Lung ultrasound predicts well extravascular lung water but is of limited usefulness in the prediction of wedge pressure.

BACKGROUND: Pulmonary congestion is indicated at lung ultrasound by detection of B-lines, but correlation of these ultrasound signs with pulmonary artery occlusion pressure (PAOP) and extravascular lung water (EVLW) still remains to be further explored. The aim of the study was to assess whether B-lines, and eventually a combination with left ventricular ejection fraction (LVEF) assessment, are useful to differentiate low/high PAOP and EVLW in critically ill patients.
METHODS: The authors enrolled 73 patients requiring invasive monitoring from the intensive care unit of four university-affiliated hospitals. Forty-one patients underwent PAOP measurement by pulmonary artery catheterization and 32 patients had EVLW measured by transpulmonary thermodilution method. Lung and cardiac ultrasound examinations focused to the evaluation of B-lines and gross estimation of LVEF were performed. The absence of diffuse B-lines (A-pattern) versus the pattern showing prevalent B-lines (B-pattern) and the combination with normal or impaired LVEF were correlated with cutoff levels of PAOP and EVLW.
RESULTS: PAOP of 18 mmHg or less was predicted by the A-pattern with 85.7% sensitivity (95% CI, 70.5 to 94.1%) and 40.0% specificity (CI, 25.4 to 56.4%), whereas EVLW 10 ml/kg or less with 81.0% sensitivity (CI, 62.6 to 91.9%) and 90.9% specificity (CI, 74.2 to 97.7%). The combination of A-pattern with normal LVEF increased sensitivity to 100% (CI, 84.5 to 100%) and specificity to 72.7% (CI, 52.0 to 87.2%) for the prediction of PAOP 18 mmHg or less.
CONCLUSIONS: B-lines allow good prediction of pulmonary congestion indicated by EVLW, whereas are of limited usefulness for the prediction of hemodynamic congestion indicated by PAOP. Combining B-lines with estimation of LVEF at transthoracic ultrasound may improve the prediction of PAOP.