Final answer:
The woman recently treated with heparin for DVT and presenting with decreased air entry in the lungs is most likely suffering from heparin-induced thrombocytopenia (HIT), a condition where heparin triggers an immune response causing increased clotting.
Step-by-step explanation:
The condition most likely affecting the 42-year-old woman with a history of deep vein thrombosis (DVT) who was initiated on heparin therapy and has now developed decreased air entry bilaterally in her lungs is heparin-induced thrombocytopenia (HIT). HIT occurs when heparin triggers the patient's immune system to form antibodies against heparin-platelet protein complexes, leading to an increased risk of clotting rather than the intended anticoagulation effect. The woman's history of smoking and birth control use for endometriosis several years ago does put her at risk for thrombosis, but the recent initiation of heparin and the symptomatic presentation suggest HIT as a more immediate and related cause.
Deep vein thrombosis is a serious condition marked by the formation of a blood clot in the deep veins, typically in the legs, which can break loose and cause a pulmonary embolism (PE). PE is critical, as it blocks blood flow to the lungs and can result in damage or even death. Given the clinical scenario, it is vital to recognize and treat HIT promptly to prevent further complications.