Nitrous Oxide - Lack of Oxygen

A friend of mine took his daughter to a periodontist for a simple procedure.  They administered Nitrous Oxide (this was over a week ago).  She has not been the same since.  She has reverted back (he says like a 5 year old) and cries alot.  She hallucinates from time to time.  She is 18 years old - straight A student and they have done a drug screen to make sure drugs aren't the issue.  They have attempted for the past week to get help from the periodontist who did the procedure and she keeps putting them off.  The daughter is scheduled on Monday for a CT scan.  Could lack of adequate oxygen during the procedure be causing this, and if so, is it temporary or has permanent brain damage occurred?  Can you recommend what he shoudl do at this point?  Thank you so much for your help.

[RockRose]

Karen - I wonder how the periodontist can legally keep putting her off?  I really don't understand that - have they gone to the emergency room and told the doctor what happened?  

By "revert to a 5 year old",  do you mean she has lost the ability to read and write?  This story is so bafflling - what do they say at school?  I would think this would almost be a police matter - or a health department matter,  if this straight A senior in high school suddenly had the intellect of a 5 year old after a dental appointment.  

I think he should call the health department today and find out what can be done right now - if the NO was mixed incorrectly or was sealed to her face,  yes,  she could have brain damage from lack of oxygen.

Best wishes.