All of the following features can seen in ARDS except:
**Core Concept**
Acute Respiratory Distress Syndrome (ARDS) is a life-threatening condition characterized by sudden onset of inflammation in the lungs, leading to impaired gas exchange and hypoxemia. It is typically triggered by a severe insult, such as pneumonia, trauma, or sepsis, which causes damage to the alveolar-capillary membrane, resulting in increased permeability and edema.
**Why the Correct Answer is Right**
ARDS is characterized by several key features, including bilateral infiltrates on chest radiographs, hypoxemia, and non-cardiogenic pulmonary edema. The non-cardiogenic aspect is crucial, as it indicates that the edema is not due to left heart failure, but rather due to increased permeability of the alveolar-capillary membrane. This is often assessed using the Berlin definition, which requires a ratio of arterial oxygen to fractional inspired oxygen (PaO2/FiO2) of ≤ 300 mmHg.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is not specified, but a common feature of ARDS is indeed the presence of bilateral infiltrates on chest radiographs. This is a hallmark of the condition.
**Option B:** Hypoxemia is a defining feature of ARDS. Patients typically have a PaO2/FiO2 ratio of ≤ 300 mmHg, indicating severe impairment of gas exchange.
**Option C:** Non-cardiogenic pulmonary edema is a key feature of ARDS. This type of edema is caused by increased permeability of the alveolar-capillary membrane, rather than left heart failure.
**Clinical Pearl / High-Yield Fact**
It's essential to note that the Berlin definition of ARDS requires a ratio of PaO2/FiO2 of ≤ 300 mmHg, rather than the older definition of ≤ 200 mmHg. This change reflects the understanding that ARDS can occur in patients with milder degrees of hypoxemia.
**Correct Answer: D.**