Brain death occurs about 4-6 minutes after respiratory arrest, because after respiratory arrest, the heart will stop functioning and blood will not be pulsed out of the heart to supply the brain with sufficient blood and oxygen supply, and confusion will occur 10 seconds after cardiac arrest, and convulsions may occur in about 10-20 seconds. Generally speaking, the heart stops breathing in about 20-30 seconds, the skin may become pale, cyanosis may occur due to poor blood supply in cardiac arrest, and the pupils may become dilated in about 30-60 seconds. At the time of 4-6 minutes, the brain will have irreversible brain damage because it does not have sufficient blood supply, so the time within 6 minutes of cardiac arrest and respiratory arrest is the golden time for resuscitation.