Association between Different Indexations of Extravascular Lung Water (EVLW) and PaO2/FiO2: A Two-Center Study in 231 Patients

BACKGROUND Variability of body weight (BW) and height calls for indexation of volumetric hemodynamic parameters. Extravascular lung water (EVLW) has formerly been indexed to actual BW (BW(act)) termed EVLW-index (EVLWI). In overweight patients indexation to BW(act) might inappropriately lower indexed EVLWI(act). Several studies suggest indexation of EVLWI to predicted BW (EVLWI(pred)). However, data regarding association of EVLWI(act) and EVLW(pred) to mortality and PaO2/FiO2 are inconsistent. Two recent studies based on biometric database-analyses suggest indexation of EVLWI to height (EVLWI(height)). Therefore, our study compared the association of un-indexed EVLW, EVLWI(height), EVLW(pred) and EVLWI(act) to PaO2/FiO2 and Oxygenation index (OI = mean airway pressure*FiO2*/PaO2). METHODS A total of 2119 triplicate transpulmonary thermodilutions (TPTDs; PiCCO; Pulsion Medical-Systems, Germany) were performed in 50 patients from the evaluation, and 181 patients from the validation groups. Correlations of EVLW and EVLWI to PaO2/FiO2, OI and ROC-AUC-analyses regarding PaO2/FiO2<200 mmHg (primary endpoint) and OI>10 were performed. RESULTS In the evaluation group, un-indexed EVLW (AUC 0.758; 95%-CI: 0.637-0.880) and EVLWI(height) (AUC 0.746; 95%-CI: 0.622-0.869) provided the largest ROC-AUCs regarding PaO2/FiO2<200 mmHg. The AUC for EVLWI(pred) was smaller (0.713). EVLWI(act) provided the smallest AUC (0.685). This was confirmed in the validation group: EVLWI(height) provided the largest AUC (0.735), EVLWI(act) (0.710) the smallest. In the merged data-pool, AUC was significantly greater for EVLWI(height) (0.729; 95%-CI: 0.674-0.784) compared to all other indexations including EVLWI(act) (ROC-AUC 0.683, p = 0.007) and EVLWI(pred) (ROC-AUC 0.707, p = 0.015). The association of EVLW(I) was even stronger to OI compared to PaO2/FiO2. In the merged data-pool, EVLWI(height) provided the largest AUC regarding "OI>10" (0.778; 95%-CI: 0.713-0.842) compared to 0.739 (95%-CI: 0.669-0.810) for EVLWI(act) and 0.756 (95%-CI: 0.688-0.824) for EVLWI(pred). CONCLUSIONS Indexation of EVLW to height (EVLWI(height)) improves the association of EVLW(I) to PaO2/FiO2 and OI compared to all other indexations including EVLWI(pred) and EVLWI(act). Also considering two recent biometric database analyses, EVLWI should be indexed to height.