Can he survive being in a coma,then cardiac arrest & seizures?

My step-dad choked on his sandwich last night and he went without oxygen for 4 minutes & has been in a coma ever since.Then this morning he went into cardiac arrest & they life flighted him to another hospital, and ever since he went into cardiac arrest hes been having seizures.From what I understand the Dr's. are giving him the best medicine there is for seizures and at the highest dose possible but it isn't doing anything or any good.What I would like to know is what does all this mean? Why did he go into cardiac arrest while in a coma, and why did he start having seizures after his cardiac arrest?And what does all this mean when it comes to his chances of survival??