[每周一问]NO.10-The Guidelines for the Performance of Neuraxial Anesthesia and Analgesia in Anticoagulated Patients
today we will be discussing Low Molecular Weight Heparin (LMWH) and regional anesthesia.
A 48 y/o white male presents to the pre-admission test center to get his workup prior to his anterior cruciate ligament repair. He takes warfarin for atrial fibrillation and was instructed to discontinue it 5 days prior to his procedure and to start lovenox (enoxaparin - the most common LMWH used in the United States) 30 mg twice a day. He is planning to inject his last dose the night prior to the surgery and desires an epidural anesthetic.
1. Is it safe to provide a regional anesthetic on this setting?
2. How about if this patient was receiving a higher dose of LMWH such as 70 mg twice a day?
3. Is there any role in monitoring the Heptest (antifactor Xa level) prior to a regional anesthetic?
今天我们讨论低子量肝素（LMWH）与区域阻滞
一48岁白种男性在行前交叉韧带手术前到院前诊断中心行手术前评估。其因房颤一直在服用华法林，医生要求其在手术前5日停止服用华发林而改用依诺肝素（美国最常用的LMWH）30mg,2次/日。患者准备在术前晚注射最后一次剂量的肝素，并希望接受硬膜外麻醉方法。
1.在该情况下实施区域阻滞是否安全？
2.如果该患者接受更高剂量肝素（如70mg,2次/日），实施区域阻滞是否安全？
3.在实施区域阻滞前监测Heptest (抗因子Xa水平)是否有用？
[每周一问]NO.10-低子量肝素（LMWH）与区域阻滞[病例讨论] 参考答案
1.在该情况下实施区域阻滞是否安全？
如上周综述中所述，LMWH的血浆半衰期在皮下注射后为3-6小时。因此，在2个半衰期后大多数抗纤维蛋白酶活性降低而抗因子Xa保持在50%水平[1]。LMWH在最后一次预防剂量后24小时完全从循环中清除。ASRA指南推荐在实施区域阻滞前给予LMWH时至少要过10-12小时方可实施。指南进一步强调在该情况下应该首选单次腰麻作为区域阻滞[2]。在Brigham and Women's Hospital (BWH)，通常要求为停止使用24小时方可实施区域阻滞。
2.如果该患者接受更高剂量肝素（如70mg,2次/日），实施区域阻滞是否安全？
急性静脉血栓或急性冠状动脉综合征的患者经常接受高剂量的LMWH (1 mg/kg，2次/日)。为治疗活动性血栓，必须监测抗Xa因子(Heptest)的水平并维持在0.4-1.0 U/mL[3]。在接受更高剂量预防性的LMWH的患者在实施穿刺时必须推迟24小时以上[2] 。
3.在实施区域阻滞前监测Heptest (抗Xa因子水平)是否有用？
ASRA指南强调，因为抗Xa因子水平并非出血危险的预测因素，因此不推荐监测抗Xa因子水平。而麻醉届以外的部分权威人士则认为heptest可以预测出血，同时他们认为，在血浆肝素水平<0.2 U/mL时实施有创性操作是安全的[3]。在BWH医院我们的作法是：仅在患者接受比常规剂量(>1 mg/kg)还高剂量的LMWH治疗时，检测heptest。接受如此大剂量肝素治疗的患者一般不实施区域阻滞，除非最后一次LMWH治疗超过24小时，同时heptest i< 0.2 U/mL.
Is it safe to provide a regional anesthetic on this setting?
As mentioned in last week's review, the plasma half-life of LMWH is three to six hours after subcutaneous injection. Therefore after 2 half-lives, most of the anti-thrombin activity has diminished but anti-Xa levels remain at 50% of peak levels (1). LMWH is completely cleared from the circulation 24 hours after the last prophylactic dose. The American Society of Regional Anesthesia (ASRA) guidelines for LMWH and neuraxial block recommend to wait at least 10-12 hours after the LMWH prior to the administration of a regional anesthetic. The guidelines further state that a single-dose spinal anesthetic is the preferred regional technique in this setting (2). It is our practice at the Brigham and Women's Hospital (BWH) to discontinue the LMWH for at least 24 hours prior to the administration of a regional anesthetic.
How about if this patient was receiving a higher dose of LMWH such as 70 mg twice a day?
Patients with acute venous thrombosis or acute coronary syndromes receive a high weight-adjusted dose of LMWH (1 mg/kg) twice a day. For treatment of active thrombosis, the plasma antifactor Xa level (Heptest) should be monitored and targeted to the range of 0.4-1.0 U/mL (3). Needle placement should be delayed greater than 24 hours in patients receiving higher doses of thromboprophylaxis with LMWH (2).
Is there any role in monitoring the Heptest (antifactor Xa level) prior to a regional anesthetic?
The ASRA guidelines state that testing of antifactor Xa level is not recommended as it is not predictive of the risk of bleeding. There are some authorities outside of the field of anesthesia that believe that the heptest is predictive of bleeding and state that a plasma heparin level <0.2 U/mL is safe prior to the performance of an invasive procedure (3). It is our practice at BWH to only measure the heptest if the patient was taking a higher than usual dose (>1 mg/kg) of LMWH. Patients receiving such a high dose will not be administered a regional anesthetic unless the last dose of LMWH was greater than 24 hours prior to the anesthetic and the heptest is < 0.2 U/mL.
Question Author: David Hepner, MD, Department of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women's Hospital, Harvard Medical School
References:
1. Horlocker TT, Heit J. Low molecular weight heparin: biochemistry, pharmacology, perioperative prophylaxis regimens, and guidelines for regional anesthetic management. Anesth Analg 1997;85:874-85.
2. Horlocker TT, Wedel DJ. Neuraxial block and low molecular weight heparin: balancing perioperative analgesia and thromboprophylaxis. Reg Anesth Pain Med 1998:23 Suppl. 7-8.
3. Aguilar D, Goldhaber SZ. Clinical uses of low-molecular-weight-heparins. Chest 1999;115:1418-23.
Site Editor: Stephen B. Corn, M.D. and B. Scott Segal, M.D.
Department of Anesthesia, Harvard Medical School
Founders and Editors-in-Chief: Stephen B. Corn, M.D. and B. Scott Segal, M.D.
Department of Anesthesiology, Perioperative and Pain Medicine, Harvard Medical School
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