B-Lines Scores Derived From Lung Ultrasound Provide Accurate Prediction of Extravascular Lung Water Index: An Observational Study in Critically Ill Patients

Abstract

Introduction: Visualization of B-lines via lung ultrasound provides a non-invasive estimation of pulmonary hydration. Extravascular lung water index (EVLWI) and pulmonary vascular permeability index (PVPI) assessed by transpulmonary thermodilution (TPTD) represent the most validated parameters of lung water and alveolocapillary permeability, but measurement is invasive and expensive. This study aimed to compare the correlations of B-lines scores from extensive 28-sector and simplified 4-sector chest scan with EVLWI and PVPI derived from TPTD in the setting of intensive care unit (primary endpoint).

Methods: We performed scoring of 28-sector and 4-sector B-Lines in 50 critically ill patients. TPTD was carried out with the PiCCO-2-device (Pulsion Medical Systems SE, Maquet Getinge Group). Median time exposure for ultrasound procedure was 12 minutes for 28-sector and 4 minutes for 4-sector scan.

Results: Primarily, we found close correlations of 28-sector as well as 4-sector B-Lines scores with EVLWI (R² = 0.895 vs. R² = 0.880) and PVPI (R² = 0.760 vs. R² = 0.742). Both B-lines scores showed high accuracy to identify patients with specific levels of EVLWI and PVPI. The extensive 28-sector B-lines score revealed a moderate advantage compared to simplified 4-sector scan in detecting a normal EVLWI ≤ 7 (28-sector scan: sensitivity = 81.8%, specificity = 94.9%, AUC = 0.939 versus 4-sector scan: sensitivity = 81.8%, specificity = 82.1%, AUC = 0.902). Both protocols were approximately equivalent in prediction of lung edema with EVLWI ≥ 10 (28-sector scan: sensitivity = 88.9%, specificity = 95.7%, AUC = 0.977 versus 4-sector scan: sensitivity = 81.5%, specificity = 91.3%, AUC = 0.958) or severe pulmonary edema with EVLWI ≥ 15 (28-sector scan: sensitivity = 91.7%, specificity = 97.4%, AUC = 0.995 versus 4-sector scan: sensitivity = 91.7%, specificity = 92.1%, AUC = 0.978). As secondary endpoints, our evaluations resulted in significant associations of 28-sector as well as simplified 4-sector B-Lines score with parameters of respiratory function.

Conclusion: Both B-line protocols provide accurate non-invasive evaluation of lung water in critically ill patients. The 28-sector scan offers a marginal advantage in prediction of pulmonary edema, but needs substantially more time than 4-sector scan.

Keywords: B-lines; acute respiratory distress syndrome (ARDS); extravascular lung water index (EVLWI); intensive care unit (ICU); lung ultrasound; pulmonary edema; pulmonary vascular permeability index (PVPI); transpulmonary thermodilution (TPTD).

Figure 1.

Exemplary pictures of B-lines-visualization of different intercostal spaces (ICS): (A) Absent B-lines and predominant horizontal A-lines, (B) 2 B-lines / ICS, (C) 4 B-lines / ICS, (D) confluent B-lines 50-75% ICS.

Figure 2.

Schematic illustration of the different scanning regions used for 28-7 sector protocol (A) as well as 4-sector chest scan (B).

Figure 3.

Correlations of summed 28-sector B-lines score (28s-BL) with: (A) Extravascular lung water index (EVLWI), (B) Pulmonary vascular permeability index (PVPI).

Figure 4.

Correlations of simplified 4-sector B-lines score (4s-BL) with: (A) Extravascular lung water index (EVLWI), (B) Pulmonary vascular permeability index (PVPI).

Figure 5.

Receiver operating characteristic (ROC) curves analyzing the diagnostic potential of 28-sector B-lines (28s-BL) and 4-sector B-lines score (4s-BL) to identify patients with: (A) EVLWI ≤ 7, (B) EVLWI ≥ 10, (C) EVLWI ≥ 15.

Figure 6.

Receiver operating characteristic (ROC) curves analyzing the diagnostic potential of 28-sector B-lines (28s-BL) and 4-sector B-lines score (4s-BL) to identify patients with: (A) PVPI < 2, (B) PVPI ≥ 3.