Before having surgery you would need to stop the coumadin. It has a really long half-life and so usually people stop it about 10 days before major surgery. Some people use LMWH shots when stopping coumadin to keep from getting a blood clot as you stop it since this has a short half life and one can stop the LMWH the day before and start back for effective anticoagulation faster while the coumadin builds back up in your body. Being on coumadin makes surgery a tiny bit more risky because it can lead to more bleeding if it is not all out of your system at the time of surgery ( a blood test will check for this) or a little risk of clotting (for the reason that you are taking it). All this can be worked through though.
WithHope for a cure of these diseases