AANA Journal course: update for nurse anesthetists--low molecular weight heparin: pharmacology and regional anesthetic implications.

Low molecular weight heparins were first introduced in the United States in May 1993 as an alternative to currently available anticoagulant therapy. Like standard heparin, these anticoagulants inhibit activation of a number of coagulation enzymes, but low molecular weight heparins have their primary inhibitory effect on factor Xa. A decrease in plasma protein binding by low molecular weight heparin results in greater bioavailability and a more predictable therapeutic response than that of standard heparin. Although drug action is not measurable by commonly available laboratory tests of coagulation, greater predictability of drug response led to acceptance of these agents for perioperative thromboprophylaxis. The introduction of low molecular weight heparin into the perioperative surgical management of patients also has influenced perioperative anesthetic care. Postmarketing reports of the formation of spinal epidural hematoma when these agents were used concurrently with regional anesthesia prompted the US Food and Drug Administration to issue an advisory to anesthesia providers. This Journal course includes the pharmacology of the class of drugs known as low molecular weight heparins, the incidence and risk factors for the development of spinal or epidural hematoma, and current recommendations for the use of these anticoagulants in conjunction with spinal or epidural anesthesia. Guidelines for the postoperative use of indwelling spinal or epidural catheters in patients who receive this drug therapy in the course of their perioperative care are presented.