What is an expected physiologic benefit of CPAP therapy for pulmonary edema?

• A. Decreases pulmonary edema by reducing fluid overload
• B. Continuous positive pressure improves oxygenation by recruiting alveoli and reducing preload/afterload
• C. Increases heart rate
• D. Completely reverses pulmonary edema immediately

Answer: (B)

CPAP works by delivering steady positive airway pressure that keeps the alveoli open, which recruits collapsed lung units. This improves oxygenation because more surface area is available for gas exchange and the work of breathing decreases as ventilation becomes more effective.

The positive pressure also changes hemodynamics: it raises intrathoracic pressure, which reduces venous return to the heart (preload) and lowers the left ventricle’s afterload by reducing the pressure against which the heart must pump. These effects help lessen pulmonary capillary pressures and the workload on the heart, contributing to better oxygen delivery and symptom relief in pulmonary edema.

Edema fluid buildup isn’t instantly removed or fully reversed by CPAP alone, and CPAP isn’t about increasing heart rate. The main benefit in this context is improved oxygenation through alveolar recruitment and favorable hemodynamic changes that reduce the heart’s work.