The effect of core temperature on the success of free tissue transfer.

During free tissue transfer, much effort is made to keep patients normothermic. It is feared that hypothermia, which is common in patients having such operations, can induce vasospasm leading to stasis and ultimately thrombogenesis. The present study was undertaken to determine the effect of core body temperature on the survival of free flaps in an animal model. Rats were anesthetized with inhaled isoflurane and randomly assigned to one of the following four core temperature groups: 34 degrees C, 35 degrees C, 37 degrees C, and 39 degrees C (n = 10 animals per group). Bilateral groin free flaps were then performed (n = 20 flaps per group) while each animal was maintained at the temperature of its assigned group. Flap survival was evaluated on postoperative day 5 by a blinded observer. The best flap survival occurred in the 34 degrees C group, with an overall flap survival rate of 95%. There was a statistical difference between the survival rate of the combined 34 degrees C and 35 degrees C group (survival rate 90%, n = 40) and the combined 37 degrees C and 39 degrees C group (survival rate 67.5%, n = 40; P = 0.027). Hypothermia may have a beneficial effect on the success of free tissue transfer.

The optimal sequence of microvascular repair during prolonged clamping in free flap transfer.

During free flap transfer, the surgeon may decide to begin with repair of the artery or the vein(s) and to unclamp the first vessel as soon as repair is completed or maintain the clamping of both vessels until completion of all repairs. Complications can lead to prolonged clamping times, potentially increasing the risk of tissue ischemia, vascular damage, and thrombosis. The goals of the present study were to determine whether the sequence of vessel repair and the duration of clamping affect the success of free flap transfer in cases requiring prolonged clamping. Sixty abdominal fasciocutaneous free flaps based on the superficial inferior epigastric vessels were created in Sprague-Dawley rats. To model clinical situations in which prolonged clamping is necessary, the study used a 1-hour delay before the repair of the second vessel. Flaps were randomized into four groups. In group I (n = 15), the artery was repaired first, and the arterial clamp was removed immediately to allow arterial inflow. In group II (n = 15), the arterial repair was first, and the arterial clamp was maintained until completion of venous repair. In group III (n = 15), venous repair was first, with venous clamping maintained until completion of the arterial repair. In group IV (n = 15), initial venous repair was followed by immediate unclamping, before arterial repair. On release of all clamps, the patency of arteries and veins was confirmed immediately and after 1 hour using a "milking" test. On the fifth postoperative day, each flap was assessed for necrosis and for patency of the anastomoses. Of 15 flaps in each group, five (33 percent) failed in group I, four (27 percent) failed in groups II and III, and six (40 percent) failed in group IV. Differences between groups were not statistically significant (p = 0.8). These results demonstrate that in cases requiring prolonged occlusive clamping (2 to 3 hours), factors such as venous congestion, possible clamp injury, and presence of static blood in contact with the new anastomosis have relatively equivalent contributions to the risk of failure. Accordingly, no advantage seems to be gained by beginning with the artery or the vein or by using early or delayed unclamping of the first vessel repaired.