Computer-aided quantitative ultrasonography for detection of pulmonary edema in mechanically ventilated cardiac surgery patients

Introduction: Lung ultrasonography (LUS) has been used for non-invasive detection of pulmonary edema. Semi-quantitative LUS visual scores (V-LUS) based on B-lines are moderately correlated with pulmonary capillary wedge pressure (PCWP) and extravascular lung water (EVLW). A new quantitative computer-aided LUS analysis (Q-LUS) has been recently proposed. Aims: This study investigated 1) whether Q-LUS better correlates with PCWP and EVLW than VLUS; 2) to which extent positive end-expiratory pressure (PEEP) affect the assessment of pulmonary edema by Q-LUS or V-LUS. Methods: 48 mechanically ventilated patients with PEEP of 5 or 10 cmH2O and monitored by PCWP (n=28) or EVLW (n=20) were studied. Results: PCWP was significantly and strongly correlated with Q-LUS Grey Unit value (r2=0.70) but weakly with V-LUS B-line score (r2=0.20). EVLW was significantly and more strongly correlated with Q-LUS Grey Unit mean value (r2=0.68) than with V-LUS B-line score (r2=0.34). Q-LUS showed a better diagnostic accuracy than V-LUS for the detection of PCWP>18 mmHg or EVLW≥10 mL/kg. With 5-cmH2O PEEP, the correlations with PCWP or EVLW were stronger for Q-LUS than V-LUS. With 10-cmH2O PEEP, the correlations with PCWP or EVLW were still significant for Q-LUS but insignificant for V-LUS. Inter-observer reproducibility was better for Q-LUS than V-LUS. Conclusions: Both V-LUS and Q-LUS are acceptable indicators of pulmonary edema in mechanically ventilated patients. However, at high PEEP only Q-LUS provides data that are significantly correlated with PCWP and EVLW. Computer-aided Q-LUS has the advantages of being not only independent of operator perception but also of PEEP.