Inclusion Criteria:  The study included patients who underwent free flap surgery between January 2006 and December 2019 in the Hospital de San José and Hospital Infantil Universitario de San José in Bogotá, Colombia.  Exclusion Criteria:  Criteria for exclusion were history of deep vein thrombosis, pulmonary embolism, systemic lupus erythematosus, antiphospholipid syndrome, hypercoagulability syndrome and previous medication with oral or parenteral anticoagulant within the past year of the surgery.