Which of the following is used to calculate the Alveolar-arteriole Gradient?

The calculation of the Alveolar-arteriole gradient, also known as the alveolar-arterial (A-a) gradient, is essential for assessing pulmonary gas exchange efficiency. The formula used for this calculation is derived from the alveolar gas equation and takes into account the partial pressure of oxygen in the alveoli and the arterial blood.

The correct formulation for calculating the A-a gradient involves subtracting the arterial oxygen partial pressure (PaO2) from the calculated alveolar oxygen partial pressure. The first step in this calculation is to determine the alveolar oxygen (PAO2) using the following simplified formula: PAO2 = 150 - (1.25 x PCO2), where PCO2 is the partial pressure of carbon dioxide in the arterial blood.

By applying the values from the question, the formulation represented corresponds to the correct understanding of how to calculate the A-a gradient. Specifically, option A correctly adapts this calculation into a format that shows this relationship, making it evident why it is the appropriate selection for calculating the alveolar-arteriole gradient.

This formulation is crucial for differentiating whether hypoxemia is due to hypoventilation, diffusion impairment, shunting, or ventilation-perfusion mismatch, allowing for