(1168) PEEP Titration Using Ventilatory Mechanics in Severe ARDS and Predicting Hyperinflation

Introduction: This is a multicenter study that evaluated the use of Time constant ( TCe), compliance ratio ( C20/Cdyn), driving pressure in PEEP titration and their ability to discriminate overdistension and tidal hyperinflation in addition to predicting PEEP-induced decrease in cardiac output.

Methods: Moderately severe ARDS patients were enrolled in this study. Ventilator care as per the standard guidelines. Bedside ventilatory mechanics were recorded immediately after intubation within 2 hours. Then the PEEP was titrated according to the lowest driving pressure. Ventilatory mechanics were recorded within 4 hours of PEEP titration. Other outcomes were recorded. Statistical analysis was done using Jamovi with R statistics.

Results: A total of 68 patients were enrolled in this study. Linear regression and logistic regression model identified that a combination of a decrease in C20/cdyn with no change in TCe was identified as a risk factor for a decrease in cardiac output due to significant hyperinflation (R2=0.61). ROC approach using the highest Youden index identified C20/Cdyn cut-off of 0.92 (45.95% sensitivity, 100% specificity, AUC of 0.724) and a time constant of 0.48 (21.62% sensitivity, 87.1 specificities with AUC 0.405), both of them had significant co-relation in predicting CO2 gap ( r= 0.487 and -0.626 respectively), ventilatory ratio ( r = 0.356 and -0.793 respectively) and need for vasopressor use ( r = 0.242 and -0.456 respectively)., whereas the driving pressure did not have significant co-relation. These correlations were further confirmed by agreement analysis using the Bland-Altman technique with a proportional bias line.

Conclusions: This study suggests that a decrease in compliance ratio ( < 0.92) and sustenance of time constant ( > 0.48) with PEEP titration indicates PEEP induced decrease in cardiac output needing inotrope, vasopressor support, whereas as a subset of patients whose time constant has decreased ( < 0.35) and compliance ratio ( > 0.92) has been sustained indicated good recruitability. In the former PEEP may need to be decreased, while in the latter, PEEP may need to be maintained. In addition, patients whose TCe < 0.25 had a 100% incidence of new-onset atrial fibrillation during the ICU stay.