How do about 5 percent of drowning victims suffer some sort permanent brain injury?

Near-drowning is a life-threatening incident involving submersion or immersion in liquid which could cause respiratory impairment. Drowning victims suffer from lack of oxygen to the brain and other parts of the body. Near-drowning can stop breathing entirely (death) or the lack of oxygen can cause significant brain damage (permanent disability). Permanent brain injury can happen from as little as 4 minutes without oxygen. Some victims (5%) that are resuscitated after near drowning suffer permanent brain injury.