Reply: One versus Two Venous Anastomoses in Microvascular Free Flap Surgery

Abstract

Sir: We thank Rozen et al. for their interest in our article and congratulate them on their article, which contributes additional data regarding the routine performance of either one or two venous anastomoses.1 In their article, they report a lower rate of venous congestion requiring reoperation in deep inferior epigastric perforator (DIEP) flaps performed with two venous anastomoses (n = 291) compared with DIEP flaps performed with one venous anastomosis (n = 273) (0 percent versus 2.6 percent, respectively; p = 0.006). The mean operative time for both operations was virtually identical (p = 0.57). They conclude that DIEP flap breast reconstructions should routinely include two venous anastomoses because of lower flap failure rates and equivalent operative times. Our findings support the practice of performing a single venous anastomosis in cases where two venae comitantes are present, based on superior blood velocity, theoretically decreasing the chance of thrombosis.1 Velocity and flow are often confused in the literature, but they are different. Low blood velocity (measured in centimeters per second), along with turbulence and intimal injury, results in thrombosis. These three conditions are commonly referred to as Virchow's triad, after the German pathologist Rudolf Virchow, who detailed the pathophysiology behind pulmonary embolism. Blood flow (measured in milliliters per second) represents the volume of blood entering and exiting an organ, or flap in this case. Both are critical to flap survival; in simplified terms, inadequate blood velocity results in thrombosis, whereas inadequate blood flow results in unsatisfactory tissue perfusion. As we acknowledged in the Discussion section of our article, the question of whether a second venous anastomosis of a separate system of veins, rather than a second anastomosis of a vein draining the same venous system (a second vena comitans), is needed to maintain adequate blood flow (not velocity) in some flaps remains unanswered by the data we have presented.2 The DIEP flap is an example of a flap that usually includes two systems of draining veins: a superficial system that empties into the superficial inferior epigastric vein, and a deep system that empties into the venae comitantes of the deep inferior epigastric artery. In their study, the vast majority (92.1 percent) of DIEP flaps that had two venous anastomoses were flaps that included one vein from the superficial system and one vein from the deep system, rather than two veins from the deep system. It is possible, then, that the difference in venous complications they noted was because some of the flaps that had only one venous anastomosis were not satisfactorily drained by a single venous system, which is a problem of flow rather than velocity. Therefore, our findings do not necessarily contradict the findings by Rozen et al. However, given the very low rate of venous complications they experienced in their series (1.2 percent of all flaps), a much larger sample would be required to obtain satisfactory statistical power to clarify the question of whether the problems they observed were problems of inadequate flow or inadequate velocity. In summary, we support performing a second venous anastomosis of a separate venous drainage system, such as the superficial inferior epigastric vein in the DIEP flap, when signs of venous insufficiency are present, as we suggested in the Discussion section of our article and as Rozen et al. described in the Methods section of their article. The only argument that we can see for performing two venous anastomoses of a single venous system (i.e., both venae comitantes of the deep inferior epigastric artery) is to have a “backup” vein should one of the veins thrombose, for example, because of imperfect technique, distal pedicle or recipient vessel injury, size mismatch, or awkward pedicle geometry with a risk of later kinking or twisting. DISCLOSURE The authors have no financial interest to declare in relation to the content of this communication or of the article being discussed. Matthew M. Hanasono, M.D. Ergun Kocak, M.D. Olubunmi Ogunleye, M.D. Craig J. Hartley, Ph.D. Michael J. Miller. M.D. Department of Plastic Surgery University of Texas M. D. Anderson Cancer Center Houston, Texas