Suggest Remedy To Know The Amount Of Brain Damage Done By Overdose Of Hydrocodone

My Son received an overdose of hydrocodone due to an error at the pharmacy. For 3 nights he had 5 times the doctors perscribed dose. He is alive and seems OK, but I am concerenced about the possibility of oxygen deprivation damage due to reduced respitory function due to the overdose. He is autistic, so most of the symptoms of brain damage are a daily part of his life. Is there any test to see if there was permanent damage? Should I be concerenced or am I just being an overprotective parent? Thanks.