Talk with your doctor during office hours today if you can, and then when you go in for the procedure, tell every nurse, technician and doctor you come in contact with that you are breastfeeding and make sure it gets put on your chart.
Most anesthesias are OK for breastfeeding, as they clear your system fairly quickly; if you are alert enough to hold your baby, it's safe to breastfeed. Always ask about specific meds, but it's likely you will not need to pump and dump at all. Consider pumping now, while you're still eating regular meals, to have some milk available for yor baby while you're having the procedure, if you do not already have a stockpile in your freezer.
Be more cautious about painkillers, but know that ibuprofen is compatible with breastfeeding if you are uncomfortable.
Consult the "Is This Safe While Breastfeeding?" chart at www.kellymom.com for more information about specific medications. The info there is frequently updated as is based on Dr. Hales' book "Medications and Mother's Milk."
Plan to spend the day after your procedure having a "milk day" and nurse on cue and extra-often, to maintain your healthy milk supply and counteract any effects of having been so low-calorie to prep for the procedure.
Consider calling your local La Leche League Leader for more free help if you have further questions. Good luck and congrats on working so hard to give top-notch care to both yourself and your baby. ;)