**Core Concept**
Pulmonary edema can be caused by various factors, including increased hydrostatic pressure, increased permeability of the capillary wall, and decreased oncotic pressure. In this scenario, the normal alveolar wedge pressure rules out the possibility of congestive heart failure or cardiogenic shock, which typically increase the pressure in the left side of the heart.

**Why the Correct Answer is Right**
Narcotic overdose can cause pulmonary edema due to increased permeability of the capillary wall, leading to fluid leakage into the alveoli. This is often referred to as "non-cardiogenic pulmonary edema." The mechanism involves the release of histamine and bradykinin, which increase the permeability of the capillary wall, causing fluid to leak into the alveoli. This type of edema is also seen in conditions such as acute respiratory distress syndrome (ARDS).

**Why Each Wrong Option is Incorrect**
**Option B:** Congestive heart failure typically increases the alveolar wedge pressure, which is not the case here. In congestive heart failure, the left ventricle fails to pump blood effectively, leading to increased pressure in the left atrium and alveolar wedge pressure.
**Option C:** Myocardial infarction can cause cardiogenic shock, which would increase the alveolar wedge pressure. Additionally, myocardial infarction can increase the permeability of the capillary wall, but this is not the primary mechanism in this scenario.
**Option D:** Cardiogenic shock would typically increase the alveolar wedge pressure, which is not the case here. Cardiogenic shock is a condition where the heart is unable to pump blood effectively, leading to decreased cardiac output and increased pressure in the left side of the heart.

**Clinical Pearl / High-Yield Fact**
Non-cardiogenic pulmonary edema should be suspected in cases where the alveolar wedge pressure is normal, and the patient has a history of recent narcotic overdose or other causes of increased capillary permeability. This type of edema can be treated with diuretics and supportive care, but the underlying cause should be identified and addressed.

**✓ Correct Answer: A. Narcotic overdose**