How many hours can you work ?

Just finished working 22 hours straight. Last week it was virtually the same except I had 1/2 hour in between where I got to sit down before my pager went off yet again. Just wondered what your policy where you work is to the amount of hours you can be made to work before you tell them you've had enough. Getting a little tired of working from 6am one day until 4am the next day, getting an hour of sleep before I have to go back to work and be expected to work from 6am again until the schedule allows me to be the first to go home. I didn't have to do this kind of massive call at my last hospital and it seems to be the normal at my new job. What did I get myself into ? Both times this has happened, I felt physically ill, my ankles and feet hurt really bad and I was starting to feel as if I was a walking zombie. If it wasn't for my nice enough boss letting me grab a bite to eat before she went home for the night, I would have worked with no break or food from noon on that day until 4 am the next. I understand taking call and doing surgery is part of the job but gimme a break. How safe is this for the patient ? Anyone else have any nice stories of long shifts to share ?

Thanks