Antithrombotic Therapy in Peripheral Arterial Occlusive Disease: Vascular surgeons
Amounts of heparin to achieve conventional systemic anticoagulation may not be adequate to prevent local clotting at the site of vascular reconstruction. This consideration, coupled with the highly variable response to heparin among patients undergoing vascular reconstruction, argues for relatively high-dose heparin therapy. Based on these considerations, a rational heparin regimen is to administer 100 to 150 U/kg IV prior to application of cross clamps and to supplement this every 45 to 50 min with 50 U/kg until cross clamps are removed and circulation is reestablished. The timing of the supplemental doses is based on the half-life of heparin (50 to 80 min). Alternatively, some surgeons routinely obtain baseline activated clotting times in the operating room and adjust heparin dosage to maintain a twofold prolongation of the activated clotting time.
Most vascular surgeons routinely use systemic heparin anticoagulation during aortic revascularization while the aorta is clamped. Other vascular surgeons do not routinely anticoagulate during aortic surgery on the basis that larger diameter, high-flow arteries do not have a significant predisposition to thrombosis. This issue was evaluated in a multicenter, randomized clinical trial of 284 patients undergoing elective abdominal aortic aneurysm repair (level I) read more natural asthma treatment. There was no difference in the incidence of blood loss, transfusion requirement, or arterial thrombosis in either group. However, those treated with heparin sustained fewer fatal (1.4 vs 5.7%; p < 0.05) and nonfatal Mis (2.0 vs 8.5%; p = 0.02) than those who did not get heparin.
At the end of the procedure, complete heparin reversal with protamine sulfate is recommended to minimize bleeding complications, particularly if perioperative antiplatelet therapy is utilized. Many surgeons do not reverse heparin with protamine because of protamine’s transient adverse effects on hemodynamics (decrease in cardiac output and BP), hemostasis (protamine-induced thrombocytopenia), and, rarely, anaphylaxis. Life-threatening anaphylaxis occurs almost exclusively in diabetics who have received NPH insulin in the past; the frequency of this complication is 0.6 to 3.0%. The need for heparin reversal with protamine was questioned in a single-center, randomized clinical trial of 120 patients undergoing peripheral vascular surgery (level II). In this double-blinded study, patients randomized to receive protamine had no difference in blood loss, bleeding complications, or transfusion requirement than those given saline solution. It should be noted that the heparin dosage used in this study was limited to a single dose of 90 U/kg. When using a higher dosage of heparin, as recommended above, failure to administer protamine would potentially result in significant bleeding complications, particularly with procedures that are associated with a higher risk of bleeding such as aortic reconstruction. Withholding protamine after procedures that are associated with a greater risk of thrombosis than bleeding, such as femorotibial bypass, would appear to be reasonable.