A 56-year-old client is on postoperative day 4 after total hip arthroplasty and has been mostly in bed. She suddenly develops dyspnea and sharp chest pain that worsens with inspiration. Heart rate is 124/min, respirations 28/min, BP 102/68 mm Hg, SpO2 84% on room air, and temperature 37.2 C. Breath sounds are present and clear bilaterally with no crackles, and the trachea is midline. She has no cough or sputum. The left calf is warm and 3 cm larger than the right. A 12-lead ECG shows sinus tachycardia without ST-segment elevation. Complete the diagram by selecting the condition the client is most likely experiencing, 2 actions the nurse should take to address that condition, and 2 parameters the nurse should monitor to assess the client's progress.

Quick answer
Condition: pulmonary embolism. Actions: apply oxygen to keep SpO2 at least 90% and start the heparin protocol as prescribed. Monitor: SpO2 and respiratory rate, and aPTT on the heparin protocol.

Why this is correct
Hip arthroplasty plus bed rest meets Virchow's triad, and the swollen, warm calf suggests the source DVT. Sudden hypoxemia with clear lungs is the signature of a perfusion problem rather than an airway or alveolar problem. Hypoxemia is the immediate threat, so oxygen comes first; unfractionated heparin stops the clot from growing while CT pulmonary angiography is obtained. aPTT (or anti-Xa, per protocol) is the lab that guides heparin dosing.

Easy analogy or mental picture
The lungs are a sponge that is still clean (clear breath sounds), but the pipe feeding it blood is plugged; air gets in, blood does not come to pick up the oxygen.

Memory hook
Clear lungs + low sat + post-op leg = clot. O2, heparin, watch sat and aPTT.

NCLEX decision rule
When sudden hypoxemia appears with clear lungs in a high-VTE-risk client, treat the hypoxemia and start prescribed anticoagulation; monitor oxygenation and the lab that doses the anticoagulant.

Why the other choices are wrong
Pneumonia is ruled out by no fever, no cough or sputum, and no crackles, so antibiotics, sputum cultures, and WBC count follow the wrong process. Myocardial infarction is ruled out by pleuritic (not pressure-type) pain and no ST elevation, so chewed aspirin is not the priority and adds bleeding risk before heparin. Pneumothorax is ruled out by bilateral breath sounds and a midline trachea, so a chest tube is not indicated. INR is tempting because it is an anticoagulation lab, but it tracks warfarin, not a heparin infusion.