What has been the anesthetic experience with LMWH and neuraxial anesthesia?
The release of LMWH for general use in the United States in May 1993 sparked a new challenge for anesthesiologists. Previously, a spinal or epidural hematoma was a rather rare occurrence, reportedly less than 1 in 150,000–220,000. Enoxaparin, the first LMWH to be approved by the United States Food and Drug Administration (FDA), had been used for many years in Europe. However, the approved dosing schedule of enoxaparin was 30 mg (3000 U) every 12 hours in the United States as opposed to 40 mg (4000 U) once daily in Europe. Within 1 year of its introduction in the United States, two cases of epidural hematoma were voluntarily reported through the MedWatch system. The warning section of the drug label was revised and a letter from the manufacturer was issued to practitioners to alert them to the risk of spinal hematoma in patients undergoing neuraxial anesthesia while receiving LMWH. Despite these warnings, a total of 40 cases of perioperative neuraxial hematoma in patients on LMWH were voluntarily reported between May 1993 and November 1997. An FDA Health Advisory was issued in December 1997.
The actual risk of spinal or epidural hematoma in patients receiving LMWH while undergoing neuraxial anesthesia is difficult to estimate. There are certainly addi-tional, unreported cases. The reported incidences of spinal or epidural hematoma in patients receiving LMWH may be approximately 1 in 3,000 for continuous epidural anesthesia and 1 in 100,000 for spinal anesthesia. Of the 40 cases of spinal or epidural hematoma associated with LMWH in conjunction with neuraxial anesthesia, two patients received epidural steroid injections, six underwent spinal anesthesia, one of which was continuous spinal anesthesia, 23 had continuous epidural anesthesia, six were unspeci-fied techniques, and three had general anesthesia after attempted or failed neuraxial anesthesia. Also, some patients had additional risk factors for the development of spinal or epidural hematoma, such as difficult needle placement or administration of antiplatelet or anticoagu-lant medication. None of the patients were pregnant.