhage. The team therefore needs urgent brain imaging before making reperfusion and antithrombotic treatment decisions.

So follow the mechanism:

artery blocked → cerebral perfusion falls → neurones lose oxygen and glucose → neurological function fails → threatened tissue may progress to infarction

or:

vessel ruptures → bleeding occurs within or around brain tissue → tissue is damaged and pressure effects may develop → neurological function changes

Why the symptoms depend on where the stroke happens

A stroke produces a focal neurological deficit because a particular region or pathway has been disrupted. Motor and sensory pathways cross at different points in the nervous system, so a cerebral hemispheric stroke commonly produces weakness or sensory change on the opposite side of the body.

FAST looks for facial weakness, arm weakness and speech disturbance, followed by the instruction that it is time to seek emergency help. These are common stroke features, but FAST is a screening tool rather than a rule-out test. A person can have a stroke without being FAST-positive.

For example, a middle cerebral artery territory stroke may produce weakness or sensory loss affecting the face and arm more than the leg. If the dominant hemisphere is affected, language may also be disrupted. Anterior cerebral artery territory strokes can produce more prominent leg deficits. Posterior circulation strokes may affect balance, coordination, eye movements, vision, swallowing or consciousness. These are useful anatomical patterns, but students should not try to diagnose the occluded artery from bedside findings alone.

Language disturbance also deserves more thought than simply writing “speech affected”. Dysarthria is a motor speech problem: the patient knows what they want to say, but the muscles and coordination required for clear speech are affected. Aphasia is a disorder of language and can affect speaking, understanding, reading or writing.

Imagine a patient who answers a question with fluent but inappropriate words and cannot follow a simple verbal instruction. It would be easy to document that the patient is “confused”. But if the problem is aphasia caused by a dominant-hemisphere stroke, that description misses an important focal neurological deficit. Use short sentences, give the patient time to respond, observe their comprehension and support alternative ways of communicating. Difficulty speaking does not automatically mean reduced intelligence, confusion or lack of decision-making capacity.

The exact time of symptom onset is also clinically important. If onset was not witnessed, the team needs the time the patient was last known well. A vague entry such as “weak this morning” is far less useful than documenting that the patient was at their neurological baseline at 08:20 and was found with new right-sided weakness and aphasia at 08:45.

Blood glucose is checked early because hypoglycaemia can produce neurological symptoms that mimic stroke. Other stroke mimics exist, but sudden focal neurological change must still be treated seriously and assessed through the appropriate emergency pathway.

Bring the pathophysiology back to the patient

Once stroke is suspected, the immediate question is not simply “is this a stroke?” The team needs to establish what has happened, where the problem is, how much brain tissue may already be injured and whether time-critical treatment is appropriate.

Current NICE guidance recommends rapid recognition using a validated tool such as FAST outside hospital and exclusion of hypoglycaemia in people with sudden neurological symptoms. People with suspected acute stroke should receive specialist stroke assessment and brain imaging according to the emergency pathway. Non-enhanced computed tomography (CT) can identify intracranial haemorrhage and other important findings. When thrombectomy may be indicated, vascular imaging such as CT angiography is used to identify an arterial occlusion, and selected later-presenting patients may require perfusion or magnetic resonance imaging to assess whether potentially salvageable tissue remains.

For selected patients with acute ischaemic stroke, intravenous thrombolysis may be used to promote reperfusion after intracranial haemorrhage has been excluded and eligibility has been assessed. NICE includes alteplase and tenecteplase as options within relevant guidance. Treatment is delivered through organised stroke services with trained staff and protocols because thrombolysis carries important bleeding risks and requires close monitoring.

Mechanical thrombectomy is different. Rather than using a medicine to promote clot breakdown, an interventional team passes a device through the arterial circulation to remove an occluding clot from an eligible large artery. Selection depends on factors including vessel location, time, imaging, the amount of established infarction, potentially salvageable tissue and the patient’s overall clinical status. Some patients may receive intravenous thrombolysis as well as thrombectomy. Importantly, a patient who wakes with stroke symptoms or presents later is not automatically “too late”: advanced imaging can identify selected patients who may still benefit from reperfusion treatment.

Haemorrhagic stroke follows another pathway. Management can include careful blood-pressure treatment in appropriate patients, reversal of anticoagulation when indicated, management of complications and neurosurgical or specialist intervention in selected cases. This is another reason students should never assume that a sudden neurological deficit should be treated with an antiplatelet or thrombolytic medicine before imaging and specialist assessment.

Now bring that into nursing care. The student nurse may be the person who first notices that an admitted patient suddenly cannot lift one arm, has developed facial asymmetry or is using the wrong words. The useful response is not to complete an elaborate neurological diagnosis. It is to recognise the change, establish the time, assess the patient, obtain appropriate observations including blood glucose according to the clinical pathway, and escalate immediately to the registered nurse and emergency or stroke team.

After an acute stroke, neurological and physiological observations help identify deterioration. Oxygen is not routinely required simply because someone has had a stroke: NICE recommends supplemental oxygen when oxygen saturation falls below 95%, while individual clinical circumstances and local protocols still need to be considered. Blood pressure also needs careful interpretation because management differs according to stroke type and potential reperfusion treatment. Students should measure and report accurately rather than independently trying to “normalise” an elevated blood pressure.

Swallowing is another immediate safety issue. Stroke can disrupt the motor control and sensation required for safe swallowing. A patient may aspirate food, drink or medication, sometimes without an obvious cough. NICE recommends that people with acute stroke have swallowing screened by an appropriately trained healthcare professional before oral food, fluid or medication is given. If swallowing difficulty is identified, further specialist assessment and a safe plan for hydration, nutrition and medicines are required.

That means “nil by mouth” is not a forgotten patient with a cup of water removed from the bedside. It is a temporary safety measure while the multidisciplinary team establishes how the person can receive fluids, nutrition and essential medicines safely.

Weakness also changes basic nursing care. An affected arm needs safe positioning and handling, particularly around the shoulder. Reduced mobility increases risks including pressure damage and venous thromboembolism, while sensory loss or neglect can make the patient less aware of the affected side. Mobilisation and rehabilitation are individualised through the specialist stroke multidisciplinary team rather than rushed simply because early movement sounds beneficial.

Stroke care is also communication care. A person who cannot find words may still understand exactly what is happening. Someone with neglect may not recognise one side of their environment. Dysphagia can remove the simple comfort of eating and drinking. Sudden dependence for washing, toileting or mobility can be frightening and humiliating. Good nursing therefore means protecting dignity, explaining what is happening, involving the person in decisions, communicating in an accessible way and noticing the psychological as well as physical effects of sudden neurological disability.

For the student nurse, the reasoning sequence is:

sudden neurological change → recognise possible stroke → establish onset or last-known-well time → assess and exclude hypoglycaemia → activate the emergency pathway → urgent imaging distinguishes the underlying process → specialist assessment determines treatment → ongoing nursing care protects neurological, respiratory, swallowing, mobility, skin, communication and psychological needs.

FAST starts the response. Understanding the cerebral circulation and the brain tissue at risk explains why that response has to be fast.

References

National Institute for Health and Care Excellence (NICE). Stroke and transient ischaemic attack in over 16s: diagnosis and initial management (NG128). Available at: NICE NG128.

Royal College of Physicians. National Clinical Guideline for Stroke. Available at: National Clinical Guideline for Stroke.

Nursing and Midwifery Council (NMC). The Code: Professional standards of practice and behaviour for nurses, midwives and nursing associates. Available at: NMC Code.