Brain ischemia is a condition in which there is insufficient bloodflow to the

brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...

to meet metabolic demand. This leads to poor oxygen supply in the brain and may be temporary such as in transient ischemic attack or permanent in which there is death of brain tissue such as in cerebral infarction (

ischemic stroke Stroke is a medical condition in which poor blood flow to a part of the brain causes cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. Both cause parts of the brain to stop ...

). The symptoms of brain ischemia reflect the anatomical region undergoing blood and oxygen deprivation, and may involve impairments in

vision Vision, Visions, or The Vision may refer to: Perception Optical perception * Visual perception, the sense of sight * Visual system, the physical mechanism of eyesight * Computer vision, a field dealing with how computers can be made to gain und ...

, body movement, and

speaking Speech is the use of the human voice as a medium for language. Spoken language combines vowel and consonant sounds to form units of meaning like words, which belong to a language's lexicon. There are many different intentional speech acts, su ...

. An interruption of blood flow to the brain for more than 10 seconds causes unconsciousness, and an interruption in flow for more than a few minutes generally results in irreversible brain damage. In 1974, Hossmann and Zimmermann demonstrated that ischemia induced in mammalian brains for up to an hour can be at least partially recovered. Accordingly, this discovery raised the possibility of intervening after brain ischemia before the damage becomes irreversible.

Symptoms and signs

The clinical presentation of brain ischemia varies depending on the affected vascular territory. Ischemia in the anterior circulation, particularly branches of the internal carotid artery, may present with unilateral weakness, speech disturbances, or visual loss in one eye (amaurosis fugax).Posterior circulation ischemia, involving the vertebrobasilar arteries, often leads to symptoms such as vertigo, diplopia, dysarthria, or bilateral motor deficits.Transient symptoms may indicate a TIA, while prolonged or severe cases may progress to permanent deficits due to cerebral infarction. Sudden loss of consciousness can occur when cerebral blood flow ceases for over 10 seconds, and irreversible brain damage generally follows within minutes.

Causes and Risk Factors

Brain ischemia results from conditions that reduce or block cerebral blood flow. Common causes of focal ischemia include arterial thrombosis due to atherosclerosis, embolism from cardiac sources such as atrial fibrillation, and small vessel disease associated with hypertension or diabetes. Global ischemia usually arises from systemic hypoperfusion following cardiac arrest or severe hypotension. Additional risk factors include smoking, hyperlipidemia, advanced age, and a history of TIA or stroke. Rare etiologies include sickle cell anemia, which promotes vascular occlusion, and Moyamoya disease, a progressive cerebrovascular disorder affecting the intracranial arteries.

Pathophysiology

When blood supply to the brain is compromised, neurons are deprived of oxygen and glucose necessary for aerobic metabolism. This leads to rapid depletion of adenosine triphosphate (ATP) within minutes. The failure of ATP-dependent ion pumps disrupts electrochemical gradients, resulting in cellular depolarization and an influx of calcium. Elevated intracellular calcium triggers glutamate release, proteolysis, and ultimately, neuronal injury. Surrounding the infarcted core is the 'ischemic penumbra,' a zone of hypoperfused tissue that retains some metabolic activity and may be salvageable with timely intervention.

Diagnosis

Diagnosis of brain ischemia begins with prompt clinical assessment of neurological deficits, often using tools such as the NIH Stroke Scale. Immediate brain imaging is essential to confirm ischemia and exclude hemorrhage. Noncontrast computed tomography (CT) is typically the first step due to its availability and speed. Magnetic resonance imaging (MRI) with diffusion-weighted imaging offers higher sensitivity for detecting acute ischemia. Additional studies, including CT or MR angiography and carotid Doppler ultrasound, help identify vascular occlusions or stenosis. Cardiac evaluation, such as echocardiography and ECG monitoring, may be necessary in cases with suspected embolic sources.

