The relationship between positive end-expiratory pressure and cardiac index in patients with acute respiratory distress syndrome

Abstract

Purpose: The purpose of the study is to evaluate the association between positive end-expiratory pressure (PEEP) and cardiac index in patients with acute respiratory distress syndrome (ARDS).

Methods: This is a secondary cross-sectional analysis of the multicenter randomized controlled Fluid and Catheter Treatment Trial enrolling adult patients within 48 hours of ARDS onset. Patients randomized to the pulmonary artery catheter arm, who had PEEP and cardiac index measurements performed within a short period of each other during the first 3 days of the FACTT study enrollment, were included in this study. Because FACTT had a 2 × 2 factorial design, half of the patients were in a "liberal fluids" study arm, and the other half were in a "conservative fluids" study arm.

Results: The final study population (833 measurements or observations, in 367 patients) was comparable with the original overall FACTT study population. The mean PEEP level used was 8.2 ± 3.4 cm H2O, and the mean cardiac index was 4.2 ± 1.2 L/min per square meter. There was no association between PEEP and cardiac index in patients with ARDS, even when adjusted for Acute Physiology and Chronic Health Evaluation score, age, fluid study arm in FACTT, and sepsis.

Conclusion: In patients with ARDS who are managed with liberal or conservative fluid management protocols, PEEP is not associated with lower cardiac index.

Trial registration: ClinicalTrials.gov NCT01714583.

Keywords: ARDS; Cardiac function; Cardiac index; Heart-lung interaction; Mechanical ventilation.

Conflict of interest statement

Conflicts of interest

The authors report no conflicts of interest with regard to this manuscript.

© 2013.

Figures

Fig. 1

Reasons for (& numbers of) exclusions from the final analysis. PEEP: positive end-expiratory pressure. Observations with missing PEEP were excluded because PEEP is the primary exposure variable. Observations with missing cardiac index were excluded because cardiac index is the primary outcome variable. Observations with missing FiO2 or PaO2 were excluded because PF ratio could not be calculated for these observations, so a diagnosis of ARDS could not be determined.

Fig. 2

Unadjusted scatterplot of Positive End-Expiratory Pressure (PEEP) and cardiac index (CI) (n=833). Correlation coefficient (r) = 0.05; p= 0.17. Numbers of observations within 4 different PEEP categories are also noted at the top of the figure, with the mean CI for each category.

Fig. 3

Predicted Cardiac Index (in liters / minute / meter2) with 95% confidence interval, based on the PEEP level in cm adjusted for APACHE III score, age, FACTT study fluids arm (liberal versus conservative), and sepsis (present versus absent). p=0.71.