Driving Pressure: Defining the Range

Abstract

BACKGROUND: Recent literature suggests that optimization of tidal driving pressure (⌬P) 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 ⌬P over time for any subject category have not been defined. This study sought to document the ⌬P ranges observed in current practice among mechanically ventilated subjects receiving routine care for diverse acute conditions in a community hospital environment. METHODS: 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. RESULTS: The mean ⌬P was significantly higher at Time 1 (mean 16.1, range 7.0 -31.0 cm H 2 O) compared to both Time 2 (mean 14.5, range 7.0 -35.0 cm H 2 O) (P < .001) and Time 3 (mean 14.8, range 8.0 -32 cm H 2 O) (P < .001). At all time points, the median ⌬P 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 ⌬P ‫؍‬ 17.2 vs 14.9 cm H 2 O, respectively) (P ‫؍‬ .01). CONCLUSIONS: Suggested safety thresholds for ⌬P are often violated by a strategy that focuses on only V T and P plat . Our data suggest that ⌬P 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 ⌬P.

Elastic Power of Mechanical Ventilation in Morbid Obesity and Severe Hypoxemia

“…However, debate continues regarding whether total power is sufficiently precise or whether one of its elastic subcomponents offers a more direct measure of VILI risk. 5 The driving power is another potential index being explored, 32 but dynamic power might better indicate the true hazard, as PEEP adds both to tissue stretch and total power. 33 There are 2 key elements to VILI risk: excessive strain per cycle and cycling frequency.…”

Driving Pressure: The Road Ahead

“…In this issue of RESPIRATORY CARE, Baldomero et al 11 took the first step in answering these questions by defining the natural range and temporal variability of driving pressure in patients who receive traditional lung-protective ventilation. In a retrospective review of 125 mechanically ventilated subjects, ϳ60% of the participants had driving pressures that exceeded a proposed safety limit of 15 cm H 2 O 5,12 within the first 8 h of mechanical ventilation.…”

“…They also noted temporal driving pressure variability over the first 24 h of mechanical ventilation, with gradually decreasing driving pressure presumed secondary to progressive lung recruitment from positive pressure ventilation improving lung compliance and treatment of the underlying illness. 11 Also, they noted intriguing findings regarding driving pressure differences related to sex, body mass index, and the presence of spontaneous respiratory efforts.…”

“…13 In the modern low-tidal volume era, the clinical range of driving pressure is not as wide as the ranges found in studies that used higher tidal volumes. 12,14 Despite this, the results from Baldomero et al 11 suggest that a majority of patients on mechanical ventilation may be eligible for interventions that attempt to reduce driving pressure, especially important because trial recruitment in critical care can be notoriously difficult. [15][16][17] Furthermore, although Baldomero et al 11 picked a safety threshold of 15 cm H 2 O, results of other studies suggested a threshold effect closer to 13 cm H 2 O, which suggests even more patients than suspected may benefit from a driving pressure-limited strategy.…”

“…12,14 Despite this, the results from Baldomero et al 11 suggest that a majority of patients on mechanical ventilation may be eligible for interventions that attempt to reduce driving pressure, especially important because trial recruitment in critical care can be notoriously difficult. [15][16][17] Furthermore, although Baldomero et al 11 picked a safety threshold of 15 cm H 2 O, results of other studies suggested a threshold effect closer to 13 cm H 2 O, which suggests even more patients than suspected may benefit from a driving pressure-limited strategy. 8,9 The true safe upper limit of driving pressure is unknown, and different cutoffs should continue to be evaluated prospectively.…”