What condition is a reduction in functional residual capacity during pregnancy most likely to predispose a patient to if critical illness develops?

A reduction in functional residual capacity (FRC) during pregnancy is primarily linked to an increased risk of atelectasis. FRC, which is the volume of air remaining in the lungs after a normal expiration, decreases due to the upward pressure from the growing uterus and diaphragm displacement. This anatomical change limits lung expansion and can lead to incomplete alveolar inflation.

In the setting of critical illness, this reduced FRC further exacerbates the potential for atelectasis, which occurs when alveoli collapse or do not fully inflate. In patients with decreased lung volumes or impaired respiratory mechanics, the likelihood of alveolar collapse increases, particularly when factors such as sedation, mechanical ventilation, or poor respiratory effort are introduced, all of which may be seen in critically ill patients.

While pneumonia, pulmonary embolism, and acute respiratory distress syndrome (ARDS) can also pose risks during pregnancy, the direct link between reduced FRC and the mechanics of atelectasis makes it the most likely condition to develop in this specific context. In critically ill patients, maintaining effective ventilation and airway patency becomes crucial, especially when the baseline respiratory function has been compromised due to gestational changes.