The Pre-brief
Protective ventilation strategies use lower tidal volumes with goals of lower end inspiratory pressures (plateau) to decrease possible injury to lungs during ARDS. Understanding the pressures applied to the patient’s lungs during mechanical ventilation can improve their mortality rate. Therapists often contend with optimizing one component that may negatively affect another component. Volume can cause strain during ventilation having both static and dynamic factors. PEEP can add another stress factor to the equation in lung protective ventilation. Often, studies conduct Tidal Volume (Vt) and PEEP as separate predictors for lung strain and mortality rate.
What is Driving Pressure?
Driving Pressure is the pressure applied to the aerated part of the lungs to achieve tidal volume. Driving pressure is calculated by subtracting the PEEP from the plateau pressure (Plat-PEEP). This calculation is considered to be equivalent to tidal volume divided by the respiratory system compliance. Since transpulmonary measurements are not available in all ICUs, this quick calculation can aid in identifying the stress that is being applied to the lungs during mechanical ventilation. (More on transpulmonary pressures HERE)
Dynamics in disease state and chest wall compliance are influencing factors in driving pressure. In diseases such as ARDS, where there is a small amount of lung available for ventilation, the driving pressure will increase when the tidal volume or PEEP are set incorrectly. Too much tidal volume can cause over-distention while too much PEEP can cause atelectrauma. These stressors will cause an increase in driving pressures. Increased stress to the available alveoli can lead to increased mortality rates among ARDS patients.
Target levels of driving pressure have been below 13-15 cmH2O. Multiple studies have shown a driving pressure greater than 15cmH2O is tied to an increase in mortality rate. Obtaining correct measurements for the calculation is imperative to its functionality. An inspiratory pause ≥3 seconds gave a more accurate plateau pressure, where an inspiratory pause of 0.5 seconds caused an overestimation in plateau pressures. Not checking for and correcting auto-PEEP prior to calculation would also be a source for errors.Â
Knowing the pressure applied to the functional alveoli will be another data point for setting the correct tidal volume and PEEP. Tailoring mechanical ventilation to each patient will improve outcomes.
The Debrief
- In addition to protective lung ventilation, measuring driving pressures can reduce injury to the lungs
- Dynamic changes in the lungs affect the driving pressure
- Accurate measurements are key to success when calculating the driving pressure
References
- Baldomero, A. K., Skarda, P. K., & Marini, J. J. (2019). Driving pressure: Defining the range. Respiratory Care, 64(8), 883–889. https://doi.org/10.4187/respcare.06599Â
- Sahetya, S. K., & Fan, E. (2019). Driving pressure: The road ahead. Respiratory Care, 64(8), 1017–1020. https://doi.org/10.4187/respcare.07226Â
- Williams, E. C., Motta-Ribeiro, G. C., & Vidal Melo, M. F. (2019). Driving Pressure and Transpulmonary Pressure: How Do We Guide Safe Mechanical Ventilation?. Anesthesiology, 131(1), 155–163. https://doi.org/10.1097/ALN.0000000000002731
- Aoyama, H., Yamada, Y. & Fan, E. The future of driving pressure: a primary goal for mechanical ventilation?. j intensive care 6, 64 (2018). https://doi.org/10.1186/s40560-018-0334-4
