Thanks for writing in to Heathcare Magic!
A air haul of 24 hour is a real risk for persons with a history of recurrent DVT and there is attached risk of life threatening pulmonary embolism
in these patients when on long hauls.
I would advise you to take Clexane
8hours prior to the flight and also on the previous and following day of flight at the same time to give an extra protection.
If you have any further query please let me know I would try to answer it for you.
Wish you a great health!