Hypothermia slows physical processes, including those that cause damage to brain tissue. Clinical trials have demonstrated that mild hypothermia therapy is beneficial after the brain has suffered a lack of oxygen.

Adverse effects are described as follows:
"...shivering, cardiac arrhythmia, sepsis, coagulopathy, and electrolytes and metabolic disturbances. However, many large clinical trials and meta-analyses have reported these adverse effects to be infrequent. A trend toward increased incidence of sepsis has been noted."
http://emedicine.medscape.com/article/812407-overv iew

He has not fully come out of a coma yet and it has been over 4 weeks he is moving arms here and there and occasionally opens his eyes and occasionally responses to verbal commands is this normal or should he be more awake by now?