**Core Concept**
The question revolves around the concept of D-dimer levels and their association with post-operative complications. D-dimer is a protein fragment produced when a blood clot dissolves, and its levels are often elevated in conditions involving clot formation or fibrinolysis.

**Why the Correct Answer is Right**
The increase in D-dimer levels in the immediate post-operative period is most commonly due to surgical trauma, which leads to activation of the coagulation cascade and subsequent clot formation. This process results in the release of fibrin degradation products, including D-dimer. The surgical incision and tissue damage trigger a systemic inflammatory response, which in turn activates the coagulation pathway, leading to increased D-dimer levels.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the immediate post-operative period, as it is more commonly associated with conditions like deep vein thrombosis or pulmonary embolism.

**Option B:** While disseminated intravascular coagulation (DIC) can indeed cause elevated D-dimer levels, it is a more severe and complex condition that is not the most common cause in the immediate post-operative period.

**Option C:** This option is not directly related to D-dimer levels, as it is more commonly associated with post-operative infections or sepsis.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that elevated D-dimer levels in the post-operative period do not necessarily indicate a specific diagnosis but rather a non-specific marker of surgical stress and coagulation activation. Therefore, it is crucial to consider the clinical context and other diagnostic findings when interpreting elevated D-dimer levels.

**Correct Answer:** B. Disseminated intravascular coagulation (DIC).