Residual anti-Xa activity in plasma of patients presenting for electively planned neuraxial regional anesthesia

Objective To determine the incidence of increased anti-Xa activity within plasma levels 24 hours after administration of therapeutic dose low-molecular-weight heparin in patients presenting for elective neuraxial anesthesia. Background Guidelines for neuroaxial regional anesthesia for patients with antithrombotic drugs recommend time intervals for waiting. There is scientific evidence to suggest that the recommended interval of 24 hours may be insufficient in patients treated with therapeutic dose low-molecular-weight heparin. Methods Retrospective cohort analysis of 74 patients who received therapeutic dose low-molecular-weight heparin before planned neuraxial anesthesia between April 1, 2015 and April 1, 2020 at Freiburg University Hospital. Primary endpoint was the occurrence of elevated plasma anti-Xa levels in prophylactic range or higher (>0.2 IU/mL) 24 hours after the last application of the therapeutic dose. Results 24 hours after the last dose of therapeutic low-molecular-weight heparin, 18.0% of patients had elevated anti-Xa activity levels >0.2 IU/mL. A weak correlation between the time since the last administration of low-molecular-weight heparin and plasma anti-Xa levels could be found. No other risk factors were seen. Conclusions Relevant residual anticoagulant activity, as measured by plasma anti-Xa levels within a prophylactic range, is measurable 24 hours after the last administration of therapeutic dose low-molecular-weight heparin. Trial registration number German Clinical Trials Register DRKS00022099.