The nurse is caring for a client with a diagnosis of venous thrombosis in the left lower leg who is receiving heparin sodium by continuous intravenous (IV) infusion. The nurse should monitor the client for which manifestation indicating an adverse effect of this therapy?

The primary adverse effect of heparin sodium therapy is bleeding, which results from the drug's anticoagulant mechanism of potentiating antithrombin III and inhibiting clot formation. A nosebleed (epistaxis) is a manifestation of excessive anticoagulation and represents a clinically significant bleeding complication that must be reported and assessed promptly. The nurse must monitor for any signs of abnormal bleeding, including epistaxis, hematuria, blood in stools, unusual bruising, bleeding gums, and prolonged bleeding from puncture sites. Left calf tenderness is actually a symptom of the underlying venous thrombosis for which heparin is being administered; it is not an adverse effect of the drug itself. Increased blood pressure is not an expected adverse effect of heparin; in fact, significant internal hemorrhage could eventually lead to hypotension, not hypertension. Nausea can occur with many medications but is not the primary or most serious adverse effect of heparin to monitor. Identifying bleeding as the hallmark complication of anticoagulant therapy and recognizing its various manifestations — including epistaxis — is essential for safe patient monitoring during heparin infusions.