Focal brain ischemia

Focal brain ischemia occurs when a

blood clot A thrombus ( thrombi) is a solid or semisolid aggregate from constituents of the blood (platelets, fibrin, red blood cells, white blood cells) within the circulatory system during life. A blood clot is the final product of the blood coagulatio ...

has occluded a cerebral vessel. Focal brain ischemia reduces blood flow to a specific brain region, increasing the risk of

cell death Cell death is the event of a biological cell ceasing to carry out its functions. This may be the result of the natural process of old cells dying and being replaced by new ones, as in programmed cell death, or may result from factors such as di ...

to that particular area. It can be either caused by

thrombosis Thrombosis () is the formation of a Thrombus, blood clot inside a blood vessel, obstructing the flow of blood through the circulatory system. When a blood vessel (a vein or an artery) is injured, the body uses platelets (thrombocytes) and fib ...

or embolism.

Global brain ischemia

Global brain ischemia occurs when blood flow to the brain is halted or drastically reduced. This is commonly caused by

cardiac arrest Cardiac arrest (also known as sudden cardiac arrest CA is when the heart suddenly and unexpectedly stops beating. When the heart stops beating, blood cannot properly Circulatory system, circulate around the body and the blood flow to the ...

. If sufficient circulation is restored within a short period of time, symptoms may be transient. However, if a significant amount of time passes before restoration, brain damage may be permanent. While reperfusion may be essential to protecting as much brain tissue as possible, it may also lead to reperfusion injury. Reperfusion injury is classified as the damage that ensues after restoration of blood supply to ischemic tissue. Carotid artery stenosis may cause focal brain ischemia through artery-to-artery embolism or global brain ischemia if very severe stenosis with limited to no blood flow through the carotid artery. Due to different susceptibility to ischemia of various brain regions, a global brain ischemia may cause focal brain infarction. The

cerebral cortex The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. It is the largest site of Neuron, neural integration in the central nervous system, and plays ...

and

striatum The striatum (: striata) or corpus striatum is a cluster of interconnected nuclei that make up the largest structure of the subcortical basal ganglia. The striatum is a critical component of the motor and reward systems; receives glutamat ...

are more susceptible than the thalamus, and the thalamus in turn is more sensitive than the brainstem. Partial cerebral cortex infarction from global brain ischemia typically manifests as watershed stroke. The outcome of brain ischemia is influenced by the quality of subsequent supportive care. Systemic blood pressure (or slightly above) should be maintained so that cerebral blood flow is restored. Also, hypoxaemia and

hypercapnia Hypercapnia (from the Greek ''hyper'', "above" or "too much" and ''kapnos'', "smoke"), also known as hypercarbia and CO2 retention, is a condition of abnormally elevated carbon dioxide (CO2) levels in the blood. Carbon dioxide is a gaseous pro ...

should be avoided. Seizures can induce more damage; accordingly, anticonvulsants should be prescribed and should a seizure occur, aggressive treatment should be undertaken. Hyperglycaemia should also be avoided during brain ischemia. A closely related disease to brain ischemia is brain hypoxia. Brain hypoxia is the condition in which there is a decrease in the oxygen supply to the brain even in the presence of adequate

blood flow Hemodynamics American and British English spelling differences#ae and oe, or haemodynamics are the Fluid dynamics, dynamics of blood flow. The circulatory system is controlled by homeostasis, homeostatic mechanisms of autoregulation, just as hydrau ...

. If hypoxia lasts for long periods of time,

coma A coma is a deep state of prolonged unconsciousness in which a person cannot be awakened, fails to Nociception, respond normally to Pain, painful stimuli, light, or sound, lacks a normal Circadian rhythm, sleep-wake cycle and does not initiate ...

seizures A seizure is a sudden, brief disruption of brain activity caused by abnormal, excessive, or synchronous neuronal firing. Depending on the regions of the brain involved, seizures can lead to changes in movement, sensation, behavior, awareness, o ...

