As a medical professional, I can tell you that the human brain is extremely sensitive to oxygen deprivation. Critical thinking and consciousness are typically lost within seconds to minutes without oxygen, but permanent brain damage can occur after about three to five minutes of oxygen deprivation, depending on factors such as the individual's health, age, and the temperature of the environment. However, after about six minutes without oxygen and without CPR, the likelihood of irreversible brain damage significantly increases. It's important to note that the exact time can vary, and immediate medical attention is crucial in such situations. read more >>

The brain can survive for up to about six minutes after the heart stops. The reason to learn cardiopulmonary resuscitation (CPR) is that if CPR is started within six minutes of cardiac arrest, the brain may survive the lack of oxygen. After about six minutes without CPR, however, the brain begins to die.read more >>