Anticoagulant and Antiplatelet Therapy

Parenteral Anticoagulants and Heparin-Induced Thrombocytopenia

Parenteral anticoagulants provide rapid suppression of blood coagulation. Heparin exerts its pharmacological effect by accelerating the action of antithrombin III, an endogenous regulatory protein. Once activated, antithrombin III acts like a biological brake, inhibiting both thrombin and factor Xa. Therapeutic intravenous unfractionated heparin is monitored using an institution-specific aPTT or anti-factor Xa target; prophylactic subcutaneous unfractionated heparin generally does not require routine coagulation monitoring. The therapeutic target for aPTT during unfractionated heparin therapy is typically 1.5 to 2.5 times the normal baseline value. If severe bleeding or extreme overdose occurs, protamine sulfate is administered as the reversal agent. Protamine sulfate fully reverses unfractionated heparin, but it only partially reverses low-molecular-weight heparins.

Administration technique requires strict adherence to safety principles to prevent localized trauma. Heparin must never be administered by intramuscular injection due to the risk of hematoma formation. In fact, intramuscular injections should be avoided whenever possible in all clients receiving therapeutic anticoagulation. Low-molecular-weight heparins such as enoxaparin do not require routine coagulation laboratory monitoring. When administering enoxaparin, the nurse must deliver a deep subcutaneous injection into the abdomen at least two inches away from the umbilicus. A small air bubble is manufactured inside the prefilled syringe of enoxaparin; this air bubble should not be expelled prior to injection. Following any subcutaneous anticoagulant administration, the nurse and client must ensure the injection site is not rubbed or massaged, as mechanical friction promotes localized tissue injury.

Another parenteral agent used for postoperative venous thromboembolism prophylaxis is fondaparinux. When fondaparinux is selected for postoperative prophylaxis, it is given subcutaneously no sooner than six to eight hours after surgery and only after hemostasis is established. Anticoagulant therapy increases the risk of spinal or epidural hematoma with neuraxial procedures; appropriate timing of anticoagulant doses and catheter placement or removal helps minimize this rare but potentially serious complication.

A critical, life-threatening complication of heparin exposure is heparin-induced thrombocytopenia. Heparin-induced thrombocytopenia is an immune-mediated disorder that paradoxically increases the risk of severe thrombosis rather than bleeding. Clinicians must suspect this condition whenever a client's platelet count drops by 50 percent or more from baseline during heparin therapy. If heparin-induced thrombocytopenia is suspected, the immediate nursing action is to discontinue all heparin products without delay. To maintain necessary anticoagulation while managing this thrombotic emergency, clients diagnosed with heparin-induced thrombocytopenia are switched to alternative non-heparin anticoagulants such as argatroban.