Comprehensive Respiratory System Disorders Q 13

---

A male patient’s X-ray result reveals bilateral white-outs, indicating acute respiratory distress syndrome (ARDS). This syndrome results from:

  

     A. Cardiogenic pulmonary edema

     B. Respiratory alkalosis

     C. Increased pulmonary capillary permeability

     D. Renal failure

    

    

Correct Answer: C. Increased pulmonary capillary permeability

---

ARDS results from increased pulmonary capillary permeability, which leads to noncardiogenic pulmonary edema. ARDS is defined as an acute disorder that starts within 7 days of the inciting event and is characterized by bilateral lung infiltrates and severe progressive hypoxemia in the absence of any evidence of cardiogenic pulmonary edema. ARDS is defined by the patient’s oxygen in arterial blood (PaO2) to the fraction of the oxygen in the inspired air (FiO2). These patients have a PaO2/FiO2 ratio of less than 300.

---

Option A: In cardiogenic pulmonary edema, pulmonary congestion occurs secondary to heart failure. The pulmonary epithelial and endothelial cellular damage is characterized by inflammation, apoptosis, necrosis, and increased alveolar-capillary permeability, which leads to the development of alveolar edema and proteinosis. Alveolar edema, in turn, reduces gas exchange, leading to hypoxemia.

Option B: In the initial stage of ARDS, respiratory alkalosis may arise secondary to hyperventilation; however, it does not cause ARDS. Segments of the lung may be more severely affected, resulting in decreased regional lung compliance, which classically involves the bases more than the apices. This intrapulmonary differential in pathology results in a variant response to oxygenation strategies.

Option D: Renal failure does not cause ARDS, either. ARDS has many risk factors. Besides pulmonary infection or aspiration, extra-pulmonary sources include sepsis, trauma, massive transfusion, drowning, drug overdose, fat embolism, inhalation of toxic fumes, and pancreatitis. These extra-thoracic illnesses and/or injuries trigger an inflammatory cascade culminating in pulmonary injury.

---