Dear patient cold and numb fingers after carpel tunnel surgery may be due to involvement of upper limb nerves due to cervical spine pathology. I hope Emg NCV was done prior to carpel tunnel surgery ad if it was done then level of pathology can be assessed. Other reason may be long standing nerve compression at the wrist with irreversible changes in nerves so that desired benefit may not be achieved after nerve release at the wrist. Other reason amy be inadequate release of the median nerve at wrist. So I mean reasons can be many but detailed assessment requires visit to your operating surgeon and investigation like MRI of wrist and cervical spine. All th best.