Acute severe lung injury is characterised by-
**Core Concept**
Acute severe lung injury, also known as acute respiratory distress syndrome (ARDS), is characterized by a rapidly developing process of lung inflammation, edema, and impaired gas exchange. This condition is often triggered by direct or indirect lung injury, leading to an imbalance between the influx of fluid into the lungs and the clearance of fluid by the lymphatic system.
**Why the Correct Answer is Right**
The pathophysiology of ARDS involves the disruption of the alveolar-capillary membrane, allowing fluid and inflammatory cells to leak into the alveoli. This results in hypoxemic respiratory failure, characterized by an inability to maintain adequate oxygenation despite an adequate respiratory rate and tidal volume. The inflammatory response in ARDS is mediated by various cytokines, including tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1β), which contribute to the recruitment of neutrophils and the release of reactive oxygen species.
**Why Each Wrong Option is Incorrect**
**Option A:** While diffuse alveolar hemorrhage is a complication of ARDS, it is not a characteristic feature of the condition.
**Option B:** Pulmonary embolism is a separate clinical entity that can cause acute respiratory distress, but it is not a defining feature of ARDS.
**Option C:** Cardiac failure is a possible cause of acute respiratory distress, but it is not a characteristic feature of ARDS.
**Clinical Pearl / High-Yield Fact**
The Berlin definition of ARDS, which is widely used, requires the presence of acute onset, a PaO2/FiO2 ratio ≤ 300 mmHg, and bilateral opacities on chest imaging that are consistent with pulmonary edema.
**Correct Answer:** C.