AbstractThe effect of hematoma formation on thrombus formation at microvascular anastomotic sites in the femoral arteries and veins of rats was investigated. No difference in anastomotic patency or thrombus formation was observed in the presence of perivascular hematoma, although compression secondary to hematoma formation was not an experimental variable. This study suggests the possibility that the velocity of blood flow (which increases with vasoconstriction) counteracts the thrombogenicity of changes in the flow volume (which decreases with vasoconstriction) by preventing the accumulation of thrombogenic materials. The authors suggest that the role of vasoconstriction in relation to thrombus formation and anastomotic patency should be explored further using topical vasoconstrictors and appropriate platelet fractions.