Sheikh `Abd al-Rahmân al-`Ajlân, lecturer at the Grand Mosque in Mecca
Being under anesthesia for half an hour does not affect the fast. What would affect it is if some anesthetic substance were to enter her stomach. Her fast would be broken only in the event that she had to eat or drink something to induce unconsciousness.
If she is not sure what had taken place and is unable to find out, it would be good for her to make up her fast on some other day.
Source: Islam Today