Largely it is going to depend on the anethetist on the day and also how you yourself are coping. You can ask for one when you see them (or if you're on the ward, start asking the nurses/midwives). You can also start talking about it with your caregivers now and gt them to make a notation in your history about your concerns and needs.

The problem with asking which anethetist will be on duty for then now is that rosters change, anethetists get moved from list to list depending on complexity of patients and surgeries happening in other theatres, also on sick leave. So it is very variable. But, like Bron said, anethetists do tend to be happy to dish out drugs