What happens to the physiologic shunt fraction as a result of absorption atelectasis?

The physiologic shunt fraction refers to the portion of blood that passes through areas of the lung that are not participating in gas exchange, typically due to issues like atelectasis. Absorption atelectasis occurs when the air in the alveoli is reabsorbed by the body, which can happen if certain gas mixtures are present, particularly ones with high levels of nitrous oxide or when inhalation of oxygen is prolonged without adequate ventilation.

When absorption atelectasis occurs, the affected alveoli collapse, reducing the surface area available for gas exchange. As a result, blood that passes through these non-ventilated areas of the lung effectively does not receive oxygen, leading to an increase in the shunt fraction. This is because more blood is shunted through regions that are not ventilated due to the collapse of the alveoli, thereby increasing the proportion of blood that bypasses effective gas exchange. Consequently, the physiologic shunt fraction increases as absorption atelectasis develops, making the initial choice correct.

In cases where the shunt fraction increases, it underscores the need for clinicians to intervene, as it indicates a worsening of oxygenation efficiency in the patient. Hence, understanding how absorption atelectasis impacts the shunt fraction is crucial