, and even

brain death Brain death is the permanent, irreversible, and complete loss of Electroencephalography, brain function, which may include cessation of involuntary activity (e.g., Control of ventilation#Control of respiratory rhythm, breathing) necessary to su ...

may occur. Symptoms of brain hypoxia are similar to ischemia and include inattentiveness, poor judgment, memory loss, and a decrease in

motor coordination In physiology, motor coordination is the orchestrated movement of multiple body parts as required to accomplish intended actions, like walking. This coordination is achieved by adjusting kinematic and kinetic parameters associated with each bo ...

. Potential causes of brain hypoxia are suffocation,

carbon monoxide poisoning Carbon monoxide poisoning typically occurs from breathing in carbon monoxide (CO) at excessive levels. Symptoms are often described as " flu-like" and commonly include headache, dizziness, weakness, vomiting, chest pain, and confusion. Large ...

, severe

anemia Anemia (also spelt anaemia in British English) is a blood disorder in which the blood has a reduced ability to carry oxygen. This can be due to a lower than normal number of red blood cells, a reduction in the amount of hemoglobin availabl ...

, and use of drugs such as

cocaine Cocaine is a tropane alkaloid and central nervous system stimulant, derived primarily from the leaves of two South American coca plants, ''Erythroxylum coca'' and ''Erythroxylum novogranatense, E. novogranatense'', which are cultivated a ...

and other

amphetamines Substituted amphetamines, or simply amphetamines, are a chemical class, class of compounds based upon the amphetamine structure; it includes all derivative (chemistry), derivative compounds which are formed by replacing, or substitution reacti ...

. Other causes associated with brain hypoxia include

drowning Drowning is a type of Asphyxia, suffocation induced by the submersion of the mouth and nose in a liquid. Submersion injury refers to both drowning and near-miss incidents. Most instances of fatal drowning occur alone or in situations where othe ...

strangling Strangling or strangulation is compression of the neck that may lead to unconsciousness or death by causing an increasingly hypoxic state in the brain by restricting the flow of oxygen through the trachea. Fatal strangulation typically occur ...

choking Choking, also known as foreign body airway obstruction (FBAO), is a phenomenon that occurs when breathing is impeded by a blockage inside of the respiratory tract. An obstruction that prevents oxygen from entering the lungs results in oxygen de ...

, head trauma, and complications during general

anesthesia Anesthesia (American English) or anaesthesia (British English) is a state of controlled, temporary loss of sensation or awareness that is induced for medical or veterinary purposes. It may include some or all of analgesia (relief from or prev ...

. Treatment strategies for brain hypoxia vary depending on the original cause of injury, primary and/or secondary.

Management and Treatment

Treatment of brain ischemia depends on the type, location, and timing of the event. For acute ischemic stroke, intravenous thrombolysis with tissue plasminogen activator (tPA) is recommended within 4.5 hours of symptom onset. In patients with large vessel occlusions, endovascular mechanical thrombectomy offers substantial benefits when performed within 6 to 24 hours, particularly if imaging shows viable penumbral tissue. Supportive care includes blood pressure optimization, oxygenation, and management of complications such as fever and seizures. In global ischemia due to cardiac arrest, targeted temperature management (32–36 °C) may improve neurologic outcomes. Long-term care focuses on secondary prevention through antithrombotic therapy, control of vascular risk factors, and rehabilitation.

Prognosis and Outcomes

The clinical outcome of brain ischemia depends on the extent of injury, time to treatment, and patient comorbidities. Rapid reperfusion has been associated with significantly improved functional recovery and reduced mortality. However, delayed treatment or severe ischemia often results in long-term neurological deficits, including motor impairment, aphasia, and cognitive dysfunction. Approximately one-third of ischemic stroke survivors experience significant disability. In cases of global ischemia, outcomes are heavily influenced by the duration of cerebral hypoperfusion and the quality of post-resuscitation care. Vascular depression and vascular dementia may develop after multiple subcortical ischemic insults, particularly in older adults.

References

{{Authority control Vascular diseases Stroke Ischemia