Patients were assigned to take aspirin ( @ mg ) or placebo @ to @ hours before surgery and then aspirin ( @ mg ) or placebo daily up to @ days after surgery , and were assigned to take oral clonidine ( @ mg ) or placebo @ to @ hours before surgery , and then a transdermal clonidine patch ( which provided clonidine at @ mg/d ) or placebo patch that remained until @ hours after surgery .