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What Are Anoxic and Hypoxic Brain Injuries?

Medically Reviewed by Melinda Ratini, DO, MS on August 12, 2022

Your brain needs a constant supply of oxygen to work properly and survive. But if something interrupts or cuts off the oxygen flow to your brain for 4 minutes or longer, brain cells begin to die. This can cause serious, and in some cases, permanent brain damage.

If your brain gets reduced oxygen flow for a few minutes, you might have hypoxic brain injury or cerebral hypoxia. But if the supply is completely cut off and no oxygen reaches the brain, it’s called anoxic brain injury or cerebral anoxia. Sometimes the two terms are used interchangeably or together as hypoxic-anoxic brain injury.

Here’s a closer look at what happens if you have this type of brain injury, the chances of recovery, and what it might mean for your loved one.

What Happens When Your Brain Lacks Oxygen?

The brain uses up to one-fifth of your body’s oxygen supply. It uses oxygen to send nerve signals to help your body work properly. But when the oxygen supply is low or cuts off, brain cells begin to die. If the brain goes too long without oxygen, it could cause brain death or coma.

What Causes Hypoxic or Anoxic Brain Injury?

Many things can cause your brain to not get enough oxygen, such as:

  • Cardiac arrest
  • Irregular heart rhythm (arrhythmia)
  • Heart attack
  • Low blood pressure from blood loss or poor heart function
  • Strangulation
  • Choking
  • Suffocation
  • Serious asthma attack
  • Complication from general anesthesia during surgery or other medical procedures
  • Near drowning
  • Exposure to high altitudes
  • Breathing in smoke
  • Inhaling carbon monoxide
  • Poisoning
  • Drug overdose
  • Electric shock
  • Seizure
  • Stroke
  • Head injury including traumatic brain injury from blunt force, which can be caused by falls, car accidents, gunshot wounds, sports injuries, or injuries at work

Symptoms of Brain Injury When You Lack Oxygen

Within 15 seconds of low oxygen supply to your brain, you’ll usually lose consciousness. Other immediate brain injury symptoms include:

  • Slurred speech
  • Trouble forming sentences
  • Confusion
  • Feeling disoriented
  • Facial drooping
  • A bluish or grayish tint to the skin and lips
  • Shallow or fast breathing
  • Dilated pupils, when the black centers of your eyes are larger than normal
  • Trouble responding to name or squeezing the hand
  • Seizures

If someone you know has such symptoms, call 911 immediately.

How Is Hypoxic or Anoxic Brain Injury Diagnosed?

Usually, doctors can figure out there’s been a brain injury from lack of oxygen at the early stage or on arrival at the hospital, especially when they hear details about what happened or what may have caused it.

To confirm the diagnosis, they’ll order a few tests to check for brain function and to see how serious the damage may be.

Angiography. This test will check blood flow to the brain.

Imaging tests like CT scan or MRI. The doctor will look for signs of stroke, bleeding in the brain, brain swelling, or other signs of injury.

Electroencephalogram (EEG). Doctors will measure electrical activity in the brain.

Evoked potentials test. Doctors do this to find out the brain’s response to sensations like sight, sound, and touch.

How Is Hypoxic or Anoxic Brain Injury Treated?

If someone you know shows symptoms of hypoxic or anoxic brain injury, they’ll need immediate medical attention. As soon as you get to the hospital, doctors will quickly try to restore good oxygen supply to the brain. They’ll also give medications to get your heartbeat and blood pressure under control.

Each brain injury case is different, and treatment will depend on how serious your condition is. For serious brain injuries, you’ll most likely be admitted to the intensive care unit (ICU), usually in an area that specializes in brain problems. This may be called the neurology ICU. You’ll most likely need a ventilator to help you breathe.

In some cases, they may use a medically induced cooling method called therapeutic hypothermia. Doctors use cooling blankets to lower your body temperature for a short period of time. It’s usually lowered to 89 F to 93 F (32C to 34C). The treatment usually lasts about 24 hours. Then they rewarm your body.

Research shows that this treatment might have a protective effect on the brain. It might lessen inflammation, injury, and reduce brain damage. There’s some evidence it may reduce the amounts of oxygen and energy brain cells need. This process might improve your odds of recovery.

Effects of Anoxic or Hypoxic Brain Injury

If you have hypoxic or anoxic brain injury, it could put you in a coma. When that happens, it looks like you’re asleep and you won’t respond if you’re called or stimulated in some way. It’s also possible to change from a coma to what’s called a vegetative state. That’s when you’re awake, but you still don’t react to stimulation. Doctors call it “wakeful unresponsiveness.”

The brain injury might also cause seizures. Death of brain cells happens within 5 minutes of decreased oxygen supply.

If you have a serious brain injury and you do regain consciousness, you’re more likely to have lingering effects such as:

  • Headache
  • A hard time keeping your balance
  • Vision problems
  • Seizures
  • Changes in how your senses help you experience your surroundings
  • Trouble speaking and swallowing
  • Changes in sleep pattern
  • Lack of bowel and bladder control
  • Changes in sexual function
  • Trouble moving all or parts of your body, especially your limbs
  • Personality changes
  • Difficulty forming sentences
  • A hard time remembering things
  • Depression
  • A hard time concentrating
  • Confusion
  • Trouble communicating
  • Difficulty with reason, focus, and logic
  • Mood swings
  • Limited attention span
  • Not knowing where you are or things like the time and date
  • Forgetfulness
  • Acting inappropriately

What Are the Odds of Recovery and Survival?

Your odds of recovery will depend on:

  • How long your brain went without oxygen
  • How serious your brain injury is
  • Your age at the time of brain injury. You’re more likely to have a better recovery if you’re younger than 50.
  • How long you’ve been in a coma

If you had mild to moderate hypoxic brain injury, you may have few symptoms and might recover without any long-term effects. But with moderate anoxic brain injury, recovery may take months or years. If your doctor sees good improvement within the first month after the injury, your long-term outcome might be better.

Studies show that if you come out of a coma in less than 4 weeks, you’re less to likely to have long-term effects than if it lasts longer.

But if you have a severe anoxic brain injury and are in a vegetative state for 3 months or more, your odds of recovery or survival are not very good.

For better results, it’s important to work with a range of specialists including physical therapists, speech-language therapists, and occupational therapists as soon as possible.

How Can You Prevent Hypoxic or Anoxic Brain Injury?

If someone you know shows signs of a lack of blood supply to the brain, perform CPR and give mouth-to-mouth breaths, especially if their heart stops or they lose consciousness. This can improve blood flow and oxygen to the brain till a medical team can help. It can also lower the risk for serious brain injury.

Here are a few safety steps you can take to lower your risk for accidents that cause brain injury.

You can:

  • Wear seatbelts.
  • Wear helmets when you bike, skate, or ski.
  • Use life vests, swim at places that have lifeguards, and supervise children around water. This includes bathtubs.
  • Install smoke detectors and carbon monoxide detectors in your home.

Show Sources

SOURCES:

Cleveland Clinic: “Cerebral Hypoxia,” “Evoked Potentials.”

Headway – The Brain Injury Association: “Hypoxic and anoxic brain injury.”

Shepherd Center: “Anoxic and Hypoxic Brain Injury.”

Johns Hopkins Medicine: “Therapeutic Hypothermia After Cardiac Arrest.”

Brain Foundation (Australia): “Vegetative State.”

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