Vascular resistance considerations in free-tissue transfer

The closure of complex wounds is facilitated by microvascular free-tissue transfer. The greatest threat to the success of a free-tissue transfer is thrombosis of the microvascular anastomosis. Technical and pharmacologic advances have decreased the thrombogenic effect of abnormalities of a vessel's endothelial lining, and have decreased the coagulation ability of blood. Equally important to patency of the microvascular anastomosis is blood flow, which is inversely proportional to the total resistance provided by the microcirculatory beds downstream. Because different tissues possess different vascular resistances, some flaps may display more favorable hemodynamics than others. This study was designed to characterize vascular resistance, weight, volume, and surface area of the flaps available for transfer, and to identify favorable tissues for reconstruction from the standpoint of outflow resistances. Data were collected on patients undergoing free-tissue transfers and on experimental free-tissue transfers harvested from canines and fresh cadavers. Results show that resistance is highest in fascial flaps, intermediate in composite bone and soft-tissue flaps, and lowest in muscle and musculocutaneous tissues. Resistance is lower in flaps harvested from the trunk, compared with those harvested from the extremities. The rate of microvascular complications increases as resistance within the flap increases. Muscle and musculocutaneous flaps harvested from the trunk have lower complication rates than fascial and fasciocutaneous flaps. Suggestions for choices of flaps are made, based on the inherent resistance in the various free flap tissues.