• Daryl S Henshaw, James D Turner, Daniel J Forest, Garrett R Thompson, and Robert S Weller.
• From the Department of Anesthesiology, Wake Forest University School of Medicine, Winston-Salem, NC.
• Reg Anesth Pain Med. 2017 Jul 1; 42 (4): 432-436.

AbstractCurrently, the American Society of Regional Anesthesia and Pain Medicine (ASRA) anticoagulation guidelines recommend that before the performance of a neuraxial procedure a minimum of 24 hours should elapse following a treatment dose of enoxaparin (1 mg/kg twice daily or 1.5 mg/kg once daily). The guidelines have since their inception also consistently recommended against the routine use of anti-Xa level monitoring for patients receiving enoxaparin. However, we noted in our clinical practice that anti-Xa levels were frequently still elevated despite patients meeting the time-based recommendation for treatment dose enoxaparin. To further investigate the possibility that residual anticoagulant activity may persist longer than 24 hours after a treatment dose of enoxaparin, we assessed anti-Xa level activity in patients presenting for elective surgery. Despite nearly universal compliance with ASRA's anticoagulation guidelines (1 sample was drawn at 23.25 hours), anti-Xa activity was found to be elevated in 11 of 19 patients. While 10 patients had an anti-Xa level within the peak prophylactic range (0.2-0.5 IU/mL), 1 patient's level was found to still be in the peak therapeutic range (0.5-1.0 IU/mL). These findings suggest that significant anticoagulant activity may persist longer than previously appreciated after the last treatment dose of enoxaparin and that the current time-based ASRA recommendation may not be conservative enough. Further research is needed to delineate the level of anti-Xa activity below which it is likely safe to proceed with a neuraxial procedure, but it may be time to reconsider the utility of anti-Xa level monitoring when it is available.

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