Relationship between flow and incidence of thrombosis in polytetrafluoroethylene vascular grafts in free microvascular flaps in lambs

We have done an experimental study in lambs in which we investigated the in fluence of flow rate on free microvascular flaps using polytetrafluoroethyl ene (PTFE) vascular grafts. We set up five surgical groups in which blood f low was progressively increased through the PTFE vascular graft. In group I (venous autograft) we observed just one vascular thrombosis which was loca ted at the site of the anastomosis. In group II (PTFE 3 x 10 mm) all the mi crovascular flaps became necrosed after the third postoperative day. In gro up III (PTFE 3 x 10 mm) necrosis also developed in all cases, but the anast omoses remained permeable no longer than eight days. In group IV (3 x 15 mm ) the permeability in the microvascular free flaps was about 40% after 21 d ays, and in group V (3 x 10 mm) it reached 70%. To match graft flow rates w ith flap survival we did a regression analysis of flow rates for groups II, III, and V and the corresponding survival periods for the flaps. There was a clear and highly significant relationship (r = 0.717, p = 0.0001). In co nclusion, it is necessary to maintain blood flow through the prosthesis at a rate higher than the thrombogenic threshold. When the flow rate in the ve ssels through the PTFE grafts was higher, the viability of the flaps was be tter. The ideal surgical technique should always be based on an arterioveno us fistula distal to the PTFE vascular graft. It is necessary to maintain b lood flow through a prosthesis at a rate higher than the thrombogenic thres hold.