Monitoring of heparin in vascular surgery

Perioperative antithrombotic therapy does not increase the incidence of early postoperative thromboembolic complications and bleeding in kidney transplantation - a retrospective study

Perioperative antithrombotic therapy could play a role in preventing thromboembolic complications (TEC) after kidney transplantation (KTx), but little is known on postoperative bleeding risks. This retrospective analysis comprises 2000 single‐organ KTx recipients transplanted between 2011 and 2016 in the two largest transplant centers of the Netherlands. TEC and bleeding events were scored ≤7 days post‐KTx. Primary analyses were for associations of antithrombotic therapy with incidence of TEC and bleeding. Secondary analyses were for associations of other potential risk factors. Mean age was 55 ± 14 years, 59% was male and 60% received a living donor kidney. Twenty‐one patients (1.1%) had a TEC. Multiple donor arteries [OR 2.79 (1.15–6.79)] and obesity [OR 2.85 (1.19–6.82)] were identified as potential risk factors for TEC. Bleeding occurred in 88 patients (4.4%) and incidence varied significantly between different antithrombotic therapies (P = 0.006). Cardiovascular disease [OR 2.01 (1.18–3.42)], pre‐emptive KTx [OR 2.23 (1.28–3.89)], postoperative heparin infusion [OR 1.69 (1.00–2.85)], and vitamin K antagonists [OR 6.60 (2.95–14.77)] were associated with an increased bleeding risk. Intraoperative heparin and antiplatelet therapy were not associated with increased bleeding risk. These regimens appear to be safe for the possible prevention of TEC without increasing the risk for bleeding after KTx.

Pharmacokinetics of low-molecular-weight heparin and unfractionated heparin during elective aortobifemoral bypass grafting

Perioperative monitoring has demonstrated that administration of heparin on an empirical basis is associated with a wide variation in patient response and elimination rate. This problem may be overcome by intervention on the basis of perioperative monitoring or by using forms of heparin with different pharmacokinetic properties. When compared with unfractionated heparin, low-molecular-weight heparin has a higher bioavailability after subcutaneous administration, a linear clearance mechanism with a prolonged half-life, and is at least as effective in preventing postoperative vein thrombosis. Theoretically these characteristics of low-molecular-weight heparin could lead to more predictable levels of heparin activity. In this study we compared the pharmacokinetics of low-molecular-weight heparin and unfractionated heparin after an intravenous injection in patients undergoing aortic graft surgery. Heparin activity was measured before heparin administration and at 5, 20, 35, 50, 65, 80, 95, and 110 minutes after administration. The anti-Xa activity in the low-molecular-weight heparin group showed less variation and was more sustained when compared to the unfractionated heparin group. Fibrin degradation products were moderately correlated with the anti-factor Xa levels of the low-molecular-weight heparin group, but no correlation was found in the unfractionated heparin group. The anti-factor Xa activity of low-molecular-weight heparin was, in contrast to that of unfractionated heparin, not completely reversible by protamine administration. The blood loss was comparable in both groups. In contrast to what was expected, the pharmacokinetic profiles of low-molecular-weight heparin and unfractionated heparin showed a similarity after intravenous injection in patients undergoing aortobifemoral bypass grafting. Factors that could have influenced the pharmacokinetic behavior of heparin are discussed.