Effects of EPAP on Normal Respiratory Physiology

Mechanisms of Action of EPAP

The American Thoracic Society suggests that EPAP maintains a positive alveolar pressure at the end of expiration, preventing alveolar collapse and improving functional residual capacity 3
In patients with COPD, EPAP counteracts the effects of intrinsic PEEP (auto-PEEP), reducing respiratory work 1, 2
EPAP eliminates exhaled air through the expiratory port, significantly reducing CO2 rebreathing 1
It acts as a "stent" that keeps the upper airways open, especially important during sleep 1, 2

EPAP promotes lung recruitment, improving ventilation in previously collapsed areas 1, 4
The American Academy of Sleep Medicine recommends that EPAP be used to reduce the threshold inspiratory load during spontaneous breathing, although the strength of evidence is not provided 4

EPAP can modify the end-expiratory lung volume (EELV), which normally decreases with increased respiratory work 5
In normal conditions, EPAP can prevent a decrease in EELV during exercise 5
The addition of EPAP to pressure support (PS) has been shown to significantly reduce respiratory work 1, 2

In bi-level pressure ventilators, EPAP is typically set between 4-8 cmH2O to reduce respiratory work 4
The minimum recommended EPAP for adults is 4 cmH2O, which can be increased according to individual needs 6
EPAP is particularly beneficial in patients with neuromuscular disorders, improving nocturnal PtcCO2 max and increasing minimum oxygen saturation, although the strength of evidence is not provided 4, 7

Excessively high EPAP can cause gastric distension or increase respiratory work 4
In patients with cardiovascular compromise, EPAP should be applied with caution as positive intrathoracic pressure can reduce venous return 3

Unlike CPAP (continuous positive airway pressure), which maintains a constant pressure, EPAP is applied only during expiration 4
In bi-level systems (BiPAP), EPAP is combined with a higher positive inspiratory pressure (IPAP), providing greater assistance during inspiration 4
EPAP is more effective than pressure support alone in reducing respiratory work in patients with acute COPD 1, 2