A person can only go 3 to 4 minutes without oxygen before they areconsidered brain dead. After 5-6 minutes more without oxygen, a person dies.
As soon as the body starts being deprived of oxygen, major organs become affected. Within minutes, the heart and liver can become too damaged too recover from the lack of oxygen. After 20 minutes, the kidneys can begin to fail.
When a person becomes deprived of oxygen, it is vital for CPR to be performed. Many conditions can cause a person to lack oxygen, such as a stroke, drug overdose, excessive bleeding and heart failure.