The following is the summary of “Mechanical ventilation variables associated with high pulmonary artery pressures in ARDS patients: a post hoc analysis” published in the December 2022 issue of Critical care by Riddell, et al.

How acute respiratory distress syndrome (ARDS) affects the link between mechanical ventilation indices and pulmonary artery pressures is still unclear. The role of high driving pressures and mechanical power in sustaining lung injury has been more recognized as our knowledge of mechanical ventilation has expanded. However, the connection between the newly generated indices of mechanical ventilation and pulmonary artery pressure needs to be better understood. To further understand the correlations between mechanical ventilation indices in ARDS patients and the incidence of pulmonary hypertension, researchers conducted a post hoc analysis of Fluid and Catheters Treatment Trial (FACTT) trials. This could illuminate potential clinical objectives for additional right ventricular protective mechanical breathing techniques.

Investigators did an ad hoc search of the FACTT database for patients with ARDS who had a pulmonary artery catheter (PAC) placed and pulmonary artery pressure measurements taken. Due to the lack of validation for driving pressure and mechanical power, they did not include patients with inserted PACs who were breathing independently. A univariate analysis was performed to look for correlations between mean pulmonary artery pressure (mPAP) and other mechanical ventilation parameters using Pearson correlation coefficients; a multivariate analysis was conducted to look for independent associations with mPAP using a multiple regression model according to Akaike’s information criteria; and a nonlinearity analysis was conducted to pick the best-fitting model from linear, quadratic, and exponential relationships using the Bayesian information criterion (BIC). Except for tidal volume (after adjusting for respiratory rate), all ventilation parameters significantly connected with mPAP in univariate analysis. Blood pH, P/F ratio, PaCO2, mPAP, and mechanical power indexed to compliance were all found to be independently linked with mPAP in a multivariate analysis. Relationships did not deviate from linearity except for the four variables for which the fractional polynomial provided the best fit in the final nonlinear analysis. 

Mechanical power (P=0.01), respiratory rate (P=0.04), peak pressure (P=0.03), and mean airway pressure (P=0.01) were all significant when compared to the linear model. About 2 nonlinear factors related to mPAP, respiratory rate, and mechanical power were evaluated in greater depth. A mechanical force of 8.8 J/min and a respiratory rate of 16.8 cycles per minute were used to demonstrate inflexion points. This analysis suggests that using classical ARDS lung protective strategies, such as low tidal volume ventilation and permissive hypercapnia, may hurt the management of the subset of ARDS patients with associated right ventricular dysfunction or ACP due to the associations found between mPAP and mechanical ventilation variables. Furthermore, mPAP is seen to grow gradually at respiratory rates greater than 17 cycles per minute. For this reason, increasing the tidal volume (within the bounds of driving pressure <18 cmH20) may be a more right ventricular protective method of controlling carbon dioxide and pH.