**Core Concept**
Polycythemia vera (PV) is a myeloproliferative neoplasm characterized by the excessive production of red blood cells, white blood cells, and platelets. The increased blood viscosity in PV patients poses a significant risk for thrombotic events.

**Why the Correct Answer is Right**
The most common postoperative complication in PV patients is thrombosis, particularly venous thrombosis, due to the increased blood viscosity and hypercoagulable state. This is because the increased red blood cell mass and platelet count lead to a higher risk of clot formation. In the postoperative period, the risk of thrombosis is further increased due to immobility, surgical trauma, and the use of intravenous lines and other devices that can cause endothelial damage.

**Why Each Wrong Option is Incorrect**
**Option A:** While infection is a significant concern in the postoperative period, it is not the most common complication in PV patients.
**Option B:** Hypotension is not a direct consequence of PV and is not the most common postoperative complication in these patients.
**Option C:** Bleeding is not a typical complication in PV patients, as they have a tendency towards thrombosis rather than bleeding.

**Clinical Pearl / High-Yield Fact**
In patients with PV, the risk of thrombosis can be reduced by perioperative anticoagulation, early mobilization, and the use of low-dose aspirin.

**Correct Answer: D. Thrombosis.**