Mean Airway Pressure Calculator

What Is Mean Airway Pressure (Paw)?

Mean airway pressure (Paw) is the average pressure applied to the airways throughout the entire respiratory cycle during mechanical ventilation. It reflects how much distending pressure the lungs receive over time and is a key determinant of oxygenation, alveolar recruitment, and hemodynamic effects. Clinicians use Paw to balance gas exchange against risks such as barotrauma and reduced venous return. Pair this with the IV Flow Rate Calculator for fluid management and the Lung Capacity Calculator for pulmonary function context.

How Paw Is Calculated

This calculator uses the simplified ventilator equation: Paw = K × (Ti / Tcycle) × (PIP − PEEP) + PEEP, where Ti is inspiratory time, Tcycle is total cycle time (or 60 divided by respiratory rate), PIP is peak inspiratory pressure, and PEEP is positive end-expiratory pressure. All pressures are in cmH₂O. The waveform factor K adjusts for the shape of the pressure curve: K = 1 for rectangular (square-wave) breaths, K = 0.5 for triangular waveforms, and K = 2/π (approximately 0.637) for sine-wave patterns.

PEEP, PIP, and Clinical Interpretation

PEEP maintains alveolar opening at end expiration and improves oxygenation in conditions such as ARDS. PIP represents the highest airway pressure during inspiration and reflects both PEEP and the driving pressure needed to deliver tidal volume. Typical Paw during two-lung ventilation falls between 10 and 15 cmH₂O. Values above 20 cmH₂O may impair cardiac output by reducing venous return and increasing intrathoracic pressure. Always interpret Paw alongside tidal volume, FiO₂, plateau pressure, and patient hemodynamics.