**Question:** A Patient comes with sudden respiratory distress. On examination, bilateral basal crepitations are present over chest suggestive of pulmonary edema. Alveolar wedge pressure is normal. The likely cause is?

**Core Concept:** Pulmonary edema is a condition characterized by the accumulation of fluid in the alveoli, leading to impaired gas exchange and respiratory distress. Although alveolar wedge pressure (a measure of left ventricular filling pressure) is typically elevated in pulmonary edema, normal values do not exclude the diagnosis.

**Why the Correct Answer is Right:** In this scenario, the presence of bilateral basal crepitations (a key sign of increased interstitial fluid accumulation and not related to alveolar wedge pressure) is more important than the normal alveolar wedge pressure. This indicates that the cause of pulmonary edema is likely due to increased hydrostatic pressure in the pulmonary capillaries, which is unrelated to left ventricular filling pressure.

**Why Each Wrong Option is Incorrect:**

A. **Cardiogenic pulmonary edema (heart failure):** This is the most common type of pulmonary edema, caused by increased left ventricular filling pressure (elevated alveolar wedge pressure). In this scenario, the normal wedge pressure rules out this option.

B. **Neurogenic pulmonary edema:** This is an uncommon cause of pulmonary edema resulting from central nervous system injury or disease. This option is ruled out by the absence of any neurological symptoms or history.

C. **Pneumonic pulmonary edema:** This is a rare type of pulmonary edema caused by inhalation of air pollutants, such as ammonia or carbon monoxide. A lack of relevant exposure history and the absence of neurological symptoms also rule out this option.

D. **Pulmonary edema due to lung injury:** Pulmonary edema can be caused by lung injury, but the absence of any history of trauma, infection, or other lung pathology suggests that this option is less likely.

**Clinical Pearl:** In cases where the cause of pulmonary edema is not immediately clear, consider the other options and investigate for factors that could lead to increased hydrostatic pressure in the pulmonary capillaries, such as myocardial infarction, pulmonary embolism, or severe asthma exacerbation.

**Correct Answer:** The correct answer is B. Pulmonary edema due to severe asthma exacerbation. Severe asthma can lead to increased airway pressure, causing increased hydrostatic pressure in the pulmonary capillaries and leading to pulmonary edema. The normal wedge pressure does not exclude this option, as the cause is related to increased hydrostatic pressure rather than increased left ventricular filling pressure.