Hypoxic Brain Injury

Feature | Hypoxic Brain Injury

A constant supply of oxygen is needed by the brain to function, but in some cases, an event that may be internal or external to the body disrupts it. Hypoxic brain injury occurs when the brain is not receiving enough oxygen, which prevents the body from functioning without impairment. Read on to know more about this type of brain injury.

Hypoxic Brain Injury | Everything You Need to Know

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Differentiating Hypoxic From Anoxic

This cerebral type of brain injury occurs when some oxygen is received by the brain but not enough to enable the body to function without impairment. If the brain is absolutely deprived of oxygen, it is called a cerebral anoxic injury.

There are four types of hypoxia in the brain - diffuse cerebral hypoxia, focal cerebral ischemia, global cerebral ischemia, and cerebral infarction. Of these, global cerebral ischemia is considered the worst. If there is a prolonged lack of enough oxygen, neuronal cell death is induced via apoptosis. This results in a hypoxic brain injury.

In cases of complete oxygen deprivation or anoxia, this can be hypoxic in origin with reduced oxygen availability, or ischemic in origin (secondary to blood flow). Brain injuries because of oxygen deprivation that is due to hypoxic or anoxic mechanisms are called hypoxic/anoxic injuries.

Hypoxic-ischemic encephalopathy is a problem that happens the brain is deprived of enough oxygen. The deprivation, though, is not complete. This condition often happens in situations of birth asphyxia. It is also a common finding in patients who have sustained a cardiac arrest. These patients recover their oxygenation, but changes occur within the damaged cells themselves that lead to programmed cell death or apoptosis in certain cells. When this happens, those cells do not recover, and there is permanent disability.

Classification of Cerebral Hypoxic Injury

Cerebral hypoxic injury can be categorized depending on the location and severity of the oxygen deprivation of the brain. Anoxic anoxia is when the body simply cannot take in enough oxygen, such as on high mountains or in tight and inadequately ventilated spaces. Anemic anoxia results from a decrease in the total hemoglobin in the blood. Toxic anoxia occurs when toxic substances in the blood restrict utilization of oxygen. This could be caused by formaldehyde, certain narcotics, carbon monoxide, or certain poisons. Finally, stagnant hypoxia is a result of very low blood pressure or a reduction of cerebral flow. This results from a stroke or heart attack.

Causes of Hypoxic Brain Injury

Hypoxic injuries can be caused by an event that interferes with the brain tissue's ability to receive or process oxygen. The actual event can be internal to the body or external.

Mild to moderate forms of hypoxic injury to the brain can be caused by things like anemia and asthma, which interfere with breathing and blood oxygenation abilities. Other causes include flying in an unpressurized cabin or at high altitudes. It can also be caused by the ascent from a deep water dive or status epilepticus. Intense exercise at high altitudes without being acclimatized to the altitude can also be a cause.

Severe instances of hypoxic injury to the brain are caused by drug overdoses or smoke inhalation. It can also be due to shock, status asthmaticus, choking, strangulation, drowning, and crushing of the trachea. They can also be caused by self-indulged blockage of the carotid artery and erotic asphyxiation.

A transient ischemic attack or TIA is sometimes called a mini-stroke. It involves having transient neurological findings without true infarction. It can affect the brain, the spinal cord, or the retina. It usually resolves without sequelae after a few minutes. The symptoms are exactly like a stroke, but they pass because the blockage resolves itself. While the symptoms usually pass within 24 hours, the brain injury itself happens for just a few minutes. Having a TIA becomes a risk factor for having a stroke in the future.

A silent stroke, however, has no outward symptoms, which leads to affected individuals being unaware that they had a stroke. Even so, there is brain damage going on and they are at risk of having a stroke in the future. In a study done in 1998, it was estimated that more than 11 million people have had a stroke in the U.S. About 770,000 of these were without symptoms and 11 million were silent infarcts found on MRI. They were either infarcts or hemorrhages. Women were also found to be at a greater risk of having a silent stroke. Predisposing factors include high blood pressure and cigarette smoking.

Pre- and Postnatal Hypoxic Injury

Hypoxic injury can affect a fetus during the various stages of fetal development, from labor to the postnatal period. Problems predisposing a fetus to this condition include maternal diabetes and preeclampsia. It also includes congenital infections and severe fetal anemia. Drug or alcohol abuse and maternal vascular are also on the list. Cardiac disease and problems affecting blood flow to the placenta can also be an issue.

