Question
What is driving pressure, and why is it a key recommendation in the PALICC 2 pediatric ARDS guidelines?
Answer
Driving pressure is entirely new to PALICC 2; it was not addressed in PALICC 1. Driving pressure is defined as the difference between plateau pressure and PEEP. It is calculated by performing a brief inspiratory pause of two to three seconds. During this pause, pressure drops slightly as the lung and circuit absorb the delivered volume. The pressure at the end of that pause is the plateau pressure, not the peak inspiratory pressure. Driving pressure equals plateau pressure minus PEEP.
PALICC 2 recommends keeping plateau pressure at or below 28 cm H2O, with low agreement at 92 percent. In patients with reduced chest wall compliance, plateau pressures of 29 to 32 cm H2O may be necessary. These values are unchanged from PALICC 1.
The new addition is a specific limit on driving pressure: it should not exceed 15 cm H2O, as measured under static conditions. Although this recommendation achieved only 82 percent agreement and is therefore categorized as very low agreement in the GRADE framework, the clinical rationale is compelling. The lower the driving pressure, the lower the alveolar strain, and the better the patient's outcomes.
Consider a patient on a PEEP of 9 with a plateau pressure of 24: the driving pressure is 15, which is exactly at the recommended limit. If PEEP is then increased to 12 to improve oxygenation, the plateau pressure may rise above 28, pushing the patient into the lung injury risk zone. The appropriate response is to lower the tidal volume, which will bring the plateau pressure and driving pressure back within acceptable limits.
In practice, the three variables of PEEP, tidal volume, and driving pressure must be managed together. Increasing PEEP may require a corresponding reduction in tidal volume to stay within driving pressure limits.
This Ask the Expert is an edited excerpt from the course, An RT Overview of the Revised PARDS Guidelines from PALICC II, presented by Evan Richards, BSc, RT.
