Heparin resistance was discovered in a patient in the surgical intensive care unit who underwent emergency endovascular coiling and later an anterior communicating artery clipping procedure to treat subarachnoid hemorrhage due to rupture of an anterior communicating artery aneurysm.

Clinical Findings

On intensive care unit day 17/postoperative day 3, the patient experienced shortness of breath, persistent tachycardia, and hypoxia. Bilateral pulmonary emboli, a saddle embolus, and lower-extremity and upper-extremity deep vein thrombi were diagnosed. The patient received high-dose unfractionated heparin (>35 000 U/24 h), and activated partial thromboplastin times remained subtherapeutic over the next 72 hours.


Factor VIII activity, fibrinogen, antithrombin activity, antithrombin antigen, and platelet factor 4 were measured. The results demonstrated an increase in factor VIII activity to 342% (reference range, 50%-200%), elevated fibrinogen level of 441 mg/dL (reference range, 200-400 mg/dL), antithrombin antigen level of 92% (reference range, 80%-130%), elevated antithrombin activity of 108% (reference range, 80%-100%), and negative platelet factor 4 result, indicating that the patient did not have heparin-induced thrombocytopenia and confirming the diagnosis of heparin resistance.


Risk factors for heparin resistance include antithrombin deficiency, elevation of factor VIII or fibrinogen level, elevation in heparin-binding proteins, increased heparin clearance, sepsis, trauma, and burns. The astute critical care nurse may be the first to recognize this condition in a patient, preventing a potentially fatal complication.

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