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Plateau airway pressure, $P_{\mathrm{plat}}$, is the airway pressure assessed during an end-inspiratory interval with no flow and sufficiently stable conditions. An end-inspiratory hold can allow the airway and communicating alveolar gas pressures to equilibrate when the respiratory system is passive and the circuit is not leaking.^[ref][ref]

The distinction from peak airway pressure follows a simple single-compartment model:During the modeled hold, $\dot{V}=0$, leavingHere $C$ is respiratory-system compliance, $R$ is airway resistance, and total positive end-expiratory pressure supplies the starting reference. The measured difference $P_{\mathrm{plat}}-P_{\mathrm{EEP},\mathrm{total}}$ is the corresponding respiratory driving pressure.

In an original example, total PEEP 8 cm H${}_2$O, tidal volume 0.40 L and compliance 0.04 L/cm H${}_2$O give $P_{\mathrm{plat}}=18$ cm H${}_2$O. If flow immediately beforehand is 0.5 L/s and resistance is 12 cm H${}_2$O·s/L, the model's airway pressure during that flow is 24 cm H${}_2$O. The 6 cm H${}_2$O difference is the modeled resistive contribution, not an extra static distending pressure.

A plateau does not directly measure pleural pressure or isolate the lung from the chest wall. For the same stipulated alveolar pressure 18 cm H${}_2$O, pleural pressures of 12 and 2 cm H${}_2$O imply transpulmonary pressures of 6 and 16 cm H${}_2$O. The airway value alone cannot distinguish those states.

Finally, a stable displayed number is not automatically the same operation as an actual hold. The manufacturer distinguishes measured holds, rapid occlusion and calculated monitoring estimates.^[ref] Reporting the method and its conditions connects plateau airway pressure to the mechanical question it can answer.