What is the function of continuous positive airway pressure (CPAP) in spontaneous breathing?

Continuous positive airway pressure (CPAP) serves the primary function of providing pressure throughout the entire respiratory cycle during spontaneous breathing. This means that CPAP maintains a positive airway pressure which keeps the alveoli open and can help prevent collapse, known as atelectasis. By providing this constant pressure, CPAP helps to improve oxygenation and ventilation, enhances functional residual capacity (FRC), and contributes to more effective gas exchange.

The other options fail to capture the essence of what CPAP is designed to do. For instance, delivering a set tidal volume is associated more with modes of mechanical ventilation that control the breath, which is not the primary role of CPAP. Similarly, while CPAP allows the patient to breathe spontaneously, it does not deliver breaths solely upon demand like some forms of ventilatory support do, which rely on patient-triggered breaths. Lastly, CPAP does not control the ventilatory effort; rather, it augments the patient’s own breathing efforts by preventing airway collapse and ensuring the pressure in the airways is maintained throughout the respiratory cycle, thus supporting the patient without fully taking over the breathing process.