An important parameter to guide safe mechanical ventilation is driving pressure. In this article, we learn how to calculate driving pressure, its origin, and most importantly, how to use it in clinical practice.
Driving pressure (DP or ΔP) is calculated by taking the difference between the pressure at end inspiration (when flow is 0) and the pressure at end expiration (when flow is 0). This means that during volume controlled ventilation, driving pressure is the difference between plateau pressure (Pplat) and total PEEP. Measurement thus requires an inspiratory and expiratory hold.
Amato et al. NEJM 2015 showed that mortality is directly related to driving pressure:
Amato defined that the target DP should be <15 cmH2O. But you can imagine that the lower the driving pressure, the better (if ventilation permits).
Now what do we do in clinical practice? We aim for a driving pressure <15, which of course is valid, but does require some nuance. In my view, merely aiming for a driving pressure below 15 is too simplistic. Driving pressure should be viewed within the context of the patients pulmonary status. Let me explain what I mean.
Compliance of the respiratory system is defined as
As compliance can be seen as a descriptive state of the respiratory system, at constant tidal volume, driving pressure is an indirect measure of compliance. In other words, and this is key for your understanding and the usefulness in daily practice:
For a standardized tidal volume (for instance 6ml/kg),
driving pressure = compliance
That means that driving pressure should always be interpreted in light of tidal volume. If you have a driving pressure of 8, you're probably pretty satisfied. However, if the patient only receives tidal volumes of 200 ml, this means that their compliance is 25, which is horrible. However, if they receive tidal volumes of 500 with those driving pressures, this patient likely has healthy lungs.