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In general, the brain can withstand up to three to six minutes without oxygen before brain damage occurs, but this may vary from person to person. If the brain goes without oxygen longer than this, serious and often irreversible damage is likely to take place. After ten minutes, severe neurological damage has generally occurred. Very few people regain any cognitive function after the brain has gone 15 or more minutes without oxygen.
Since the brain cannot retain oxygen on its own, it relies on a steady supply provided through the bloodstream. Brain death can occur rapidly as cells begin to die off without any oxygen stores or new oxygen circulating to the brain. Almost immediately after oxygen intake has ceased, brain cells begin to perish. The brain usually only lasts a few short minutes without oxygen before damage occurs on some level.
Occasionally, the brain can last longer without oxygen before brain damage becomes severe, but this usually requires very specific circumstances. It usually requires that oxygen cessation happen at the same time as the body becomes cold very rapidly, such as if a person falls into icy water and begins to drown. Young children have been known to go up to half an hour without oxygen and still survive in situations like this.
In most cases, brain damage is irreversible when it occurs due to long-term oxygen deprivation. For this reason, during cases of illness or injury where breathing ceases, it is vital that emergency personnel work to provide steady oxygen flow to the heart and brain. This can be done through artificial means or by getting the patient to breathe again on his or her own. Death is usually declared once the brain has gone more than 15 minutes without oxygen.
Although the brain can only go a few minutes without oxygen before some type of brain damage occurs, patients can often regain cognitive function if treated quickly. The severity of long-term complications is usually in direct correlation with the length of time the person has gone without oxygen. A patient’s exact outcome and level of damage may also depend on why he or she stopped breathing to begin with.