A 32-year-old man is involved in a vehicular accident and sustains fractures of the right femur and tibia and the left humerus. The fractures are stabilized surgically. He is in stable condition for 2 days, but then suddenly becomes severely dyspneic. Which of the following complications from his injuries is the most likely cause of his sudden respiratory difficulty?

**Core Concept**
Pulmonary thromboembolism (PTE) is a potentially life-threatening complication that can arise in patients with long bone fractures, particularly when associated with immobilization and venous stasis.

**Why the Correct Answer is Right**
The sudden onset of dyspnea in this patient is most likely due to a pulmonary thromboembolism (PTE) caused by a dislodged clot from the lower extremity. The fractures of the femur and tibia lead to venous stasis and increased coagulability, which can result in the formation of deep vein thrombosis (DVT). If a portion of the clot breaks off and travels to the lungs, it can cause a PTE, leading to severe respiratory distress. This is a well-known complication of long bone fractures and is often referred to as "fat embolism syndrome" (FES), although fat globules are not always present.

**Why Each Wrong Option is Incorrect**
* **Option A:** Myocardial infarction is an unlikely cause of sudden respiratory difficulty in this scenario, as there is no mention of cardiac risk factors or symptoms.
* **Option B:** Cardiac tamponade is a possible complication of trauma, but it would typically present with hypotension, muffled heart sounds, and jugular venous distension, rather than isolated respiratory distress.
* **Option D:** Pneumothorax is a possible complication of trauma, but it would typically present with sudden onset of chest pain and decreased breath sounds on the affected side, rather than isolated respiratory distress.

**Clinical Pearl / High-Yield Fact**
Long bone fractures, particularly those involving the femur and tibia, are associated with an increased risk of pulmonary thromboembolism (PTE) due to venous stasis and increased coagulability. This is a critical consideration in the management of patients with multiple trauma and long bone fractures.

**Correct Answer:** C.

✓ Correct Answer: B. Fat embolism