driving pressure is plateau pressure minus PEEP
- related: ICU intensive care unit
- tags: #literature #boards
Driving pressure (DP) is the pressure required to tidally distend and inflate the alveolar structures. It is a static measurement (plateau pressure minus PEEP) that reflects only compliance properties of the respiratory system during tidal breath delivery, not flow resistive properties. Mathematically, DP is tidal volume/compliance (Vt/C).
Excessive tidal stretch (strain) of alveolar structures during mechanical ventilation can produce ventilator-induced lung injury (VILI). A practical way to address this is the use of “normal” tidal volumes based on ideal lung size (ie, 5-7 mL/kg IBW). However, this may be too simplistic in lungs with extensive regional consolidation. Under these conditions, the volume of lung capable of being ventilated may be markedly reduced (“baby lungs”). Thus, delivery of a normal-sized Vt based on IBW may produce excessive regional tidal stretch in the reduced functional lung. Because compliance may be considered a surrogate for functional lung size, DP has been proposed as a tool to more appropriately scale Vt.
A threshold for a “safe” DP is not clear. Retrospective analyses of multiple randomized clinical trials (most of which were evaluating PEEP strategies, not Vt settings) have suggested that DP values <15 cm H2O seem safer than higher values. Recommendations to keep DP below this threshold have been made by several authorities. In our patient, the DP is 29 (plateau pressure) – 12 (PEEP) or 17 cm H2O. Given the choices offered, the only way to reduce the DP would be to reduce the Vt (choice A is correct; choice D is incorrect).1
Another way to perhaps reduce DP in our patient might be to improve compliance with small, sequential increases or decreases in PEEP. A novel way to assess this is to measure a stress index.