Hypoxic Brain Injury

How lack of oxygen damages the brain

The brain uses about 20 percent of the body's oxygen and has almost no reserve. When oxygen falls:

• within seconds, consciousness is lost
• after about 4 to 5 minutes, brain cells begin to die
• damage continues for hours to days after oxygen is restored, through swelling, inflammation and chemical injury (reperfusion injury)

Some brain areas are especially vulnerable: the hippocampus (memory), cerebral cortex (thinking), basal ganglia (movement) and cerebellum (coordination).

Causes

Reduced blood flow (hypoxic-ischemic)

• Cardiac arrest: the most common cause in adults
• severe low blood pressure from shock or blood loss
• stroke (localized)

Reduced oxygen in the blood

• drowning and near-drowning
• choking and airway obstruction
• respiratory failure from severe asthma, pneumonia or COPD
• drug overdose, especially opioid overdose, which slows or stops breathing
• strangulation and hanging
• high altitude

Oxygen cannot be used

• carbon monoxide poisoning, which binds to hemoglobin and blocks oxygen delivery
• cyanide poisoning

In newborns

Hypoxic-ischemic encephalopathy (HIE) results from reduced oxygen or blood flow around birth, for example from placental abruption or cord problems. It can lead to cerebral palsy, epilepsy or developmental delay.

Symptoms and effects

Effects depend on how long and how severe the oxygen loss was:

Mild

• short-term memory problems
• difficulty concentrating and slowed thinking
• headaches and fatigue
• mood changes, irritability or depression

Moderate to severe

• confusion and disorientation
• loss of coordination, tremor or involuntary jerks (myoclonus)
• weakness, stiffness or abnormal postures
• speech and swallowing problems
• vision problems, including cortical blindness
• seizures
• personality and behavior changes

Disorders of consciousness

• Coma: unresponsive, eyes closed
• Unresponsive wakefulness syndrome (vegetative state): eyes open, sleep-wake cycles, but no signs of awareness
• Minimally conscious state: inconsistent but definite signs of awareness

Diagnosis

• Neurological examination, repeated over days
• Brain MRI: shows patterns of damage, best several days after the event
• CT scan: to exclude bleeding or other causes early on
• EEG: detects seizures and abnormal brain activity
• Blood tests: markers of brain injury, carbon monoxide levels, toxicology
• Somatosensory evoked potentials: test nerve pathways and help predict outcome

Doctors usually wait at least 72 hours after cardiac arrest, and after rewarming if temperature control was used, before drawing firm conclusions about prognosis, combining several tests.

Treatment

Emergency care

• CPR and defibrillation for cardiac arrest
• securing the airway, oxygen and ventilation
• naloxone for opioid overdose
• 100 percent oxygen for carbon monoxide poisoning, sometimes hyperbaric oxygen

Hospital care after cardiac arrest

• Temperature control: preventing fever, and sometimes cooling to a target temperature, to reduce brain injury
• maintaining blood pressure, oxygen and blood sugar within target ranges
• treating seizures
• treating the cause of the arrest

Newborns

Therapeutic hypothermia, cooling the baby to about 33.5 °C (92.3 °F) for 72 hours, started within 6 hours of birth, reduces death and disability in moderate to severe HIE.

Rehabilitation

Recovery relies on a team: physical, occupational and speech therapy, neuropsychology, and support with daily living, returning to work or school, and mood.

Outlook

Outcomes vary from full recovery to severe lasting disability or death. Better outcomes are associated with shorter oxygen loss, fast CPR, younger age, early return of reflexes and consciousness, and favorable MRI and EEG findings. Most recovery happens in the first 6 to 12 months, though improvement can continue for longer.

Prevention

• Learn CPR and how to use an AED.
• Install carbon monoxide alarms and service fuel-burning appliances.
• Supervise children around water and teach swimming.
• Cut food into small pieces for young children and keep small objects out of reach.
• Carry naloxone if you or someone you know uses opioids.
• Keep asthma well controlled.

Frequently asked questions

How long can the brain go without oxygen?

Brain cells begin to die after about 4 to 5 minutes without oxygen, and the risk of permanent damage rises sharply after that. Cold water drowning in children can be an exception, with occasional survival after longer periods. Fast CPR is critical.

Can you recover from a hypoxic brain injury?

Many people recover partly or fully, especially after brief oxygen loss. Recovery depends on the cause, duration and severity, and is assessed over days to weeks. Rehabilitation helps people regain skills, and improvement can continue for many months.

What is the difference between hypoxic and anoxic brain injury?

Hypoxic brain injury results from reduced oxygen supply to the brain. Anoxic brain injury results from a complete lack of oxygen. Anoxic injuries tend to be more severe, but both are treated similarly.

What are the long-term effects of a hypoxic brain injury?

Long-term effects can include memory and concentration problems, fatigue, mood and personality changes, movement and coordination difficulties, seizures, and speech or swallowing problems. Severe injuries may lead to prolonged disorders of consciousness. Rehabilitation and support address many of these.