Problems during the labor and delivery process involve umbilical cord occlusion and umbilical cord torsion or prolapse. It also includes rupture of the uterus and the placenta. Bleeding from behind the placenta and abnormal fetal position can also be an issue. Very low blood pressure in the mother and prolonged late stages of labor are also on the list.

Meanwhile, problems also occur after the delivery is over with. These include congenital malformations of the brain, very low blood pressure in the baby, trauma to the fetal skull or brain, serious infections in the newborn, severe lung or heart disease in the baby, or extreme prematurity.

It is possible to assess the degree of neonatal hypoxic-ischemic brain trauma using the Sarnat Staging. This staging is based on MRI findings and EEG results.

Signs and Symptoms of Hypoxic Brain Injury

The body responds to a lowering of the oxygen by sending more blood to the brain and less blood to the peripheral tissues. Cerebral blood flow is increased up to twice the normal amount. If the increased blood flow is enough, then there will be no symptoms. If, on the other hand, the twice-increased blood flow is not enough, then symptoms of cerebral hypoxia begin.

In the second scenario, the first things to go are complex learning tasks and short-term memory skills. If the cognitive deprivation is allowed to continue, there will be cognitive disturbances and deficits in the motor control. The skin may be cyanotic (bluish) and the heart rate goes up. Even more oxygen deprivation and there is fainting, coma, loss of consciousness, seizures, loss of brainstem function, and death.

Blood oxygen saturation can be used in situations of hypoxic hypoxia. Although, it means nothing in other types of hypoxia. Normal pulse oximeter reading is 95 to 100 percent. Any reading below 86 percent is considered severe hypoxia.

Cerebral hypoxia is a reference to the oxygen levels in the brain's tissue and not in the blood. Often, blood oxygenation will be normal in situations of ischemic, hypemic, and hystoxic cerebral hypoxic injuries. The degree of oxygenation in the brain tissue will depend upon how well the body copes with the reduced oxygen content in the blood.

Treatment of Hypoxic Injuries

For newborns starved of oxygen during the birth process, the latest treatment is hypothermic therapy. It is done within six hours of the cerebral hypoxia and improves neonatal outcomes and survivability. Yet, it is a less effective treatment for adults and the major objective is to restore oxygen to the brain as quickly as possible. If the hypoxia is mild, simply removing the cause is enough in clearing up the problem. Life support measures and measures to reduce damage to the brain are also important. Doctors can also apply inhaled oxygen to bring up the oxygen tension.

A person in a deep coma will have problems with the body's breathing reflexes. This is even after the initial hypoxia has been taken care of and mechanical ventilation might be necessary. In severe cases of hypoxia, there is elevated heart rate or even heart failure. CPR, epinephrine, defibrillation, and atropine may be used in resuscitation efforts. Because of the probability of seizures following severe cerebral asphyxia, anticonvulsants may be necessary.

Complications of Hypoxic Injury

Brain damage is possible during or after oxygen deprivation. Cells develop acidosis during oxygen deprivation and free radicals build up. When the oxygen comes back into the tissues that were hypoxic, the cellular material mixes with oxygen to create a lot of oxidants. These oxidants interfere with normal brain chemistry. This is a reperfusion injury and creates more problems for the brain.

Research Into Hypoxic Injuries

Research is ongoing on some techniques preventing damage to brain cells. Things like hypothermia for neonatal hypoxia are an evidence-based treatment. Antioxidant drugs and controlling blood glucose can help. Thinning of the blood can also help. Some doctors are also looking into drug-induced hypertension. Hyperbaric oxygen might work in some circumstances as it might reduce the overall systemic inflammatory response.

 

Check out this clip from WaysAndHow, which talks about the signs and symptoms of Hypoxia:

Brain cells are very sensitive to reduced oxygen levels. They will begin to die within five minutes when they lack oxygen. This is why it is important to act as soon as possible after the hypoxic the brain injury. Learning about its causes, symptoms, and treatment can help a lot in lowering or avoiding its risks.

 

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Editor's Note: This article has been updated for accuracy and relevancy. 

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