Anoxic Brain Injury

Anoxic brain injury is a type of brain injury that isn't usually caused by a blow to the head. Instead, anoxic brain injury occurs when the brain is deprived of oxygen. Left without oxygen for too long, neural cells begin to die through a process called apoptosis. And though cell death is a normal part of the human experience, when a large number of brain cells simultaneously die, patients can be left with diminished brain function. If the oxygen deprivation continues, anoxic brain injuries may even become fatal.

What Causes Anoxic Brain Injury?

Anything that deprives the brain of oxygen can lead to an anoxic brain injury. Some of the most common causes include:

• Oxygen deprivation at birth among babies; this is particularly common when a baby becomes trapped in the birth canal or the umbilical cord is wrapped around his or her neck. 
• A traumatic attack or assault, such as being choked unconscious. 
• A stroke, which can deprive the brain of oxygen and blood for several minutes. 
• A transient ischemic attack (TIA), often called a mini-stroke, which deprives the brain of oxygen for anywhere from a few seconds to several minutes. 
• Choking.
• Anaphylactic shock due to allergic reactions. 
• Swallowing your own vomit. 
• Drug overdose. 
• A sudden blow to the windpipe. 

How Long Can the Brain Survive Without Oxygen?

Every brain is different, of course, and the extent of oxygen deprivation varies depending on the injury. Some causes of anoxic brain injuries only reduce oxygen and blood flow, while others eliminate it entirely. On average, the brain can survive a mere four minutes without oxygen, so if you suspect a stroke or other injury that is cutting off oxygen to the brain, you need to act immediately.

As easily as 30 seconds in, brain damage can begin, and at two minutes brain damage becomes almost inevitable. Even if you or your loved one feel fine after a loss of oxygen to the brain, you need to seek prompt medical treatment to reduce the potential long-term harm.

Signs and Symptoms of Anoxic Brain Injury

Immediately after an anoxic brain injury occurs, some telltale symptoms include:

• Confusion
• Loss of consciousness
• Feeling woozy or dizzy
• Vomiting
• Changes in behavior or sensation; your arms or legs may feel tingly or numb.
• Intense headache

The longer term effects of an anoxic brain injury vary greatly, and are largely dependent upon the area of the brain affected. For instance, if the brain's speech centers are affected, it's common to have difficulty speaking, remembering words, or even understanding speech. Anoxic brain injury sufferers can therefore suffer hundreds of symptoms, and one person's symptom profile might be quite different from the next. Some common signs, though, include:

• Changes in behavior or personality. 
• Difficulty with previously unchallenging tasks. 
• Changes in relationships. 
• Difficulty with short or long-term memory. 
• Trouble recognizing familiar people or animals. 
• New fears or phobias. 
• Psychological symptoms such as unexplained depression or anxiety. 
• Frequent headaches.
• Unexplained pain in the limbs. 

Degree and Extent of Anoxic Brain Injury

Doctors typically classify anoxic brain injuries into one of four categories. The classification can provide some insight into the long-term prognosis:

• Diffuse cerebral hypoxia: This is a mild to moderate injury that causes minimal brain impairment due to low blood oxygen levels.
• Focal cerebral ischemia: This is oxygen deprivation, usually due to a stroke, that occurs in a single area of the brain. This brain region may be affected, while other areas of the brain are left unharmed.
• Global cerebral ischemia: This is a complete cessation of blood flow and oxygen to the brain, and typically causes catastrophic harm.
• Cerebral infarction: This is a brain injury due to a stroke that completely deprives multiple brain regions of oxygen, leading to serious side effects.

Treatment and Prognosis

In the immediate aftermath of an anoxic brain injury, treatment focuses on locating the cause of the injury and ensuring it does not happen again. For instance, a stroke may be caused by a blood clot or other cardiovascular health issues that can be prevented with a combination of blood thinners and lifestyle changes.

From there, the prognosis depends on the extent of the injury, the age you are when the injury occurs, your access to quality care, and your commitment to your own recovery. Some strategies that improve outcomes include:

• Speech therapy with a skilled speech-language pathologist.
• Participating in a support group, particularly one that focuses on helping you regain the skills you have lost.
• Family support and mental health counseling.
• Occupational therapy to help you regain skills such as shopping and eating.
• Physical therapy to help rewire brain connections so that you can regain mobility.
• Education about your condition.
• Nutritional and exercise support and counseling.

Additional materials for further reading:

• Mount Sinai Hospital