Driving Pressure: Defining the Range

Recent literature suggests that optimization of tidal driving pressure (ΔP) would be a better variable to target for lung protection at the bedside than tidal volume (V_T) or plateau pressure (P_plat), the traditional indicators of ventilator-induced lung injury. However, the usual range or variability of ΔP over time for any subject category have not been defined. This study sought to document the ΔP ranges observed in current practice among mechanically ventilated subjects receiving routine care for diverse acute conditions in a community hospital environment.

This was a retrospective, observational study in a university-affiliated and house staff-aided institution with respiratory care protocols based on extant lung-protective guidelines for V_T. Demographic characteristics and measured parameters related to mechanical ventilation and hemodynamics were extracted from electronic records of intubated subjects for each 8-h period of the first 24 h in the ICU. P_plat values reported by the ventilator were validated by the respiratory therapist before those data were entered into the electronic medical record.

The mean ΔP was significantly higher at Time 1 (mean 16.1, range 7.0-31.0 cm H₂O) compared to both Time 2 (mean 14.5, range 7.0-35.0 cm H₂O) (P < .001) and Time 3 (mean 14.8, range 8.0-32 cm H₂O) (P < .001). At all time points, the median ΔP was higher for completely passive breathing compared to triggered breathing. The widest difference between presumed entirely passive and presumed intermittently or consistently triggered breaths occurred at Time 1 (mean ΔP = 17.2 vs 14.9 cm H₂O, respectively) (P = .01).

Suggested safety thresholds for ΔP are often violated by a strategy that focuses on only V_T and P_plat. Our data suggest that ΔP is lower for passive versus triggered breathing cycles. Vigilance is especially important in the initial stages of mechanical ventilator support, and attention should be paid to triggering efforts when interpreting and comparing machine-determined numerical values for ΔP.