Physiologic alteration of fibrinogen levels: influence upon patency of microvenous anastomoses

Hyperfibrinogenemia Alone Does Not Affect the Patency of Microvascular Anastomosis

Preventing vascular thrombosis in microsurgery is a prerequisite for a successful outcome. High plasma fibrinogen levels have been associated with thromboembolic risk in patients with cancer or cardiovascular disease. Patients with these comorbidities and associated hyperfibrinogenemia oftentimes require microsurgical reconstruction. This situation causes us to hesitate. Previously in our experience, 8 of 10 patients with hyperfibrinogenemia (> 500 mg/dL) underwent successful free-tissue transfer after oral cancer ablation. Based on this clinical observation, we investigated whether hyperfibrinogenemia contributes to the patency of a microvascular anastomosis. Optimal dosage of fibrinogen (300 mg/kg, intravenously) significantly increased the fibrinogen level in the plasma of the rodent hyperfibrinogenemia model. Forty male Lewis rats (weight = 300-350 g) were injected intravenously by normal saline and fibrinogen (300 mg/kg), respectively (n = 20 in each subgroup). Femoral artery and femoral vein division and reanastomosis were performed after 2 hours in rats with or without fibrinogen injection. The platelet count, prothrombin time (PT), activated partial thromboplastin time (APTT), and the platelet aggregation test induced with adenosine diphosphate (ADP) were also measured preoperatively. The ratios of circulating activated platelets as demonstrated by p-selectin (CD62P) was analyzed by flow cytometry preoperatively and 2 hours postoperatively. Laser Doppler flowmetry was used to assess the patency of the anastomosis preoperatively and 2 hours postoperatively. Vascular patency was assessed 7 days postoperatively. The results showed that the platelet count, PT and APTT levels had no significant difference among the control and the experimental group. There were no significant differences found in the ratios of CD62P expression (P = 0.65) and ADP aggregation test (P = 0.17) in comparing both groups. There were no statistical differences in the patency rates (P > 0.05) or perfusion units of femoral arteries (P = 0.84) and femoral veins (P = 0.51) after vessels division and reanastomosis, respectively. In summary, there was no correlation between experimentally induced hyperfibrinogenemia and the enhancement of thrombosis risk after microvascular surgery. This experimental data can lend support to the idea that microvascular anastomosis could be safely performed in patients with hyperfibrinogenemia alone without untoward thrombotic complications.

Sensitivity of experimental venous and arterial thrombosis and bleeding to ancrod-induced defibrinogenation

The effect of ancrod-induced defibrinogenation on thrombosis and bleeding time was determined in anesthetized rats. Functional plasma fibrinogen levels were reduced 42, 71, 94 and 93% by ancrod doses of 5, 10, 20 and 30 U/kg, respectively, while a 2.5 U/kg dose was without significant effect. Ancrod inhibited vena cava thrombosis induced by partial stasis of blood flow combined with mild vascular injury. Thrombus weight was decreased 85 and 93% by the 10 and 20 U/kg doses, but was unaffected at lower doses. In contrast, ancrod doses of up to 30 U/kg did not significantly decrease carotid artery thrombi formed in response to oxidative transmural vessel injury. Ancrod caused a dose-dependent increase in bleeding time measured by puncturing small mesenteric arteries with a hypodermic needle. The bleeding time increase was approximately 38% in response to the 2.5 and 5 U/kg doses, and 182% in response to the 10 U/kg dose. These studies demonstrate that ancrod-induced reductions in plasma fibrinogen more effectively inhibit venous compared to arterial thrombosis, although these activities require doses that also increase bleeding time in small arteries.