Answer:
Generally, muscle does not tolerate warm ischemia for more than 2 hours. Skin and fasciocutaneous flaps can tolerate longer ischemic times (4-6 hours). With proper planning, these times are rarely exceeded. Cooling increases tolerance of tissue to ischemia. Some surgeons cool the transplant with cold wraps and ice, but cooling is not routinely done.
Several perfusates have been tried to prolong tissue tolerance to ischemia. In one study, Ringer’s lactate (LR), University of Wisconsin solution (UW), and urokinase were compared in 75 rat abdominal free flaps subjected to 12 or 18 hours of primary ischemia. Perfusion washout with urokinase resulted in significantly increased survival following both periods of ischemia. When urokinase was combined with UW, there was an additive benefit on flap survival following 12 hours ischemia. (J Reconstr Surg May 1993)