A 55 year old man who has been on bed rest for the past 10 days, complains of breathlessness. The chest X-ray shows hampton’s hump. The next investigation should be:
**Core Concept**
Hampton's hump refers to a specific radiographic appearance of pulmonary embolism (PE) seen on chest X-ray, characterized by a wedge-shaped pleural-based consolidation. This finding is associated with a pulmonary infarct due to the obstruction of blood flow to the lung parenchyma.
**Why the Correct Answer is Right**
In the context of a patient on bed rest for 10 days, who complains of breathlessness, a high index of suspicion for deep vein thrombosis (DVT) and pulmonary embolism (PE) is warranted. The presence of Hampton's hump on chest X-ray is a strong indicator of PE. Given the clinical scenario and radiographic findings, the next investigation should be a **venous ultrasound of the lower limbs** to confirm the presence of DVT, which is a direct cause of PE. This test is non-invasive, readily available, and can be performed quickly to guide further management.
**Why Each Wrong Option is Incorrect**
**Option A:** CT Pulmonary Angiogram (CTPA) is a sensitive and specific test for diagnosing PE but is not the next investigation in this scenario. While CTPA can confirm the diagnosis of PE, it is more expensive and exposes the patient to radiation and contrast. A venous ultrasound is a more appropriate initial step.
**Option B:** ECG is not the next investigation in this scenario. While an ECG can show signs of PE such as T-wave inversion or right bundle branch block, it is not specific for diagnosing PE.
**Option C:** Arterial Blood Gas (ABG) analysis may show hypoxemia and hypocarbia in patients with PE, but it is not a diagnostic test for PE. ABG analysis can be performed at a later stage to assess the severity of respiratory compromise.
**Option D:** Chest CT scan without contrast may show signs of pulmonary embolism such as oligemia or the "Westermark sign", but it is not as sensitive as a venous ultrasound for detecting DVT.
**Clinical Pearl / High-Yield Fact**
In patients suspected of having PE, a venous ultrasound of the lower limbs should be performed as the next investigation, as it is a quick, non-invasive, and cost-effective method to detect DVT, which is a direct cause of PE.
**Correct Answer:** . Venous ultrasound of the lower limbs.