Assessment of variables affecting the accuracy of extravascular lung water (EVLW) by single versus double indicator dilution techniques in ARDS patients

Abstract

Estimation of extravascular lung water (EVLW) by the single indicator dilution technique (SDT) implemented in the PICCO monitoring system relies on a relationship between intrathoracic blood volume (ITBV) and global end diastolic volume (GEDV), which has been derived from a large population of mixed critically ill patients using the double indicator dilution technique (thermal and indocyanine green dyes, DDT): ITBV sdt = 1.25 × GEDV [ 1 ]. Since the difference between ITBV and GEDV corresponds to pulmonary blood volume (PBV), we can write: PBV sdt = 0.25 × GEDV. Any factor influencing this relationship can affect SDT accuracy. The aims of our study were: 1) to compare SDT versus DDT for EVLW measurements in ARDS patients; and 2) to explore factors influencing the PBV and GEDV relationship, and affecting SDT accuracy.