Mean Airway Pressure (P̄aw) Calculator
The average pressure the airway sees each cycle — P̄aw = K × (PIP − PEEP) × (Ti/Ttot) + PEEP — the pressure term that drives oxygenation and feeds the oxygenation index, with the waveform constant and I:E derivation shown.
Written by Apex Respiratory Editorial Team
Enter PIP, PEEP, and the I:E ratio to calculate mean airway pressure.
Reading mean airway pressure
P̄aw rises with PEEP, PIP, inspiratory time, and flow, and it tracks oxygenation — but higher P̄aw also raises intrathoracic pressure (reduced venous return, hypotension) and barotrauma risk. There is no single “normal”; it is set by the ventilator.
The waveform constant K refers to the pressurewaveform: 1.0 for a square pressure waveform (pressure control), 0.5 for the ascending-ramp pressure of a constant-flow volume-control breath. Same settings, different K, give a different P̄aw — so the mode is selected here rather than typed.
The inspiratory fraction comes from the I:E ratio as I ÷ (I + E) — 1:2 → 0.33, 1:1 → 0.5. P̄aw then feeds the oxygenation index (OI = FiO₂ × P̄aw × 100 ÷ PaO₂, FiO₂ as a fraction).
Educational use only. This material supports respiratory therapy education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional protocols, or physician orders. Always follow facility policies and current provider orders, and verify calculations independently before clinical use.
Sources
- Kacmarek RM, Stoller JK, Heuer AJ. Egan's Fundamentals of Respiratory Care. 12th ed. Elsevier; 2021.
- Marini JJ, Ravenscraft SA. Mean airway pressure: physiologic determinants and clinical importance. Crit Care Med. 1992;20(10):1461-1472.