when I have surgery they give me a dose of the pain med that works for me IV which is demerol but whatever works for you should work then during the surgery they hook me up to ketamine and leave me on it for 5 days after it. when I wake up after the surgeyr they give me my pain meds IV right away and give it to me every 2 hours to keep pain down. They also keep me on oxygeon I dont know how it helps but it seems to work. When the surgery was below my waist they did a epidural for 5 days to keep me numb.
hope this helps

Sam