A AaDO2 ratio less than 0.21 is used as an indication for which therapy?

A AaDO2 ratio less than 0.21 is used as an indication for which therapy?

• A. Oxygen therapy
• B. Diuresis
• C. Vasodilation
• D. Surfactant administration

Answer: (D)

The key idea is how the alveolar-arterial oxygen difference reflects where the oxygen isn’t getting across the lung. In neonates with surfactant deficiency, alveoli collapse and gas exchange becomes poor, so PaO2 falls well below PAO2, widening the A-aO2 gradient. Giving surfactant reopens the collapsed alveoli, improves the transfer of oxygen, and lowers the A-aO2 gradient. When the AaDO2 ratio is less than 0.21, it suggests the hypoxemia is due to a reversible surfactant deficiency and is likely to respond to surfactant therapy. So surfactant administration is the appropriate treatment. Oxygen therapy alone may help, but it doesn’t correct the underlying alveolar collapse; diuresis and vasodilation target other problems and aren’t addressing the surfactant deficiency.

The key idea is how the alveolar-arterial oxygen difference reflects where the oxygen isn’t getting across the lung. In neonates with surfactant deficiency, alveoli collapse and gas exchange becomes poor, so PaO2 falls well below PAO2, widening the A-aO2 gradient. Giving surfactant reopens the collapsed alveoli, improves the transfer of oxygen, and lowers the A-aO2 gradient. When the AaDO2 ratio is less than 0.21, it suggests the hypoxemia is due to a reversible surfactant deficiency and is likely to respond to surfactant therapy. So surfactant administration is the appropriate treatment. Oxygen therapy alone may help, but it doesn’t correct the underlying alveolar collapse; diuresis and vasodilation target other problems and aren’t addressing the surfactant deficiency.