Stage 3 — Prioritize hypotheses. The RN, working with one LPN/VN and one UAP, has completed focused assessments after handoff. Patient A, 72, is postoperative day 1 after right total hip arthroplasty and receives prescribed VTE prophylaxis. At 0500 he developed sudden shortness of breath with new right calf tenderness and unilateral swelling. BP is 138/86, HR 110, RR 24, temperature 37.6°C (99.7°F), and SpO2 89% on room air. He is anxious but alert and oriented, breath sounds are clear, and there are no petechiae. Patient D, 81, with a UTI, is oriented to person and place (baseline oriented x3) and is trying to get out of bed; a bed alarm is active. Patients B and C are stable. For Patient A, 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
Acute pulmonary embolism in Patient A. Stay with him, stop activity, and apply prescribed oxygen; notify the provider and activate the rapid response team. Monitor oxygen saturation and heart rate.

Why this is correct
Hip arthroplasty is one of the highest-risk operations for VTE, and new unilateral calf tenderness and swelling suggest a DVT source. Sudden dyspnea with hypoxemia, tachycardia, and tachypnea despite clear breath sounds fits an embolus. An airway-breathing-circulation threat outranks Patient D's safety risk, which is covered by the bed alarm and can be handed to staff once help arrives for Patient A.

Easy analogy or mental picture
Four call lights are on, but only one is a fire alarm. The RN goes to the fire (Patient A), calls the fire department (rapid response), and sends others to watch the smaller risks.

Memory hook
"New hip + sudden breathless + one fat calf = PE; RN stays, calls, gives oxygen."

NCLEX decision rule
Use ABCs to pick the first client, keep assessment and evaluation of an unstable client with the RN, and delegate only stable, predictable tasks.

Why the other choices are wrong
Atelectasis is common after surgery and can cause low-grade fever, but it develops gradually with diminished breath sounds, so incentive spirometry and spirometer volumes do not fit sudden hypoxemia with clear lungs. Fat embolism syndrome can follow orthopedic surgery, but it brings petechiae and confusion, which are absent, so petechiae checks do not track progress. Anxiety can cause rapid breathing, but it does not drop SpO2 to 89%. Having the UAP take vital signs or the LPN/VN complete the initial assessment delegates the evaluation of an unstable client, and calf circumference tracks the DVT, not the embolism's effect on gas exchange.