Abstract
Background In microvascular surgery, patients often receive unfractionated heparin infusions
to minimize risk for microvascular thrombosis. Patients who receive intravenous (IV)
heparin are believed to have adequate prophylaxis against venous thromboembolism (VTE).
Whether a fixed dose of IV heparin provides detectable levels of anticoagulation,
or whether the “one size fits all” approach provides adequate prophylaxis against
VTE remains unknown. This study examined the pharmacodynamics of fixed-dose heparin
infusions and the effects of real-time, anti-factor Xa (aFXa) level driven heparin
dose adjustments.
Methods This prospective clinical trial recruited adult microvascular surgery patients placed
on a fixed-dose (500 units/h) unfractionated heparin infusion during their initial
microsurgical procedure. Steady-state aFXa levels, a marker of unfractionated heparin
efficacy and safety, were monitored. Patients with out-of-range aFXa levels received
protocol-driven real-time dose adjustments. Outcomes of interest included aFXa levels
in response to heparin 500 units/h, number of dose adjustments required to achieve
goal aFXa levels, time to reach goal aFXa level, and 90-day clinically relevant bleeding
and VTE.
Results Twenty patients were recruited prospectively. None of 20 patients had any detectable
level of anticoagulation in response to heparin infusions at 500 units/h. The median
number of dose adjustments required to reach goal level was five, and median weight-based
dose to reach goal level was 11.8 units/kg/h. Real-time dose adjustments significantly
increased the proportion of patients with in-range levels (60 vs. 0%, p = 0.0001). The 90-day VTE rate was 5% and 90-day clinically relevant bleeding rate
was 5%.
Conclusions Fixed-dose heparin infusions at a rate of 500 units/h do not provide a detectable
level of anticoagulation after microsurgical procedures and are insufficient for the
majority of patients who require VTE prophylaxis. Weight-based heparin infusions at
10 to 12 units/kg/h deserve future study in patients undergoing microsurgical procedures
to increase the proportion of patients receiving adequate VTE prophylaxis.
Keywords
heparin - plastic surgery - microvascular surgery - venous thromboembolism - anti-factor
Xa
