Beyond the high risk of death, one major concern is the impact of prolonged oxygen deprivation on the brain and the damage that can occur within three minutes of the heart stopping.
This article explores what happens when oxygen is cut off to the brain during a cardiac arrest, and the common symptoms seen when a person is revived. It also looks at problems that arise when blood flow begins again in tissues that are damaged.
What Happens During Cardiac Arrest
A person becomes unconscious quickly during cardiac arrest. This usually happens within 20 seconds after the heart stops beating. Without the oxygen and sugars it needs to function, the brain is unable to deliver the electrical signals needed to maintain breathing and organ function.
This can lead to a hypoxic-anoxic injury (HAI). Hypoxia refers to a partial lack of oxygen, while anoxia means a total lack of oxygen. In general, the more complete the oxygen loss, the more severe the harm to the brain.
With cardiac arrest, all parts of the brain that rely on blood flow are affected by its failure. An injury caused by anoxia is called anoxic brain injury. Among the parts of the brain most vulnerable to injury is the temporal lobe, where memories are stored.
Timeline
When cardiac arrest occurs, cardiopulmonary resuscitation (CPR) must be started within two minutes. Effective CPR, if started immediately with a witnessed arrest can have positive outcomes.
If CPR is delayed more than three minutes, global cerebral ischemia—the lack of blood flow to the entire brain—can lead to brain injury that gets progressively worse.
By nine minutes, severe and permanent brain damage is likely. After 10 minutes, the chances of survival are low.
Even if a person is resuscitated, eight out of every 10 will be in a coma and sustain some level of brain damage. Simply put, the longer the brain is deprived of oxygen, the worse the damage will be.
Resuscitation and Symptoms
People are most likely to be successfully revived in a hospital or another site with quick access to defibrillators. These are devices that send electrical impulses to the chest to restart the heart. These devices are found in many workplaces, sports arenas, and other public places.
When a cardiac arrest is treated very quickly, a person may recover with no signs of injury. Others may have mild to severe damage.
Memory is most profoundly affected by hypoxia, so memory loss will often be the first sign of the damage. Other symptoms, both physical and psychiatric, may be obvious, while some may only be noticed months or years later.
For those who are resuscitated and are not in a coma, hypoxia may cause:
Severe memory loss (amnesia)Involuntary muscle contractions (spasticity)Loss of muscle controlLoss of mobility and fine motor controlIncontinenceImpaired speechChanges in personalityDisorientation as to place, person, or time
Some symptoms may improve over time. Others, however, may be lasting and require a person to be under lifelong assisted care.
Coma
People who are comatose after a cardiac arrest will often have damage to different parts of the brain, such as the:
Cerebral cortex Hippocampus Cerebellum Basal ganglia
Even the spinal cord will sometimes be damaged. People who are in a coma for 12 hours or more will usually have lasting problems with thinking, movement, and sensation. Recovery will often be incomplete and slow, taking weeks to months.
The most severely affected people may end up in a vegetative state, more appropriately known as unresponsive wakefulness syndrome (UWS). The eyes may open in people with UWS, and voluntary movements may occur, but the person does not respond and is unaware of their surroundings.
Reperfusion Injury
Restoring the flow of blood through the body is called reperfusion. It is key to reviving the person and preventing or limiting brain damage.
Reperfusion is necessary, but it has to be done methodically and in a highly controlled way. That’s because the sudden rush of blood to areas of damaged tissues can cause injury.
It may seem counterintuitive because restarting the flow of blood is the critical goal. But the lack of oxygen and nutrients during the time of cardiac arrest means that when blood flow is restored, it places oxidative stress on the brain as toxins flood already-damaged tissues.
The inflammation and nerve injury this causes can trigger a cascade of symptoms, including:
Severe headaches or migrainesSeizuresWeakness or paralysis on one side of the bodyVision loss or blindness in one eyeDifficulty understanding things heard or spokenLoss of awareness of one side of your environment (hemispatial neglect)Slurred or jumbled speechDizziness or vertigoDouble visionLoss of coordination
The severity of these symptoms is closely linked to how long the person went without oxygen. Other factors include any pre-existing conditions affecting the brain and cardiovascular system.
Summary
When the heart stops, so does the flow of blood that’s pumped throughout the body. Brain damage will begin in a matter of minutes because of the lack of oxygen.
Cardiac arrest is usually fatal outside of a hospital setting, but even those who are revived may have severe and lasting impacts. It’s important to act quickly to restart the heart and limit these catastrophic effects.
A Word From Verywell
All brain activity is thought to cease by around three to four minutes from the moment the heart stops. Thus, every second counts if someone suddenly collapses in front of you and stops breathing.
Rather than wasting time putting the victim in the car and rushing to the hospital, call 911 and start hands-only CPR immediately. You may buy enough time until the paramedics arrive to restart the heart.
