Experimental study of the relationship between alterations in tissue perfusion and anastomotic patency

It is generally believed that alterations in perfusion which endanger a free flap or replant are directly related to thrombus formation and obstruction of blood flow at the anastomotic site. Recent experimental work in our laboratory suggests that the presence of platelet emboli downstream in the microcirculation might be responsible at least in part for postoperative perturbations in perfusion. To determine whether changes in tissue perfusion can occur in the absence of corresponding changes in anastomotic patency we studied microvascular blood flow in the exposed rat cremaster flap model. We made continuous measurements of both anastomotic patency and downstream microcirculatory perfusion following small vessel repair. Using this approach we found that during one hour after clamp release and reperfusion in the 10 animals studied, pedicle artery blood pressure, which indicates pedicle patency in this model, was functionally normal 97% +/- 2 of the time while blood flow in the downstream tissue (cremaster) remained normal an average of only 65% +/- 7 of the time. In most cases these flow alterations were associated with the presence of visible platelet emboli in the microcirculation. From these studies we conclude that when flap perfusion failure temporarily occurs, a microsurgeon must consider not only the anastomosis but also the downstream microcirculation when searching for a possible cause.