Effects of extravascular lung water on the measurement of transpulmonary thermodilution cardiac output in acute respiratory distress syndrome patients

Objective: Transpulmonary thermodilution cardiac output is used in calculating aortic impedance for calibrating the pulse-contour analysis and is applied to calculate extravascular lung water (EVLW). Whether pulmonary edema affects the accuracy of transpulmonary thermodilution is controversial. This study aimed to investigate the effects of extravascular lung water index (EVLWI) on the transpulmonary thermodilution measurement in acute respiratory distress syndrome (ARDS). Design: A prospective study. Setting: The medical intensive care unit of one medical center. Participants: Twenty-four ARDS patients. Interventions: The continuous pulmonary artery thermodilution cardiac index (CCIpa) and the bolus transpulmonary thermodilution cardiac index (BCItp) data were recorded at baseline and repeated immediately and at 2, 4, and 6 hours after volume expansion with a 500-mL infusion of 10% pentastarch (hydroxyethyl starch 200/0.5) at a rate of 10 mL/kg/h. Measurements and Main Results: A total of 120 paired CI measurements were analyzed. Linear regression analysis showed a close correlation between BCItp and CCIpa (R = 0.87). The mean BCItp was higher than CCIpa, and the Bland-Altman analysis revealed a bias of 0.51 ± 0.78 L/min/m ². The limits of agreement (2 standard deviations) was 1.66 L/min/m ² (+2.07 and -1.05 L/min/m ²), and the percentage error was 31.5%. Levels of EVLWI negatively correlated with the difference between BCItp and CCIpa (R = -0.19). Conclusion: In ARDS patients, the agreement between transpulmonary thermodilution and pulmonary artery thermodilution for cardiac output measurement is marginally acceptable. The severity of pulmonary edema expressed as EVLWI weakly and negatively correlates with the difference between BCItp and CCIpa derived from the two techniques.