Anoxic Brain Injury
Cerebral hypoxia occurs when there is not enough oxygen getting to the brain. The brain needs a constant supply of oxygen and nutrients to function. Cerebral hypoxia affects the largest parts of the brain, called the cerebral hemispheres. However, the term is often used to refer to a lack of oxygen supply to the entire brain.
In cerebral hypoxia, sometimes only the oxygen supply is interrupted. This can be caused by:
- Breathing in smoke (smoke inhalation), such as during a fire
- Carbon monoxide poisoning
- Diseases that prevent movement (paralysis) of the breathing muscles, such as amyotrophic lateral sclerosis (ALS)
- High altitudes
- Pressure on (compression) the windpipe (trachea)
In other cases, both oxygen and nutrient supply are stopped, caused by:
- Cardiac arrest (when the heart stops pumping)
- Cardiac arrhythmia (heart rhythm problems)
- Complications of general anesthesia
- Drug overdose
- Injuries to a newborn that occurred before, during, or soon after birth such as cerebral palsy
- Very low blood pressure
Brain cells are very sensitive to a lack of oxygen. Some brain cells start dying less than 5 minutes after their oxygen supply disappears. As a result, brain hypoxia can rapidly cause severe brain damage or death.
Symptoms of mild cerebral hypoxia include:
- Change in attention (inattentiveness)
- Poor judgment
- Uncoordinated movement
Symptoms of severe cerebral hypoxia include:
- Complete unawareness and unresponsiveness (coma)
- No breathing
- No response of the pupils of the eye to light
Exams and Tests
Cerebral hypoxia can usually be diagnosed based on the person's medical history and a physical exam. Tests are done to determine the cause of the hypoxia, and may include:
- Angiogram of the brain
- Blood tests, including arterial blood gases and blood chemical levels
- CT scan of the head
- Echocardiogram which uses ultrasound to view the heart
- Electrocardiogram (ECG), a measurement of the heart's electrical activity
- Electroencephalogram (EEG), a test of brain waves that can identify seizures and show how well brain cells work
- Evoked potentials, a test that determines whether certain sensations, such as vision and touch, reach the brain
- Magnetic resonance imaging (MRI) of the head
If only blood pressure and heart function remain, the brain may be completely dead.
Cerebral hypoxia is an emergency condition that needs to be treated right away. The sooner the oxygen supply is restored to the brain, the lower the risk for severe brain damage and death. Basic life-support systems have to be put in place: mechanical ventilation to secure the airway; fluids, blood products, or medications to support blood pressure and heart rate; and medications to suppress seizures.
Recovery depends on how long the brain has been deprived of oxygen and how much brain damage has occurred, although carbon monoxide poisoning can cause brain damage days to weeks after the event. Most people who make a full recovery have only been briefly unconscious. The longer someone is unconscious, the higher the chances of death or brain death and the lower the chances of a meaningful recovery. Problems that persist in sever anoxic brain injury can include persistent unawareness and unresponsiveness, inability to move arms or legs, muscle spasticity, and other issues like those with severe brain injury. Some children require a comprehensive, interdisciplinary inpatient rehabilitation program to maximize recovery and function after anoxic brain injury. Pediatric physiatrists prescribe programs, therapies, medications and equipment to help maximize recovery and function in an inpatient rehabilitation program, and throughout early adulthood.
NIH: National Institute of Neurological Disorders and Stroke