A 56-year-old female client is on postoperative day 4 after a right total hip arthroplasty and has declined the last two doses of prophylactic enoxaparin. At 1400 she suddenly develops dyspnea, pleuritic chest pain, and anxiety. HR 124/min, RR 28/min, BP 102/68 mm Hg, temperature 37.3 C, SpO2 84% on room air. Lungs are clear with equal breath sounds and no sputum; the trachea is midline. There is no rash on the chest or axillae, and the client is alert and oriented. The 12-lead ECG shows sinus tachycardia without ST elevation. The right calf is 2 cm larger than the left. 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
Pulmonary embolism. Take action: apply oxygen to a saturation above 90% and start the IV heparin protocol. Monitor: oxygen saturation and anti-factor Xa or aPTT level.

Why this is correct
Orthopedic surgery, immobility, and missed enoxaparin create the Virchow triad; the enlarged right calf suggests the source DVT. Hypoxemia with clear lungs means a perfusion problem rather than an airway or alveolar one. The client is hypotensive-borderline but not in shock, so anticoagulation is the standard therapy; heparin dosing is titrated to anti-Xa or aPTT results, and oxygenation shows whether gas exchange is improving.

Easy analogy or mental picture
A clot has plugged a pipe to the lungs: air still reaches the rooms (clear lungs) but blood cannot pick it up. Oxygen raises what reaches the blood; heparin stops the plug from growing.

Memory hook
CLEAR lungs + LOW sat + SUDDEN = clot: O2 + HEPARIN; watch SAT and the heparin level.

NCLEX decision rule
When hypoxemia is out of proportion to lung sounds after surgery, think perfusion; treat hypoxemia first, start the definitive therapy, and monitor both oxygenation and the drug's therapeutic level.

Why the other choices are wrong
Fat embolism typically appears 24–72 hours after long-bone fracture or surgery with petechiae and confusion, which are absent. Acute coronary syndrome is less likely with pleuritic pain and an ECG without ST elevation, so nitroglycerin is not indicated. Pneumonia would bring fever, sputum, and focal findings; incentive spirometry and WBC count track atelectasis or infection. A rapid large-volume bolus can worsen right ventricular strain in a client who is not in shock. Incision drainage tracks surgical-site bleeding rather than the embolism.