Final answer:
In a side-lying position with the foot of the bed elevated and a pillow under the knees, the right lower lobe lateral basal segments of the lung are being drained, which is important for cystic fibrosis treatment.
Step-by-step explanation:
When the patient is positioned in a right side-lying position with the foot of the bed elevated 18 inches, and a pillow placed between and under the knees, the goal is to facilitate postural drainage for certain regions of the lungs. In this position, the right lower lobe of the lung, specifically the lateral basal segments, is being targeted for drainage. This treatment is part of managing cystic fibrosis, a condition where mucus can obstruct the airways and foster bacterial growth.