**Question:** Acute Lung Injury (ALI) is characterized by all except-

A. Increased alveolar-capillary membrane permeability
B. Reduced respiratory rate
C. Enhanced surfactant production
D. Normal lung compliance

**Core Concept:** Acute Lung Injury (ALI) is a severe form of respiratory distress syndrome that occurs within 48 hours of an insult. It is characterized by increased alveolar-capillary membrane permeability, resulting in acute respiratory distress, impaired gas exchange, and hypoxemia.

**Why the Correct Answer is Right:** The correct answer is "normal lung compliance," which is not a defining feature of ALI. Normal lung compliance refers to the lung's ability to expand and contract with minimal resistance, while ALI causes increased lung stiffness and reduced lung expansion.

**Why Each Wrong Option is Incorrect:**

A. **Increased alveolar-capillary membrane permeability:** This is a crucial feature of ALI, as increased permeability leads to protein and fluid leak from the blood vessels into the alveoli, impairing gas exchange and causing hypoxemia.

B. **Reduced respiratory rate:** ALI does not directly affect the respiratory rate. Instead, it results in hypoxia and hypercapnia, prompting the body to increase respiratory rate to compensate for inadequate oxygenation.

C. **Enhanced surfactant production:** ALI does not directly stimulate surfactant production. Instead, it disrupts the surfactant function, leading to alveolar collapse and hypoxemia.

D. **Normal lung compliance:** As explained earlier, normal lung compliance is incorrect.

**Clinical Pearl:** Understanding the key features of ALI (increased permeability, hypoxemia, and hypercapnia) is crucial for accurate diagnosis and appropriate treatment strategies.