Okay, let's tackle this question. The patient is a 60-year-old obese male with a history of chronic smoking. He had a pelvic fracture from a fall and is in the ICU. On day four, he develops sudden tachypnea, low SpO2, and hypotension. The echo shows right ventricular dilation and tricuspid regurgitation.

Hmm, so the key points here are the sudden onset of respiratory and circulatory symptoms, along with the echocardiogram findings. Right ventricular dilation and tricuspid regurgitation are classic signs of pulmonary hypertension. What can cause acute pulmonary hypertension in this context?

Well, considering the patient's history of chronic smoking and obesity, he might have chronic obstructive pulmonary disease (COPD), but that's more of a chronic condition. However, the acute presentation here suggests something else. The most likely culprit in this scenario is a pulmonary embolism (PE). A large PE can cause acute pulmonary hypertension, leading to right heart strain. The right ventricle can't handle the increased afterload, causing dilation and tricuspid regurgitation. The symptoms of tachypnea, hypoxia, and hypotension are consistent with a massive PE leading to shock.

Now, looking at the options, the next immediate step would be to confirm the diagnosis. The options aren't listed, but common next steps include imaging like CTPA (CT pulmonary angiogram) or a V/Q scan. However, in an ICU setting where the patient is unstable, maybe a D-dimer test first? Wait, but D-dimer isn't reliable in all cases, especially in someone with a recent surgery or trauma, which this patient has due to the pelvic fracture. So maybe directly proceeding to CTPA is better here.

Alternatively, if the patient is hemodynamically unstable, maybe they need immediate intervention like thrombolysis or even embolectomy. But the question asks for the next immediate step, not the treatment. So probably the next step is to confirm the diagnosis with imaging. Let me check the standard approach. In suspected massive PE, CTPA is the gold standard. So the next step would be to perform a CTPA to confirm PE. The other options might include things like starting anticoagulation, but that's treatment after diagnosis. So the answer is likely to perform a CTPA.

**Core Concept**
This case tests recognition of acute pulmonary embolism (PE) and its hemodynamic consequences. Massive PE causes acute pulmonary hypertension, right ventricular strain (evidenced by RV dilation and tricuspid regurgitation on echo), and systemic hypotension, requiring prompt diagnosis and intervention.

**Why the Correct Answer is Right**
The patient’s sudden hypoxia, hypotension, and echocardiographic findings (RV dilation, tricuspid regurgitation) point to acute right heart strain, most likely from a massive PE. The next step is **CT pulmonary angiography (CTPA)** to confirm the diagnosis. CTPA is the gold standard for imaging PE, especially in ICU patients, as it directly visualizes thrombi in pulmonary arteries. Early diagnosis is critical to initiate thrombolytic therapy or interventions in hemodynamically unstable patients.

**Why Each Wrong Option is Incorrect**
**Option A:** D-dimer testing is nonspecific and unreliable in trauma/

✓ Correct Answer: B. Administration of heparin