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.