Salicylates for post-operative pain can affect coagulation of blood by

interfering with normal platelet functions resulting in a prolonged bleeding time.

exhibiting a coumadin - like effect resulting in an increase of vitamin K dependent factors.

exhibiting a coumadin - like effect resulting in a decrease of vitamin K dependent factors

(interfering with normal platelet functions resulting in a prolonged bleeding time. )
AND
(exhibiting a coumadin - like effect resulting in an decrease of vitamin K dependent factors. )

(exhibiting a coumadin - like effect resulting in an increase of vitamin K dependent factors.)
AND
(interfering with normal platelet functions resulting in a prolonged bleeding time.)