The authors reply
We believe that patients’ outcomes are determined not only by alveolar stretching but also, and more importantly, the heart-lung interaction on the first day of mechanical ventilation. As you mentioned, the Pmean differs from the plateau pressure (Pplat) and driving pressure (DP); the Pmean is much more hemodynamically accurate because it reflects the whole respiratory cycle; the latter variables reflect alveolar stretching, which only occurs during the inspiratory phase. Our study revealed that an elevated Pmean (odds ratio, 1.125; 95% CI, 1.069–1.184; p < 0.001) was independently associated with 28-day mortality instead of Pplat and DP. We provided evidence and discussed why Pmean was employed in our study (2).
We agree that our study had limitations because of its retrospective and single-center design. However, both CVP and Pmean are easy to measure consecutively at the bedside and have a greater possibility to be generalized. As mentioned above, CVP and Pmean may be variables that serve as a bridge between right heart function and the respiratory system, reflecting the cardiopulmonary interaction in critically ill patients undergoing mechanical ventilation. Certainly, elucidation of the exact effect of Pmean and CVP on right ventricular function requires the use of specific right ventricular function variables by echocardiography or Swan-Ganz catheterization to reveal the mechanism.