Is pressure support the same as inspiratory positive airway pressure (IPAP)?

Pressure Support vs IPAP: Understanding the Relationship

Pressure support (PS) and inspiratory positive airway pressure (IPAP) are not the same thing—pressure support is the difference between IPAP and EPAP, while IPAP is the absolute pressure level delivered during inspiration. 1

Key Definitions

• IPAP is the higher pressure level delivered during the inspiratory phase of bi-level positive airway pressure (BiPAP/BPAP) ventilation 1

• EPAP (expiratory positive airway pressure) is the lower pressure maintained during expiration 1

• Pressure support is calculated as the mathematical difference: PS = IPAP - EPAP 1, 2

How This Works Mechanically

• The IPAP provides the actual ventilatory support during inspiration by generating higher pressure that overcomes lung and chest wall impedance 2

• The pressure support (IPAP-EPAP difference) is what actually augments tidal volume and improves ventilation 1, 2

• EPAP serves multiple functions: it maintains upper airway patency, recruits underventilated lung tissue, offsets intrinsic PEEP, and actively flushes exhaled CO₂ from the circuit 1, 2, 3

Clinical Example

• If you set IPAP at 15 cm H₂O and EPAP at 5 cm H₂O, the pressure support is 10 cm H₂O 1

• If you set IPAP at 20 cm H₂O and EPAP at 10 cm H₂O, the pressure support is still 10 cm H₂O—same pressure support but different absolute pressures 1

• Typical initial settings start with IPAP 8-10 cm H₂O and EPAP 4-5 cm H₂O, providing pressure support of 4-6 cm H₂O 2

Why This Distinction Matters Clinically

• When titrating BiPAP, you must adjust both IPAP and EPAP independently to optimize both ventilation (via pressure support) and airway patency/PEEP effects (via EPAP) 1

• Inadequate EPAP (<3 cm H₂O) allows CO₂ rebreathing in single-limb circuits, negating the ventilatory benefits of higher IPAP 2

• The IPAP-EPAP difference (pressure support) is what determines the delivered tidal volume, not IPAP alone 1, 2

Common Pitfall to Avoid

• Do not confuse "pressure support ventilation" (PSV) mode—where you set a single pressure support level above PEEP—with the pressure support value in BiPAP, which is derived from two separately set pressures 1

• In assisted spontaneous breathing (pressure support mode), you typically set one pressure value, whereas in bi-level support you set both IPAP and EPAP independently 1