= Respiratory driving pressure
{title2=$\Delta P$}
\b[Respiratory driving pressure], $\Delta P$, is the difference between <plateau airway pressure> and total end-expiratory pressure when measured under suitable passive conditions:
$$
\Delta P=P_{\rm plat}-P_{\rm EEP,tot}.
$$
The total baseline includes <intrinsic positive end-expiratory pressure> when present; substituting only the externally imposed baseline can overestimate this tidal pressure difference.<How to measure driving pressure by Hamilton Medical>[Definition and conditions for measurement]{ref}
For the linear static model, <respiratory-system compliance> is $C_{\rm rs}=V_T/\Delta P$. An original calculation with <tidal volume> 0.45 L, plateau pressure 23 cm H$_2$O and total baseline 8 cm H$_2$O gives $\Delta P=15$ cm H$_2$O and $C_{\rm rs}=0.030$ L/cm H$_2$O. If the external baseline alone were 5 cm H$_2$O, incorrectly subtracting it would give 18 cm H$_2$O and a different apparent compliance.
This pressure difference loads both the lung and chest wall. At static endpoints, <transpulmonary pressure> gives the partition
$$
\Delta P_{\rm aw}=\Delta P_L+\Delta P_{\rm pl}.
$$
Thus a stipulated airway increment of 12 cm H$_2$O corresponds to a lung increment of 4 when the pleural increment is 8, but to a lung increment of 10 when the pleural increment is 2. Equal airway driving pressures do not establish equal lung distension without information about the chest-wall contribution.
The measurement method matters as much as the subtraction. A dynamic estimate during flow can include resistance; an <end-inspiratory hold> and an end-expiratory occlusion address different endpoints. The primary pilot study explicitly compared static and dynamic ways of obtaining whole-respiratory-system compliance and driving pressure.<Static and Dynamic Measurements of Compliance and Driving Pressure: A Pilot Study by Pierre Tawfik and others>[Introduction, Figure 1 and Study Procedures]{ref} These distinctions explain the quantity's mechanical meaning without turning an illustrative number into an individual ventilation recommendation.
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