"Free" implies that the tissue is completely detached from its blood supply at the original location ("donor site") and then transferred to another location ("recipient site") and the circulation in the tissue re-established by anastomosis of artery(s) and vein(s).
Various types of tissue may be transferred as a "free flap" including skin and fat, muscle, nerve, bone, cartilage (or any combination of these), lymph nodes and intestinal segments.
Close monitoring of the flap both by nurses and by the surgeon is mandatory following the completion of the operation.
[2][3] If detected early, loss of either the venous or arterial blood supply may be corrected by operative intervention.
Many times an implantable Doppler probe or other devices can be installed during surgery to provide better monitoring in the post-operative period.