Lack of oxygen in the brain for 5 to 10 minutes results in permanent brain damage.

At the one-minute mark, brain cells begin dying. At three minutes, neurons suffer more extensive damage, and lasting brain damage becomes more likely. At five minutes, death becomes imminent. At 10 minutes, even if the brain remains alive, a coma and lasting brain damage are almost inevitable.

Source: nlm.nih.gov/med…